dual/triple ultra-low-voltage sot23 µp supervisory …€“max6729 dual/triple ultra-low-voltage...

General DescriptionThe MAX6715–MAX6729 are ultra-low-voltage microproces-sor (µP) supervisory circuits designed to monitor two or threesystem power-supply voltages. These devices assert a sys-tem reset if any monitored supply falls below its factory-trimmed or adjustable threshold and maintain reset for aminimum timeout period after all supplies rise above theirthresholds. The integrated dual/triple supervisory circuits sig-nificantly improve system reliability and reduce size com-pared to separate ICs or discrete components.

These devices monitor primary supply voltages (VCC1) from1.8V to 5.0V and secondary supply voltages (VCC2) from0.9V to 3.3V with factory-trimmed reset threshold voltageoptions (see Reset Voltage Threshold Suffix Guide). Anexternally adjustable RSTIN input option allows customers tomonitor a third supply voltage down to 0.62V. These devicesare guaranteed to be in the correct reset output logic statewhen either VCC1 or VCC2 remains greater than 0.8V.

A variety of push-pull or open-drain reset outputs along withwatchdog input, manual reset input, and power-fail input/out-put features are available (see Selector Guide). Select resettimeout periods from 1.1ms to 1120ms (min) (see ResetTimeout Period Suffix Guide). The MAX6715–MAX6729 areavailable in small 5, 6, and 8-pin SOT23 packages and oper-ate over the -40°C to +85°C temperature range.

ApplicationsMultivoltage Systems

Telecom/Networking Equipment

Computers/Servers

Portable/Battery-Operated Equipment

Industrial Equipment

Printer/Fax

Set-Top Boxes

Features♦ VCC1 (primary supply) Reset Threshold Voltages

from 1.58V to 4.63V

♦ VCC2 (secondary supply) Reset ThresholdVoltages from 0.79V to 3.08V

♦ Externally Adjustable RSTIN Threshold forAuxiliary/Triple-Voltage Monitoring (0.62V internal reference)

♦ Watchdog Timer Option35s (min) Long Startup Period1.12s (min) Normal Timeout Period

♦ Manual Reset Input Option

♦ Power-Fail Input/Power-Fail Output Option (Push-Pull and Open-Drain Active-Low)

♦ Guaranteed Reset Valid Down to VCC1 or VCC2 = 0.8V

♦ Reset Output Logic Options

♦ Immune to Short VCC Transients

♦ Low Supply Current 14µA (typ) at 3.6V

♦ Small 5, 6, and 8-Pin SOT23 Packages

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Dual/Triple Ultra-Low-Voltage SOT23 µPSupervisory Circuits

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

IN

OUT2

OUT1

DC/DC CONVERTER

UNREGULATEDDC

R1

R2

VCC1 VCC2

RSTIN/PFI

MR

RST

WDI

PFO

MAX67_ _PUSHBUTTONSWITCH

I/OSUPPLY

CORESUPPLY

RESET

I/O

NMI

µP

1.8V 0.9V

Typical Operating Circuit

19-2325; Rev 5; 12/05

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Pin Configurations and Selector Guide appear at end ofdata sheet.

PART TEMP RANGE PIN-PACKAGE

MAX6715UT_ _D_ -T -40°C to +85°C 6 SOT23-6

MAX6716UT_ _D_ -T -40°C to +85°C 6 SOT23-6

MAX6717UK_ _D_ -T -40°C to +85°C 5 SOT23-5

MAX6718UK_ _D_ -T -40°C to +85°C 5 SOT23-5

MAX6719UT_ _D_ -T -40°C to +85°C 6 SOT23-6

MAX6720UT_ _D_ -T -40°C to +85°C 6 SOT23-6

Note: The first “_ _” are placeholders for the threshold voltagelevels of the devices. Desired threshold levels are set by the partnumber suffix found in the Reset Voltage Threshold Suffix Guide.The “_” after the D is a placeholder for the reset timeout delaytime. Desired delay time is set using the timeout period suffixfound in the Reset Timeout Period Suffix Guide. For example theMAX6716UTLTD3-T is a dual-voltage supervisor VTH1 = 4.625V,VTH2 = 3.075V, and 210ms (typ) timeout period.

Devices are available in both leaded and lead-free packaging.Specify lead-free by replacing "-T" with "+T" when ordering.

Ordering Information continued at end of data sheet.

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ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS(VCC1 = VCC2 = 0.8V to 5.5V, GND = 0, TA = -40°C to +85°C, 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 functionaloperation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure toabsolute maximum rating conditions for extended periods may affect device reliability.

