Datasheet MAX6304ESA, MAX6304EPA, MAX6304CUA, MAX6304CSA, MAX6304CPA Datasheet (Maxim)

RESET

RESET

19-1078; Rev 0; 6/96

+5V, Low-Power µP Supervisory Circuits

with Adjustable Reset/Watchdog

_______________General Description

The MAX6301/MAX6302/MAX6303/MAX6304* low­power microprocessor (µP) supervisory circuits provide
maximum adjustability for reset and watchdog functions.
The reset threshold can be adjusted to any voltage
above 1.22V, using external resistors. In addition, the
reset and watchdog timeout periods are adjustable
using external capacitors. A watchdog select pin
extends the watchdog timeout period to 500x. The reset
function features immunity to power-supply transients.

These four devices differ only in the structure of their reset
outputs (see

Selector Guide

). The MAX6301–MAX6304
are available in the space-saving 8-pin µMAX package,
as well as 8-pin DIP/SO.

________________________Applications

Medical Equipment Embedded Controllers
Intelligent Instruments Critical µP Monitoring
Portable Equipment Set-Top Boxes
Battery-Powered Computers

Computers/Controllers

_____________________Selector Guide

FEATURE MAX6301 MAX6302 MAX6303 MAX6304

Active-Low
Reset

Active-High
Reset

Open-Drain
Reset Output

Push/Pull
Reset Output

Pins-Package

✓

—

✓ ✓

— —

8-DIP/SO/

µMAX

—

✓

8-DIP/SO/

µMAX

✓

—

— —

✓ ✓

8-DIP/SO/

µMAX

—

✓

8-DIP/SO/

µMAX

__________________Pin Configuration

TOP VIEW



RESET IN

( ) ARE FOR MAX6302/MAX6304.

* Patents pending

1

GND

2

MAX6301

SRT

SWT

MAX6302

3

MAX6303
MAX6304

4

DIP/SO/µMAX

________________________________________________________________

V

8

CC

RESET (RESET)

7

WDI

6

WDS

5

____________________________Features

♦ Adjustable Reset Threshold
♦ Adjustable Reset Timeout
♦ Adjustable Watchdog Timeout
♦ 500x Watchdog Timeout Multiplier
♦ 4µA Supply Current
♦ RESET or
♦ Push/Pull or Open-Drain Output Options
♦ Guaranteed

= 1V (MAX6301/MAX6303)

V

CC

Output Options

Asserted At or Above

♦ Power-Supply Transient Immunity
♦ Watchdog Function Can Be Disabled
♦ DIP/SO/µMAX Packages Available

______________Ordering Information

PART

MAX6301CPA

MAX6301CSA
MAX6301CUA 0°C to +70°C
MAX6301EPA
MAX6301ESA -40°C to +85°C

Ordering Information continued at end of data sheet.

TEMP. RANGE PIN-PACKAGE

0°C to +70°C
0°C to +70°C

-40°C to +85°C 8 Plastic DIP

8 Plastic DIP
8 SO
8 µMAX

8 SO

__________Typical Operating Circuit

V

IN

MAX6301

ONLY

R1

1

RESET IN

R2

2

GND

3

SRT

4

SWT

C

C

SWT

SRT

( ) ARE FOR MAX6302/MAX6304.

MAX6301
MAX6302
MAX6303
MAX6304

8

V

CC

0.1µF

RESET

7

(RESET)

6

WDI

5

WDS

Maxim Integrated Products

R

R

MAX6302

L

ONLY

WDS = 0 FOR NORMAL MODE
WDI = 1 FOR EXTENDED MODE

L

RESET

µP

I/O

MAX6301–MAX6304

1

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone]

+5V, Low-Power µP Supervisory Circuits
with Adjustable Reset/Watchdog

ABSOLUTE MAXIMUM RATINGS

VCC.......................................................................-0.3V to +7.0V

RESET IN, SWT, SRT..................................-0.3V to (V

WDI, WDS..............................................................-0.3V to +7.0V

RESET, RESET

MAX6301...........................................................-0.3V to +7.0V

MAX6302/6303/6304..............................-0.3V to (V

Input Current

...............................................................................±20mA

V

CC

GND..............................................................................±20mA

Output Current

RESET, RESET..............................................................±20mA

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.

