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___________________________________________________________________Selector Guide

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.

For small orders, phone 1-800-835-8769.

________________General Description

The MAX6316–MAX6322 family of microprocessor (µP)

supervisory circuits monitors power supplies and

microprocessor activity in digital systems. It offers sev-

eral combinations of push/pull, open-drain, and bidirec-

tional (such as Motorola 68HC11) reset outputs, along

with watchdog and manual-reset features. The 

Selector

Guide

below lists the specific functions available from

each device. These devices are specifically designed

to ignore fast negative transients on V

CC

. Resets are

guaranteed valid for V

CC

down to 1V.

These devices are available in 26 factory-trimmed reset

threshold voltages (from 2.5V to 5V, in 100mV incre-

ments), featuring four minimum power-on reset timeout

periods (from 1ms to 1.12sec), and four watchdog time-

out periods (from 6.3ms to 25.6sec). Nine standard ver-

sions are available with an order increment requirement

of 2500 pieces (see 

Standard Versions

table); contact

the factory for availability of other versions, which have

an order increment requirement of 10,000 pieces.

The MAX6316–MAX6322 are offered in a miniature 

5-pin SOT23 package.

________________________Applications

Portable Computers

Computers

Controllers

Intelligent Instruments

Portable/Battery-Powered Equipment

Embedded Control Systems

____________________________Features

o

Small 5-Pin SOT23 Package

o

Available in 26 Reset Threshold Voltages

2.5V to 5V, in 100mV Increments

o

Four Reset Timeout Periods

1ms, 20ms, 140ms, or 1.12sec (min)

o

Four Watchdog Timeout Periods

6.3ms, 102ms, 1.6sec, or 25.6sec (typ) 

o

Four Reset Output Stages

Active-High, Push/Pull

Active-Low, Push/Pull

Active-Low, Open-Drain 

Active-Low, Bidirectional

o

Guaranteed Reset Valid to V

CC

= 1V

o

Immune to Short Negative V

CC

Transients

o

Low Cost

o

No External Components

MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

________________________________________________________________

Maxim Integrated Products

1

19-0496; Rev 3; 1/99

PART

MAX6316

LUK____-T

MAX6316MUK____-T

-40°C to +85°C

-40°C to +85°C

TEMP. RANGE

PIN-PACKAGE

5 SOT23-5

5 SOT23-5

_______________Ordering Information

Ordering Information continued at end of data sheet.

MAX6317

HUK____-T

-40°C to +85°C

5 SOT23-5

MAX6318

HUK____-T

-40°C to +85°C

5 SOT23-5

ACTIVE-LOW

OPEN-DRAIN

MAX6316L

MAX6316M

MAX6317H

 

 

 

MAX6321HP

 

 

 

 

MAX6318LH

 

MAX6318MH**

 

MAX6319LH

 

MAX6319MH**

 

MAX6320P

 

 

ACTIVE-LOW

PUSH/PULL

 

 

 

ACTIVE-HIGH

PUSH/PULL

 

 

 

 

 

ACTIVE-LOW

BIDIRECTIONAL

 

 

 

PART

WATCHDOG

INPUT

MANUAL

RESET

INPUT

 

 

MAX6322HP

 

 

RESET OUTPUTS*

 

 

*

The MAX6318/MAX6319/MAX6321/MAX6322 feature two types of reset output on each device.

**

Future product—contact factory for availability.

MAX6318MHUK____-T

-40°C to +85°C

5 SOT23-5

Typical Operating Circuit and Pin Configurations appear at

end of data sheet.

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ELECTRICAL CHARACTERISTICS

(V

CC

= 2.5V to 5.5V, T

A

= -40°C to +85°C, unless otherwise noted. Typical values are at T

A

= +25°C.) (Note 1)

MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

2

_______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional

operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability.

Voltage (with respect to GND)

V

CC

......................................................................-0.3V to +6V

RESET (MAX6320/MAX6321/MAX6322 only)...... -0.3V to +6V

All Other Pins.........................................-0.3V to (V

CC

+ 0.3V)

Input/Output Current, All Pins .............................................20mA

Continuous Power Dissipation (T

A

= +70°C)

SOT23-5 (derate 7.1mW/°C above +70°C)...............571mW

Operating Temperature Range............................-40°C to +85°C

Junction Temperature ......................................................+150°C

