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September 29, 2000

1

MIC284

MIC284

Micrel

MIC284

Two-Zone Thermal Supervisor

Advance Information

Typical Application

CLK

FROM

SERIAL BUS

HOST

OVER-TEMP

SHUTDOWN

REMOTE

DIODE

2200pF

0.1

µF

MIC284

/INT

/CRIT

3.3V

DATA

× 10k

pull-ups

VDD

T1

A0

GND

2-Channel SMBus Temperature Measurement System

Features

• Optimized for CPU Thermal Supervision in Computing

Applications

• Measures Local and Remote Temperature

• Sigma-Delta ADC for 8-Bit Temperature Results

• 2-Wire SMBus-compatible Interface

• Programmable Thermostat Settings for both Internal and

External Zones

• Open-Drain Interrupt Output Pin

• Open-Drain Over Temperature Output Pin for Fan

Control or Hardware Shutdown

• Interrupt Mask and Status Bits

• Low Power Shutdown Mode

• Failsafe response to diode faults

• 2.7V to 5.5V Power Supply Range

• 8-Lead SOIC and MSOP Packages

Applications

• Desktop, Server and Notebook Computers

• Power Supplies

• Test and Measurement Equipment

• Wireless Systems

• Networking/Datacom Hardware

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com

General Description

The MIC284 is a versatile digital thermal supervisor capable

of measuring temperature using its own internal sensor and

an inexpensive external sensor or embedded silicon diode

such as those found in the Intel Pentium III* CPU. A 2-wire

serial interface is provided to allow communication with either

I

2

C** or SMBus* masters. Features include an open-drain

over-temperature output with dedicated registers for imple-

menting fan control or over-temperature shutdown circuits.

Interrupt status and mask bits are provided for reduced

software overhead. The open-drain interrupt output pin can

be used as either an overtemperature alarm or a thermostatic

control signal. A programmable address pin permits two

devices to share the bus. (Alternate base addresses avail-

able-contact Micrel.) Superior performance, low power and

small size makes the MIC284 an excellent choice for the most

demanding thermal management applications.

*SMBus and Pentium III are trademarks of Intel Corporation.

**I

2

C is a trademark of Philips Electronics, N.V.

Ordering Information

Part Number

Base Address

(

*

)

Junction Temp. Range

Package

Notes

MIC284-0BM

100 100x

–55

°C to +125°C

8-Lead SOP

MIC284-1BM

100 101x

–55

°C to +125°C

8-Lead SOP

Contact Factory

MIC284-2BM

100 110x

–55

°C to +125°C

8-Lead SOP

Contact Factory

MIC284-3BM

100 111x

–55

°C to +125°C

8-Lead SOP

Contact Factory

MIC284-0BMM

100 100x

–55

°C to +125°C

8-Lead MSOP

MIC284-1BMM

100 101x

–55

°C to +125°C

8-Lead MSOP

Contact Factory

MIC284-2BMM

100 110x

–55

°C to +125°C

8-Lead MSOP

Contact Factory

MIC284-3BMM

100 111x

–55

°C to +125°C

8-Lead MSOP

Contact Factory

* The least-significant bit of the slave address is determined by the state of the A0 pin.

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MIC284

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MIC284

2

September 29, 2000

Pin Description

Pin Number

Pin Name

Pin Function

1

DATA

Digital I/O:  Open-drain. Serial data input/output.

2

CLK

Digital Input: The host provides the serial bit clock on this input.

3

/INT

Digital Output:  Open-drain. Interrupt or thermostat output.

4

GND

Ground:  Power and signal return for all IC functions.

5

/CRIT

Digital Output: Open-Drain. Over-temperature indication

6

T1

Analog Input: Connection to remote temperature sensor (diode junction)

7

A0

Digital Input:  Slave address selection input. See Table 1. MIC284 Slave

Address Settings.

8

VDD

Analog Input:  Power supply input to the IC.

Pin Configuration

1

DATA

CLK

/INT

GND

8

VDD

A0

T1

/CRIT

7

6

5

2

3

4

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September 29, 2000

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MIC284

MIC284

Micrel

Absolute Maximum Ratings 

(Note 1)

Power Supply Voltage, V

DD ...................................................

6.0V

Voltage on Any Pin ................................ –0.3V to V

DD

+0.3V

Current Into Any Pin ................................................

±10 mA

Power Dissipation, T

A

 = +125

°C ............................... 30mW

Junction Temperature ............................................. +150

°C

Storage Temperature ............................... –65

°C to +150°C

ESD Ratings (Note 3)

Human Body Model .................................................. TBD V

Machine Model ......................................................... TBD V

Soldering

Vapor Phase (60 sec.) ............................. +220

°C 

+5

–0

°C

Infrared (15 sec.) ...................................... +235

°C 

+5

–0

°C

Operating Ratings 

(Note 2)

Power Supply Voltage, V

DD ..............................

+2.7V to +5.5V

Ambient Temperature Range (T

A

) ............ -55

°C to +125°C

Package Thermal Resistance (

θ

JA

)

SOP ................................................................. +152

°C/W

MSOP .............................................................. +206

°C/W

Electrical Characteristics

2.7V 

≤ V

DD

 

≤ 5.5; T

A

 = +25

°C, bold values indicate –55°C ≤ T

A

 

≤ +125°C, Note 4; unless noted.

Symbol

Parameter

Condition

Min

Typ

Max

Units

Power Supply

I

DD

Supply Current

/INT, open,  A0 = V

DD

 or GND,

350

750

µA

CLK = DATA = high, normal mode

/INT, /CRIT open, A0 = V

DD

 or GND

shutdown mode, CLK = 100kHz

3

µA

/INT, /CRIT open, A0 = V

DD

 or GND

shutdown mode, CLK = DATA = high

1

10

µA

t

POR

Power-On Reset Time, Note 7

V

DD

 > V

POR

200

µs

V

POR

Power-On Reset Voltage

all registers reset to default values,

2.0

2.7

V

A/D conversions initiated

V

HYST

Power-On Reset Hysteresis Voltage

250

mV

Temperature-to-Digital Converter Characteristics

Accuracy—Local Temperature

0

°C ≤ T

A

 

≤ +100°C, /INT and /CRIT open,

±1

±

2

°C

Note 4, 9

3V 

≤ V

DD

 

≤ 3.6V

–55

°C ≤ T

A

 

≤ +125°C, /INT and /CRIT open,

±2

±

3

°C

3V 

≤ V

DD

 

≤ 3.6V

Accuracy—Remote Temperature

0

°C ≤ T

D

 

≤ +100°C, /INT and /CRIT open,

±1

±

3

°C

Note 4, 5, 9

3V 

≤ V

DD

 

≤ 3.6V, 0°C ≤ T

A

 

≤ +85°C

–55

°C ≤ T

D

 

≤ +125°C, /INT and /CRIT open,

±2

±

5

°C

3V 

≤ V

DD

 

≤ 3.6V, 0°C ≤ T

A

 

≤ +85°C

t

CONV0

Conversion Time, local zone

50

80

ms

 Note 7

t

CONV1

Conversion Time, remote zone

Note 7

100

160

ms

Remote Temperature Input (T1)

I

F

Current to External Diode

high level, T1 forced to 1.5V

224

400

µA

Note 7

low level

7.5

14

µA

Address Input (A0)

V

IL

Low Input Voltage

2.7V 

≤ V

DD

 

≤ 5.5V

0.6

V

V

IH

High Input Voltage

2.7V 

≤ V

DD

 

≤ 5.5V

2.0

V

C

IN

Input Capacitance

10

pF

I

LEAK

Input Current

±0.01

±

1

µA

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MIC284

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MIC284

4

September 29, 2000

Symbol

Parameter

Condition

Min

Typ

Max

Units

Serial Data I/O Pin (DATA)