CC

CC

+ 0.3V)

+ 0.3V)

ELECTRICAL CHARACTERISTICS

(VCC= +2V to +5.5V, TA= T

MIN

to T

, unless otherwise noted. Typical values are at VCC= +5V and TA= +25°C.)

MAX

MAX6301–MAX6304

Operating Voltage Range
(Note 1)

Supply Current (Note 2)

RESET TIMER

Reset Input Threshold Voltage
Reset Input Hysteresis

Reset Input Leakage Current

Reset Output Voltage High
(MAX6302/MAX6303/MAX6304)

Reset Output Voltage Low
(MAX6301/MAX6303/MAX6304)

VCCto Reset Delay
Reset Input Pulse Width
Reset Timeout Period (Note 3)

Reset Output Leakage Current

V

V

HYST

RESET IN

V

V

MAX6301C/MAX6303C
MAX6301E/MAX6303E

CC

MAX6302/MAX6304
No load

CC

V

TH

OH

OL

RD

RI

RP

RESET IN

V

RESET IN

VCC≥ 4.5V, I
VCC= 2V, I
MAX6302/MAX6304, VCC= 1.31V, RL= 10kΩ
VCC≥ 4.5V, I
VCC= 2V, I

MAX6301/
MAX6303

VCCfalling at 1mV/µs
Comparator overdrive = 50mV
C

SRT

MAX6301, V
MAX6302, V

falling, VCC= 5.0V
rising, VCC= 5.0V

SOURCE

SOURCE

SINK

SINK

VCC= 1V, I
TA= 0°C to +70°C

VCC= 1.2V, I
TA= -40°C to +85°C

= 1500pF

RESET

RESET

Continuous Power Dissipation (TA= +70°C)

Plastic DIP (derate 9.09mW/°C above +70°C) ............727mW

SO (derate 5.88mW/°C above +70°C).........................471mW

µMAX (derate 4.10mW/°C above +70°C) ....................330mW

Operating Temperature Ranges

MAX630_C_A......................................................0°C to +70°C

MAX630_E_A...................................................-40°C to +85°C

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

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

CONDITIONS

1.00 5.50

1.20 5.50

1.31 5.50

1.195 1.220 1.245

1.240 1.265

= 0.8mA

= 0.4mA

= 3.2mA

= 1.6mA

= V

CC

= GND

SINK

SINK

= 50µA,

= 100µA,

VCC- 0.4

VCC - 0.4

VCC- 0.3

0.4

0.4

0.3

0.3

±1
±1

UNITSMIN TYP MAXSYMBOLPARAMETER

V

µA4.0 7.0I

V

mV20V

nA±0.01 ±1I

V

V

µs63t
µs26t

ms2.8 4.0 5.2t
µA

2 _______________________________________________________________________________________

+5V, Low-Power µP Supervisory Circuits

with Adjustable Reset/Watchdog

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +2V to +5.5V, TA= T

WATCHDOG TIMER

WDI, WDS Input Threshold

WDI Pulse Width
WDI, WDS Leakage Current Extended mode disabled ±1 µA

WDI Sink/Source Current
(Note 4)

Watchdog Timeout Period
(Note 3)

Note 1: Reset is guaranteed valid from the selected reset threshold voltage down to the minimum VCC.
Note 2: VDS = V

, WDI unconnected.

CC

Note 3: Precision timing currents of 500nA are present at both the SRT and SWT pins. Timing capacitors connected to these nodes

must have low leakage consistent with these currents to prevent timing errors.

Note 4: The sink/source is supplied through a resistor, and is proportional to V

MIN

to T

, unless otherwise noted. Typical values are at VCC= +5V and TA= +25°C.)

MAX

CONDITIONS

V

t

V

IH

IL

VCC= 4.5V to 5.5V

WP

VCC= 2V to 4.5V 60

0.7V

Extended mode enabled ±70 µA

t

WD

WDS = GND, C
WDS = VCC, C

= 1500pF 2.8 4.0 5.2

SWT

= 1500pF 1.4 2.0 2.6 sec

SWT

(Figure 8). At VCC= 2V, it is typically ±24µA.