Terminal Voltage (with respect to GND)VCC1, VCC2 ..........................................................-0.3V to +6V

Open-Drain RST, RST1, RST2, PFO, RST ................-0.3V to +6VPush-Pull RST, RST1, PFO, RST...............-0.3V to (VCC1 + 0.3V)Push-Pull RST2 .........................................-0.3V to (VCC2 + 0.3V)RSTIN, PFI, MR, WDI ................................................-0.3V to +6VInput Current/Output Current (all pins) ...............................20mA

Continuous Power Dissipation (TA = +70°C)5-Pin SOT23-5 (derate 7.1mW/°C above +70°C) ........571mW 6-Pin SOT23-6 (derate 8.7mW/°C above +70°C) ........696mW 8-Pin SOT23-8 (derate 8.9mW/°C above +70°C) ........714mW

Operating Temperature Range ...........................-40°C to +85°CStorage Temperature Range .............................-65°C to +150°CJunction Temperature ......................................................+150°CLead Temperature (soldering, 10s) .................................+300°C

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage VCC 0.8 5.5 V

VCC1 < 5.5V, all I/O pins open 15 39ICC1

VCC1 < 3.6V, all I/O pins open 10 28

VCC2 < 3.6V, all I/O pins open 4 11Supply Current

ICC2VCC2 < 2.75V, all I/O pins open 3 9

µA

L (falling) 4.500 4.625 4.750

M (falling) 4.250 4.375 4.500

T (falling) 3.000 3.075 3.150

S (falling) 2.850 2.925 3.000

R (falling) 2.550 2.625 2.700

Z (falling) 2.250 2.313 2.375

Y (falling) 2.125 2.188 2.250

W (falling) 1.620 1.665 1.710

VCC1 Reset Threshold VTH1

V (falling) 1.530 1.575 1.620

V

T (falling) 3.000 3.075 3.150

S (falling) 2.850 2.925 3.000

R (falling) 2.550 2.625 2.700

Z (falling) 2.250 2.313 2.375

Y (falling) 2.125 2.188 2.250

W (falling) 1.620 1.665 1.710

V (falling) 1.530 1.575 1.620

I (falling) 1.350 1.388 1.425

H (falling) 1.275 1.313 1.350

G (falling) 1.080 1.110 1.140

F (falling) 1.020 1.050 1.080

E (falling) 0.810 0.833 0.855

VCC2 Reset Threshold VTH2

D (falling) 0.765 0.788 0.810

V

Reset Threshold Tempco 20 ppm/°C

Reset Threshold Hysteresis VHYST Referenced to VTH typical 0.5 %

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ELECTRICAL CHARACTERISTICS (continued)(VCC1 = VCC2 = 0.8V to 5.5V, GND = 0, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)


VCC to Reset Output Delay tRDV C C 1 = ( V TH 1 + 100m V ) to ( V TH 1 - 100m V ) or V C C 2 = ( V TH 2 + 75m V ) to ( V TH 2 - 75m V )

20 µs

D1 1.1 1.65 2.2

D2 8.8 13.2 17.6

D3 140 210 280

D5 280 420 560

D6 560 840 1120

Reset Timeout Period tRP

D4 1120 1680 2240

ms

ADJUSTABLE RESET COMPARATOR INPUT (MAX6719/MAX6720/MAX6723–MAX6727)

RSTIN Input Threshold VRSTIN 611 626.5 642 mV

RSTIN Input Current IRSTIN -25 +25 nA

RSTIN Hysteresis 3 mV

RSTIN to Reset Output Delay tRSTIND VRSTIN to (VRSTIN - 30mV) 22 µs

POWER-FAIL INPUT (MAX6728/MAX6729)

PFI Input Threshold VPFI 611 626.5 642 mV

PFI Input Current IPFI -25 +25 nA

PFI Hysteresis VPFH 3 mV

PFI to PFO Delay tDPF (VPFI + 30mV) to (VPFI - 30mV) 2 µs

MANUAL RESET INPUT (MAX6715–MAX6722/MAX6725–MAX6729)

VIL 0.3 VCC1MR Input Voltage

VIH 0.7 VCC1V

MR Minimum Pulse Width 1 µs

MR Glitch Rejection 100 ns

MR to Reset Delay tMR 200 ns

MR Pullup Resistance 25 50 80 kΩWATCHDOG INPUT (MAX6721–MAX6729)

First watchdog period after reset timeoutperiod

35 54 72Watchdog Timeout Period tWD

Normal mode 1.12 1.68 2.24

s

WDI Pulse Width tWDI (Note 2) 50 ns

VIL 0.3 VCC1WDI Input Voltage

VIH 0.7 VCC1V

WDI Input Current IWDI WDI = 0 or VCC1 -1 +1 µA

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Note 1: Devices tested at +25°C. Overtemperature limits are guaranteed by design and not production tested.Note 2: Parameter guaranteed by design.

