Datasheet MAX824LEUK, MAX824MEUK, MAX824REUK, MAX823MEUK, MAX823REUK Datasheet (Maxim)

_______________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 VCC.

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 VCCdown 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

CC

= 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

1

1

5

2

3

4

1

5

2

3

4

1

5

2

3

4

GND

WDI

MR

V

CC

RESET

MAX823

SOT23-5

TOP VIEW

GND

WDI

RESET

V

CC

RESET

MAX824

SOT23-5

GND

MR

RESET

V

CC

RESET

MAX825

SOT23-5

__________________________________________________________Pin Configurations

_____________________Selector Guide

19-0487; Rev 1; 6/97

PART

†

MAX823_EUK
MAX824_EUK -40°C to +85°C

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

5 SOT23-5
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 [phone].
For small orders, phone [phone] 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)

L 4.63

M 4.38

T 3.08
S 2.93
R 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

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= +4.75V to +5.5V for MAX82_L, VCC= +4.5V to +5.5V for MAX82_M, VCC= +3.15V to +3.6V for MAX82_T, VCC= +3V
to +3.6V for MAX82_S, VCC= +2.7V to +3.6V for MAX82_R, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at

TA= +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.

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

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

CC

+ 0.3V)

Input Current, All Pins Except RESET and

RESET..............20mA

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

Rate of Rise, V

CC

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

Continuous Power Dissipation (T

A

= +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

TA= +25°C
TA= -40°C to +85°C

WDI and MR
unconnected

4.25 4.50

TA= -40°C to +85°C

TA= 0°C to +70°C

4.31 4.38 4.45

MAX82_T/S/R

MAX82_L/M

MAX82_L

TA= +25°C
TA= -40°C to +85°C

MR unconnected

MAX82_S

CONDITIONS

TA= +25°C
TA= -40°C to +85°C 2.85 3.00

2.89 2.93 2.96

MAX82_T

TA= +25°C
TA= -40°C to +85°C 3.00 3.15

3.04 3.08 3.11

MAX82_L/M
MAX82_T/S/R

mV

5

Reset Threshold Hysteresis

10

MAX82_R

TA= +25°C
TA= -40°C to +85°CV2.55 2.70

V

RST

Reset Threshold

2.59 2.63 2.66

MAX823T/S/R,
MAX824T/S/R

5 12

V

1.2

V

CC

1.0 5.5

MAX823L/M,
MAX824L/M

MAX825L/M

Operating Voltage Range

ms

140 200 280

t

RP

Reset Timeout Period

140 200 280

ppm/°C40

Reset Threshold Temperature
Coefficient

4.50 4.75

10 24

4.5 12

µA

3 8

I

SUPPLY

Supply Current

4.56 4.63 4.70

UNITSMIN TYP MAXSYMBOLPARAMETER

MAX825T/S/R

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +4.75V to +5.5V for MAX82_L, VCC= +4.5V to +5.5V for MAX82_M, VCC= +3.15V to +3.6V for MAX82_T, VCC= +3V
to +3.6V for MAX82_S, V

CC

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

MIN

to T

MAX

, unless otherwise noted. Typical values are at

T

A

= +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

_______________________________________________________________________________________ 3

V

RST

- VCC= 100mV

MAX824T/S/R, MAX825T/S/R,
VCC= V

RST

max, I

SINK

= 1.2mA

MAX82_L/M, VCC= V

RST

max,

I

SOURCE

= 120µA

MAX824L/M, MAX825L/M,
VCC= V

RST

max, I

SINK

= 3.2mA

VCC> 1.8V, I

SOURCE

= 150µA

MAX82_L/M, RESET = 0V, VCC= 5.5V

CONDITIONS

µs20

VCCto RESET Delay

V

0.3

V

OL

RESET Output Voltage

VCC- 1.5

0.4

0.8V

CC

V

OH

800

UNITSMIN TYP MAXSYMBOLPARAMETER

MAX82_T/S/R, VCC= V

RST

max,

I

SOURCE

= 30µA

0.8V

CC

V

OH

MAX82_T/S/R, VCC= V

RST

min,

I

SINK

= 1.2mA

MAX82_L/M, VCC= V

RST

min,

I

SINK

= 3.2mA

0.3

0.4

TA= -40°C to +85°C, VCC= 1.2V,
VCCfalling, V

BATT

= 0V, I

SINK

= 100µA

TA= 0°C to +70°C, VCC= 1V,
VCCfalling, I

SINK

= 50µA

V

0.3

V

OL

RESET Output Voltage

0.3

MAX82_T/S/R, RESET = 0V, VCC= 3.6V

µA

400

I

SOURCE

RESET Output Short-Circuit
Current (Note 2)

VIL= 0.4V, VIH= 0.8V

CC

ns50t

WDI

WDI Pulse Width

sec1.12 1.60 2.40t

WD

Watchdog Timeout Period

WDI = 0V, time average

WDI = VCC, time average

VCC= 5V

µA

-20 -15

WDI Input Current (Note 4)

120 160

V

0.7V

CC

V

IH

WDI Input Threshold (Note 3)

0.3V

CC

V

IL

µs1.0

MR Pulse Width

V

0.7V

CC

V

IH

MR Input Threshold

0.3V

CC

V

IL

kΩ35 52 75

MR Pull-Up Resistance (internal)

ns500

MR to Reset Delay

ns100

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

4 _______________________________________________________________________________________

__________________________________________Typical Operating Characteristics

(MAX823L, VCC= +5V, TA= +25°C, unless otherwise noted.)