CC

30

CC

0.3V

CC

UNITSMIN TYP MAXSYMBOLPARAMETER

V

ns

ms

__________________________________________Typical Operating Characteristics

(C

SWT

= C

= 1500pF, TA= +25°C, unless otherwise noted.)

SRT

MAX6301–MAX6304

RESET TIMEOUT PERIOD

vs. C

10,000

VCC = 5V

1000

100

10

1

RESET TIMEOUT PERIOD (ms)

0

0.001 0.01 0.1 1 10 100 1000

SRT

C

(nF)

SRT

_______________________________________________________________________________________

WATCHDOG TIMEOUT PERIOD vs. C

10,000

6301-4 TOC-01

VCC = 5V

1000

100

10

1

WATCHDOG TIMEOUT PERIOD (sec)

0

0.001 0.01 0.1 1 10 100 1000

EXTENDED-MODE 

(WDS = V

C

SWT

(nF)

)

CC

SWT



6301-4 TOC-02

WATCHDOG TIMEOUT PERIOD vs. C

10,000

VCC = 5V

1000

100

10

1

WATCHDOG TIMEOUT PERIOD (ms)

0.1

0.001 0.01 0.1 1 10 100 1000

NORMAL-MODE 

(WDS = GND)

C

(nF)

SWT

SWT



6301-4 TOC-03

3

+5V, Low-Power µP Supervisory Circuits
with Adjustable Reset/Watchdog

____________________________Typical Operating Characteristics (continued)

(C

= C

SWT

4.2

4.0

3.8

3.6

3.4

3.2

SUPPLY CURRENT (µA)

3.0

2.8

2.6

MAX6301–MAX6304

= 1500pF, TA= +25°C, unless otherwise noted.)

SRT

SUPPLY CURRENT vs.

SUPPLY VOLTAGE

RESET DEASSERTED
NO LOAD

3.0 5.01.5 2.5 4.53.5 5.5

SUPPLY VOLTAGE (V)

6.02.0 4.0

6301-4 TOC-04

(ms)

WD

/t

RP

t

WATCHDOG TIMEOUT PERIOD

4.20
VCC = 5.0V

4.15

4.10

4.05

4.00

3.95

3.90

3.85

3.80

-40 40

RESET AND NORMAL-MODE

vs. TEMPERATURE

080-60 -20 6020 100

TEMPERATURE (°C)

6301-4 TOC-05

MAXIMUM TRANSIENT DURATION vs.

RESET THRESHOLD OVERDRIVE (V

120
110
100

90

RESET OCCURS 

80

ABOVE THE CURVE

70
60

50
40

30

TRANSIENT DURATION (µs)

20
10

0

0 200 400 600 1000800

RESET THRESHOLD OVERDRIVE (mV)

SEE

NEGATIVE-GOING VCC

TRANSIENTS

SECTION

V

RST

RST

= 4.60V

)

6301-4 TOC-06

5.00

4.75

4.50

4.25

4.00

3.75

3.50

3.25

SUPPLY CURRENT (µA)

3.00

2.75

2.50

76

72

68

64

60

PROPAGATION DELAY (µs)

56

SUPPLY CURRENT 

vs. TEMPERATURE

RESET DEASSERTED

NO LOAD

VCC = 5.0V

VCC = 2.0V

-40 40

080-60 -20 6020 100

TEMPERATURE (°C)

VCC TO RESET DELAY 

vs. TEMPERATURE (V

VCC FALLING AT 1mV/µs

FALLING)

CC

6301-4 TOC-07

6301-4 TOC-09

RESET IN THRESHOLD VOLTAGE 

vs. TEMPERATURE

1.226

1.224

1.222

1.220

1.218

1.216

RESET REFERENCE VOLTAGE (V)

1.214

-40 40

080-60 -20 6020 100

TEMPERATURE (°C)

RESET AND WATCHDOG 

TIMEOUT vs. V

4.16

4.12

4.08

(ms)

WP

/t

RP

4.04

t

4.00

6301-4 TOC-08

CC

6301-4 TOC-10

52

-40 40

080-60 -20 6020 100

TEMPERATURE (°C)