ELECTRICAL CHARACTERISTICS (continued)(VCC1 = VCC2 = 0.8V to 5.5V, GND = 0, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)


RESET/POWER-FAIL OUTPUTS

VCC1 or VCC2 ≥ 0.8V, ISINK = 1µA,output asserted

0.3


0.3


0.3

VCC1 or VCC2 ≥ 2.7V, ISINK = 1.2mA,output asserted

0.3

RST/RST1/RST2/PFOOutput LOW(Push-Pull or Open-Drain)

VOL

VCC1 or VCC2 ≥ 4.5V, ISINK = 3.2mA,output asserted

0.4

V

VCC1 ≥ 1.8V, ISOURCE = 200µA, output notasserted

0.8 VCC1


0.8 VCC1RST/RST1/PFOOutput HIGH(Push-Pull Only)

VOH


0.8 VCC1

V


0.8 VCC2


0.8 VCC2RST2Output HIGH(Push-Pull Only)

VOH


0.8 VCC2

V

VCC1 ≥ 1.0V, ISOURCE = 1µA, reset asserted 0.8 VCC1

VCC1 ≥ 1.8V, ISOURCE = 150µA,reset asserted

0.8 VCC1


0.8 VCC1

RSTOutput HIGH(Push-Pull Only)

VOH


0.8 VCC1

V

VCC1 or VCC2 ≥ 1.8V, ISINK = 500µA,reset not asserted

0.3

VCC1 or VCC2 ≥ 2.7V, ISINK = 1.2mA,reset not asserted

0.3RSTOutput LOW(Push-Pull or Open Drain)

VOL

VCC1 or VCC2 ≥ 4.5V, ISINK = 3.2mA,reset not asserted

0.4

V

RST/RST1/RST2/PFO OutputOpen-Drain Leakage Current

Output not asserted 0.5 µA

RST Output Open-DrainLeakage Current

Output asserted 0.5 µA

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0

4

2

10

8

6

16

14

12

18

-40 10-15 35 60 85

SUPPLY CURRENT vs. TEMPERATUREVCC1 = 5V, VCC2 = 3.3V

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TEMPERATURE (°C)

SUPP

LY C

URRE

NT (µ

A)

TOTAL

ICC1

ICC2

0

4

2

10

8

6

16

14

12

18

-40 10-15 35 60 85

SUPPLY CURRENT vs. TEMPERATUREVCC1 = 3.3V, VCC2 = 2.5V

MAX

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2

TEMPERATURE (°C)

SUPP

LY C

URRE

NT (µ

A)TOTAL

ICC1

ICC2

0

4

2

10

8

6

16

14

12

18

-40 10-15 35 60 85


MAX

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3

TEMPERATURE (°C)

SUPP

LY C

URRE

NT (µ

A)

TOTAL

ICC1

ICC2

0

4

2

10

8

6

16

14

12

18

-40 10-15 35 60 85


MAX

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4

TEMPERATURE (°C)

SUPP

LY C

URRE

NT (µ

A)

TOTAL

ICC1

ICC2

0.998

1.000

0.999

1.003

1.002

1.001

1.006

1.005

1.004

1.007

-40 10-15 35 60 85

NORMALIZED RESET/WATCHDOGTIMEOUT PERIOD vs. TEMPERATURE

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TEMPERATURE (°C)

RESE

T/W

ATCH

DOG

PERI

OD

10,000

1000

100

101 10010 1000

MAXIMUM VCC TRANSIENT DURATIONvs. RESET THRESHOLD OVERDRIVE

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RESET THRESHOLD OVERDRIVE (mV)

MAX

IMUM

VCC

TRA

NSIE

NT D

URAT

ION

(µs)

RESET OCCURS ABOVETHIS LINE

0.996

0.997

0.998

0.999

1.000

1.001

1.002

1.003

1.004

-40 -15 10 35 60 85

NORMALIZED VCC RESET THRESHOLDvs. TEMPERATURE

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TEMPERATURE (°C)

RESE

T TH

RESH

OLD

625

627

626

629

628

630

631

-40 85

RESET INPUT AND POWER-FAIL INPUTTHRESHOLD vs. TEMPERATURE

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TEMPERATURE (°C)

THRE

SHOL

D (m

V)

10-15 35 6044

47

46

45

48

49

50

51

52

53

54

-40 10-15 35 60 85

VCC TO RESET DELAYvs. TEMPERATURE

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TEMPERATURE (°C)

V CC

TO R

ESET

DEL

AY (µ

s)

100mV OVERDRIVE

Typical Operating Characteristics(VCC1 = 5V, VCC2 = 3.3V, TA = +25°C, unless otherwise noted.)