Storage Temperature Range..............................-65°C to +160°C

Lead Temperature (soldering, 10sec)..............................+300°C

V

CC

- 1.5

0.8 x V

CC

V

OH

0.4

0.3

0.3

V

0.3

V

OL

RESET Output Voltage

µs

40

t

RD

V

CC

to RESET Delay

1120

1600

2240

140

200

280

20

28

40

ms

1

1.4

2

t

RP

Reset Active Timeout Period

mV

3

Reset Threshold Hysteresis

V

1

5.5

V

CC

Operating Voltage Range

V

TH

-2.5% V

TH

V

TH

+2.5%

V

V

TH

-1.5% V

TH

V

TH

+1.5%

V

RST

Reset Threshold (Note 2)

ppm/°C

40

V

TH

/°C

Reset Threshold Temperature

Coefficient

UNITS

MIN

TYP

MAX

SYMBOL

PARAMETER

V

CC

4.5V, I

SOURCE

= 800µA

V

CC

2.7V, I

SOURCE

= 500µA

V

CC

4.5V, I

SINK

= 3.2mA

V

CC

2.7V, I

SINK

= 1.2mA

V

CC

1.2V, I

SINK

= 100µA

V

CC

1.0V, I

SINK

= 50µA

T

A

= -40°C to +85°C

V

CC

falling at 1mV/µs

MAX63_ _D_-T

T

A

= -40°C to +85°C

T

A

= +25°C

MAX63_ _C_-T

MAX63_ _B_-T

MAX63_ _A_-T

CONDITIONS

V

0.3

V

OL

RESET Output Voltage

V

CC

2.7V, I

SINK

= 1.2mA

0.4

V

CC

4.5V, I

SINK

= 3.2mA

0.8 x V

CC

V

OH

V

CC

1.8V, I

SOURCE

= 150µA

0.8 x V

CC

V

CC

2.7V, I

SOURCE

= 500µA

V

CC

- 1.5

V

CC

4.5V, I

SOURCE

= 800µA

Note 1:

Over-temperature limits are guaranteed by design, not production tested.

Note 2:

A factory-trimmed voltage divider programs the nominal reset threshold (V

TH

). Factory-trimmed reset thresholds are 

available in 100mV increments from 2.5V to 5V (see Table 1 at end of data sheet). 

MAX6316/MAX6317/MAX6318/

MAX6320/MAX6321:  

MR and WDI unconnected

µA

10

20

I

CC

Supply Current

V

CC

= 5.5V

5

12

V

CC

= 3.6V

MAX6319/MAX6322: 

MR unconnected

5

12

V

CC

= 5.5V

3

8

V

CC

= 3.6V

PUSH/PULL RESET OUTPUT (MAX6316L/MAX6317H/MAX6318_H/MAX6319_H/MAX6321HP/MAX6322HP)

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MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

_______________________________________________________________________________________

3

Note 3:

This is the minimum time RESET must be held low by an external pull-down source to set the active pull-up flip-flop.  

Note 4:

Measured from RESET V

OL

to (0.8 x V

CC

), R

LOAD

.

Note 5:

WDI is internally serviced within the watchdog period if WDI is left unconnected.

Note 6:

The WDI input current is specified as the average input current when the WDI input is driven high or low. The WDI input is

designed for a three-stated-output device with a 10µA maximum leakage current and capable of driving a maximum capaci-

tive load of 200pF. The three-state device must be able to source and sink at least 200µA when active.

µA

1.0

I

LKG

Open-Drain Reset Output

Leakage Current

ns

400

t

S

Transition Flip-Flop Setup Time 

333

ns

333

t

R

RESET Output Rise Time 

(Note 4)

UNITS

MIN

TYP

MAX

SYMBOL

PARAMETER

(Note 3)

V

CC

= 5.0V, C

L

= 200pF

V

CC

= 3.0V, C

L

= 120pF

CONDITIONS

ELECTRICAL CHARACTERISTICS (continued)

(V

CC

= 2.5V to 5.5V, T

A

= -40°C to +85°C, unless otherwise noted. Typical values are at T

A

= +25°C.) (Note 1)

666

666

V

CC

= 5.0V, C

L

= 400pF

V

CC

= 3.0V, C

L

= 250pF

V

0.4

0.65

V

PTH

Active Pull-Up Enable Threshold

V

CC

= 5.0V

mA

20

RESET Active Pull-Up Current

V

CC

= 5.0V

k

4.2

4.7

5.2

RESET Pull-Up Resistance

V

0.3

V

OL

RESET Output Voltage

V

CC

1.0V, I

SINK

= 50µA

0.3

V

CC

1.2V, I

SINK

= 100µA

0.3

V

CC

2.7V, I

SINK

= 1.2mA

0.4

V

CC

4.5V, I

SINK

= 3.2mA

ms

4.3

6.3

9.3

t

WD

Watchdog Timeout Period

MAX63_ _ _ W-T

71

102

153

MAX63_ _ _ X-T

sec

1.12

1.6

2.4

MAX63_ _ _ Y-T

17.9

25.6

38.4

MAX63_ _ _ Z-T

ns

50

t

WDI

WDI Pulse Width

V

IL

= 0.3 x V

CC

, V

IH

= 0.7 x V

CC

V

0.3 x V

CC

V

IL

WDI Input Threshold

(Note 5)