3.96


23 546

SUPPLY VOLTAGE (V)

4 _______________________________________________________________________________________

+5V, Low-Power µP Supervisory Circuits

with Adjustable Reset/Watchdog

______________________________________________________________Pin Description

PIN

1

2 GND Ground

3 SRT

4 SWT

5 WDS

6 WDI

NAME FUNCTION

Reset Input. High-impedance input to the reset comparator. Connect this pin to the center point of an

RESET IN

external resistor voltage-divider network to set the reset threshold voltage. The reset threshold voltage
is calculated as follows: V

Set Reset-Timeout Input. Connect a capacitor between this input and ground to select the reset timeout
period (tRS). Determine the period as follows: tRP= 2.67 x C

Typical Operating Circuit

Set Watchdog-Timeout Input. Connect a capacitor between this input and ground to select the basic
watchdog timeout period (tWD). Determine the period as follows: tWD= 2.67 x C
and tWDin µs. The watchdog function can be disabled by connecting this pin to ground.

Watchdog-Select Input. This input selects the watchdog mode. Connect to ground to select normal mode
and the basic watchdog timeout period. Connect to VCCto select extended mode, multiplying the basic
timeout period by a factor of 500. A change in the state of this pin resets the watchdog timer to zero.

Watchdog Input. A rising or falling transition must occur on this input within the selected watchdog
timeout period, or a reset pulse will occur. The capacitor value selected for SWT and the state of WDS
determine the watchdog timeout period. The watchdog timer clears and restarts when a transition
occurs on WDI or WDS. The watchdog timer is cleared when reset is asserted and restarted after reset
deasserts. In the extended watchdog mode (WDS = VCC), the watchdog function can be disabled by
driving WDI with a three-stated driver or by leaving WDI unconnected.

= 1.22 x (R1 + R2) / R2 (see

RST

).

Typical Operating Circuit

SRT

, with C

in pF and tRPin µs (see

SRT

SWT

).

, with C

SWT

in pF

MAX6301–MAX6304

7

8

RESET

(MAX6301/3)

RESET

(MAX6302/4)

V

CC

Open-Drain, Active-Low Reset
Output (MAX6301)

Push/Pull, Active-Low Reset
Output (MAX6303)

Open-Drain, Active-High Reset
Output (MAX6302)

Push/Pull, Active-High Reset
Output (MAX6304)

Supply Voltage

RESET changes from high to low whenever the monitored voltage

) drops below the selected reset threshold (V

(V

IN

remains low as long as V
RESET remains low for the reset timeout period and then goes high.
The watchdog timer triggers a reset pulse (t
dog timeout period (tWD) is exceeded.

RESET changes from low to high whenever the monitored voltage
(VIN) drops below the selected reset threshold (V
remains high as long as VINis below V
RESET remains high for the reset timeout period and then goes low.
The watchdog timer triggers a reset pulse (tRP) whenever the watch­dog timeout period (tWD) is exceeded.

is below V

IN

. Once VINexceeds V

RST

RP

. Once VINexceeds V

RST

). RESET

RST

RST

) whenever the watch-

). RESET

RST

RST

,

,

_______________________________________________________________________________________ 5

+5V, Low-Power µP Supervisory Circuits
with Adjustable Reset/Watchdog

_______________Detailed Description

Reset Function/Output

The reset output is typically connected to the reset
input of a microprocessor (µP). A µP’s reset input starts
or restarts the µP in a known state. The MAX6301–
MAX6304 µP supervisory circuits provide the reset
logic to prevent code-execution errors during power­up, power-down, and brownout conditions (see

Operating Circuit

For the MAX6301/MAX6303, RESET changes from high
to low whenever the monitored voltage (VIN) drops
below the reset threshold voltage (V
remains low as long as VINis below V
exceeds V
period, then goes high. When a reset is asserted due to
a watchdog timeout condition, RESET stays low for the
reset timeout period. Anytime reset asserts, the watch­dog timer clears. At the end of the reset timeout period,

MAX6301–MAX6304

RESET goes high and the watchdog timer is restarted
from zero. If the watchdog timeout period is exceeded
again, then RESET goes low again. This cycle contin­ues unless WDI receives a transition.