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Pin Description

22.8

23.0

23.2

23.4

23.6

23.8

24.0

24.2

24.4

-40 -15 10 35 60 85

RESET INPUT TO RESET OUTPUT DELAYvs. TEMPERATURE

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0

TEMPERATURE (°C)

RSTI

N TO

RES

ET D

ELAY

(µs)

30mV OVERDRIVE

2.0

2.1

2.2

2.4

2.3

-40 10-15 35 60 85

POWER-FAIL INPUT TO POWER-FAILOUTPUT DELAY vs. TEMPERATURE

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TEMPERATURE (°C)

RSTI

N TO

RES

ET D

ELAY

(µs)

30mV OVERDRIVE

0

0

VRST2V/div

MAX6715-29 toc12

50ns/div

MR TO RESET OUTPUT DELAY

VMR2V/div

Typical Operating Characteristics (continued)(VCC1 = 5V, VCC2 = 3.3V, TA = +25°C, unless otherwise noted.)

PIN

MAX6715/MAX6716

MAX6717/MAX6718

MAX6719/MAX6720

MAX6721/MAX6722

MAX6723/MAX6724

MAX6725/MAX6726

MAX6727MAX6728/MAX6729

NAME FUNCTION

1 1 1 1 1 1 1, 4 1RST/RST1

Active-Low Reset Output,Open-Drain or Push-Pull.RST/RST1 changes fromhigh to low when VCC1 orVCC2 drops below theselected reset thresholds,RSTIN is below threshold,MR is pulled low, or thewatchdog triggers areset. RST/RST1 remainslow for the reset timeoutperiod after VCC1/VCC2/RSTIN exceed thedevice reset thresholds,MR goes low to high, orthe watchdog triggers areset. Open-drain outputsrequire an external pullupresistor. Push-pulloutputs are referenced toVCC1.

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Pin Description (continued)

PIN

MAX6715/MAX6716

MAX6717/MAX6718

MAX6719/MAX6720

MAX6721/MAX6722

MAX6723/MAX6724

MAX6725/MAX6726


NAME FUNCTION

5 — — — — — — — RST2

Active-Low Reset Output,Open-Drain or Push-Pull.RST2 changes from highto low when VCC1 orVCC2 drops below theselected reset thresholdsor MR is pulled low. RST2remains low for the resettimeout period afterVCC1/VCC2 exceed thedevice reset thresholdsor MR goes low to high.Open-drain outputsrequire an external pullupresistor. Push-pulloutputs are referenced toVCC2.

2 2 2 2 2 2 2 2 GND Ground

3 3 3 3 — 5 5 5 MR

Active-Low Manual ResetInput. Internal 50kΩpullup to VCC1. Pull lowto force a reset. Resetremains active as long asMR is low and for thereset timeout period afterMR goes high. Leaveunconnected or connectto VCC1 if unused.

4 4 4 4 4 6 6 6 VCC2

Secondary SupplyVoltage Input. Powers thedevice when it is aboveVCC1 and input forsecondary resetthreshold monitor.

6 5 6 6 6 8 8 8 VCC1

Primary Supply VoltageInput. Powers the devicewhen it is above VCC2and input for primaryreset threshold monitor.

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PIN

MAX6715/MAX6716

MAX6717/MAX6718

MAX6719/MAX6720

MAX6721/MAX6722

MAX6723/MAX6724

MAX6725/MAX6726


NAME FUNCTION

— — — 5 3 3 3 3 WDI

Watchdog Input. If WDIremains high or low forlonger than the watchdogtimeout period, theinternal watchdog timerruns out and the resetoutput asserts for thereset timeout period. Theinternal watchdog timerclears whenever a resetis asserted or WDI sees arising or falling edge. Thewatchdog has a longtimeout period (35s min)after each reset eventand a short timeoutperiod (1.12s min) afterthe first valid WDItransition.

— — 5 — 5 7 7 — RSTIN

Undervoltage ResetComparator Input. High-impedance input foradjustable reset monitor.The reset output isasserted when RSTIN fallsbelow the 0.626V internalreference voltage. Set themonitored voltage resetthreshold with an externalresistor-divider network.Connect RSTIN to VCC1 orVCC2 if not used.