V

OL

Low Output Voltage

I

OL

 = 3mA

0.4

V

Note 6

I

OL

 = 6mA

0.8

V

V

IL

Low Input Voltage

2.7V 

≤ V

DD

 

≤ 5.5V

0.3V

DD

V

V

IH

High Input Voltage

2.7V 

≤ V

DD

 

≤ 5.5V

0.7V

DD

V

C

IN

Input Capacitance

10

pF

I

LEAK

Input current

±0.01

±

1

µA

Serial Clock Input (CLK)

V

IL

Low Input Voltage

2.7V 

≤ V

DD

 

≤ 5.5V

0.3V

DD

V

V

IH

High Input Voltage

2.7V 

≤ V

DD

 

≤ 5.5V

0.7V

DD

V

C

IN

Input Capacitance

10

pF

I

LEAK

Input current

±0.01

±

1

µA

Status Output (/INT)

V

OL

Low Output Voltage,

I

OL

 = 3mA

0.4

V

Note 6

I

OL

 = 6mA

0.8

V

t

INT

Interrupt Propagation Delay,

from TEMP > T_SET or TEMPx < T_HYSTx

t

CONV

+1

µs

Note 7, 8

to INT < V

OL

, FQ = 00, R

PULLUP

 = 10k

t

nINT

Interrupt Reset Propagation Delay,

from any register read to /INT > V

OH

1

µs

Note 7

FQ = 00, R

PULLUP

 = 10k

T_SET0

Default T_SET0 Value

t

POR

 after V

DD

 > V

POR

81

81

81

°C

T_HYST0

Default T_HYST0 Value

t

POR

 after V

DD

 > V

POR

76

76

76

°C

T_SET1

Default T_SET1 Value

t

POR

 after V

DD

 > V

POR

97

97

97

°C

T_HYST1

Default T_HYST1 Value

t

POR

 after V

DD

 > V

POR

92

92

92

°C

Over-Temperature Output (/CRIT)

V

OL

Low Output Voltage,

I

OL

 = 3mA

0.4

V

Note 6

I

OL

 = 6mA

0.8

V

t

CRIT

/CRIT Propagation Delay,

from TEMPx > T_SETx or TEMPx < T_HYSTx

t

CONV

+1

µs

Note 7, 8

to INT < V

OL

, FQ = 00, R

PULLUP

 = 10k

t

nCRIT

/CRIT Reset Propagation Delay,

from TEMPx < nCRITx to /CRIT > V

OH

1

µs

Note 7

FQ = 00, R

PULLUP

 = 10k

CRIT1

Default CRIT1 Value

t

POR

 after V

DD

 > V

POR

97

97

97

°C

nCRIT1

Default nCRIT1 Value

t

POR

 after V

DD

 > V

POR

92

92

92

°C

Serial Interface Timing (Note 7)

t

1

CLK (Clock) Period

2.5

µs

t

2

Data In Setup Time to CLK High

100

ns

t

3

Data Out Stable After CLK Low

0

ns

t

4

DATA Low Setup Time to CLK Low

start condition

100

ns

t

5

DATA High Hold Time

stop condition

100

ns

After CLK High

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September 29, 2000

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MIC284

MIC284

Micrel

Note 1.

Exceeding the absolute maximum rating may damage the device.

Note 2.

The device is not guaranteed to function outside its operating rating.

Note 3.

Devices are ESD sensitive. Handling precautions recommended.

Human body model: 1.5k in series with 100pF.  Machine model: 200pF, no series resistance.

Note 4.

Final test on outgoing product is performed at T

A

 = TBD

°C.

Note 5.

T

D

 is the temperature of the remote diode junction. Testing is performed using a single unit of one of the transistors listed in Table 6.

Note 6.

Current into this pin will result in self-heating of the MIC284. Sink current should be minimized for best accuracy.

Note 7.

Guaranteed by design over the operating temperature range. Not 100% production tested.

Note 8.

t

CONV

 = t

CONV0

 + t

CONV1

. t

CONV0

 is the conversion time for the local zone; t

CONV1

 is the conversion time for the remote zone.`

Note 9.

Accuracy specification does not include quantization noise, which may be as great as 

±

1

2

LSB (

±0.5°C).

Timing Diagram

t

1

t

2

t

5

t

4

t

3

SCL

SDA Data In

SDA Data Out

Serial Interface Timing

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MIC284

Micrel

MIC284

6

September 29, 2000

FUNCTIONAL DESCRIPTION

Pin Descriptions

VDD:  Power supply input.  See electrical specifications.

GND: Ground return for all MIC284 functions.

CLK: Clock input to the MIC284 from the two-wire serial bus.

The clock signal is provided by the host, and is shared by all

devices on the bus.

DATA: Serial data I/O pin that connects to the two-wire serial

bus.  DATA is bi-directional and has an open-drain output

driver.  An external pull-up resistor or current source some-

where in the system is necessary on this line. This line is

shared by all devices on the bus.

A0: This inputs sets the least significant bit of the MIC284’s

7-bit slave address.  The six most-significant bits are fixed

and are determined by the part number ordered. (See order-

ing information table above.)  Each MIC284 will only respond

to its own unique slave address, allowing up to eight MIC284s

to share a single bus.  A match between the MIC284’s

address and the address specified in the serial bit stream

must be made to initiate communication.   A0 should be tied

directly to VDD or ground.  See "Temperature Measurement

Functional Diagram

2:1

MUX

TEMPERATURE-TO-DIGITAL

CONVERTER

1-Bit

DAC

A0

DATA

VDD

MIC284

CLK

/CRIT 

GND

2-Wire

Serial Bus

Interface

Temperature

Hysteresis

Registers

State

Machine

and

Digital

Comparator

Digital Filter

and

Control

Logic

Open-Drain

Output

Configuration

Register

Bandgap

Sensor 

and 

Reference

Result

Registers

T_SET & /CRIT

Setpoint

Registers

T1

/INT

Pointer

Register

and Power On" for more information. A0 determines the slave

address as shown in Table 1:

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 Table 1. MIC284 Slave Address Settings

/INT: Temperature events are indicated to external circuitry

via this output.  Operation of the /INT output is controlled by

the MODE and IM bits in the MIC284’s configuration register.

See "Comparator and Interrupt Modes" below.  This output is

open-drain and may be wire-OR’ed with other open-drain

signals.  Most systems will require a pull-up resistor or current

source on this pin.  If the IM bit in the configuration register is

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September 29, 2000

7

MIC284

MIC284

Micrel

set, it prevents the /INT output from sinking current.  In I

2

C

and SMBus systems, the IM bit is therefore an interrupt mask

bit.

/CRIT: Over-temperature events are indicated to external

circuitry via this output.  This output is open-drain and may be

wire-OR’ed with other open-drain signals.  Most systems will

require a pull-up resistor or current source on this pin.

T1: This pin connects to an off-chip PN diode junction, for

monitoring the junction temperature at a remote location. The

remote diode may be an embedded thermal sensing junction

in an integrated circuit so equipped (such as Intel's Pentium

III), or a discrete 2N3906-type bipolar transistor with base and

collector tied together.

Temperature Measurement

The temperature-to-digital converter is built around a switched

current source and an eight-bit analog-to-digital converter.