0.7 x V

CC

120

160

I

WDI

WDI Input Current

(Note 6)

WDI = V

CC

, time average

-20

-15

V

WDI

= 0, time average

V

IH

V

0.8

V

IL

MR Input Threshold

V

TH

> 4.0V

2.0

V

IH

0.3 x V

CC

V

IL

V

TH

< 4.0V

0.7 x V

CC

V

IH

µs

1

MR Input Pulse Width

ns

100

MR Glitch Rejection

k

35

52

75

MR Pull-Up Resistance

ns

230

MR to Reset Delay

V

CC

= 5V                                                      

µA

BIDIRECTIONAL 

RESET

OUTPUT (MAX6316M/MAX6318MH/MAX6319MH)

OPEN-DRAIN 

RESET

OUTPUT (MAX6320P/MAX6321HP/MAX6322HP)

WATCHDOG INPUT (MAX6316/MAX6317H/MAX6318_H/MAX6320P/MAX6321HP)

MANUAL-RESET INPUT (MAX6316_/MAX6317H/MAX6319_H/MAX6320P/MAX6322HP)

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MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

4

_______________________________________________________________________________________

__________________________________________Typical Operating Characteristics

(T

= +25°C, unless otherwise noted.)

0

2

1

4

3

8

7

6

5

10

9

-40

0

20

-20

40

60

80

100

MAX6316/17/18/20/21

SUPPLY CURRENT vs. TEMPERATURE

MAX6316toc01

TEMPERATURE (°C)

SUPPLY CURRENT (

µ

A)

V

CC

 = 5V

V

CC

 = 3V

V

CC

 = 1V

0

30

20

10

50

40

90

80

70

60

100

-40

-20

0

20

40

60

80

100

V

CC

 FALLING TO RESET PROPAGATION 

DELAY vs. TEMPERATURE

MAX6316toc03

TEMPERATURE (°C)

RESET PROPAGATION DELAY (

µ

s)

V

CC

 FALLING AT 1mV/

µ

s

V

RST

 - V

CC

 = 100mV

140

180

160

240

220

200

300

280

260

320

-40

0

20

-20

40

60

80

100

MAX6316/17/19/20/22

MANUAL-RESET TO RESET

PROPAGATION DELAY vs. TEMPERATURE

MAX6316toc04

TEMPERATURE (°C)

PROPAGATION DELAY (ns)

V

CC

 = 5V

0.95

0.98

0.97

0.96

1.00

0.99

1.04

1.03

1.02

1.01

1.05

-40

-20

0

20

40

60

80

100

NORMALIZED RESET TIMEOUT

PERIOD vs. TEMPERATURE

MAX6316toc05

TEMPERATURE (°C)

NORMALIZED RESET TIMEOUT PERIOD

0.95

0.98

0.97

0.96

1.00

0.99

1.04

1.03

1.02

1.01

1.05

-40

-20

0

20

40

60

80

100

MAX6316/17/18/20/21

NORMALIZED WATCHDOG TIMEOUT

PERIOD vs. TEMPERATURE

MAX6316toc06

TEMPERATURE (°C)

NORMALIZED WATCHDOG TIMEOUT PERIOD

80

0

10

100

1000

MAXIMUM V

CC

 TRANSIENT DURATION

vs. RESET THRESHOLD OVERDRIVE

20

10

MAX6316toc08

RESET THRESHOLD OVERDRIVE (mV) V

RST

 - V

CC

TRANSIENT DURATION (

µ

s)

30

50

60

40

70

V

RST

 = 3.3V

V

RST

 = 4.63V

V

RST

 = 2.63V

RESET OCCURS ABOVE LINES

PASSIVE

4.7k

 

PULL-UP

2V/div

RESET, ACTIVE

PULL-UP

2V/div

RESET

INPUT

5V/div

200ns/div

MAX6316M/6318MH/6319MH

BIDIRECTIONAL 

PULL-UP CHARACTERISTICS

MAX6316toc09

100pF

4.7k

+5V

74HC05

74HC05

V

CC

GND

MR

100pF

INPUT

INPUT

+5V

RESET

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MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

_______________________________________________________________________________________

5

______________________________________________________________Pin Description

1

1

MAX6316M/MAX6318MH/MAX6319MH:

Bidirectional, Active-Low, Reset Output.