On power-up, once VCCreaches 1V, RESET is guaran­teed to be a logic low. For information about applica­tions where VCCis less than 1V, see the section

Ensuring a Valid RESET/RESET Output Down to VCC=
0V (MAX6303/MAX6304)

low. When VINrises above V
and RESET remains low. When the reset timeout period
ends, RESET goes high.

On power-down, once VINgoes below V
goes low and is guaranteed to be low until VCCdroops
below 1V. For information about applications where
VCCis less than 1V, see the section

RESET/RESET Output Down to VCC= 0V (MAX6303/
MAX6304)

The MAX6302/MAX6304 active-high RESET output is
the inverse of the MAX6301/MAX6303 active-low
RESET output, and is guaranteed valid for VCC> 1.31V.

These supervisors monitor the voltage on RESET IN.
The MAX6301–MAX6304 have an adjustable reset
threshold voltage (V
voltage divider (Figure 1). Use the following formula to
calculate V
age triggers a reset):

where V
VTHis the reset input threshold (1.22V). Resistors R1 and

RST

).

). RESET

RST

. Once V

, RESET remains low for the reset timeout

RST

. As VCCrises, RESET remains

, the reset timer starts

RST

RST

RST

, RESET

Ensuring a Valid

.

Reset Threshold

) set with an external resistor

RST

(the point at which the monitored volt-

RST

VR1R2

×+

()

V

RST

is the desired reset threshold voltage and

TH

=

R2

V

()

Typical

IN

V

IN

R1

RESET IN

R2

Figure 1. Calculating the Reset Threshold Voltage (V

R2 can have very high values to minimize current con­sumption. Set R2 to some conveniently high value (1MΩ,
for example) and calculate R1 based on the desired
reset threshold voltage, using the following formula:

MAX6301
MAX6302
MAX6303
MAX6304

R1 R2

=× −

V



V



V



CC

RST

TH

V

RST



1

Ω

()




0.1µF

= 1.22

R1 + R2

(

)

R2

)

RST

Watchdog Timer

The watchdog circuit monitors the µP’s activity. If the µP
does not toggle the watchdog input (WDI) within t
(user selected), reset asserts. The internal watchdog
timer is cleared by reset, by a transition at WDI (which
can detect pulses as short as 30ns), or by a transition
at WDS. The watchdog timer remains cleared while
reset is asserted; as soon as reset is released, the timer
starts counting (Figure 2).

The MAX6301–MAX6304 feature two modes of watch­dog timer operation: normal mode and extended mode.
In normal mode (WDS = GND), the watchdog timeout
period is determined by the value of the capacitor con­nected between SWT and ground (see the section

WD

Selecting the Reset and Watchdog Timeout Capacitor

In extended mode (WDS = VCC), the watchdog timeout
period is multiplied by 500. For example, in the extend­ed mode, a 1µF capacitor gives a watchdog timeout
period of 22 minutes (see the graph Extended-Mode
Watchdog Timeout Period vs. C

Operating Characteristics

In extended mode, the watchdog function can be dis­abled by leaving WDI unconnected or by three-stating
the driver connected to WDI. In this mode, the watch­dog input is internally driven low during the watchdog

).

SWT

in the

Typical

).

6 _______________________________________________________________________________________

+5V, Low-Power µP Supervisory Circuits

with Adjustable Reset/Watchdog

V

CC

WDI

0V

V

CC

RESET

0V

NORMAL MODE (WDS = GND)

Figure 2a. Watchdog Timing Diagram, WDS = GND

V

CC

WDI

0V

MAX6301–MAX6304

t

WD

t

x 500 t

WD

t

RP

RP

V

CC

RESET

0V

EXTENDED MODE (WDS = V

Figure 2b. Watchdog Timing Diagram, WDS = V

)

CC

CC

timeout period, then momentarily pulses high, resetting
the watchdog counter. When WDI is left unconnected,
the watchdog timer is cleared by this internal driver just
before the timeout period is reached (the internal driver
pulls WDI high at about 94% of tWD). When WDI is
three-stated, the maximum allowable leakage current of
the device driving WDI is 10µA.