Each diode's temperature is calculated by measuring its

forward voltage drop at two different current levels.  An

internal multiplexer directs the MIC284's current source out-

put to either an internal or external diode junction.  The

MIC284 uses two’s-complement data to represent tempera-

tures.  If the MSB of a temperature value is zero, the

temperature is zero or positive.  If the MSB is one, the

temperature is negative.  More detail on this is given in the

"Temperature  Data Format" section below.  A “temperature

event” results if the value in either of the temperature result

registers (TEMPx) becomes greater than the value in the

corresponding temperature setpoint register (T_SETx).  An-

other temperature event occurs if and when the measured

temperature subsequently falls below the temperature hys-

teresis setting in T_HYSTx.

During normal operation the MIC284 continuously performs

temperature-to-digital conversions, compares the results

against the setpoint registers, and updates the states of /INT,

/CRIT, and the status bits accordingly.  The remote zone is

converted first, followed by the local zone.  The states of /INT,

/CRIT, and the status bits are updated after each measure-

ment is taken.  The remote diode junction connected to T1

may be embedded in an integrated circuit such as a CPU,

ASIC, or graphics processor, or it may be a diode-connected

discrete transistor.

Diode Faults

The MIC284 is designed to respond in a failsafe manner to

hardware faults in the external sensing circuitry.  If the

connection to the external diode is lost or the sense line (T1)

is shorted to VDD or ground, the temperature data reported

by the A/D converter will be forced to its full-scale value

(+127

°C).  This will cause a temperature event to occur if

T_SET1 or CRIT1 are set to any value less than 127

°C (7F

h

= 0111 1111

b

).  An interrupt will be generated on /INT if so

enabled.  The temperature reported for the external zone will

remain +127

°C until the fault condition is cleared.  This fault

detection mechanism requires that the MIC284 complete the

number of conversion cycles specified by Fault_Queue.  The

part will therefore require one or more conversion cycles

following power-on or a transition from shutdown to normal

operation before reporting an external diode fault.

Serial Port Operation

The MIC284 uses standard SMBus Write_Byte and

Read_Byte operations for communication with its host.  The

SMBus Write_Byte operation involves sending the device’s

slave address (with the R/W bit low to signal a write opera-

tion), followed by a command byte and a data byte.  The

SMBus Read_Byte operation is similar, but is a composite

write and read operation: the host first sends the device’s

slave address followed by the command byte, as in a write

operation.  A new start bit must then be sent to the MIC284,

followed by a repeat of the slave address with the R/W bit

(LSB) set to the high (read) state.  The data to be read from

the part may then be clocked out.

The command byte is eight bits wide.  This byte carries the

address of the MIC284 register to be operated upon, and is

stored in the part’s pointer register.  The pointer register is an

internal write-only register.  The command byte (pointer

register) values corresponding to the various MIC284 regis-

ter addresses are shown in Table 2.  Command byte values

other than those explicitly shown are reserved, and should

not be used. Any command byte sent to the MIC284 will

persist in the pointer register indefinitely until it is overwritten

by another command byte.  If the location latched in the

pointer register from the last operation is known to be correct

(i.e., points to the desired register), then the Receive_Byte

procedure may be used. To perform a Receive_Byte, the host

sends an address byte to select the MIC284, and then

retrieves the data byte.  Figures 1 through 3 show the formats

for these procedures.

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MIC284

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MIC284

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September 29, 2000

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e

t

-

r

e

v

o

Table 2.  MIC284 Register Addresses

background image

September 29, 2000

9

MIC284

MIC284

Micrel

S

1001

XX

A

0

0

A

0

0

XXXXXXA

X

X

X

XXXX

X

/A

P

MIC284 Sla

v

e

 Address

D

ATA

CLK

Command Byte

Data Byte to MIC284

ST

AR

T

ST

OP

R/W = 

WRITE

A

CKNO

WLEDGE

A

CKNO

WLEDGE

NO

T A

CKNO

WLEDGE

Master-to-sla

v

e

 tr

ansmission

Sla

v

e-to-master response

Figure 1. WRITE_BYTE Protocol

S

1001

XX

A

0

XX

A

0

0

A

0

0

XXXXXXAS

1

1

1

00

X

X

X

XXXX

A

X

/A

P

MIC284 Sla

v

e

 Address

D

ATA

CLK

Command Byte

MIC284 Sla

v

e

 Address

Data Read F

rom MIC284

ST

AR

T

ST

AR

T

ST

OP

R/W = 

WRITE

R/W = READ

A

CKNO

WLEDGE

A

CKNO

WLEDGE

A

CKNO

WLEDGE

NO

T A

CKNO

WLEDGE

Master-to-sla

v

e

 tr

ansmission

Sla

v

e-to-master response

Figure 2. READ_BYTE Protocol

S

1001

XX

A

0

1A

/A

X

X

X

XXX

P

X

X

MIC284 Sla

v

e

 Address

D

ATA

CLK

Data Byte from MIC284

ST

AR

T

ST

OP

R/W = READ

A

CKNO

WLEDGE

NO

T A

CKNO

WLEDGE

Master-to-sla

v

e

 tr

ansmission

Sla

v

e-to-master response

Figure 3. RECEIVE_BYTE

background image

MIC284

Micrel

MIC284

10

September 29, 2000

S

1001

XXX

AX

X

XXXXXXXA

MIC284 Sla

v

e

 Address

First Byte of 

T

ransaction

ST

AR

T

A

CKNO

WLEDGE

A

CKNO

WLEDGE

R/W = DONT CARE

/A

P

X

X

XXXXXX

Last Byte of 

T

ransaction

A/D Con

v

e

rter

in Standb

y

Con

v

ersion

in Prog

ress

Ne

w Con

v

ersion

in Prog

ress

Ne

w Con

v

ersion

Begins

Con

v

ersion Interr

upted

By MIC284 Ac

kno

wledge

First

Result

Ready

t

CONV1

ST

OP

NO

T A

CKNO

WLEDGE

Master-to-sla

v

e

 tr

ansmission

Sla

v

e-to-master response

Figure 4. A/D Converter Timing

A

SS

1000

XX

A

0

XX

A

0

0

A

00000001

A

1

0

1

00

X

X

XXXXXX

/A

P

MIC284 Sla

v

e

 Address

 

T

emper

ature e

v

ent occurs

MIC284 Sla

v

e

 Address

 

INT

Command Byte = 01

h

 = CONFIG

CONFIG V

alue*

ST

AR

T

ST

AR

T

ST

OP

R/W = 

WRITE

A

CKNO

WLEDGE

A

CKNO

WLEDGE

A

CKNO

WLEDGE

R/W = READ

NO

T A

CKNO

WLEDGE

Master-to-sla

v

e

 tr

ansmission

Sla

v

e-to-master response

t

n/INT

t

/INT

*

Status bits in CONFIG are cleared to z

ero f

ollo

wing this oper

ation

Figure 5. Responding to Interrupts

background image

September 29, 2000

11

MIC284

MIC284

Micrel

e

r

u

t

a

r

e

p

m

e

T

y

r

a

n

i

B

x

e

H

C

°

5

2

1

+

1

0

1

1

1

1

1

0

b

D

7

h

C

°

5

2

+

1

0

0

1

1

0

0

0

b

9

1

h

C

°

0

.

1

+

1

0

0

0

0

0

0

0

b

1

0

h

C

°

0

0

0

0

0

0

0

0

0

b

0

0

h

C

°

0

.

1

1

1

1

1

1

1

1

1

b

F

F

h

C

°

5

2

1

1

1

0

0

1

1

1

b

7

E

h

C

°

0

4

0

0

0

1

1

0

1

1

b

8

D

h

C

°

5

5

1

0

0

1

0

0

1

1

b

9

C

h

Table 3.  Digital Temperature Format

Temperature Data Format

The LSB of each register represents one degree Centigrade.

