MAX6747KA46+T - Maxim Integrated

General Description

The MAX6746–MAX6753 low-power microprocessor

(μP) supervisory circuits monitor single/dual system

supply voltages from 1.575V to 5V and provide maximum

adjustability for reset and watchdog functions. These

devices assert a reset signal whenever the VCC

supply voltage or RESET IN falls below its reset threshold

or when manual reset is pulled low. The reset output

remains asserted for the reset timeout period after VCC

and RESET IN rise above the reset threshold. The reset

function features immunity to power-supply transients.

The MAX6746–MAX6753 have ±2% factory-trimmed

reset threshold voltages in approximately 100mV

increments from 1.575V to 5.0V and/or adjustable reset

threshold voltages using external resistors.

The reset and watchdog delays are adjustable with

external capacitors. The MAX6746–MAX6751 contain

a watchdog select input that extends the watchdog

timeout period by 128x. The MAX6752/MAX6753 contain

a window watchdog timer that looks for activity outside an

expected window of operation.

The MAX6746–MAX6753 are available with a push-pull

or open-drain active-low RESET output. The MAX6746–

MAX6753 are available in an 8-pin SOT23 package and

are fully specified over the automotive temperature range

(-40°C to +125°C).

Applications

● Medical Equipment

● Automotive

● Intelligent Instruments

● Portable Equipment

● Battery-Powered Computers/Controllers

● Embedded Controllers

● Critical μP Monitoring

● Set-Top Boxes

● Computers

Benets and Features

● Configurable Reset and Watchdog Options Enables

Wide Variety of Applications

• Factory-Set Reset Threshold Options from 1.575V

to 5V in ~100mV Increments

• Adjustable Reset Threshold Options

• Single/Dual Voltage Monitoring

• Capacitor-Adjustable Reset Timeout

• Capacitor-Adjustable Watchdog Timeout

• Min/Max (Windowed) Watchdog Option

• Manual-Reset Input Option

• Push-Pull or Open-Drain RESET Output Options

● 3.7μA Supply Current Reduces System Power

Consumption

● Integrated Power Supply Protection Increases

Robustness

• Power-Supply Transient Immunity

• Guaranteed RESET Valid for VCC ≥ 1V

● 8-Pin SOT23 Packages Saves Board Space

Selector Guide and Ordering Information appear at end of

data sheet.

19-2530; Rev 15; 1/17

MAX6748

MAX6749

MAX6750

MAX6751

RESET IN

GND

SRT

VCC

SWT

CSRT

CSWT

VIN

WDI

WDS

I/O

WDS = 0 FOR NORMAL MODE

WDS = VCC FOR EXTENDED MODE

MAX6749

MAX4751

µP

RESET RESET

Typical Operating Circuit

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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

SRT, SWT, SET0, SET1, RESET IN, WDS, MR,

WDI, to GND......................................…-0.3V to (VCC + 0.3V)

RESET (Push-Pull) to GND....................…-0.3V to (VCC + 0.3V)

RESET (Open-Drain) to GND.............................…-0.3V to +6.0V

Input Current (All Pins).....................................................±20mA

Output Current (RESET) ...................................................±20mA

Continuous Power Dissipation (TA = +70°C)

8-Pin SOT23 (derate 8.9mW/°C above +70°C)...........714mW

Operating Temperature Range .........................-40°C to +125°C

Storage Temperature Range ............................-65°C to +150°C

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

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

Soldering Temperature (reflow) .......................................+260°C

(VCC = +1.2V to +5.5V, TA = TMIN to TMAX, unless otherwise specified. Typical values are at VCC = +5V and TA = +25°C.) (Note 1)

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.