Intended to interface directly to microprocessors

with bidirectional resets such as the Motorola

68HC11.

MAX6320P/MAX6321HP/MAX6322HP:

Open-Drain, Active-Low, Reset Output. NMOS out-

put (sinks current only). Connect a pull-up resistor

from RESET to any supply voltage up to 6V.

MAX6316L/MAX6318LH/MAX6319LH:

Active-Low, Reset Output. CMOS push/pull

output (sources and sinks current).

RESET

1

4

5

3

2

MAX6319LH

MAX6319MH

MAX6322HP

PIN

4

5

3

2

MAX6318LH

MAX6318MH

MAX6321HP

3

4

5

1

2

MAX6317H

Active-Low, Manual Reset Input. Pull low to force a

reset. Reset remains asserted for the duration of

the Reset Timeout Period after MR transitions from

low to high. Leave unconnected or connected to

V

CC

if not used.

MR

3

Watchdog Input. Triggers a reset if it remains

either high or low for the duration of the watchdog

timeout period. The internal watchdog timer clears

whenever a reset asserts or whenever WDI sees a

rising or falling edge. To disable the watchdog fea-

ture, leave WDI unconnected or three-state the dri-

ver connected to WDI.

WDI

4

Supply Voltage. Reset is asserted when V

CC

drops below the Reset Threshold Voltage (V

RST

).

Reset remains asserted until V

CC

rises above

V

RST

and for the duration of the Reset Timeout

Period (t

RP

) once V

CC

rises above V

RST

.

V

CC

5

Active-High, Reset Output. CMOS push/pull output

(sources and sinks current). Inverse of RESET.

RESET

Ground

GND

2

MAX6316L

MAX6316M

MAX6320P 

FUNCTION

NAME

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MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

6

_______________________________________________________________________________________

_______________Detailed Description

A microprocessor’s (µP) reset input starts or restarts the

µP in a known state. The reset output of the MAX6316–

MAX6322 µP supervisory circuits interfaces with the

reset input of the µP, preventing code-execution errors

during power-up, power-down, and brownout condi-

tions (see the 

Typical Operating Circuit

). The MAX6316/

MAX6317/MAX6318/MAX6320/MAX6321 are also capa-

ble of asserting a reset should the µP become stuck in

an infinite loop. 

Reset Output

The MAX6316L/MAX6318LH/MAX6319LH feature an

active-low reset output, while the MAX6317H/

MAX6318_H/MAX6319_H/MAX6321HP/MAX6322HP

feature an active-high reset output. RESET is guaran-

teed to be a logic low and RESET is guaranteed to be a

logic high for V

CC

down to 1V. 

The MAX6316–MAX6322 assert reset when V

CC

is below

the reset threshold (V

RST

), when MR is pulled low

(MAX6316_/MAX6317H/MAX6319_H/MAX6320P/

MAX6322HP only), or if the WDI pin is not serviced within

the watchdog timeout period (t

WD

). Reset remains assert-

ed for the specified reset active timeout period (t

RP

) after

V

CC

rises above the reset threshold, after MR transitions

low to high, or after the watchdog timer asserts the reset

(MAX6316_/MAX6317H/MAX6318_H/MAX6320P/

MAX6321HP). After the reset active timeout period (t

RP

)

expires, the reset output deasserts, and the watchdog

timer restarts from zero (Figure 2). 

MAX6316–MAX6322

V

CC

V

CC

WDI

(ALL EXCEPT 

MAX6319/MAX6322)

1.23V

52k

52k

GND

RESET

(ALL EXCEPT 

MAX6316/MAX6320P)

RESET

(ALL EXCEPT MAX6317)

MR

(ALL EXCEPT 

MAX6318/MAX6321)

RESET

GENERATOR

WATCHDOG

TIMER

WATCHDOG

TRANSITION

DETECTOR

Figure 1.  Functional Diagram

V

CC

1V

1V

t

RD

V

RST

V

RST

t

RD

RESET

GND

RESET

t

RP

t

RP

GND

Figure 2.  Reset Timing Diagram

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MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

_______________________________________________________________________________________

7

Bidirectional 

R

RE

ES

SE

ETT  Output

The MAX6316M/MAX6318MH/MAX6319MH are designed

to interface with µPs that have bidirectional reset pins,

such as the Motorola 68HC11. Like an open-drain output,

these devices allow the µP or other devices to pull the

bidirectional reset (RESET) low and assert a reset condi-

tion. However, unlike a standard open-drain output, it

includes the commonly specified 4.7k

pull-up resistor

with a P-channel active pull-up in parallel.

