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_______________General Description

The MAX823/MAX824/MAX825* microprocessor (µP)

supervisory circuits combine reset output, watchdog,

and manual-reset input functions in a 5-pin SOT23-5

package. They significantly improve system reliability

and accuracy compared to separate ICs or discrete

components. The MAX823/MAX824/MAX825 are

specifically designed to ignore fast transients on V

Five preprogrammed reset threshold voltages are

available, designated by the following package

suffixes: L = 4.63V, M = 4.38V, T = 3.08V, S = 2.93V,

and R = 2.63V. All three devices have an active-low

reset output, which is guaranteed to be in the correct

state for V

down to 1V. The MAX824/MAX825 also

have an active-high reset output. The following

Selector

Guide explains the functions offered in this series of

parts.

________________________Applications

Battery-Powered Computers and Controllers

Embedded Controllers

Intelligent Instruments

Automotive Systems

Critical µP Monitoring

Portable/Battery-Powered Equipment

____________________________Features

Precision Monitoring of +3V, +3.3V, and +5V

Power Supplies

Operating Current: 10µA (MAX823L/M)

3µA (MAX825T/S/R)

Fully Specified Over Temperature

140ms Min Power-On Reset

Guaranteed RESET Valid to V

= 1V

Power-Supply Transient Immunity

Watchdog Timer with 1.6sec Timeout

(MAX823/MAX824)

Manual-Reset Input (MAX823/MAX825)

No External Components

MAX823/MAX824/MAX825

5-Pin Microprocessor Supervisory Circuits

________________________________________________________________

Maxim Integrated Products

GND

WDI

RESET

MAX823

SOT23-5

TOP VIEW

GND

WDI

RESET

MAX824

SOT23-5

GND

RESET

MAX825

SOT23-5

__________________________________________________________Pin Configurations

_____________________Selector Guide

19-0487; Rev 1; 6/97

PART

†

MAX823_EUK

MAX824_EUK

-40°C to +85°C

TEMP. RANGE

PIN-PACKAGE

5 SOT23-5

______________Ordering Information

†Insert the desired suffix letter (from the table below) into the

blank to complete the part number.

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

For small orders, phone 408-737-7600 ext. 3468.

MAX825_EUK

-40°C to +85°C

5 SOT23-5

MAX823

Active-Low Reset

Active-High Reset

—

FUNCTION

Watchdog Input

MAX824

MAX825

—

Manual-Reset Input

—

SUFFIX

RESET

THRESHOLD (V)

4.63

4.38

3.08

2.93

2.63

Typical Operating Circuit appears at end of data sheet.

Marking Information appears at end of data sheet.

*Patents Pending

MAX823/MAX824/MAX825

5-Pin Microprocessor Supervisory Circuits

_______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

= +4.75V to +5.5V for MAX82_L, V

= +4.5V to +5.5V for MAX82_M, V

= +3.15V to +3.6V for MAX82_T, V

= +3V

to +3.6V for MAX82_S, V

= +2.7V to +3.6V for MAX82_R, T

= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at

= +25°C.) (Note 1)

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.

........................................................................-0.3V to +6.0V

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

+ 0.3V)

Input Current, All Pins Except RESET and RESET..............20mA

Output Current, RESET, RESET ..........................................20mA

Rate of Rise, V

............................................................100V/µs

Continuous Power Dissipation (T

= +70°C)

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

Operating Temperature Range

MAX82_EUK .....................................................-40°C to +85°C

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

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

MAX82_M

= +25°C

= -40°C to +85°C

WDI and MR

unconnected

4.25

4.50

= -40°C to +85°C

= 0°C to +70°C

4.31

4.38

4.45

MAX82_T/S/R

MAX82_L/M

MAX82_L

= +25°C

= -40°C to +85°C

MR unconnected

MAX82_S

CONDITIONS

= +25°C

= -40°C to +85°C

2.85

3.00

2.89

2.93

2.96

MAX82_T

= +25°C

= -40°C to +85°C

3.00

3.15

3.04

3.08

3.11

MAX82_L/M

MAX82_T/S/R

Reset Threshold Hysteresis

MAX82_R

= +25°C

= -40°C to +85°C

2.55

2.70

RST

Reset Threshold

2.59

2.63

2.66

MAX823T/S/R,

MAX824T/S/R

1.2

1.0

5.5

MAX823L/M,

MAX824L/M

MAX825L/M

Operating Voltage Range

140

200

280

Reset Timeout Period

140

200

280

ppm/°C

Reset Threshold Temperature

Coefficient

4.50

4.75

4.5

µA

SUPPLY

Supply Current

4.56

4.63

4.70

UNITS

MIN

TYP

MAX

SYMBOL

PARAMETER

MAX825T/S/R

ELECTRICAL CHARACTERISTICS (continued)