Electrical Characteristics

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage VCC

TA = 0°C to +125°C 1.0 5.5 V

TA = -40°C to 0°C 1.2 5.5

Supply Current ICC

VCC ≤ 5.5V 510

µAVCC ≤ 3.3V 4.2 9

VCC ≤ 2.0V 3.7 8

VCC Reset Threshold VTH See VTH

selection table TA = -40°C to +125°C VTH -

2% VTH +

2% V

Hysteresis VHYST 0.8 %

VCC Reset Threshold

(MAX6752AKA32 Only) TA = -40°C to +125°C 3.136 3.224 V

Hysteresis

(MAX6752AKA32 Only) VHYST 0.65 0.80 0.90 %

VCC to Reset Delay VCC falling from VTH + 100mV to VTH

-100mV at 1mV/µs 20 µs

Reset Timeout Period tRP

CSRT = 1500pF 5.692 7.590 9.487 ms

CSRT = 100pF 0.506

SRT Ramp Current IRAMP VSRT = 0 to 1.23V; VCC = 1.6V to 5V 200 250 300 nA

SRT Ramp Threshold VRAMP VCC = 1.6V to 5V (VRAMP rising) 1.173 1.235 1.297 V

Normal Watchdog Timeout Period

(MAX6746–MAX6751) tWD

CSWT = 1500pF 5.692 7.590 9.487 ms

CSWT = 100pF 0.506

Extended Watchdog Timeout

(MAX6746–MAX6751) tWD

CSWT = 1500pF 728.6 971.5 1214.4 ms

CSWT = 100pF 64.77

Slow Watchdog Period

(MAX6752/MAX6753) tWD2

CSWT = 1500pF 728.6 971.5 1214.4 ms

CSWT = 100pF 64.77

Fast Watchdog Timeout Period,

SET Ratio = 8,

(MAX6752/MAX6753) tWD1

CSWT = 1500pF 91.08 121.43 151.80 ms

CSWT = 100pF 8.09

Fast Watchdog Timeout Period,

SET Ratio = 16,

(MAX6752/MAX6753) tWD1

CSWT = 1500pF 45.53 60.71 75.89

CSWT = 100pF 4.05

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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(VCC = +1.2V to +5.5V, TA = TMIN to TMAX, unless otherwise specified. Typical values are at VCC = +5V and TA = +25°C.) (Note 1)

Note 1: Production testing done at TA = +25°C. Over temperature limits are guaranteed by design.

Electrical Characteristics (continued)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Fast Watchdog Timeout Period,

SET Ratio = 64,

(MAX6752/MAX6753) tWD1

CSWT = 1500pF 11.38 15.18 18.98

CSWT = 100pF 1.01

Fast Watchdog Minimum Period

(MAX6752/MAX6753) 2000 ns

SWT Ramp Current IRAMP VSWT = 0 to 1.23V, VCC = 1.6V to 5V 200 250 300 nA

SWT Ramp Threshold VRAMP VCC = 1.6V to 5V (VRAMP rising) 1.173 1.235 1.297 V

RESET Output-Voltage Low

Open-Drain, Push-Pull

(Asserted)

VOL

VCC ≥ 1.0V, ISINK = 50µA 0.3

VVCC ≥ 2.7V, ISINK = 1.2mA 0.3

VCC ≥ 4.5V, ISINK = 3.2mA 0.4

RESET Output-Voltage High,

Push-Pull (Not Asserted) VOH

VCC ≥ 1.8V, ISOURCE = 200µA 0.8 x VCC

VVCC ≥ 2.25V, ISOURCE = 500µA 0.8 x VCC

VCC ≥ 4.5V, ISOURCE = 800µA 0.8 x VCC

RESET Output Leakage Current,

Open Drain ILKG VCC > VTH, reset not asserted,

VRESET = 5.5V 1.0 µA

DIGITAL INPUTS (MR, SET0, SET1, WDI, WDS)

Input Logic Levels

VIL VCC ≥ 4.0V 0.8

VIH 2.4

VIL VCC < 4.0V 0.3 x VCC

VIH 0.7 x VCC

MR Minimum Pulse Width 1µs

MR Glitch Rejection 100 ns

MR-to-RESET Delay 200 ns

MR Pullup Resistance Pullup to VCC 12 20 28 kΩ

WDI Minimum Pulse Width 300 ns

RESET IN

RESET IN Threshold VRESET IN TA = -40°C to +125°C 1.216 1.235 1.254 V

RESET IN Leakage Current IRESET IN -50 ±1+50 nA

RESET IN to RESET Delay RESET IN falling at 1mV/µs 20 µs

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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

Typical Operating Characteristics

WATCHDOG TIMEOUT PERIOD vs. CSWT

MAX6746 toc02

CSWT (pF)

WATCHDOG TIMEOUT PERIOD (ms)

10,0001000

100

1000

10,000

100,000

0.1

100

100,000

MAX6746–MAX6751

EXTENDED MODE

NORMAL MODE

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX6746 toc03

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (µA)

5432

1 6

NORMALIZED RESET TIMEOUT PERIOD

vs. TEMPERATURE

MAX6746 toc04

TEMPERATURE (°C)

NORMALIZED TIMEOUT PERIOD

1007550250-25

0.95

1.00

1.05

1.10

1.15

1.20

0.90

-50 125

CSRT = 100pF

CSRT = 1500pF

NORMALIZED WATCHDOG TIMEOUT PERIOD

vs. TEMPERATURE

MAX6746 toc05

TEMPERATURE (°C)