This configuration allows the MAX6316M/MAX6318MH/

MAX6319MH to solve a problem associated with µPs

that have bidirectional reset pins in systems where sev-

eral devices connect to RESET (Figure 3). These µPs

can often determine if a reset was asserted by an exter-

nal device (i.e., the supervisor IC) or by the µP itself

(due to a watchdog fault, clock error, or other source),

and then jump to a vector appropriate for the source of

the reset. However, if the µP does assert reset, it does

not retain the information, but must determine the

cause after the reset has occurred.

The following procedure describes how this is done in

the Motorola 68HC11. In all cases of reset, the µP pulls

RESET low for about four external-clock cycles. It then

releases RESET, waits for two external-clock cycles,

then checks RESET’s state. If RESET is still low, the µP

concludes that the source of the reset was external

and, when RESET eventually reaches the high state, it

jumps to the normal reset vector. In this case, stored-

state information is erased and processing begins from

scratch. If, on the other hand, RESET is high after a

delay of two external-clock cycles, the processor

knows that it caused the reset itself and can jump to a

different vector and use stored-state information to

determine what caused the reset.

A problem occurs with faster µPs; two external-clock

cycles are only 500ns at 4MHz. When there are several

devices on the reset line, and only a passive pull-up resis-

tor is used, the input capacitance and stray capacitance

can prevent RESET from reaching the logic high state (0.8

x V

CC

) in the time allowed. If this happens, all resets will

be interpreted as external. The µP output stage is guaran-

teed to sink 1.6mA, so the rise time can not be reduced

considerably by decreasing the 4.7k

internal pull-up

resistance. See Bidirectional Pull-Up Characteristics in the

Typical Operating Characteristics

.

The MAX6316M/MAX6318MH/MAX6319MH overcome

this problem with an active pull-up FET in parallel with the

4.7k

resistor (Figures 4 and 5). The pull-up transistor

holds RESET high until the µP reset I/O or the supervisory

circuit itself forces the line low. Once RESET goes below

V

PTH

, a comparator sets the transition edge flip-flop, indi-

cating that the next transition for RESET will be low to

high. When RESET is released, the 4.7k

resistor pulls

RESET up toward V

CC

. Once RESET rises above V

PTH

but is below (0.85 x V

CC

), the active P-channel pull-up

turns on. Once RESET rises above (0.85 x V

CC

) or the

2µs one-shot times out, the active pull-up turns off. The

parallel combination of the 4.7k

pull-up and the 

4.7k

MR**

C

IN

RESET

RESET

CIRCUITRY

RESET***

WDI*

V

CC

MAX6316M

MAX6318MH

MAX6319MH

C

STRAY

68HC11

RESET

CIRCUITRY

C

IN

RESET

V

CC

OTHER DEVICES

C

IN

RESET

MAX6316M/MAX6318MH

MAX6316M/MAX6319MH

ACTIVE-HIGH PUSH/PULL MAX6318MH/MAX6319MH

*

**

***

Figure 3.  MAX6316M/MAX6318MH/MAX6319MH Supports Additional Devices on the Reset Bus

background image

MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

8

_______________________________________________________________________________________

V

CC

MAX6316M  

MAX6318MH

MAX6319MH

LASER-

TRIMMED

RESISTORS

VREF

V

CC

52k

MR

WDI

(MAX6316M/

MAX6318MH)

(MAX6316M/

MAX6319MH)

RESET

GENERATOR

2µs ONE SHOT

2µs ONE SHOT

WATCHDOG ON

CIRCUITRY

TRANSITION

FLIP-FLOP

R

Q

S

FF

V

CC

4.7k

RESET

ACTIVE PULL-UP

ENABLE COMPARATOR

0.65V

0.85V

CC

GND

Figure 4.  MAX6316/MAX6318MH/MAX6319MH Bidirectional Reset Output Functional Diagram

background image

MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

_______________________________________________________________________________________

9

P-channel transistor on-resistance quickly charges

stray capacitance on the reset line, allowing RESET to

transition from low to high within the required two elec-

tronic-clock cycles, even with several devices on the

reset line. This process occurs regardless of whether

the reset was caused by V

CC

dipping below the reset

threshold, the watchdog timing out, MR being asserted,

or the µP or other device asserting RESET. The parts do

not require an external pull-up. To minimize supply cur-

rent consumption, the internal 4.7k

pull-up resistor

disconnects from the supply whenever the MAX6316M/

MAX6318MH/MAX6319MH assert reset.