In normal mode (WDS = GND), the watchdog timer
cannot be disabled by three-stating WDI. WDI is a
high-impedance input in this mode. Do not leave WDI
unconnected in normal mode.

V

CC

GND

MAX6301

SRT

MAX6302
MAX6303

SWT

MAX6304

=
in pF

t

2.67

C

SWT

RP

=

C

SWT

2.67

C

in pF

SWT

in µs

t

WD

C

SRT

C

RST

C

RST

in µs

t

WD

V

CC

0.1µF

t

WD

Figure 3. Calculating the Reset (C

) Timeout Capacitor Values

(C

SWT

) and Watchdog

SRT

_______________________________________________________________________________________ 7

+5V, Low-Power µP Supervisory Circuits
with Adjustable Reset/Watchdog

V

IN

R1

RESET IN

R2

Figure 4. Monitoring a Voltage Other than V

MAX6301
MAX6302
MAX6303
MAX6304

V

CC

V

CC

0.1µF

= 1.22

CC

R1 + R2

(

R2

V

RST

MAX6301–MAX6304

__________Applications Information

Selecting the Reset and

Watchdog Timeout Capacitor

The reset timeout period is adjustable to accommodate
a variety of µP applications. Adjust the reset timeout
period (tRS) by connecting a specific value capacitor
(C

) between SRT and ground (Figure 3). Calculate

SRT

the reset timeout capacitor as follows:

C

= tRP⁄ 2.67

SRT

with C
age (<10nA) type capacitor. Ceramic is recommended.

The watchdog timeout period is adjustable to accom­modate a variety of µP applications. With this feature,
the watchdog timeout can be optimized for software
execution. The programmer can determine how often
the watchdog timer should be serviced. Adjust the
watchdog timeout period (tWD) by connecting a specif­ic value capacitor (C
(Figure 3). For normal-mode operation, calculate the
watchdog timeout capacitor as follows:

where C
low leakage (<10nA) type capacitor. Ceramic is recom­mended.

The
monitoring other voltages is simple, and Figure 4 shows
a circuit that accomplishes this. Calculate V
shown in the

in pF and tRPin µs. C

SRT

C

SWT

is in pF and tWDis in µs. C

SWT

) between SWT and ground

SWT

= tWD⁄ 2.67

must be a low-leak-

SRT

SRT

Monitoring Voltages Other than V

Typical Operating Circuit

Reset Threshold

monitors VCC. However,

section.

must be a

)

RST

CC

as

MAX6302

* THREE-STATE LEAKAGE MUST BE <10µA.

Figure 5. Wake-Up Timer

GND

V

RESET

WDI

WDS

CC

V

CC

80C51

RST

*

I/O
I/O
I/O

GND

V

CC

V

CC

Wake-Up Timer

In some applications, it is advantageous to put a µP
into sleep mode, periodically “wake it up” to perform
checks and/or tasks, then put it back into sleep mode.
The MAX6301 family supervisors can easily accommo­date this technique. Figure 5 illustrates an example
using the MAX6302 and an 80C51.

In Figure 5, just before the µC puts itself into sleep
mode, it pulls WDS high. The µC’s I/O pins maintain
their logic levels while in sleep mode and WDS remains
high. This places the MAX6302 in extended mode,
increasing the watchdog timeout 500 times. When the
watchdog timeout period ends, a reset is applied on
the 80C51, “waking it up” to perform tasks. While the µP
is performing tasks, the 80C51 pulls WDS low (select­ing normal mode), and the MAX6302 monitors the µP
for hang-ups. When the µP finishes its tasks, it puts
itself back into sleep mode, drives WDS high, and
starts the cycle over again. This is a power-saving tech­nique, since the µP is operating only part of the time
and the MAX6302 has very low quiescent current.

Adding a Manual Reset Function

A manual reset option can easily be implemented by
connecting a normally open momentary switch in paral­lel with R2 (Figure 6). When the switch is closed, the
voltage on RESET IN goes to zero, initiating a reset.
When the switch is released, reset remains asserted for
the reset timeout period and then is cleared. The push­button switch is effectively debounced by the reset
timer.