NORMALIZED TIMEOUT PERIOD

1007550250-25

0.95

0.90

0.85

1.00

1.05

1.10

1.15

1.20

0.80

-50 125

CSWT = 100pF

CSWT = 1500pF

MAXIMUM TRANSIENT DURATION

vs. RESET THRESHOLD OVERDRIVE

MAX6746 toc06

RESET THRESHOLD OVERDRIVE (mV)

TRANSIENT DURATION (µs)

800600400200

100

125

150

175

0 1000

RESET OCCURS

ABOVE THE CURVE

VTH = 2.92V

SUPPLY CURRENT

vs. TEMPERATURE

MAX6746 toc07

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

1007525 500-25

-50 125

VCC = 3.3V

VCC = 1.8V

VCC = 5V

RESET TIMEOUT PERIOD vs. CSRT

MAX6746 toc01

CSRT (pF)

RESET TIMEOUT PERIOD (ms)

10,0001000

100

1000

0.1

100 100,000

NORMALIZED RESET IN THRESHOLD VOLTAGE

vs. TEMPERATURE

MAX6746 toc08

TEMPERATURE (°C)

NORMALIZED RESET THRESHOLD VOLTAGE

1007550250-25

0.994

0.992

0.996

1.000

0.998

1.004

1.002

1.008

1.006

1.010

0.990

-50 125

VCC = 5V

RESET IN THRESHOLD

vs. SUPPLY VOLTAGE

MAX6746 toc08b

SUPPLY VOLTAGE (V)

RESET IN THRESHOLD (V)

5432

1.236

1.237

1.238

1.239

1.240

1.235

1 6

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MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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

Typical Operating Characteristics (continued)

Pin Descriptions

( ) ARE FOR MAX6746 AND MAX6747 ONLY.

TOP VIEW

WDI

WDSGND

VCC

RESETSWT

SRT

RESET IN (MR)

MAX6746–

MAX6751

SOT23

WDI

SET1GND

RESETSWT

SRT

SET0

MAX6752

MAX6753

SOT23

Pin Congurations

VCC TO RESET DELAY

vs. TEMPERATURE (VCC FALLING)

MAX6746 toc09

TEMPERATURE (°C)

VCC TO RESET DELAY (µs)

1007550250-25

25.4

25.8

26.2

26.6

27.0

25.0

-50 125

VCC FALLING AT 1mV/µs

RESET AND WATCHDOG

TIMEOUT PERIOD vs. SUPPLY VOLTAGE

MAX6746 toc10

VCC (V)

TIMEOUT PERIOD (ms)

5.55.04.0 4.52.5 3.0 3.52.0

0.44

0.48

0.52

0.56

0.60

0.40

1.5 6.0

CSWT = CSRT = 100pF

RESET AND WATCHING TIMEOUT

PERIOD vs. SUPPLY VOLTAGE

MAX6746 toc11

VCC (V)

TIMEOUT PERIOD (ms)

5.55.04.54.03.53.02.52.0

6.5

7.0

7.5

8.0

8.5

9.0

6.0

1.5 6.0

CSWT = CSRT = 1500pF

RESET

WATCHDOG

NAME FUNCTION

MAX6746

MAX6747

MAX6748–

MAX6751

MAX6752

MAX6753

1— — MR Manual-Reset Input. Pull MR low to manually reset the device. Reset

remains asserted for the reset timeout period after MR is released.

—1—RESET IN Reset Input. High-impedance input to the adjustable reset comparator.

Connect RESET IN to the center point of an external resistor-divider to

set the threshold of the externally monitored voltage.

— — 1 SET0 Logic Input. SET0 selects watchdog window ratio or disables the

watchdog timer. See Table 1.

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MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

Pin Descriptions (continued)

NAME FUNCTION

MAX6746

MAX6747

MAX6748–

MAX6751

MAX6752

MAX6753

2 2 2 SWT

Watchdog Timeout Input.

MAX6746–MAX6751: Connect a capacitor between SWT and ground to

set the basic watchdog timeout period (tWD). Determine the period by

the formula tWD = 4.94 x 106 x CSWT with tWD in seconds and CSWT

in Farads. Extend the basic watchdog timeout period by using the WDS

input. Connect SWT to ground to disable the watchdog timer function.

MAX6752/MAX6753: Connect a capacitor between SWT and ground

to set the slow watchdog timeout period (tWD2). Determine the slow

watchdog period by the formula: tWD2 = 0.65 x 109 x CSWT with tWD2 in

seconds and CSWT in Farads. The fast watchdog timeout period is set

by pin strapping SET0 and SET1 (Connect SET0 high and SET1 low to

disable the watchdog timer function.) See Table 1.