— — — — — — — 7 PFI

Power-Fail VoltageMonitor Input. High-impedance input forinternal power-fail monitorcomparator. Connect PFIto an external resistor-divider network to set thepower-fail thresholdvoltage (0.626V typicalinternal referencevoltage). Connect toGND, VCC1, or VCC2 ifnot used.

Detailed DescriptionSupply Voltages

The MAX6715–MAX6729 microprocessor (µP) supervi-sory circuits maintain system integrity by alerting the µPto fault conditions. These ICs are optimized for systemsthat monitor two or three supply voltages. The output-reset state is guaranteed to remain valid while eitherVCC1 or VCC2 is above 0.8V.

Threshold LevelsInput voltage threshold level combinations are indicat-ed by a two-letter code in the Reset Voltage Threshold

Suffix Guide (Table 1). Contact factory for availability ofother voltage threshold combinations.

Reset OutputsThe MAX6715–MAX6729 provides an active-low resetoutput (RST) and the MAX6725/MAX6726 providesboth an active-high (RST) and an active-low reset out-put (RST). RST, RST, RST1, and RST2 are assertedwhen the voltage at either VCC1 or VCC2 falls below thevoltage threshold level, RSTIN drops below threshold,or MR is pulled low. Once reset is asserted it stays lowfor the reset timeout period (see Table 2). If VCC1,VCC2, or RSTIN goes below the reset threshold beforethe reset timeout period is completed, the internal timer

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PIN

MAX6715/MAX6716

MAX6717/MAX6718

MAX6719/MAX6720

MAX6721/MAX6722

MAX6723/MAX6724

MAX6725/MAX6726


NAME FUNCTION

— — — — — — — 4 PFO

Active-Low Power-FailMonitor Output, Open-Drain or Push-Pull. PFO isasserted low when PFI isless than 0.626V. PFOdeasserts without a resettimeout period. Open-drain outputs require anexternal pullup resistor.Push-pull outputs arereferenced to VCC1.

— — — — — 4 — — RST

Active-High ResetOutput, Open-Drain orPush-Pull. RST changesfrom low to high whenVCC1 or VCC2 dropsbelow selected resetthresholds, RSTIN isbelow threshold, MR ispulled low, or thewatchdog triggers areset. RST remains HIGHfor the reset timeoutperiod after VCC1/VCC 2/RSTIN exceed thedevice reset thresholds,MR goes low to high, orthe watchdog triggers areset. Open-drain outputsrequire an external pullupresistor. Push-pulloutputs are referenced toVCC1.

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MAX6723/MAX6725/MAX6727/MAX6728 contain open-drain reset outputs, while the MAX6716/MAX6718/MAX6720/MAX6722/MAX6724/MAX6726/MAX6729contain push-pull reset outputs. The MAX6727 providestwo separate open-drain RST outputs driven by thesame internal logic.

Manual Reset InputMany microprocessor-based products require manualreset capability, allowing the operator, a test techni-cian, or external logic circuitry to initiate a reset. A logiclow on MR asserts the reset output. Reset remainsasserted while MR is low and for the reset timeout peri-od (tRP) after MR returns high. This input has an internal50kΩ pullup resistor to VCC1 and can be left uncon-nected if not used. MR can be driven with TTL orCMOS logic levels, or with open-drain/collector outputs.Connect a normally open momentary switch from MR toGND to create a manual reset function; externaldebounce circuitry is not required. If MR is driven fromlong cables or if the device is used in a noisy environ-ment, connect a 0.1µF capacitor from MR to GND toprovide additional noise immunity.

Adjustable Input VoltageThe MAX6719/MAX6720 and MAX6723–MAX6727 providean additional input to monitor a third system voltage. Thethreshold voltage at RSTIN is typically 626mV. Connect aresistor-divider network to the circuit as shown in Figure 1to establish an externally controlled threshold voltage,VEXT_TH.

VEXT_TH = 626mV((R1 + R2)/R2)

Low leakage current at RSTIN allows the use of large-valued resistors resulting in reduced power consump-tion of the system.

Watchdog InputThe watchdog monitors µP activity through the watch-dog input (WDI). To use the watchdog function, con-nect WDI to a bus line or µP I/O line. When WDIremains high or low for longer than the watchdog time-out period, the reset output asserts.

The MAX6721–MAX6729 include a dual-mode watch-dog timer to monitor µP activity. The flexible timeoutarchitecture provides a long period initial watchdogmode, allowing complicated systems to completelengthy boots, and a short period normal watchdogmode, allowing the supervisor to provide quick alerts

when processor activity fails. After each reset event(VCC power-up/brownout, manual reset, or watchdogreset), there is a long initial watchdog period of 35sminimum. The long watchdog period mode provides anextended time for the system to power-up and fully ini-tialize all µP and system components before assumingresponsibility for routine watchdog updates.