Open-Drain 

R

RE

ES

SE

ETT Output

The MAX6320P/MAX6321HP/MAX6322HP have an

active-low, open-drain reset output. This output struc-

ture will sink current when RESET is asserted. Connect

a pull-up resistor from RESET to any supply voltage up

to 6V (Figure 6). Select a resistor value large enough to

register a logic low (see 

Electrical Characteristics

), and

small enough to register a logic high while supplying all

input current and leakage paths connected to the RESET

line. A 10k

pull-up is sufficient in most applications. 

Manual-Reset Input

The MAX6316_/MAX6317H/MAX6319_H/MAX6320P/

MAX6322HP feature a manual-reset input. A logic low on

MR asserts a reset. After MR transitions low to high, reset

remains asserted for the duration of the reset timeout peri-

od (t

RP

). The MR input is connected to V

CC

through an

internal 52k

pull-up resistor and therefore can be left

unconnected when not in use. MR can be driven with

TTL-logic levels in 5V systems, with CMOS-logic levels in

3V systems, or with open-drain or open-collector output

devices. A normally-open momentary switch from MR to

ground can also be used; it requires no external

debouncing circuitry. MR is designed to reject fast, 

negative-going transients (typically 100ns pulses). A

0.1µF capacitor from MR to ground provides additional

noise immunity.

The MR input pin is equipped with internal ESD-protection

circuitry that may become forward biased. Should MR be

driven by voltages higher than V

CC

, excessive current

would be drawn, which would damage the part. For

example, assume that MR is driven by a +5V supply other

than V

CC

. If V

CC

drops lower than +4.7V, MR’s absolute 

maximum rating is violated [-0.3V to (V

CC

+ 0.3V)], and

undesirable current flows through the ESD structure from

MR to V

CC

. To avoid this, use the same supply for MR as

the supply monitored by V

CC

. This guarantees that the

voltage at MR will never exceed V

CC

Watchdog Input

The MAX6316_/MAX6317H/MAX6318_H/MAX6320P/

MAX6321HP feature a watchdog circuit that monitors

the µP’s activity. If the µP does not toggle the watchdog

input (WDI) within the watchdog timeout period (t

WD

),

reset asserts. The internal watchdog timer is cleared by

reset or by a transition at WDI (which can detect pulses

as short as 50ns). The watchdog timer remains cleared

while reset is asserted. Once reset is released, the

timer begins counting again (Figure 7).  

The WDI input is designed for a three-stated output

device with a 10µA maximum leakage current and the

capability of driving a maximum capacitive load of 200pF.

The three-state device must be able to source and sink at

least 200µA when active. Disable the watchdog function

by leaving WDI unconnected or by three-stating the driver

connected to WDI. When the watchdog timer is left open

circuited, the timer is cleared internally at intervals equal

to 7/8 of the watchdog period.

MAX6320

MAX6321

MAX6322

V

CC

GND

RESET

WDI**

MR*

RESET***

MAX6320/MAX6322

MAX6320/MAX6321

MAX6321/MAX6322

*

**

***

5V SYSTEM

+5.0V

+3.3V

10k

Figure 6.  MAX6320P/MAX6321HP/MAX6322HP Open-Drain

RESET Output Allows Use with Multiple Supplies

t

R

t

S

RESET

RESET PULLED LOW

BY µC OR

RESET GENERATOR 

ACTIVE

PULL-UP

TURNS ON

V

CC

0.7V

0.8 x V

CC

t

RP

OR

µC RESET DELAY

Figure 5.  Bidirectional RESET Timing Diagram

background image

MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

10

______________________________________________________________________________________

Applications Information

Watchdog Input Current

The WDI input is internally driven through a buffer and

series resistor from the watchdog counter. For minimum

watchdog input current (minimum overall power con-

sumption), leave WDI low for the majority of the watch-

dog timeout period. When high, WDI can draw as much

as 160µA. Pulsing WDI high at a low duty cycle will

reduce the effect of the large input current. When WDI

is left unconnected, the watchdog timer is serviced

within the watchdog timeout period by a low-high-low

pulse from the counter chain.

Negative-Going V

CC

Transients

These supervisors are immune to short-duration, nega-

tive-going V

CC

transients (glitches), which usually do

not require the entire system to shut down. Typically,

200ns large-amplitude pulses (from ground to V

CC

) on

the supply will not cause a reset. Lower amplitude puls-

es result in greater immunity. Typically, a V

CC

transient

that goes 100mV under the reset threshold and lasts

less than 4µs will not trigger a reset. An optional 0.1µF

bypass capacitor mounted close to V

CC

provides addi-

tional transient immunity.  