333SRT Reset Timeout Input. Connect a capacitor from SRT to GND to select

the reset timeout period. Determine the period as follows: tRP = 4.94 x

106 x CSRT with tRP in seconds and CSRT in Farads.

444GND Ground

5 5 — WDS

Watchdog Select Input. WDS selects the watchdog mode. Connect

WDS to ground to select normal mode and the watchdog timeout

period. Connect WDS to VCC to select extended mode, multiplying the

basic timeout period by a factor of 128. A change in the state of WDS

clears the watchdog timer.

— — 5 SET1 Logic Input. SET1 selects the watchdog window ratio or disables the

watchdog timer. See Table 1.

666WDI

Watchdog Input.

MAX6746–MAX6751: A falling transition must occur on WDI within

the selected watchdog timeout period or a reset pulse occurs. The

watchdog timer clears when a transition occurs on WDI or whenever

RESET is asserted. Connect SWT to ground to disable the watchdog

timer function.

MAX6752/MAX6753: WDI falling transitions within periods shorter than

tWD1 or longer than tWD2 force RESET to assert low for the reset

timeout period. The watchdog timer begins to count after RESET is

deasserted. The watchdog timer clears when a valid transition occurs

on WDI or whenever RESET is asserted. Connect SET0 high and SET1

low to disable the watchdog timer function. See the Watchdog Timer

section.

777RESET

Push/Pull or Open-Drain Reset Output. RESET asserts whenever VCC

or RESET IN drops below the selected reset threshold voltage (VTH or

VRESET IN, respectively) or manual reset is pulled low. RESET remains

low for the reset timeout period after all reset conditions are deasserted,

and then goes high. The watchdog timer triggers a reset pulse (tRP)

whenever a watchdog fault occurs.

8 8 8 VCC Supply Voltage. VCC is the power-supply input and the input for xed

threshold VCC monitor.

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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Detailed Description

The MAX6746–MAX6753 assert a reset signal whenever

the VCC supply voltage or RESET IN falls below its reset

threshold. The reset output remains asserted for the reset

timeout period after VCC and RESET IN rise above its

respective reset threshold. A watchdog timer triggers a

reset pulse whenever a watchdog fault occurs.

The reset and watchdog delays are adjustable with

external capacitors. The MAX6746–MAX6751 contain a

watchdog select input that extends the watchdog timeout

period to 128x.

The MAX6752 and MAX6753 have a sophisticated watchdog

timer that detects when the processor is running outside

an expected window of operation. The watchdog signals a

fault when the input pulses arrive too early (faster that the

selected tWD1 timeout period) or too late (slower than the

selected tWD2 timeout period) (see Figure 1).

Reset Output

The reset output is typically connected to the reset input

of a μP. A μP’s reset input starts or restarts the μP in a

known state. The MAX6746–MAX6753 μP supervisory

circuits provide the reset logic to prevent code-execution

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

(see the Typical Operating Circuit). RESET changes from

high to low whenever the monitored voltage, RESET

IN and/or VCC drop below the reset threshold voltages.

Once VRESET IN and/or VCC exceeds its respective reset

threshold voltage(s), RESET remains low for the reset

timeout period, then goes high.

RESET is guaranteed to be in the correct logic

state for VCC greater than 1V. For applications

requiring valid reset logic when VCC is less than 1V,

see the Ensuring a Valid RESET Down to VCC = 0V

(Push-Pull RESET) section.

RESET IN Threshold

The MAX6748–MAX6751 monitor the voltage on RESET

IN using an adjustable reset threshold (VRESET IN) set

with an external resistor voltage-divider (Figure 2). Use

the following formula to calculate the externally monitored

voltage (VMON_TH):

VMON_TH = VRESET IN x (R1 + R2)/R2

Figure 1. MAX6752/MAX6753 Detailed Watchdog Input Timing Relationship

Figure 2. Calculating the Monitored Threshold Voltage

(VMON_TH)

WDI CONDITION 1

WDI CONDITION 2

WDI CONDITION 3

GUARANTEED TO

NOT ASSERT

RESET

GUARANTEED TO

ASSERT

RESET

tWD1 (MIN) tWD1 (MAX)

*UNDETERMINED *UNDETERMINED

FAST FAULT

NORMAL OPERATION

SLOW FAULT

*UNDETERMINED STATES MAY OR MAY NOT GENERATE A FAULT CONDITION

GUARANTEED

TO ASSERT

RESET

tWD2 (MIN) tWD2 (MAX)

MAX6748

MAX6749

MAX6750

MAX6751

RESET IN

GND

VCC

VMON_TH

VMON_TH = 1.235 x (R1 + R2) / R2

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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where VMON_TH is the desired reset threshold voltage

and VTH is the reset input threshold (1.235V). Resistors

R1 and R2 can have very high values to minimize

current consumption due to low leakage currents. Set R2

to some conveniently high value (500kΩ, for example)

and calculate R1 based on the desired reset threshold

voltage, using the following formula:

R1 = R2 x (VMON_TH/VRESET IN - 1) (Ω)

The MAX6748 and MAX6749 do not monitor VCC

supply voltage; therefore, VCC must be greater than

1.5V to guarantee RESET IN threshold accuracy and

timing performance. The MAX6748 and MAX6749 can be

configured to monitor VCC voltage by connecting VCC to

VMON_TH.