The values are in a two’s complement format, wherein the

most significant bit (D7), represents the sign: zero for positive

temperatures and one for negative temperatures. Table 3

shows examples of the data format used by the MIC284 for

temperatures.

A/D Converter Timing

Whenever the MIC284 is not in its low power shutdown mode,

the internal A/D converter (ADC) attempts to make continu-

ous conversions unless interrupted by a bus transaction

accessing the MIC284.  When the part is accessed, the

conversion in progress will be halted, and the partial result

discarded. When the access to the MIC284 is complete, the

ADC will begin a new conversion cycle with results for the

remote zone valid t

CONV1

 after that, and for the local zone

t

CONV0

 later.  Figure 4  shows this behavior.  The conversion

time is twice as long for external conversions as it is for

internal conversions.  This allows the use of a filter capacitor

on T1 without a loss of accuracy due to the resulting longer

settling times.

Upon powering-up, coming out of shutdown mode, or resum-

ing operation following a serial bus transaction, the ADC will

begin acquiring temperature data starting with the external

zone (zone 1), followed by the internal zone (zone 0).  If the

ADC is interrupted by a serial bus transaction, it will restart the

conversion that was interrupted and then continue in the

normal sequence.   This sequence will repeat indefinitely until

the MIC284 is shut down, powered off, or is interrupted by a

serial bus transaction as described above.

Power-On

When power is initially applied, the MIC284’s internal regis-

ters are set to their default states, and  A0  is read to establish

the device’s slave address.  The MIC284’s power-up default

state can be summarized as follows:

• Normal Mode operation (i.e., part is not in shut-

down)

• /INT function is set to Comparator Mode

• Fault  Queue depth = 1 (FQ=00)

• Interrupts are enabled (IM = 0)

• T_SET0 =  81

°C; T_HYST0  = 76°C

• T_SET1 =  97

°C; T_HYST1  = 92°C

• CRIT1 =  97

°C; nCRIT1 =  92°C

• Initialized to recognize overtemperature faults

Comparator and Interrupt Modes

Depending on the setting of the MODE bit in the configuration

register, the /INT output will behave either as an interrupt

request signal or a thermostatic control signal.  Thermostatic

operation is known as 

comparator mode.   The /INT output is

asserted when the measured temperature, as reported in

either of the TEMPx registers, exceeds the threshold pro-

grammed into the corresponding T_SETx register for the

number of conversions specified by Fault_Queue (described

below).  In comparator mode, /INT will remain asserted and

the status bits will remain high unless and until the measured

temperature falls below the value in the T_HYSTx register for

Fault_Queue conversions.  No action on the part of the host

is required for operation in comparator mode.  Note that

entering shutdown mode will not affect the state of /INT when

the device is in comparator mode.

In 

interrupt mode, once a temperature event has caused a

status bit (Sx) to be set, and the /INT output to be asserted,

they will not be automatically de-asserted when the mea-

sured temperature falls below T_HYSTx.  They can only be

de-asserted by reading any of the MIC284’s internal registers

or by putting the device into shutdown mode.  If the most

recent temperature event was an overtemperature condition,

Sx will not be set again, and /INT cannot be reasserted, until

the device has detected that TEMPx < T_HYSTx.  Similarly,

if the most recent temperature event was an undertemperature

condition, Sx will not be set again, and /INT cannot be

reasserted, until the device has detected that TEMPx >

T_SETx. This keeps the internal logic of the MIC284 back-

ward compatible with that of the LM75 and similar devices. In

both modes, the MIC284 will be responsive to over-tempera-

ture events at power-up.  See "Interrupt Generation", below.

Shutdown Mode

Setting the SHDN bit in the configuration register halts the

otherwise continuous conversions by the A/D converter.  The

MIC284’s power consumption drops to 1

µA typical in shut-

down mode.  All registers may be read from or written to while

in shutdown mode. Serial bus activity will slightly increase the

part’s power consumption.

Entering shutdown mode will not affect the state of /INT when

the device is in comparator mode (MODE = 0).  It will retain

its state until after the device exits shutdown mode and

resumes A/D conversions.

background image

MIC284

Micrel

MIC284

12

September 29, 2000

If the device is shut down while in interrupt mode (mode = 1),

the /INT pin will be unconditionally de-asserted and the

internal latches holding the interrupt status will be cleared.

Therefore, no interrupts will be generated while the MIC284

is in shutdown mode, and the interrupt status will not be

retained.  Regardless of the setting of the MODE bit, the state

of /CRIT and its corresponding status bit, CRIT1, does not

change when the MIC284 enters shutdown mode. They will

retain their states until after the device exits shutdown mode

and resumes A/D conversions.  Since entering shutdown

mode stops A/D conversions, the MIC284 is incapable of

detecting or reporting temperature events of any kind while in

shutdown.  Diode fault detection requires one or more A/D

conversion cycles to detect external sensor faults, therefore

diode faults will not be reported until the MIC284 exits

shutdown (see "Diode Faults" above).

Fault Queues

Fault queues (programmable digital filters) are provided in

the MIC284 to prevent false tripping due to thermal or

electrical noise. The two bits in CONFIG[4:3] set the depth of

Fault_Queue.  Fault_Queue then determines the number of

consecutive temperature events (TEMPx  > T_SETx, TEMPx

< T_HYSTx, TEMP1 > CRIT1, or TEMP1 < nCRIT1) which

must occur in order for the condition to be considered valid.

There are separate fault queues for each zone and for the

over-temperature detect function.  As an example, assume

the part is in comparator mode, and CONFIG[4:3] is pro-

grammed with 10

b

.  The measured temperature in zone one

would have to exceed T_SET1 for four consecutive A/D

conversions before /INT would be asserted or the S1 status

bit set.  Similarly, TEMP1 would have to be less than T_HYST1

for four consecutive conversions before /INT would be reset.

Like any filter, the fault queue function also has the effect of

delaying the detection of temperature events.  In this ex-

ample, it would take 4 x  t

CONV

 to detect a temperature event.

The depth of Fault_Queue vs. D[4:3] of the configuration

register is shown in Table 4:

]

3

:

4

[

G

I

F

N

O

C

h

t

p

e

D

e

u

e

u

Q

_

t

l

u

a

F

0

0

*

n

o

i

s

r

e

v

n

o

c

1

1

0

s

n

o

i

s

r

e

v

n

o

c

2

0

1

s

n

o

i

s

r

e

v

n

o

c

4

1

1

s

n

o

i

s

r

e

v

n

o

c

6

g

n

i

t

t

e

s

t

l

u

a

f

e

D

*

Table 4. Fault_Queue Depth Settings

Interrupt Generation

Assuming the MIC284 is in interrupt mode and interrupts are

enabled, there are five different conditions that will cause the

MIC284 to set one of the status bits (S0, S1, or CRIT1) in

CONFIG and assert the /INT output and/or the /CRIT output.

These conditions are listed in Table 5. When a temperature

event occurs, the corresponding status bit will be set in

CONFIG.  This action cannot be masked.  However, a

temperature event will only generate an interrupt signal on /

INT if it is specifically enabled by the interrupt mask bit (IM =0

in the configuration register). Following an interrupt, the host

should read the contents of the configuration register to

confirm that the MIC284 was the source of the interrupt.  A

read operation on 

any register will cause /INT to be de-

asserted.  This is shown in Figure 5.  The status bits will be

cleared once CONFIG has been read.