The normal watchdog timeout period (1.12s min)begins after the first transition on WDI before the con-clusion of the long initial watchdog period (Figure 2).During the normal operating mode, the supervisor willissue a reset pulse for the reset timeout period if the µPdoes not update the WDI with a valid transition (high-to-low or low-to-high) within the standard timeout period(1.12s min).

Power-Fail ComparatorPFI is the noninverting input to a comparator. If PFI isless than VPFI (626.5mV), PFO goes low. Common usesfor the power-fail comparator include monitoring prereg-ulated input of the power supply (such as a battery) or


10 ______________________________________________________________________________________

MAX6719/MAX6720/MAX6723–MAX6727

VEXT_TH

R1

R2

RSTIN

GND

Figure 1. Monitoring a Third Voltage

1.12s MAX

tWDI-NORMAL1.12s MAX

tWDI-STARTUP35s MAX

VTH

VCC

WDI

RESET tRP

Figure 2. Normal Watchdog Startup Sequence

providing an early power-fail warning so software canconduct an orderly system shutdown. It can also beused to monitor supplies other than VCC1 or VCC2 bysetting the power-fail threshold with a resistor-divider, asshown in Figure 3. PFI is the input to the power-fail com-parator. The typical comparator delay is 2µs from PFI toPFO. Connect PFI to ground of VCC1 if unused.

Ensuring a Valid Reset Output Down to VCC = 0

The MAX6715–MAX6729 are guaranteed to operateproperly down to VCC = 0.8V. In applications thatrequire valid reset levels down to VCC = 0 use a pull-down resistor at RST to ground. The resistor value usedis not critical, but it must be large enough not to loadthe reset output when VCC is above the reset threshold.For most applications, 100kΩ is adequate. This config-uration does not work for the open-drain outputs of theMAX6715/MAX6717/MAX6719/MAX6721/MAX6723/MAX6725/MAX6727/MAX6728. For push-pull, active-high RST output connect the external resistor as apullup from RST to VCC1.

Applications InformationInterfacing to µPs with Bidirectional

Reset PinsMost microprocessors with bidirectional reset pins caninterface directly to open-drain RST output options.Systems simultaneously requiring a push-pull RST out-put and a bidirectional reset interface can be in logiccontention. To prevent contention, connect a 4.7kΩresistor between RST and the µP’s reset I/O port asshown in Figure 4.

Adding Hysteresis to the Power-FailComparator

The power-fail comparator has a typical input hysteresisof 3mV. This is sufficient for most applications where apower-supply line is being monitored through an externalvoltage-divider (see the Power-Fail Comparator section).If additional noise margin is desired, connect a resistorbetween PFO and PFI as shown in Figure 5. Select thevalues of R1, R2, and R3 so PFI sees VPFI (626mV) whenVEXT falls to its power-fail trip point (VFAIL) and when VINrises to its power-good trip point (VGOOD). The hysteresiswindow extends between the specified VFAIL and VGOODthresholds. R3 adds the additional hysteresis by sinkingcurrent from the R1/R2 divider network when PFO is logiclow and sourcing current into the network when PFO islogic high. R3 is typically an order of magnitude greaterthan R1 or R2.

The current through R2 should be at least 2.5µA toensure that the 25nA (max) PFI input current does notsignificantly shift the trip points. Therefore, R2 <VPFI/2.5µA < 248kΩ for most applications. R3 will provideadditional hysteresis for PFO push-pull (VOH = VCC1) oropen-drain (VOH = VPULLUP) applications.

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______________________________________________________________________________________ 11

MAX6728/MAX6729

R1

R2

PFI

GND

VIN

PFO

VTRIP = VPFIR1 + R2

R2( )

MAX6728/MAX6729

R1

R2

PFI

GND

VCC

VIN

PFOVTRIP = R2 (VPFI)

1R1

1R2

+ - VCCR1[ ]( )

VPFI = 626.5mV

A

B

Figure 3. Using Power-Fail Input to Monitor an AdditionalPower-Supply a) VIN is Positive b) VIN is Negative

MAX6715–MAX6729

GND GND

VCC1 VCC2

VCC2

VCC1

RST

RESET TO OTHER SYSTEM COMPONENTS

RESET

µP4.7kΩ

Figure 4. Interfacing to µPs with Bidirectional Reset I/O

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Monitoring an Additional Power SupplyThese µP supervisors can monitor either positive ornegative supplies using a resistor voltage-divider toPFI. PFO can be used to generate an interrupt to the µPor cause reset to assert (Figure 3).