8 _______________________________________________________________________________________

+5V, Low-Power µP Supervisory Circuits

with Adjustable Reset/Watchdog

V

CC

R1

RESET IN

MAX6301
MAX6302

R2

MAX6303
MAX6304

Figure 6. Adding a Manual Reset Function

V

CC

0.1µF

Interfacing to µPs with

Bidirectional Reset Pins

Since RESET is open-drain, the MAX6301 interfaces
easily with µPs that have bidirectional reset pins, such
as the Motorola 68HC11 (Figure 7). Connecting RESET
directly to the µP’s reset pin with a single pull-up allows
either device to assert reset.

RESET TO 
OTHER SYSTEM 
COMPONENTS

V

CC

MAX6301

V

CC

0.1µF

GND

RESET

Figure 7. Interfacing to µPs with Bidirectional Reset I/O Pins

WDI

4.7k

WATCHDOG

TIMER

V

CC

µP

RESET

TO RESET

GENERATOR

MAX6301–MAX6304

Negative-Going VCCTransients

In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, these supervisors
are relatively immune to short-duration negative-going
transients (glitches). The graph Maximum Transient
Duration vs. Reset Threshold Overdrive in the

Operating Characteristics

shows this relationship.

Typical

The area below the curves of the graph is the region in
which these devices typically do not generate a reset
pulse. This graph was generated using a negative­going pulse applied to VIN, starting above the actual
reset threshold (V

) and ending below it by the mag-

RST

nitude indicated (reset-threshold overdrive). As the
magnitude of the transient increases (farther below the
reset threshold), the maximum allowable pulse width
decreases. Typically, a VCCtransient that goes 100mV
below the reset threshold and lasts 50µs or less will not
cause a reset pulse to be issued.

Watchdog Input Current

Extended Mode

In extended mode (WDS = VCC), the WDI input is inter­nally driven through a buffer and series resistor from
the watchdog counter (Figure 8). When WDI is left
unconnected, the watchdog timer is serviced within the

MAX6301
MAX6302

WDS

Figure 8. Watchdog Input Structure

TO MODE
CONTROL

MAX6303
MAX6304

watchdog timeout period by a very brief 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 (>30ns) once within the
period to reset the watchdog timer. If instead WDI is
externally driven high for the majority of the timeout
period, typically 70µA can flow into WDI.

Normal Mode

In normal mode (WDS = GND), the internal buffer that
drives WDI is disabled. In this mode, WDI is a standard
CMOS input and leakage current is typically 100pA,
regardless of whether WDI is high or low.

_______________________________________________________________________________________ 9

+5V, Low-Power µP Supervisory Circuits
with Adjustable Reset/Watchdog

V

CC

MAX6303

Figure 9. Ensuring RESET Valid to VCC= 0V

MAX6301–MAX6304

Ensuring a Valid

Down to V

CC

V

CC

0.1µF

RESET

GND

RESET

100k

/RESET Output

= 0V (MAX6303/MAX6304)

When VCCfalls below 1V, RESET/RESET current sink­ing (sourcing) capabilities decline drastically. In the
case of the MAX6303, high-impedance CMOS-logic
inputs connected to RESET can drift to undetermined
voltages. This presents no problem in most applica­tions, since most µPs and other circuitry do not operate
with VCCbelow 1V.

In those applications where RESET must be valid down
to 0V, adding a pull-down resistor between RESET and
ground sinks any stray leakage currents, holding
RESET low (Figure 9). The value of the pull-down resis­tor is not critical; 100kΩ is large enough not to load
RESET and small enough to pull RESET to ground. For
applications using the MAX6304, a 100kΩ pull-up resis­tor between RESET and VCCwill hold RESET high when
VCCfalls below 1V (Figure 10).

V

CC

MAX6304

Figure 10. Ensuring RESET Valid to VCC= 0V

V

CC

RESET

GND

START

SET WDI

LOW

SUBROUTINE OR
PROGRAM LOOP

SET WDI HIGH

RETURN

END

0.1µF

100k

Watchdog-Software Considerations

To help the watchdog timer monitor software execution
more closely, 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 within the loop, keep­ing the watchdog from timing out.