Ensuring Valid Reset Outputs 

Down to V

CC

= 0

The MAX6316_/MAX6317H/MAX6318_H/MAX6319_H/

MAX6321HP/MAX6322HP are guaranteed to operate

properly down to V

CC

= 1V. In applications that require

valid reset levels down to V

CC

= 0, a pull-down resistor

to active-low outputs (push/pull and bidirectional only,

Figure 8) and a pull-up resistor to active-high outputs

(push/pull only, Figure 9) will ensure that the reset line

is valid while the reset output can no longer sink or

source current. This scheme does not work with the

open-drain outputs of the MAX6320/MAX6321/MAX6322.

The resistor value used is not critical, but it must be

large enough not to load the reset output when V

CC

is

above the reset threshold. For most applications,

100k

is adequate. 

Watchdog Software Considerations

(MAX6316/MAX6317/MAX6318/

MAX6320/MAX6321)

One way to help the watchdog timer monitor software

execution more closely is to set and reset the watchdog

input at different points in the program, rather than

pulsing the watchdog input high-low-high or low-high-

low. This technique avoids a stuck loop, in which the

watchdog timer would continue to be reset inside the

loop, keeping the watchdog from timing out.

V

CC

t

WD

t

RP

t

RP

t

RST

WDI

RESET

MAX6316/MAX6317

MAX6318/MAX6320

MAX6321

Figure 7.  Watchdog Timing Relationship

GND

*THIS SCHEMATIC DOES NOT WORK ON THE OPEN-DRAIN

  OUTPUTS OF THE MAX6321/MAX6322.

100k

V

CC

V

CC

RESET

MAX6317

MAX6318

MAX6319

MAX6321*

MAX6322*

Figure 9.  Ensuring RESET Valid to V

CC

= 0 on Active-High

Push/Pull Outputs

GND

100k

V

CC

V

CC

RESET

MAX6316

MAX6318

MAX6319

Figure 8.  Ensuring RESET Valid to V

CC

= 0 on Active-Low

Push/Pull and Bidirectional Outputs

background image

MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

______________________________________________________________________________________

11

Figure 10 shows an example of a flow diagram where

the I/O driving the watchdog input is set high at the

beginning of the program, set low at the end of every

subroutine or loop, then set high again when the pro-

gram returns to the beginning. If the program should

hang in any subroutine, the problem would be quickly

corrected, since the I/O is continually set low and the

watchdog timer is allowed to time out, causing a reset

or interrupt to be issued. As described in the 

Watchdog

Input Current

section, this scheme results in higher time

average WDI current than does leaving WDI low for the

majority of the timeout period and periodically pulsing it

low-high-low.