Since temperature-to-digital conversions continue while /INT

is asserted, the measured temperature could change be-

tween the MIC284’s assertion of /INT or /CRIT and the host’s

response.  It is good practice for the interrupt service routine

to read the value in TEMPx, to verify that the over-tempera-

ture or under-temperature condition still exists.  In addition,

more than one temperature event may have occurred simul-

taneously or in rapid succession between the assertion of

/INT and servicing of the MIC284 by the host.  The interrupt

service routine should allow for this eventuality. Keep in mind

that clearing the status bits and deasserting /INT is 

not

sufficient to allow further interrupts to occur.  TEMPx must

become less than T_HYSTx if the last event was an over-

temperature condition, or greater than T_SETx if the last

event was an under-temperature condition, before /INT can

be asserted again.

Putting the device into shutdown mode will de-assert /INT

and clear the S0 and S1 status bits. This should not be done

before completing the appropriate interrupt service routine(s).

/CRIT Output

If and when the measured remote temperature exceeds the

value programmed into the CRIT1 register, the /CRIT output

will be asserted and CRIT1 in the configuration register will be

set.  If and when the measured temperature in zone one

subsequently falls below the value programmed into nCRIT1,

the /CRIT output will be de-asserted and the CRIT1 bit in

CONFIG will be cleared.  This action cannot be masked and

is completely independent of the settings of the mode bit and

interrupt mask bit.  The host may poll the state of the /CRIT

output at any time by reading the configuration register.  The

state of the CRIT1 bit exactly follows the state of the /CRIT

output.  The states of /CRIT and CRIT1 do not change when

the MIC284 enters shutdown mode. Entering shutdown mode

stops A/D conversions, however, so their states will not

change while the device is shut down.

Polling

The MIC284 may either be polled by the host, or request the

host’s attention via the /INT pin.  In the case of polled

operation, the host periodically reads the contents of CONFIG

to check the state of the status bits.  The act of reading

CONFIG clears the status bits.   If more than one event that

sets a given status bit occurs before the host polls the

MIC284, only the fact that at least one such event has

occurred will be apparent to the host.  For polled systems, the

interrupt mask bit should be set (IM = 1).  This will disable

interrupts from the MIC284, and prevent the /INT pin from

sinking current.  The host may poll the state of the /CRIT

output at any time by reading the configuration register.  The

state of the CRIT1 bit exactly follows the state of the /CRIT

output.

background image

September 29, 2000

13

MIC284

MIC284

Micrel

T

N

E

V

E

*

N

O

I

T

I

D

N

O

C

*

*

e

s

n

o

p

s

e

R

4

8

2

C

I

M

e

t

o

m

e

r

,

e

r

u

t

a

r

e

p

m

e

t

h

g

i

H

1

T

E

S

_

T

>

1

P

M

E

T

T

N

I

/

t

r

e

s

s

a

,

G

I

F

N

O

C

n

i

1

S

t

e

S

l

a

c

o

l

,

e

r

u

t

a

r

e

p

m

e

t

h

g

i

H

0

T

E

S

_

T

>

0

P

M

E

T

T

N

I

/

t

r

e

s

s

a

,

G

I

F

N

O

C

n

i

0

S

t

e

S

e

t

o

m

e

r

,

e

r

u

t

a

r

e

p

m

e

t

w

o

L

1

T

S

Y

H

_

T

<

1

P

M

E

T

T

N

I

/

t

r

e

s

s

a

,

G

I

F

N

O

C

n

i

1

S

t

e

S

l

a

c

o

l

,

e

r

u

t

a

r

e

p

m

e

t

w

o

L

0

T

S

Y

H

_

T

<

0

P

M

E

T

T

N

I

/

t

r

e

s

s

a

,

G

I

F

N

O

C

n

i

0

S

t

e

S

e

t

o

m

e

r

,

e

r

u

t

a

r

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p

m

e

t

-

r

e

v

O

1

T

I

R

C

>

1

P

M

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T

T

I

R

C

/

t

r

e

s

s

a

,

G

I

F

N

O

C

n

i

T

I

R

C

t

e

S

e

t

o

m

e

r

,

e

r

u

t

a

r

e

p

m

e

t

-

r

e

v

O

T

O

N

1

T

I

R

C

n

<

P

M

E

T

T

I

R

C

/

t

r

e

s

s

a

-

e

d

,

G

I

F

N

O

C

n

i

T

I

R

C

r

a

e

l

C

t

l

u

a

F

e

d

o

i

D

D

N

G

r

o

D

D

V

o

t

d

e

t

r

o

h

s

1

T

r

o

n

e

p

o

1

T

T

N

I

/

t

r

e

s

s

a

,

G

I

F

N

O

C

n

i

1

S

d

n

a

T

I

R

C

t

e

S

*

*

*

T

I

R

C

/

d

n

a

d

e

z

i

n

g

o

c

e

r

e

b

o

t

s

n

o

i

s

r

e

v

n

o

c

e

u

e

u

Q

_

t

l

u

a

F

r

o

f

e

u

r

t

e

b

t

s

u

m

N

O

I

T

I

D

N

O

C

*

d

e

l

b

a

n

e

s

t

p

u

r

e

t

n

i

s

e

m

u

s

s

A

*

*

F

7

=

C

°

7

2

1

+

n

a

h

t

s

s

e

l

e

u

l

a

v

y

n

a

o

t

t

e

s

e

r

a

1

T

I

R

C

d

n

a

1

T

E

S

_

T

t

a

h

t

s

e

m

u

s

s

A

*

*

*

h

1

1

1

1

1

1

1

0

=

b

.

Table 5. MIC284 Temperature Events

background image

MIC284

Micrel

MIC284

14

September 29, 2000

Register Set and Programmer’s Model

Internal Register Set

e

m

a

N

n

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d

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p

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-

r

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M

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8

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h

)

C

°

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(

)

1

(

G

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d

a

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)

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(

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(

)

1

(

1

T

S

Y

H

_

T

s

i

s

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t

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d

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5

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)

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t

n

i

o

p

t

e

s

3

1

h

e

t

i

r

w

/

d

a

e

r

t

i

b

-

8

1

6

h

)

C

°

7

9

+

(

1

T

I

R

C

n

e

r

u

t

a

r

e

p

m

e

t

-

r

e

v

o

s

i

s

e

r

e

t

s

y

h

2

2

h

e

t

i

r

w

/

d

a

e

r

t

i

b

-

8

C

5

h

)

C

°

2

9

+

(

1

T

I

R

C

e

r

u

t

a

r

e

p

m

e

t

-

r

e

v

o

t

n

i

o

p

t

e

s

e

r

u

t

a

r

e

p

m

e

t

3

2

h

e

t

i

r

w

/

d

a

e

r

t

i

b

-

8

1

6

h

)

C

°

7

9

+

(

(1)

TEMP0 and TEMP1 will contain measured temperature data after the completion of one conversion cycle.

(2)

After the first Fault_Queue conversions are complete, status bits will be set if TEMPx > T_SETx or TEMP1 > CRIT1.