= +4.75V to +5.5V for MAX82_L, V

= +4.5V to +5.5V for MAX82_M, V

= +3.15V to +3.6V for MAX82_T, V

= +3V

to +3.6V for MAX82_S, V

= +2.7V to +3.6V for MAX82_R, T

= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at

= +25°C.) (Note 1)

Note 1:

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

Note 2:

The RESET short-circuit current is the maximum pull-up current when RESET is driven low by a µP bidirectional reset pin.

Note 3:

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

Note 4:

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 to drive a three-stated-output device with a 10µA maximum leakage current and a maximum capacitive load of

200pF. This output device must be able to source and sink at least 200µA when active.

MAX823/MAX824/MAX825

5-Pin Microprocessor Supervisory Circuits

_______________________________________________________________________________________

RST

- V

= 100mV

MAX824T/S/R, MAX825T/S/R,

= V

RST

max, I

SINK

= 1.2mA

MAX82_L/M, V

= V

RST

max,

SOURCE

= 120µA

MAX824L/M, MAX825L/M,

= V

RST

max, I

SINK

= 3.2mA

> 1.8V, I

SOURCE

= 150µA

MAX82_L/M, RESET = 0V, V

= 5.5V

CONDITIONS

µs

to RESET Delay

0.3

RESET Output Voltage

- 1.5

0.4

0.8V

800

UNITS

MIN

TYP

MAX

SYMBOL

PARAMETER

MAX82_T/S/R, V

= V

RST

max,

SOURCE

= 30µA

0.8V

MAX82_T/S/R, V

= V

RST

min,

SINK

= 1.2mA

MAX82_L/M, V

= V

RST

min,

SINK

= 3.2mA

0.3

0.4

= -40°C to +85°C, V

= 1.2V,

falling, V

BATT

= 0V, I

SINK

= 100µA

= 0°C to +70°C, V

= 1V,

falling, I

SINK

= 50µA

0.3

RESET Output Voltage

0.3

MAX82_T/S/R, RESET = 0V, V

= 3.6V

µA

400

SOURCE

RESET Output Short-Circuit

Current (Note 2)

= 0.4V, V

= 0.8V

WDI

WDI Pulse Width

sec

1.12

1.60

2.40

Watchdog Timeout Period

WDI = 0V, time average

WDI = V

, time average

= 5V

µA

-20

-15

WDI Input Current (Note 4)

120

160

0.7V

WDI Input Threshold (Note 3)

0.3V

µs

1.0

MR Pulse Width

0.7V

MR Input Threshold

0.3V

Ω

MR Pull-Up Resistance (internal)

500

MR to Reset Delay

100

MR Noise Immunity (pulse width

with no reset)

MANUAL-RESET INPUT (MAX823/MAX825)

WATCHDOG INPUT (MAX823/MAX824)

MAX823/MAX824/MAX825

5-Pin Microprocessor Supervisory Circuits

_______________________________________________________________________________________

__________________________________________Typical Operating Characteristics

(MAX823L, V

= +5V, T

= +25°C, unless otherwise noted.)

12.5

7.5

-40

-20

100

SUPPLY CURRENT

vs. TEMPERATURE

8.5

8.0

9.0

11.5

12.0

MAX823/4/5-01

TEMPERATURE (°C)

SUPPLY CURRENT (

10.5

11.0

9.5

10.0

250

150

-40

-20

100

RESET TIMEOUT PERIOD

vs. TEMPERATURE

170

160

180

230

240

MAX823/4/5-02

TEMPERATURE (°C)

RESET TIMEOUT PERIOD (ms)

210

220

190

200

-40

-20

100

RESET COMPARATOR PROPAGATION DELAY

vs. TEMPERATURE

MAX823/4/5-03

TEMPERATURE (°C)

PROPAGATION DELAY (

FALLING

2.0

1.0

-40

-20

100

WATCHDOG TIMEOUT PERIOD

vs. TEMPERATURE

1.2

1.1

1.3

1.8

1.9

MAX823/4/5-04

TEMPERATURE (°C)