Dual-Voltage Monitoring (MAX6750/MAX6751)

The MAX6750 and MAX6751 contain both factory-trimmed

threshold voltages and an adjustable reset threshold input,

allowing the monitoring of two voltages, V

and V

MON_

(see Figure 2). RESET is asserted when either of the

voltages fall below its respective threshold voltages.

Manual Reset (MAX6746/MAX6747)

Many μP-based products require manual-reset capability

to allow an operator or external logic circuitry to initiate a

reset. The manual-reset input (MR) can connect directly

to a switch without an external pullup resistor or debouncing

network. MR is internally pulled up to VCC and, therefore,

can be left unconnected if unused.

MR is designed to reject fast, falling transients (typically

100ns pulses) and must be held low for a minimum of

1μs to assert the reset output. A 0.1μF capacitor from MR

to ground provides additional noise immunity. After MR

transitions from low to high, reset remains asserted for the

duration of the reset timeout period.

A manual-reset option can easily be implemented with

the MAX6748–MAX6751 by connecting a normally open

momentary switch in parallel with R2 (Figure 3). When

the switch is closed, the voltage on RESET IN goes to

zero, initiating a reset. Similar to the MAX6746/MAX6747

manual reset, reset remains asserted while the voltage at

RESET IN is zero and for the reset timeout period after

the switch is opened.

Figure 4a. Watchdog Timing Diagram, WDS = GND

Figure 3. Adding an External Manual-Reset Function to the

MAX6748–MAX6751

VCC

WDI tWD tRP

RESET

NORMAL MODE (WDS = GND)

VCC

MAX6748

MAX6749

MAX6750

MAX6751

RESET IN

GND

VCC

VMON_TH

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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Watchdog Timer

MAX6746–MAX6751

The watchdog’s circuit monitors the μP’s activity. It the μP

does not toggle the watchdog input (WDI) within tWD (user-

selected), RESET asserts for the reset timeout period. The

internal watchdog timer is cleared by any event that asserts

RESET, by a falling transition at WDI (which can detect

pulses as short as 300ns), 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.

The MAX6746–MAX6751 feature two modes of watch-

dog operation: normal mode and extended mode. In

normal mode (Figure 4a), the watchdog timeout period

is determined by the value of the capacitor connected

between SWT and ground. In extended mode (Figure

4b), the watchdog timeout period is multiplied by 128. For

example, in extended mode, a 0.1μF capacitor gives a

watchdog timeout period of 65s (see the Extended-Mode

Watchdog Timeout Period vs. CSWT graph in the Typical

Operating Circuit). To disable the watchdog timer function,

connect SWT to ground.

MAX6752/MAX6753

The MAX6752 and MAX6753 have a windowed watchdog

timer that asserts RESET for the adjusted reset timeout

period when the watchdog recognizes a fast watchdog fault

(tWDI < tWD1), or a slow watchdog fault (period > tWD2).

The reset timeout period is adjusted independently of the

watchdog timeout period.

The slow watchdog period (tWD2) is calculated as follows:

tWD2 = 0.65 x 109 x CSWT

with tWD2 in seconds and CSWT in Farads.

The fast watchdog period (tWD1) is selectable as a ratio

from the slow watchdog fault period (tWD2). Select the

fast watchdog period by pin strapping SET0 and SET1,

where high is VCC and low is GND. Table 1 illustrates

the SET0 and SET1 configuration for the 8, 16, and 64

window ratio ( tWD2/tWD1).

For example, if CSWT is 1500pF, and SET0 and SET1 are

low, then tWD2 is 975ms (typ) and tWD1 is 122ms (typ).

RESET asserts if the watchdog input has two falling edges

too close to each other (faster than tWD1) (Figure 5a) or

falling edges that are too far apart (slower than tWD2)

(Figure 5b). Normal watchdog operation is displayed in

Figure 5c. The internal watchdog timer is cleared when

a WDI falling edge is detected within the valid watchdog

window or when RESET is deasserted. All WDI inputs are

ignored while RESET is asserted.