Detailed Register Descriptions

Configuration Register

)

G

I

F

N

O

C

(

R

E

T

S

I

G

E

R

N

O

I

T

A

R

U

G

I

F

N

O

C

e

t

i

r

W

/

d

a

e

R

t

i

B

-

8

]

7

[

D

]

6

[

D

]

5

[

D

]

4

[

D

]

3

[

D

]

2

[

D

]

1

[

D

]

0

[

D

y

l

n

o

d

a

e

r

y

l

n

o

d

a

e

r

y

l

n

o

d

a

e

r

e

t

i

r

w

/

d

a

e

r

e

t

i

r

w

/

d

a

e

r

e

t

i

r

w

/

d

a

e

r

e

t

i

r

w

/

d

a

e

r

l

a

c

o

l

s

u

t

a

t

s

)

0

S

(

e

t

o

m

e

r

s

u

t

a

t

s

)

1

S

(

T

I

R

C

/

s

u

t

a

t

s

)

1

T

I

R

C

(

e

u

e

u

q

t

l

u

a

f

h

t

p

e

d

)

]

0

:

1

[

Q

F

(

t

p

u

r

r

e

t

n

i

k

s

a

m

)

M

I

(

T

N

I

/

P

M

C

e

d

o

m

)

E

D

O

M

(

n

w

o

d

t

u

h

S

)

N

D

H

S

(

s

t

i

B

n

o

i

t

c

n

u

F

n

o

i

t

a

r

e

p

O

0

S

)

y

l

n

o

d

a

e

r

(

s

u

t

a

t

s

t

p

u

r

r

e

t

n

i

l

a

c

o

l

t

n

e

v

e

o

n

=

0

,

d

e

r

u

c

c

o

t

n

e

v

e

=

1

1

S

)

y

l

n

o

d

a

e

r

(

s

u

t

a

t

s

t

p

u

r

r

e

t

n

i

e

t

o

m

e

r

t

n

e

v

e

o

n

=

0

,

d

e

r

u

c

c

o

t

n

e

v

e

=

1

1

T

I

R

C

)

y

l

n

o

d

a

e

r

(

s

u

t

a

t

s

e

r

u

t

a

r

e

p

m

e

t

-

r

e

v

o

e

t

o

m

e

r

t

n

e

v

e

o

n

=

0

,

e

r

u

t

a

r

e

p

m

e

t

-

r

e

v

o

=

1

]

0

:

1

[

Q

F

h

t

p

e

d

e

u

e

u

Q

_

t

l

u

a

F

,

s

n

o

i

s

r

e

v

n

o

c

2

=

1

0

,

n

o

i

s

r

e

v

n

o

c

1

=

0

0

s

n

o

i

s

r

e

v

n

o

c

6

=

1

1

,

s

n

o

i

s

r

e

v

n

o

c

4

=

0

1

M

I

k

s

a

m

t

p

u

r

r

e

t

n

i

d

e

l

b

a

n

e

s

t

p

u

r

r

e

t

n

i

=

0

,

d

e

l

b

a

s

i

d

=

1

E

D

O

M

t

p

u

r

r

e

t

n

i

/

r

o

t

a

r

a

p

m

o

c

n

i

p

T

N

I

/

r

o

f

n

o

i

t

c

e

l

e

s

e

d

o

m

,

e

d

o

m

t

p

u

r

r

e

t

n

i

=

1

e

d

o

m

r

o

t

a

r

a

p

m

o

c

=

0

N

D

H

S

n

w

o

d

t

u

h

s

/

l

a

m

r

o

n

n

o

i

t

c

e

l

e

s

e

d

o

m

g

n

i

t

a

r

e

p

o

,

n

w

o

d

t

u

h

s

=

1

l

a

m

r

o

n

=

0

CONFIG Power-Up Value: 0000 0000

b

 = 00

h

(*)

• not in shutdown mode

• comparator mode

• /INT = active low

• Fault_Queue depth = 1

• interrupts enabled.

• no temperature events pending

CONFIG Command Byte Value: 0000 0001

b

 = 01

h

* Following the first Fault_Queue conversions, one or more of the status bits may be set.

background image

September 29, 2000

15

MIC284

MIC284

Micrel

T_SET0 Power-Up Value: 0101 0001

= 51

(+81

°C)

T_SET0 Command Byte Value: 0000 0011

b

 = 03

h

Each LSB represents one degree Centigrade. The values are

in a two's complement format such that 0

°C is reported as

0000 0000

b

. See "Temperature Data Format" for more details.

Local Temperature Setpoint Register

)

0

T

E

S

_

T

(

T

N

I

O

P

T

E

S

E

R

U

T

A

R

E

P

M

E

T

L

A

C

O

L

e

t

i

r

W

/

d

a

e

R

t

i

B

-

8

]

7

[

D

]

6

[

D

]

5

[

D

]

4

[

D

]

3

[

D

]

2

[

D

]

1

[

D

]

0

[

D

B

S

M

6

t

i

b

5

t

i

b

4

t

i

b

3

t

i

b

2

t

i

b

1

t

i

b

B

S

L

t

n

i

o

p

t

e

s

e

r

u

t

a

r

e

p

m

e

t

l

a

c

o

l

s

t

i

B

n

o

i

t

c

n

u

F

n

o

i

t

a

r

e

p

O

]

0

:

7

[

D

*

t

n

i

o

p

t

e

s

e

r

u

t

a

r

e

p

m

e

t

l

a

c

o

l

e

t

i

r

w

/

d

a

e

r

T_HYST0 Power-Up Value: 0100 1100

b

 = 4C

(+76

°C)

T_HYST0 Command Byte Value: 0000 0010

b

 = 02

h

* Each LSB represents one degree Centigrade. The values are

in a two's complement format such that 0

°C is reported as

0000 0000

b

. See "Temperature Data Format" for more details.

Local Temperature Hysteresis Register

)

0

T

S

Y

H

_

T

(

S

I

S

E

R

E

T

S

Y

H

E

R

U

T

A

R

E

P

M

E

T

L

A

C

O

L

e

t

i

r

W

/

d

a

e

R

t

i

B

-

8

]

7

[

D

]

6

[

D

]

5

[

D

]

4

[

D

]

3

[

D

]

2

[

D

]

1

[

D

]

0

[

D

B

S

M

6

t

i

b

5

t

i

b

4

t

i

b

3

t

i

b

2

t

i

b

1

t

i

b

B

S

L

g

n

i

t

t

e

s

s

i

s

e

r

e

t

s

y

h

e

r

u

t

a

r

e

p

m

e

t

l

a

c

o

l

s

t

i

B

n

o

i

t

c

n

u

F

n

o

i

t

a

r

e

p

O

]

0

:

7

[

D

*

g

n

i

t

t

e

s

s

i

s

e

r

e

t

s

y

h

e

r

u

t

a

r

e

p

m

e

t

l

a

c

o

l

e

t

i

r

w

/

d

a

e

r

Local Temperature Result Register

)

0

P

M

E

T

(

S

T

L

U

S

E

R

E

R

U

T

A

R

E

P

M

E

T

L

A

C

O

L

y

l

n

O

d

a

e

R

t

i

B

-

8

]

7

[

D

]

6

[

D

]

5

[

D

]

4

[

D

]

3

[

D

]

2

[

D

]

1

[

D

]

0

[

D

B

S

M

6

t

i

b

5

t

i

b

4

t

i

b

3

t

i

b

2

t

i

b

1

t

i

b

B

S

L

*

C

D

A

m

o

r

f

a

t

a

d

e

r

u

t

a

r

e

p

m

e

t

l

a

c

o

l

s

t

i

B

n

o

i

t

c

n

u

F

n

o

i

t

a

r

e

p

O

]

0

:

7

[

D

l

a

c

o

l

e

h

t

r

o

f

a

t

a

d

e

r

u

t

a

r

e

p

m

e

t

d

e

r

u

s

a

e

m

*

e

n

o

z

y

l

n

o

d

a

e

r

TEMP0 Power-Up Value: 0000 0000

b

 = 00

h

 (0

°C)

TEMP0 Command Byte Value: 0000 0000

b

 = 00

h

* Each LSB represents one degree Centigrade. The values are

in a two's complement format such that 0

°C is reported as

0000 0000

b

. See "Temperature Data Format" for more details.

TEMP0 will contain measured temperature data after the

completion of one conversion.

background image

MIC284

Micrel

MIC284

16

September 29, 2000

T_SET1 Power-Up Value: 0110 0001

b

 = 61

(+97

°C)

T_SET1 Command Byte Value: 0001 0011

b

 = 13

h

* Each LSB represents one degree Centigrade. The values are

in a two's complement format such that 0

°C is reported as

0000 0000

b

. See "Temperature Data Format" for more details.