WATCHDOG TIMEOUT PERIOD (sec)

1.6

1.7

1.4

1.5

1.06

0.94

0.96

0.98

1.00

1.02

1.04

-40

-20

100

NORMALIZED RESET THRESHOLD

VOLTAGE vs. TEMPERATURE

MAX823/4/5-05

TEMPERATURE (°C)

NORMALIZED RESET THRESHOLD (V)

100

120

140

160

100

200

180

120 140 160

MAXIMUM V

TRANSIENT DURATION

vs. RESET THRESHOLD OVERDRIVE

MAX823/4/5-06

RESET THRESHOLD OVERDRIVE (mV), V

RST

- V

TRANSIENT DURATION (

RESET OCCURS

ABOVE CURVE

MAX823/MAX824/MAX825

5-Pin Microprocessor Supervisory Circuits

_______________________________________________________________________________________

______________________________________________________________Pin Description

MAX823

MAX824

MAX825

WDI

(MAX823/MAX824

ONLY)

1.25V

GND

RESET

(MAX824/MAX825

ONLY)

RESET

(MAX823/MAX825

ONLY)

RESET

GENERATOR

WATCHDOG

TIMER

WATCHDOG

TRANSITION

DETECTOR

FUNCTION

Active-Low Reset Output. Pulses low for 200ms when triggered, and remains

low whenever V

is below the reset threshold or when MR is a logic low. It

remains low for 200ms after one of the following occurs: V

rises above the

reset threshold, the watchdog triggers a reset, or MR goes low to high.

Ground. 0V reference for all signals.

—

Manual-Reset Input. A logic low on MR asserts reset. Reset remains asserted as

long as MR is held low and for 200ms after MR returns high. The active-low input

has an internal 52k

Ω

pull-up resistor. It can be driven from a CMOS-logic line or

shorted to ground with a switch. Leave open or connect to V

if unused.

—

Active-High Reset Output. Inverse of RESET.

Supply Voltage

Watchdog Input. If WDI remains either high or low for longer than the watch-

dog timeout period, the internal watchdog timer runs out and a reset is trig-

gered. The internal watchdog timer clears whenever reset is asserted, or

whenever WDI sees a rising or falling edge. If WDI is left unconnected or is

connected to a three-stated buffer output, the watchdog feature is disabled.

NAME

RESET

GND

RESET

—

WDI

Figure 1. Functional Diagram

MAX824

MAX823

MAX825

PIN

MAX823/MAX824/MAX825

5-Pin Microprocessor Supervisory Circuits

_______________________________________________________________________________________

_______________Detailed Description

RESET Output

A microprocessor’s (µP’s) reset input starts the µP in a

known state. The MAX823/MAX824/MAX825 µP super-

visory circuits assert a reset to prevent code-execution

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

conditions. RESET is guaranteed to be a logic low for

down to 1V. Once V

exceeds the reset thresh-

old, an internal timer keeps RESET low for the specified

reset timeout period (t

); after this interval, RESET

returns high (Figure 2).

If a brownout condition occurs (V

dips below the

reset threshold), RESET goes low. Each time RESET is

asserted it stays low for the reset timeout period. Any

time V

goes below the reset threshold the internal

timer restarts. RESET both sources and sinks current.

RESET on the MAX824/MAX825 is the inverse of

RESET.

Manual-Reset Input (MAX823/MAX825)

Many µP-based products require manual-reset capabili-

ty, allowing the operator, a test technician, or external

logic circuitry to initiate a reset. On the MAX823/

MAX825, a logic low on MR asserts reset. Reset remains

asserted while MR is low, and for t

(200ms nominal)

after it returns high. MR has an internal 52k

Ω

pull-up

resistor, so it can be left open if not used. This input can

be driven with CMOS-logic levels or with open-drain/

collector outputs. Connect a normally open momentary

switch from MR to GND to create a manual-reset func-

tion; external debounce circuitry is not required. If MR is

driven from long cables or the device is used in a noisy

environment, connect a 0.1µF capacitor from MR to

GND to provide additional noise immunity.

Watchdog Input (MAX823/MAX824)

In the MAX823/MAX824, the watchdog circuit monitors

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

input (WDI) within t

(1.6sec), reset asserts. The inter-

nal 1.6sec timer is cleared by either a reset pulse or by

toggling WDI, which detects pulses as short as 50ns.