START

SET WDI

HIGH

PROGRAM

CODE

SUBROUTINE OR

PROGRAM LOOP

SET WDI LOW

RETURN

POSSIBLE 

INFINITE LOOP PATH

Figure 10.  Watchdog Flow Diagram

GND

WDI

MR

1

5

V

CC

RESET

MAX6316

MAX6320

SOT23-5

TOP VIEW

2

3

4

GND

WDI

MR

1

5

V

CC

RESET

MAX6317

SOT23-5

2

3

4

GND

WDI

RESET

1

5

V

CC

RESET

MAX6318

MAX6321

SOT23-5

2

3

4

GND

MR

RESET

1

5

V

CC

RESET

MAX6319

MAX6322

SOT23-5

2

3

4

__________________Pin Configurations

MAX6316

GND

MANUAL

RESET

I/O

WDI

MR

GND

µ

P

V

CC

V

IN

V

CC

RESET

RESET

Typical Operating Circuit

background image

Table 2. Standard Versions

Table 1. Factory-Trimmed Reset Thresholds

MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

12

______________________________________________________________________________________

2.438

2.563

2.463

2.500

2.538

MAX63___25_ _-T

2.564

2.696

2.591

2.630

2.669

MAX63___26_ _-T

2.633

2.768

2.660

2.700

2.741

MAX63___27_ _-T

2.730

2.870

2.758

2.800

2.842

MAX63___28_ _-T

2.857

3.000

2.886

2.930

2.974

MAX63___29_ _-T

2.925

3.075

2.955

3.000

3.045

MAX63___30_ _-T

3.003

3.157

3.034

3.080

3.126

MAX63___31_ _-T

3.120

3.280

3.152

3.200

3.248

MAX63___32_ _-T

3.218

3.383

3.251

3.300

3.350

MAX63___33_ _-T

3.315

3.485

3.349

3.400

3.451

MAX63___34_ _-T

3.413

3.588

3.448

3.500

3.553

MAX63___35_ _-T

3.510

3.690

3.546

3.600

3.654

MAX63___36_ _-T

3.608

3.793

3.645

3.700

3.756

MAX63___37_ _-T

3.705

3.895

3.743

3.800

3.857

MAX63___38_ _-T

3.803

3.998

3.842

3.900

3.959

MAX63___39_ _-T

3.900

4.100

3.940

4.000

4.060

MAX63___40_ _-T

3.998

4.203

4.039

4.100

4.162

MAX63___41_ _-T

4.095

4.305

4.137

4.200

4.263

MAX63___42_ _-T

4.193

4.408

4.236

4.300

4.365

MAX63___43_ _-T

4.270

4.490

4.314

4.390

4.446

MAX63___44_ _-T

4.388

4.613

4.433

4.500

4.568

MAX63___45_ _-T

4.514

4.746

4.561

4.630

4.699

MAX63___46_ _-T

4.583

4.818

4.630

4.700

4.771

MAX63___47_ _-T

4.680

4.920

4.728

4.800

4.872

MAX63___48_ _-T

4.778

5.023

7.827

4.900

4.974

MAX63___49_ _-T

MIN

MAX

MIN

TYP

MAX

4.875

5.125

T

A

= -40°C to +85°C

T

A

= +25°C

4.925

5.000

5.075

MAX63___50_ _-T

PART

1.6

MAX6316LUK46CY-T

MAX6316LUK29CY-T

MAX6316MUK46CY-T

4.63

2.93

4.63

MAX6320PUK29CY-T

2.93

140

140

140

MAX6316MUK29CY-T

2.93

140

MAX6317HUK46CY-T

4.63

140

MAX6318LHUK46CY-T

4.63

140

MAX6319LHUK46C-T

4.63

140

MAX6320PUK46CY-T

4.63

140

1.6

1.6

1.6

1.6

1.6

1.6

TYPICAL

WATCHDOG

TIMEOUTS (sec)

1.6

ACDD

ACDE

ACDF

ACDG

ACDQ

ACDH

ACDK

ACDN

SOT 

TOP MARK

ACDO

PART

RESET

THRESHOLD

(V)

MINIMUM RESET

TIMEOUT

(ms)

140

Note:

Nine standard versions are available, with a required order increment of 2500 pieces. Sample stock is generally held on standard

versions only. The required order increment for nonstandard versions is 10,000 pieces. Contact factory for availability.

Contact factory for availability of these versions.

background image

Table 3. Reset/Watchdog Timeout Periods

MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

______________________________________________________________________________________

13

__Ordering Information (continued)

Note:

These devices are available with factory-set V

CC

reset

thresholds from 2.5V to 5V, in 0.1V increments. Insert the

desired nominal reset threshold (25 to 50, from Table 1) into the

blanks following the letters UK. All devices offer factory-pro-

grammed reset timeout periods. Insert the letter corresponding

to the desired reset timeout period (A, B, C, or D from Table 3)

into the blank following the reset threshold suffix. Parts that offer

a watchdog feature (see Selector Guide) are factory-trimmed to

one of four watchdog timeout periods. Insert the letter corre-

sponding to the desired watchdog timeout period (W, X, Y, or Z

from Table 3) into the blank following the reset timeout suffix.

PART

MAX6319

LHUK____-T

MAX6319MHUK____-T

MAX6320

PUK____-T

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

TEMP. RANGE

PIN-PACKAGE

5 SOT23-5

5 SOT23-5

5 SOT23-5

MAX6321

HPUK____-T

-40°C to +85°C

5 SOT23-5

MAX6322

HPUK____-T

-40°C to +85°C

5 SOT23-5

W

4.3

6.3

9.3

ms

X

71

102

153

Y

1.12

1.6

2.4

Z

17.9

25.6

38.4

sec

RESET TIMEOUT PERIODS

WATCHDOG TIMEOUT

TRANSISTOR COUNT: 191

SUBSTRATE IS INTERNALLY CONNECTED TO V+

Chip Information

sec

2.24

1.60

1.12

D

280

200

140

C

40

30

20

B

2

1.6

1

A

UNITS

MAX

TYP

MIN

SUFFIX

ms

background image

MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

14

______________________________________________________________________________________

SOT5L.EPS

Package Information

background image

MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

______________________________________________________________________________________

15

NOTES

background image

MAX6316–MAX6322

5-Pin µP Supervisory Circuits with  

Watchdog and Manual Reset

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

16

____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA  94086 408-737-7600

© 1999 Maxim Integrated Products 

Printed USA

is a registered trademark of Maxim Integrated Products.

NOTES