Monitoring a Negative VoltageThe power-fail comparator can be used to monitor anegative supply voltage using the circuit shown inFigure 3. When the negative supply is valid, PFO is low.When the negative supply voltage drops, PFO goeshigh. The circuit’s accuracy is affected by the PFIthreshold tolerance, VCC, R1, and R2.

Negative-Going VCC TransientsThe MAX6715–MAX6729 supervisors are relativelyimmune to short-duration negative-going VCC transients(glitches). It is usually undesirable to reset the µP whenVCC experiences only small glitches. The TypicalOperating Characteristics show Maximum TransientDuration vs. Reset Threshold Overdrive, for which resetpulses are not generated. The graph was producedusing negative-going VCC pulses, starting above VTHand ending below the reset threshold by the magnitudeindicated (reset threshold overdrive). The graph showsthe maximum pulse width that a negative-going VCCtransient may typically have without causing a resetpulse to be issued. As the amplitude of the transientincreases (i.e., goes farther below the reset threshold),the maximum allowable pulse width decreases. A 0.1µFbypass capacitor mounted close to the VCC pin pro-vides additional transient immunity.

Watchdog Software ConsiderationsSetting and resetting the watchdog input at differentpoints in the program, rather than “pulsing” the watch-dog input high-low-high or low-high-low, helps the

watchdog timer to closely monitor software execution.This technique avoids a “stuck” loop where the watch-dog timer continues to be reset within the loop, keepingthe watchdog from timing out. Figure 6 shows an exam-ple flow diagram where the I/O driving the watchdoginput is set high at the beginning of the program, set lowat the beginning of every subroutine or loop, then sethigh again when the program returns to the beginning. Ifthe program should “hang” in any subroutine, the I/O iscontinually set low and the watchdog timer is allowed totime out, causing a reset or interrupt to be issued.

Chip InformationTRANSISTOR COUNT: 1072

PROCESS: BiCMOS


12 ______________________________________________________________________________________

MAX6728/MAX6729

VEXT

R1

R3

R2

PFI

GND

PFO

A

VGOOD = DESIRED VEXT GOOD VOLTAGE THRESHOLDVFAIL = DESIRED VEXT FAIL VOLTAGE THRESHOLDVOH = VCC1 (FOR PUSH-PULL PFO)R2 = 200kΩ (FOR > 2.5µA R2 CURRENT)R1 = R2 ((VGOOD - VPFI) - (VPFI)(VGOOD - VFAIL) / VOH) / VPFIR3 = (R1 x VOH) / (VGOOD - VFAIL)

VGOODVFAILVIN

PFO

Figure 5. Adding Hysteresis to Power-Fail for Push-Pull PFO

START

SET WDIHIGH

PROGRAMCODE

SUBROUTINE ORPROGRAM LOOP

SET WDI LOW

RETURN

SUBROUTINECOMPLETED

HANG INSUBROUTINE

Figure 6. Watchdog Flow Diagram

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______________________________________________________________________________________ 13

Functional Diagram

VCC1

VREF

VCC2

RSTIN/PFI

VREF VCC1

MR

VCC1

VCC1

VCC1

RESETTIMEOUTPERIOD

VCC2

RST

RST

PFO

WATCHDOGTIMER WDI

VCC1

MRPULLUP

RESETOUTPUTDRIVER

VREF/2

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14 ______________________________________________________________________________________

Selector Guide

PARTNUMBER

NUMBER OFVOLTAGEMONITORS

OPEN-DRAINRESET

OPEN-DRAINRESET

PUSH-PULL

RESET

PUSH-PULL

RESET

MANUALRESET

WATCH-DOG

INPUT

POWER-FAIL

INPUT/OUTPUT

MAX6715 2 2 — — — √ — —

MAX6716 2 — — 2 — √ — —

MAX6717 2 1 — — — √ — —

MAX6718 2 — — 1 — √ — —

MAX6719 3 1 — — — √ — —

MAX6720 3 — — 1 — √ — —

MAX6721 2 1 — — — √ √ —

MAX6722 2 — — 1 — √ √ —

MAX6723 3 1 — — — — √ —

MAX6724 3 — — 1 — — √ —

MAX6725 3 1 1 — — √ √ —

MAX6726 3 — — 1 1 √ √ —

MAX6727 3 2 — — — √ √ —

MAX6728 3 1 — — — √ √ √ (open drain)

MAX6729 3 — — 1 — √ √ √ (push-pull)