12.5

7.5

-40 -20 40 100

VCC SUPPLY CURRENT

vs. TEMPERATURE

8.5

8.0

9.0

11.5

12.0

MAX823/4/5-01

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

0 20 8060

10.5

11.0

9.5

10.0

250

150

-40 -20 40 100

RESET TIMEOUT PERIOD

vs. TEMPERATURE

170
160

180

230

240

MAX823/4/5-02

TEMPERATURE (°C)

RESET TIMEOUT PERIOD (ms)

0 20 8060

210

220

190

200

30

0

-40 -20 40 100

RESET COMPARATOR PROPAGATION DELAY

vs. TEMPERATURE

5

25

MAX823/4/5-03

TEMPERATURE (°C)

PROPAGATION DELAY (µs)

0 20 8060

20

10

15

VCC FALLING

2.0

1.0

-40 -20 40 100

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)

0 20 8060

1.6

1.7

1.4

1.5

1.06

0.94

0.96

0.98

1.00

1.02

1.04

-40 -20 40 100

NORMALIZED RESET THRESHOLD

VOLTAGE vs. TEMPERATURE

MAX823/4/5-05

TEMPERATURE (°C)

NORMALIZED RESET THRESHOLD (V)

0 20 8060

0

20

40

60

80

100

120

140

160

40 100 200180120 140 160

MAXIMUM VCC TRANSIENT DURATION

vs. RESET THRESHOLD OVERDRIVE

MAX823/4/5-06

RESET THRESHOLD OVERDRIVE (mV), V

RST

- V

CC

TRANSIENT DURATION (µs)

0 20 8060

RESET OCCURS
ABOVE CURVE

MAX823/MAX824/MAX825

5-Pin Microprocessor Supervisory Circuits

_______________________________________________________________________________________ 5

______________________________________________________________Pin Description

MAX823
MAX824
MAX825

V

CC

V

CC

WDI

(MAX823/MAX824

ONLY)

1.25V

GND

RESET
(MAX824/MAX825
ONLY)

RESET

MR

(MAX823/MAX825

ONLY)

RESET

GENERATOR

WATCHDOG

TIMER

WATCHDOG
TRANSITION

DETECTOR

FUNCTION

1 1

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

CC

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

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

CC

rises above the

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

2 2 Ground. 0V reference for all signals.

3 —

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 52kΩ 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

CC

if unused.

— 3

Active-High Reset Output. Inverse of RESET.

5 5 Supply Voltage

4 4

Watchdog Input. If WDI remains either high or low for longer than the watch­dog timeout period, the internal watchdog timer runs out and a reset is trig­gered. 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

1

RESET

2 GND

4

MR

3 RESET

5 V

CC

— WDI

Figure 1. Functional Diagram

MAX824MAX823 MAX825

PIN

MAX823/MAX824/MAX825

5-Pin Microprocessor Supervisory Circuits

6 _______________________________________________________________________________________

_______________Detailed Description

RESET Output

A microprocessor’s (µP’s) reset input starts the µP in a
known state. The MAX823/MAX824/MAX825 µP super­visory 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
VCCdown to 1V. Once VCCexceeds the reset thresh­old, an internal timer keeps RESET low for the specified
reset timeout period (tRP); after this interval, RESET
returns high (Figure 2).

If a brownout condition occurs (VCCdips below the
reset threshold), RESET goes low. Each time RESET is
asserted it stays low for the reset timeout period. Any
time VCCgoes 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 capabili­ty, 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 tRP(200ms nominal)
after it returns high. MR has an internal 52kΩ 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 func­tion; 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 tWD(1.6sec), reset asserts. The inter­nal 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 uncon­nected 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 uncon­nected, 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.

V

CC

1V

1V

t

RD

V

RST

V

RST

t

RD

RESET

GND

RESET

t

RP

t

RP

Figure 2. Reset Timing Diagram

V

CC

t

WD

t

RP

t

RP

t

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 VCCTransients

These supervisors are relatively immune to short­duration, negative-going VCCtransients (glitches), which
usually do not require the entire system to shut down.
Resets are issued to the µP during power-up, power­down, and brownout conditions.

The

Typical Operating Characteristics

show a graph of
the MAX823L’s Maximum VCCTransient Duration vs.
Reset Threshold Overdrive, for which reset pulses are
not generated. The graph was produced using nega ­tive-going VCCpulses, 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 VCCtransient 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 VCCtransient 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
V

CC

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-high­low. 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 begin­ning of the program, set low at the beginning of every
subroutine or loop, then set high again when the pro­gram 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

_______________________________________________________________________________________ 7

MAX823
MAX824
MAX825

µP

V

CC

V

CC

V

CC

GND

GND

RESET

I

SOURCE

MAX = 800µA L, M

400µA 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.

8

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

© 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

__________Typical Operating Circuit ___________________Chip Information

______________Package Information

TRANSISTOR COUNT: 607

MAX823

µP

V

CC

V

CC

V

CC

GND

MANUAL

RESET

RESET

I/O

RESET

MR

WDI

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

SOT5L.EPS