Remote Temperature Setpoint Register

)

1

T

E

S

_

T

(

T

N

I

O

P

T

E

S

E

R

U

T

A

R

E

P

M

E

T

E

T

O

M

E

R

e

t

i

r

W

/

d

a

e

R

t

i

B

-

8

]

7

[

D

]

6

[

D

]

5

[

D

]

4

[

D

]

3

[

D

]

2

[

D

]

1

[

D

]

0

[

D

B

S

M

6

t

i

b

5

t

i

b

4

t

i

b

3

t

i

b

2

t

i

b

1

t

i

b

B

S

L

t

n

i

o

p

t

e

s

e

r

u

t

a

r

e

p

m

e

t

e

t

o

m

e

r

s

t

i

B

n

o

i

t

c

n

u

F

n

o

i

t

a

r

e

p

O

]

0

:

7

[

D

*

t

n

i

o

p

t

e

s

e

r

u

t

a

r

e

p

m

e

t

e

t

o

m

e

r

e

t

i

r

w

/

d

a

e

r

T_HYST1 Power-Up Value: 0101 1100

b

 = 5C

(+92

°C)

T_HYST1 Command Byte Value: 0001 0010

b

 = 12

h

* Each LSB represents one degree Centigrade. The values are

in a two's complement format such that 0

°C is reported as

0000 0000

b

. See "Temperature Data Format" for more details.

Remote Temperature Hysteresis Register

)

1

T

S

Y

H

_

T

(

S

I

S

E

R

E

T

S

Y

H

E

R

U

T

A

R

E

P

M

E

T

E

T

O

M

E

R

e

t

i

r

W

/

d

a

e

R

t

i

B

-

8

]

7

[

D

]

6

[

D

]

5

[

D

]

4

[

D

]

3

[

D

]

2

[

D

]

1

[

D

]

0

[

D

B

S

M

6

t

i

b

5

t

i

b

4

t

i

b

3

t

i

b

2

t

i

b

1

t

i

b

B

S

L

g

n

i

t

t

e

s

s

i

s

e

r

e

t

s

y

h

e

r

u

t

a

r

e

p

m

e

t

e

t

o

m

e

r

s

t

i

B

n

o

i

t

c

n

u

F

n

o

i

t

a

r

e

p

O

]

0

:

7

[

D

*

g

n

i

t

t

e

s

s

i

s

e

r

e

t

s

y

h

e

r

u

t

a

r

e

p

m

e

t

e

t

o

m

e

r

e

t

i

r

w

/

d

a

e

r

Remote Temperature Result Register

)

1

P

M

E

T

(

T

L

U

S

E

R

E

R

U

T

A

R

E

P

M

E

T

E

T

O

M

E

R

y

l

n

O

d

a

e

R

t

i

B

-

8

]

7

[

D

]

6

[

D

]

5

[

D

]

4

[

D

]

3

[

D

]

2

[

D

]

1

[

D

]

0

[

D

B

S

M

6

t

i

b

5

t

i

b

4

t

i

b

3

t

i

b

2

t

i

b

1

t

i

b

B

S

L

*

C

D

A

m

o

r

f

a

t

a

d

e

r

u

t

a

r

e

p

m

e

t

e

t

o

m

e

r

s

t

i

B

n

o

i

t

c

n

u

F

n

o

i

t

a

r

e

p

O

]

0

:

7

[

D

e

t

o

m

e

r

e

h

t

r

o

f

a

t

a

d

e

r

u

t

a

r

e

p

m

e

t

d

e

r

u

s

a

e

m

*

e

n

o

z

y

l

n

o

d

a

e

r

TEMP1 Power-Up Value: 0000 0000

b

 = 00

(0

°C)

TEMP1 Command Byte Value: 0001 0000

b

 = 10

h

* Each LSB represents one degree Centigrade. The values are

in a two's complement format such that 0

°C is reported as

0000 0000

b

. See "Temperature Data Format" for more details.

TEMP1 will contain measured temperature data for the

selected zone after the completion of one conversion.

background image

September 29, 2000

17

MIC284

MIC284

Micrel

CRIT1 Power-Up Value: 0110 0001

b

 = 61

(+97

°C)

CRIT1 Command Byte Value: 0010 0011b = 23

h

* Each LSB represents one degree Centigrade. The values are

in a two's complement format such that 0

°C is reported as

0000 0000

b

. See "Temperature Data Format" for more details.

Remote Over-Temperature Setpoint Register

)

1

T

I

R

C

(

T

N

I

O

P

T

E

S

E

R

U

T

A

R

E

P

M

E

T

-

R

E

V

O

E

T

O

M

E

R

e

t

i

r

W

/

d

a

e

R

t

i

B

-

8

]

7

[

D

]

6

[

D

]

5

[

D

]

4

[

D

]

3

[

D

]

2

[

D

]

1

[

D

]

0

[

D

B

S

M

6

t

i

b

5

t

i

b

4

t

i

b

3

t

i

b

2

t

i

b

1

t

i

b

B

S

L

t

n

i

o

p

t

e

s

e

r

u

t

a

r

e

p

m

e

t

-

r

e

v

o

e

t

o

m

e

r

s

t

i

B

n

o

i

t

c

n

u

F

n

o

i

t

a

r

e

p

O

]

0

:

7

[

D

*

t

n

i

o

p

t

e

s

e

r

u

t

a

r

e

p

m

e

t

-

r

e

v

o

e

t

o

m

e

r

e

t

i

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Remote Over-Temperature Hysteresis Register

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nCRIT Power-Up Value: 0101 1100

b

 = 5C

(+92

°C)

nCRIT1 Command Byte Value: 0010 0010

b

 = 22

h

* Each LSB represents one degree Centigrade. The values are

in a two's complement format such that 0

°C is reported as

0000 0000

b

. See "Temperature Data Format" for more details.

background image

MIC284

Micrel

MIC284

18

September 29, 2000

Applications

Remote Diode Selection

Most small-signal PNP transistors with characteristics similar

to the JEDEC 2N3906 will perform well as remote tempera-

ture sensors.  Table 6 lists several examples of such parts

that Micrel has tested for use with the MIC284.  Other

transistors equivalent to these should also work well.

Minimizing Errors

Self-Heating

One concern when using a part with the temperature accu-

racy and resolution of the MIC284 is to avoid errors induced

by self-heating (V

DD

 

×  I

DD

) + (V

OL

 

×  I

OL

).  In order to

understand what level of error this might represent, and how

to reduce that error, the dissipation in the MIC284 must be

calculated and its effects reduced to a temperature offset.

The worst-case operating condition for the MIC284 is when

V

DD

 = 5.5V, MSOP-08 package.  T he maximum power

dissipated in the part is given in Equation 1 below.

In most applications, the /INT output will be low for at most a

few milliseconds before the host resets it back to the high

state, making its duty cycle low enough that its contribution to

self-heating of the MIC284 is negligible.  Similarly, the DATA

pin will in all likelihood have a duty cycle of substantially below

25% in the low state.  These considerations, combined with

more typical device and application parameters, give a better

system-level view of device self-heating in interrupt-mode

usage. This is illustrated by Equation 2.

If the part is to be used in comparator mode, calculations

similar to those shown in Equation 2 (accounting for the

expected value and duty cycle of I

OL(/INT)

 and I

OL(/CRIT)

)

will give a good estimate of the device’s self-heating error.