Figure 11 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

10 ______________________________________________________________________________________

Figure 11. Watchdog Flow Diagram

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. When using extended mode,
as described in the

Watchdog Input Current

this scheme does result in higher average WDI input
current than does the method of leaving WDI low for the
majority of the timeout period and periodically pulsing it
low-high-low.

section,

+5V, Low-Power µP Supervisory Circuits

with Adjustable Reset/Watchdog

_____________Layout Considerations

SRT and SWT are precision current sources. When
developing the layout for the application, be careful to
minimize board capacitance and leakage currents
around these pins. Traces connected to these pins
should be kept as short as possible. Traces carrying
high-speed digital signals and traces with large voltage
potentials should be routed as far from these pins as
possible. Leakage currents and stray capacitance (e.g.,
a scope probe) at these pins could cause errors in the
reset and/or watchdog timeout period. When evaluating
these parts, use clean prototype boards to ensure accu­rate reset and watchdog timeout periods.

RESET IN is a high-impedance input which is typically
driven by a high-impedance resistor-divider network
(e.g., 1MΩ to 10MΩ). Minimize coupling to transient
signals by keeping the connections to this input short.
Any DC leakage current at RESET IN (e.g., a scope
probe) causes errors in the programmed reset thresh­old. Note that sensitive pins are located on the GND
side of the device, away from the digital I/O, to simplify
board layout.

__Ordering Information (continued)

PART

MAX6302CPA

MAX6302CSA
MAX6302CUA 0°C to +70°C
MAX6302EPA
MAX6302ESA -40°C to +85°C
MAX6303CPA
MAX6303CSA 0°C to +70°C 8 SO
MAX6303CUA 0°C to +70°C 8 µMAX
MAX6303EPA -40°C to +85°C 8 Plastic DIP
MAX6303ESA -40°C to +85°C 8 SO
MAX6304CPA
MAX6304CSA 0°C to +70°C 8 SO
MAX6304CUA 0°C to +70°C 8 µMAX
MAX6304EPA -40°C to +85°C 8 Plastic DIP
MAX6304ESA -40°C to +85°C 8 SO

TEMP. RANGE PIN-PACKAGE

0°C to +70°C
0°C to +70°C

-40°C to +85°C 8 Plastic DIP

0°C to +70°C 8 Plastic DIP

0°C to +70°C 8 Plastic DIP

8 Plastic DIP
8 SO
8 µMAX

8 SO

___________________Chip Information

TRANSISTOR COUNT: 580

MAX6301–MAX6304

______________________________________________________________________________________ 11

+5V, Low-Power µP Supervisory Circuits
with Adjustable Reset/Watchdog

________________________________________________________Package Information

C

A

0.101mm

e

MAX6301–MAX6304

D

E H

0.004 in

A1B

D

A

0.101mm

e

A1

B

0.004in.

DIM

α

L

A1

8-PIN µMAX

MICROMAX SMALL-OUTLINE

PACKAGE

DIM

A1

0°-8°

C

L

INCHES MILLIMETERS



A

0.036

0.004

B

0.010

C

0.005

D

0.116

E

0.116
e
H

0.188
L

0.016

α



A

0.053

0.004
B

0.014
C

0.007
E

0.150
e
H

0.228
L

0.016

MAX

MIN

0.044

0.008

0.014

0.007

0.120

0.120



0°

MIN





0.198

0.026
6°

INCHES MILLIMETERS

MAX

0.069

0.010

0.019

0.010

0.157


0.244

0.050

MIN

0.91

0.10

0.25

0.13

2.95

2.95

4.78

0.41
0°

MIN

1.35

0.10

0.35

0.19

3.80

5.80

0.40

MAX

1.11

0.20

0.36

0.18

3.05

3.05

0.650.0256





1.270.050



5.03

0.66
6°

21-0036D

MAX

1.75

0.25

0.49

0.25

4.00



6.20

1.27

PINS

Narrow SO

HE

SMALL-OUTLINE

PACKAGE

(0.150 in.)

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

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.

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

12

__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 [phone]

12

__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 [phone]

© 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

© 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

DIM

D
D
D



INCHES MILLIMETERS

MIN

MAX

8

0.189

0.197

14

0.337

0.344

16

0.386

0.394

MIN

4.80

8.55

9.80

MAX

5.00

8.75

10.00

21-0041A