The watchdog timer begins to count after RESET is

deasserted. The watchdog timer clears and begins to

count after a valid WDI falling logic input. WDI falling

transitions within periods shorter than tWD1 or longer than

tWD2 force RESET to assert low for the reset timeout

period. WDI falling transitions within the tWD1 and tWD2

window do not assert RESET. WDI transitions between

tWD1(min) and tWD1(max) or tWD2(min) and tWD2(max)

are not guaranteed to assert or deassert RESET. To

guarantee that the window watchdog does not assert

RESET, strobe WDI between tWD1(max) and tWD2(min).

The watchdog timer is cleared when RESET is asserted

or after a falling transition on WDI, or after a state

change on SET0 or SET1. Disable the watchdog timer by

connecting SET0 high and SET1 low.

Figure 4b. Watchdog Timing Diagram, WDS = VCC

Table 1. Min/Max Watchdog Setting

SET0 SET1 RATIO

Low Low 8

Low High 16

High Low Watchdog Disabled

High High 64

tWD x 128 tRP

VCC

WDI

RESET

EXTENDED MODE (WDS = VCC)

VCC

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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Applications Information

Selecting Reset/Watchdog Timeout Capacitor

The reset timeout period is adjustable to accommodate a

variety of μP applications. Adjust the reset timeout period

(tRP) by connecting a capacitor (CSRT) between SRT and

ground. Calculate the reset timeout capacitor as follows:

CSRT = tRP/(4.94 x 106)

with tRP in seconds and CSRT in Farads.

The watchdog timeout period is adjustable to

accommodate a variety of μP applications. With this

feature, the watchdog timeout can be optimized for soft-

ware 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 (CSWT) between SWT and GND.

For normal mode operation, calculate the watchdog

timeout capacitor as follows:

CSWT = tWD/(4.94 x 106)

with tWD in seconds and CSWT in Farads.

For the MAX6752 and MAX6753 windowed watchdog

function, calculate the slow watchdog period, tWD2 as

follows:

tWD2 = 0.65 x 109 x CSWT

CSRT and CSWT must be a low-leakage (< 10nA) type

capacitor. Ceramic capacitors are recommended.

Transient Immunity

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 supply transients

(glitches). The Maximum Transient Duration vs. Reset

Threshold Overdrive graph in the Typical Operating

Characteristics shows this relationship.

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 falling pulse

applied to VCC, starting above the actual reset threshold

(VTH) and ending below it by the magnitude indicated

(reset threshold overdrive). As the magnitude of the transient

increases (farther below the reset threshold), the maxi-

mum allowable pulse width decreases. Typically, a VCC

transient that goes 100mV below the reset threshold and

lasts 50μs or less does not cause a reset pulse to be

issued. For applications where the power supply to VCC

has high transient rates, dV/dt > 5V/50µS, an RC filter on

VCC is required. See Figure 8.

Figure 5. MAX6752/MAX6753 Window Watchdog Diagram

Figure 6. Interfacing to Other Voltage Levels

WDI

(a) FAST FAULT

(b) SLOW FAULT

WDI

RESET

WDI

RESET

tWDI < tWD1 (MIN)

tWDI > tWD2 (MAX)

tWD1 (MAX) < tWDI < tWD2 (MIN)

MAX6747

MAX6749

MAX6451

MAX6753

GND

RESET RESET

VCC

GND

3.3V

µP

100kΩ

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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Interfacing to Other Voltages for

Logic Compatibility

The open-drain RESET output can be used to interface

to a μP with other logic levels. As shown in Figure 6, the

open-drain output can be connected to voltages from 0

to 6V.

Generally, the pullup resistor connected to RESET

connects to the supply voltage that is being monitored at

the IC’s VCC pin. However, some systems can use the

open-drain output to level-shift from the monitored supply

to reset circuitry powered by some other supply. Keep

in mind that as the supervisor’s VCC decreases towards

1V, so does the IC’s ability to sink current at RESET.

Also, with any pullup resistor, RESET is pulled high as

VCC decays toward zero. The voltage where this occurs

depends on the pullup resistor value and the voltage to

which it is connected.

Ensuring a Valid RESET Down to VCC = 0V

(Push-Pull RESET)

When VCC falls below 1V, RESET current sinking capabilities

decline drastically. The high-impedance CMOS logic

inputs connected to RESET can drift to undetermined

voltages. This presents no problems in most applications,

since most μPs and other circuitry do not operate with

VCC below 1V.