In any application, the best test is to verify performance

against calculation in the final application environment.  This

is especially true when dealing with systems for which some

Vendor

Part Number

Package

Fairchild

MMBT3906

SOT-23

On Semiconductor

MMBT3906L

SOT-23

Phillips Semiconductor

PMBT3906

SOT-23

Samsung

KST3906-TF

SOT-23

Table 6. Transistors Suitable for Remote Temperature Sensing Use

of the thermal data (e.g., PC board thermal conductivity and

ambient temperature) may be poorly defined or unobtainable

except by empirical means.

Series Resistance

The operation of the MIC284 depends upon sensing the

∆V

CB-E

 of a diode-connected PNP transistor (“diode”) at two

different current levels. For remote temperature measure-

ments, this is done using an external diode connected be-

tween T1 and ground.

Since this technique relies upon measuring the relatively

small voltage difference resulting from two levels of current

through the external diode, any resistance in series with the

external diode will cause an error in the temperature reading

from the MIC284.  A good rule of thumb is this: for each ohm

in series with the external transistor, there will be a 0.9

°C error

in the MIC284’s temperature measurement.  It isn’t difficult to

keep the series resistance well below an ohm (typically <

0.1

Ω), so this will rarely be an issue.

Filter Capacitor Selection

It is sometimes desirable to use a filter capacitor between the

T1 and GND pins of the MIC284.  The use of this capacitor is

recommended in environments with a lot of high frequency

noise (such as digital switching noise), or if long wires are

used to attach to the remote diode.  The maximum recom-

mended total capacitance from the T1 pin to GND is 2700pF.

This typically suggests the use of a 2200pF NP0 or C0G

ceramic capacitor with a 10% tolerance.

If the remote diode is to be at a distance of more than 

≈ 6" —

12" from the MIC284, using twisted pair wiring or shielded

microphone cable for the connections to the diode can

significantly help reduce noise pickup. If using a long run of

shielded cable, remember to subtract the cable’s conductor-

to-shield capacitance from the 2700pF maximum total ca-

pacitance.

P

[(I

V

) (I

V

) (I

V

) (I

V

)]

P

[(0.75mA

5.5V) + (6mA

0.8V) + (6mA

0.8V) + (6mA

0.8V)

P

18.53mW

R

of MSOP - 08 package is 206 C / W

Maximum  T  relative to T  due to self heating is 18.53mW 206 C / W = 3.82 C

D

DD

DD

OL(DATA)

OL(DATA)

OL(/INT)

OL(/INT)

OL(/CRIT)

OL(/CRIT)

D

D

(j-a)

J

A

=

×

+

×

+

×

+

×

=

×

×

×

×

=

°

×

°

°

θ

Equation 1. Worst-case self-heating

[(0.35mA I

3.3V) (25% 1.5mA I

0.3V) (1% 1.5mA I

0.3V) + (25% 1.5mA I

0.3V) = 1.38mW

T

(1.38mW

206 C / W)

DD(typ)

OL(DATA)

OL(/INT)

OL(/CRIT)

J

×

+

×

×

+

×

×

×

×

∆ =

×

°

=

°

0.29 C

Equation 2. Real-world self-heating example

background image

September 29, 2000

19

MIC284

MIC284

Micrel

REMOTE DIODE (T1)

GUARD/RETURN

1

2

3

DATA

CLK

/INT

GND

8

7

6

5

4

VDD

A0

T1

/CRIT

GUARD/RETURN

MIC284

Figure 6. Guard Traces/Kelvin Ground Returns

CLK

FROM

SERIAL BUS

HOST

OVER-TEMP

SHUTDOWN

Remote

Diode

2200pF

MIC284

/INT

/CRIT

DATA

100

3.3V

10k pull-ups

VDD

T1

A0

GND

4.7

µF

0.1

µF

Figure 7. V

DD

 Decoupling for Very Noisy Supplies

Layout Considerations

The following guidelines should be kept in mind when design-

ing and laying out circuits using the MIC284:

1. Place the MIC284 as close to the remote diode

as possible, while taking care to avoid severe

noise sources such as high frequency power

transformers, CRTs, memory and data busses,

and the like.

2. Since any conductance from the various volt-

ages on the PC Board and the T1 line can

induce serious errors, it is good practice to

guard the remote diode’s emitter trace with a

pair of ground traces.  These ground traces

should be returned to the MIC284’s own ground

pin.  They should not be grounded at any other

part of their run.  However, it is highly desirable

to use these guard traces to carry the diode’s

own ground return back to the ground pin of the

MIC284, thereby providing a Kelvin connection

for the base of the diode.  See Figure 6.

3. When using the MIC284 to sense the tempera-

ture of a processor or other device which has an

integral thermal diode, e.g., Intel’s Pentium III,

connect the emitter and base of the remote

sensor to the MIC284 using the guard traces

and Kelvin return shown in Figure 6.  The

collector of the remote diode is typically inacces-

sible to the user on these devices.  To allow for

this, the MIC284 has superb rejection of noise

appearing from collector to GND, as long as the

base to ground connection is relatively quiet.

4. Due to the small currents involved in the mea-

surement of the remote diode’s 

∆V

BE

, it is

important to adequately clean the PC board after

soldering to prevent current leakage.  This is

most likely to show up as an issue in situations

where water-soluble soldering fluxes are used.

5. In general, wider traces for the ground and T1

lines will help reduce susceptibility to radiated

noise (wider traces are less inductive).  Use

trace widths and spacing of 10 mils wherever

possible and provide a ground plane under the

MIC284 and under the connections from the

MIC284 to the remote diode.  This will help

guard against stray noise pickup.

6. Always place a good quality power supply

bypass capacitor directly adjacent to, or under-

neath, the MIC284.  This should be a 0.1

µF

ceramic capacitor.  Surface-mount parts provide

the best bypassing because of their low induc-

tance.

7. When the MIC284 is being powered from

particularly noisy power supplies, or from

supplies which may have sudden high-amplitude

spikes appearing on them, it can be helpful to

add additional power supply filtering.  This

should be implemented as a 100

Ω resistor in

series with the part’s VDD pin, and a 4.7

µF,

6.3V electrolytic capacitor from VDD to GND.

See Figure 7.

background image

MIC284

Micrel

MIC284

20

September 29, 2000

Package Information

45

°

0

°–8°

0.244 (6.20)

0.228 (5.79)

0.197 (5.0)

0.189 (4.8)

SEATING

PLANE

0.026 (0.65)

MAX

)

0.010 (0.25)

0.007 (0.18)

0.064 (1.63)

0.045 (1.14)

0.0098 (0.249)

0.0040 (0.102)

0.020 (0.51)

0.013 (0.33)

0.157 (3.99)

0.150 (3.81)

0.050 (1.27)

TYP

PIN 1

DIMENSIONS:

INCHES (MM)

0.050 (1.27)

0.016 (0.40)

8-Lead SOP (M)

0.008 (0.20)

0.004 (0.10)

0.039 (0.99)

0.035 (0.89)

0.021 (0.53)

0.012 (0.03) R

0.0256 (0.65) TYP

0.012 (0.30) R

5

° MAX

0

° MIN

0.122 (3.10)

0.112 (2.84)

0.120 (3.05)

0.116 (2.95)

0.012 (0.03)

0.007 (0.18)

0.005 (0.13)

0.043 (1.09)

0.038 (0.97)

0.036 (0.90)

0.032 (0.81)

DIMENSIONS:

INCH (MM)

0.199 (5.05)

0.187 (4.74)

8-Lead MSOP (MM)

MICREL INC.

1849 FORTUNE DRIVE

SAN JOSE, CA 95131

USA

TEL

 + 1 (408) 944-0800  

FAX

 + 1 (408) 944-0970  

WEB

 http://www.micrel.com

This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or

other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.

© 2000 Micrel Incorporated