While reset is asserted, the timer remains cleared and

does not count. As soon as reset is released, the timer

starts counting (Figure 3).

Disable the watchdog function by leaving WDI uncon-

nected or by three-stating the driver connected to WDI.

The watchdog input is internally driven low during the

first 7/8 of the watchdog timeout period and high for the

last 1/8 of the watchdog timeout period. When WDI is

left unconnected, this internal driver clears the 1.6sec

timer every 1.4sec. When WDI is three-stated or uncon-

nected, the maximum allowable leakage current is

10µA and the maximum allowable load capacitance is

200pF.

__________Applications Information

Watchdog Input Current

The MAX823/MAX824 WDI inputs are internally driven

through a buffer and series resistor from the watchdog

counter (Figure 1). 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.

For minimum watchdog input current (minimum overall

power consumption), leave WDI low for the majority of

the watchdog timeout period, pulsing it low-high-low

once within the first 7/8 of the watchdog timeout period

to reset the watchdog timer. If WDI is externally driven

high for the majority of the timeout period, up to 160µA

can flow into WDI.

RST

RESET

GND

RESET

Figure 2. Reset Timing Diagram

RST

WDI

RESET*

*RESET ON THE MAX824/MAX825 IS THE INVERSE OF RESET.

Figure 3. MAX823/MAX824 Watchdog Timing Relationship

Interfacing to µPs with

Bidirectional Reset Pins

The RESET output maximum pull-up current is 800µA

for L/M versions (400µA for T/S/R versions). This allows

µPs with bidirectional resets, such as the 68HC11, to

force RESET low when the MAX823/MAX824/MAX825

are pulling RESET high (Figure 4).

Negative-Going V

Transients

These supervisors are relatively immune to short-

duration, negative-going V

transients (glitches), which

usually do not require the entire system to shut down.

Resets are issued to the µP during power-up, power-

down, and brownout conditions.

The

Typical Operating Characteristics show a graph of

the MAX823L’s Maximum V

Transient Duration vs.

Reset Threshold Overdrive, for which reset pulses are

not

generated. The graph was produced using nega-

tive-going V

pulses, starting at 5V and ending below

the reset threshold by the magnitude indicated (reset

threshold overdrive). The graph shows the maximum

pulse width that a negative-going V

transient can

typically have without triggering a reset pulse. As the

amplitude of the transient increases (i.e., goes farther

below the reset threshold), the maximum allowable

pulse width decreases. Typically, a V

transient that

goes 100mV below the reset threshold and lasts for

15µs or less will not trigger a reset pulse.

An optional 0.1µF bypass capacitor mounted close to

provides additional transient immunity.

Watchdog Software Considerations

(MAX823/MAX824)

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.

Figure 5 shows an example of a flow diagram where the

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

ning of the program, set low at the beginning 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 quickly be

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 input current than does leaving WDI low

for the majority of the timeout period and periodically

pulsing it low-high-low.

MAX823/MAX824/MAX825

5-Pin Microprocessor Supervisory Circuits

_______________________________________________________________________________________

MAX823

MAX824

MAX825

GND

RESET

SOURCE

MAX = 800

A L, M

400

A T, S, R

RESET

GENERATOR

Figure 4. Interfacing to µPs with Bidirectional Resets

START

SET WDI

HIGH

PROGRAM

CODE

SUBROUTINE OR

PROGRAM LOOP

SET WDI LOW

RETURN

Figure 5. Watchdog Flow Diagram

MAX823/MAX824/MAX825

5-Pin Microprocessor Supervisory Circuits

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.

____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-377-7600

Printed USA

is a registered trademark of Maxim Integrated Products.

__________Typical Operating Circuit

___________________Chip Information

______________Package Information

TRANSISTOR COUNT: 607

MAX823

GND

MANUAL

RESET

I/O

RESET

WDI

SOT5L.EPS

MARKING INFORMATION (TOP)

AAAI = MAX823L

AAAJ = MAX823M

AAAK = MAX823T

AAAL = MAX823S

AAAM = MAX823R

AAAN = MAX824L

AAAO = MAX824M

AAAP = MAX824T

AAAQ = MAX824S

AAAR = MAX824R

AAAS = MAX825L

AAAT = MAX825M

AAAU = MAX825T

AAAV = MAX825S

AAAW = MAX825R

XXXX