In those applications where RESET must be valid down to

0V, add a pulldown resistor between RESET and GND for

the MAX6746/MAX6748/MAX6750/MAX6752 push/pull

outputs. The resistor sinks any stray leakage currents,

holding RESET low (Figure 7). The value of the pulldown

resistor is not critical; 100kΩ is large enough not to load

RESET and small enough to pull RESET to ground. The

external pulldown cannot be used with the open-drain

reset outputs.

Figure 7. Ensuring RESET Valid to VCC = 0V Figure 8. Application Circuit for High-Input Voltage Transient

Applications

MAX6746

MAX6748

MAX6450

MAX6752

GND

RESET

VCC

100kΩ

MAX6753

RESET

GND

100Ω

1µF

3.3V

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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Table 2. Reset Threshold Voltage Suffix

(TA = -40°C to +125°C)

Table 3. Standard Version Table

Note: Standard versions are shown in bold. There is a 2500-piece

minimum order increment for standard versions.

Sample stock is typically held on standard versions only.

Nonstandard versions require a minimum order increment

of 10,000 pieces. Contact factory for availability

SUFFIX MIN TYP MAX

50 4.900 5.000 5.100

49 4.802 4.900 4.998

48 4.704 4.800 4.896

47 4.606 4.700 4.794

46 4.533 4.625 4.718

45 4.410 4.500 4.590

44 4.288 4.375 4.463

43 4.214 4.300 4.386

42 4.116 4.200 4.284

41 4.018 4.100 4.182

40 3.920 4.000 4.080

39 3.822 3.900 3.978

38 3.724 3.800 3.876

37 3.626 3.700 3.774

36 3.528 3.600 3.672

35 3.430 3.500 3.570

34 3.332 3.400 3.468

33 3.234 3.300 3.366

32 3.136 3.200 3.264

32A

(MAX6752AKA32 Only) 3.136 3.200 3.224

31 3.014 3.075 3.137

30 2.940 3.000 3.060

29 2.867 2.925 2.984

28 2.744 2.800 2.856

27 2.646 2.700 2.754

26 2.573 2.625 2.678

25 2.450 2.500 2.550

24 2.352 2.400 2.448

23 2.267 2.313 2.359

22 2.144 2.188 2.232

21 2.058 2.100 2.142

20 1.960 2.000 2.040

19 1.862 1.900 1.938

18 1.764 1.800 1.836

17 1.632 1.665 1.698

16 1.544 1.575 1.607

PART TOP MARK

MAX6746KA16 AEDI

MAX6746KA23 AEDJ

MAX6746KA26 AEDK

MAX6746KA29 AALN

MAX6746KA46 AEDL

MAX6747KA16 AALO

MAX6747KA23 AEDM

MAX6747KA26 AEDN

MAX6747KA29 AEDO

MAX6747KA46 AEDP

MAX6748KA AALP

MAX6749KA AALQ

MAX6750KA16 AEDQ

MAX6750KA23 AALR

MAX6750KA26 AEDR

MAX6750KA29 AEDS

MAX6750KA46 AEDT

MAX6751KA16 AEDU

MAX6751KA23 AEDV

MAX6751KA26 AEDW

MAX6751KA29 AEDX

MAX6751KA46 AEDY

MAX6752KA16 AEDZ

MAX6752KA23 AEEA

MAX6752KA26 AALT

MAX6752KA29 AEEB

MAX6752KA46 AEEC

MAX6753KA16 AEED

MAX6753KA23 AEEE

MAX6753KA26 AEEF

MAX6753KA29 AEEG

MAX6753KA46 AEEH

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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│

Selector Guide

PART

FIXED VCC

RESET

THRESHOLD

ADJUSTABLE

RESET

THRESHOLD

STANDARD

WATCHDOG

TIMER

MIN/MAX

WATCHDOG

TIMER

PUSH/ PULL

RESET

OPEN-DRAIN

RESET

MANUAL-

RESET

INPUT

MAX6746 X — X — X — X

MAX6747 X — X — — X X

MAX6748 — X X — X — —

MAX6749 — X X — — X —

MAX6750 X X X — X — —

MAX6751 X X X — — X —

MAX6752 X — — X X — —

MAX6753 X — — X — X —

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

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│

Note: “_ _” represents the two number suffix needed when order-

ing the reset threshold voltage value for the MAX6746/MAX6747

and MAX6750–MAX6753. The reset threshold

voltages are available in approximately 100mV increments. Table 2

contains the suffix and reset factory-trimmed voltages. All devices

are available in tape-and-reel only. There is a

2500-piece minimum order increment for standard versions (see

Table 3). Sample stock is typically held on standard

versions only. Nonstandard versions require a minimum order

increment of 10,000 pieces. Contact factory for availability.

Devices are available in both leaded and lead(Pb)-free packaging.

+Denotes a lead(Pb)-free/RoHS-compliant package.

T = Tape and reel.

/V denotes an automotive qualified part.

*Future product—contact factory for availability.

Chip Information

PROCESS: BiCMOS

PART TEMP RANGE PIN-PACKAGE

MAX6746KA_ _-T -40°C to +125°C 8 SOT23

MAX6746KA_ _+T -40°C to +125°C 8 SOT23

MAX6747KA_ _+T -40°C to +125°C 8 SOT23

MAX6746KA_ _/V+T -40°C to +125°C 8 SOT23

MAX6747KA_ _-T -40°C to +125°C 8 SOT23

MAX6747KA_ _/V+T -40°C to +125°C 8 SOT23

MAX6748KA+T -40°C to +125°C 8 SOT23

MAX6749KA+T -40°C to +125°C 8 SOT23

MAX6750KA_ _+T -40°C to +125°C 8 SOT23

MAX6750KA_ __/V+T -40°C to +125°C 8 SOT23

MAX6751KA_ _-T -40°C to +125°C 8 SOT23

MAX6751KA_ _+T -40°C to +125°C 8 SOT23

MAX6751KA_ _/V+T* -40°C to +125°C 8 SOT23

MAX6752KA_ _+T -40°C to +125°C 8 SOT23

MAX6752KA_ _/V+T* -40°C to +125°C 8 SOT23

MAX6752AKA32+T -40°C to +125°C 8 SOT23

MAX6752AKA32/V+T* -40°C to +125°C 8 SOT23

MAX6753KA_ _-T -40°C to +125°C 8 SOT23

MAX6753KA_ _+T -40°C to +125°C 8 SOT23

MAX6753KA_ _/V+T -40°C to +125°C 8 SOT23

PACKAGE

TYPE

PACKAGE

CODE

OUTLINE

NO.

LAND

PATTERN NO.

8 SOT23 K8+5, K8-5 21-0078 90-0176

Package Information

For the latest package outline information and land patterns

(footprints), go to www.maximintegrated.com/packages. Note

that a “+”, “#”, or “-” in the package code indicates RoHS status

only. Package drawings may show a different suffix character, but

the drawing pertains to the package regardless of RoHS status.

Ordering Information

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

www.maximintegrated.com Maxim Integrated

│

Revision History

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

0 7/02 Initial release —

312/05 Added the lead-free notation 1

49/10 Added the automotive version of the MAX6746 and the MAX6753 and

revised the Typical Operating Characteristics 1, 4

512/10 Added the automotive version of the MAX6750 1

64/11 Added the automotive version of the MAX6747 1

712/13 Added the automotive version of the MAX6751 1

8 2/14 Added a future product reference to MAX6751KA_ _ /V+T 1

9 5/14 Corrected typo 10

10 6/14 Added the automotive version of the MAX6752 1

11 9/15 Added MAX6752A to data sheet with new limits 2, 12, 14

12 12/15 Added lead-free part numbers to Ordering Information table and lead-free

package code to Package Information table 14

13 2/16 Added MAX6752AKA32+T to Ordering Information table 14

14 9/16 Updated tWD equation value in Pin Conguration table and Applications

Information section 6, 10

15 1/17 Added text to Transient Immunity section and added Figure 8 10, 11

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

are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)

shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.

│

MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable

Reset/Watchdog Timeout Delay

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.

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MAX6751KA16+T MAX6746KA29+T MAX6747KA29+T MAX6747KA46+T MAX6749KA+T MAX6750KA29+T

MAX6751KA29+T MAX6752KA46+T MAX6753KA46+T MAX6746KA16+T MAX6746KA23+T MAX6746KA26+T

MAX6746KA31+T MAX6747KA23+T MAX6747KA31+T MAX6748KA+T MAX6751KA+T MAX6751KA22+T

MAX6751KA26+T MAX6751KA31+T MAX6751KA46+T MAX6752KA29+T MAX6753KA29+T MAX6753KA29/V+T

MAX6751KA30/V+T MAX6752KA31+T MAX6747KA46/V+T MAX6751KA30+T MAX6751KA17/V+T MAX6747KA23+

MAX6747KA16+T MAX6747KA26+ MAX6750KA46+T MAX6753KA26+T MAX6751KA43+T MAX6753KA30/V+T

MAX6747KA33+T MAX6747KA31+ MAX6753KA16+T MAX6752KA16+T MAX6747KA30/V+T MAX6747KA26+T

MAX6753KA31+T MAX6750KA32/V+T MAX6746KA29/V+T MAX6753KA28/V+T MAX6751KA50/V+T

MAX6753KA42/V+T