Ordering Information (continued)PART TEMP RANGE PIN-PACKAGE

MAX6721UT_ _D_ -T -40°C to +85°C 6 SOT23-6

MAX6722UT_ _D_ -T -40°C to +85°C 6 SOT23-6

MAX6723UT_ _D_ -T -40°C to +85°C 6 SOT23-6

MAX6724UT_ _D_ -T -40°C to +85°C 6 SOT23-6

MAX6725KA_ _D_ -T -40°C to +85°C 8 SOT23-8

MAX6726KA_ _D_ -T -40°C to +85°C 8 SOT23-8

MAX6727KA_ _D_ -T -40°C to +85°C 8 SOT23-8

MAX6728KA_ _D_ -T -40°C to +85°C 8 SOT23-8

MAX6729KA_ _D_ -T -40°C to +85°C 8 SOT23-8

Note: The first “_ _” are placeholders for the threshold voltagelevels of the devices. Desired threshold levels are set by the partnumber suffix found in the Reset Voltage Threshold Suffix Guide.The “_” after the D is a placeholder for the reset timeout delaytime. Desired delay time is set using the timeout period suffixfound in the Reset Timeout Period Suffix Guide. For example theMAX6716UTLTD3-T is a dual-voltage supervisor VTH1 = 4.625V,VTH2 = 3.075V, and 210ms (typ) timeout period.

Devices are available in both leaded and lead-free packaging.Specify lead-free by replacing "-T" with "+T" when ordering.

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______________________________________________________________________________________ 15

Table 1. Reset Voltage Threshold SuffixGuide**

PART NUMBERSUFFIX (_ _)

VCC1 NOMINALVOLTAGE

THRESHOLD (V)

VCC2 NOMINALVOLTAGE

THRESHOLD (V)

LT 4.625 3.075

MS 4.375 2.925

MR 4.375 2.625

TZ 3.075 2.313

SY 2.925 2.188

RY 2.625 2.188

TW 3.075 1.665

SV 2.925 1.575

RV 2.625 1.575

TI 3.075 1.388

SH 2.925 1.313

RH 2.625 1.313

TG 3.075 1.110

SF 2.925 1.050

RF 2.625 1.050

TE 3.075 0.833

SD 2.925 0.788

RD 2.625 0.788

ZW 2.313 1.665

YV 2.188 1.575

ZI 2.313 1.388

YH 2.188 1.313

ZG 2.313 1.110

YF 2.188 1.050

ZE 2.313 0.833

YD 2.188 0.788

WI 1.665 1.388

VH 1.575 1.313

WG 1.665 1.110

VF 1.575 1.050

WE 1.665 0.833

VD 1.575 0.788

Table 2. Reset Timeout Period SuffixGuide

ACTIVE TIMEOUT PERIODTIMEOUTPERIOD SUFFIX MIN [ms] MAX [ms]

D1 1.1 2.2

D2 8.8 17.6

D3 140 280

D5 280 560

D6 560 1120

D4 1120 2240

**Standard versions are shown in bold and are available in a D3timeout option only. Standard versions require 2,500 piece orderincrements and are typically held in sample stock. There is a10,000 order increment on nonstandard versions. Other thresh-old voltages may be available, contact factory for availability.

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16 ______________________________________________________________________________________

Pin Configurations

GND

VCC2

1 6 VCC1

5MAX6715/MAX6716

SOT23

TOP VIEW

2

3 4

RST1

MR

RST2

GND

VCC2

1 6 VCC1

5MAX6721/MAX6722

SOT23

2

3 4

RST

MR

WDI GND

VCC2

1 6 VCC1

5MAX6723/MAX6724

SOT23

2

3 4

RST

WDI

RSTIN

5 RSTINGND

VCC2

1 5 VCC1

MAX6717/MAX6718

SOT23

2

3 4

RST

MR

GND

VCC2

1 6 VCC1

MAX6719/MAX6720

SOT23

2

3 4

RST

MR

VCC2

MRRST

1

2

8

7

VCC1

RSTINGND

WDI

RST

SOT23

3

4

6

5

MAX6725/MAX6726

VCC2

MR

1

2

8

7

VCC1

RSTINGND

WDI

RST

SOT23

3

4

6

5

MAX6727

RST

VCC2

MR

1

2

8

7

VCC1

PFIGND

WDI

RST

SOT23

3

4

6

5

MAX6728/MAX6729

PFO

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______________________________________________________________________________________ 17

SO

T-23

5L

.EP

S

E1

121-0057

PACKAGE OUTLINE, SOT-23, 5L

Package Information(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline informationgo to www.maxim-ic.com/packages.)

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18 ______________________________________________________________________________________

6LS

OT.

EP

S

PACKAGE OUTLINE, SOT 6L BODY

21-0058 11

G

Package Information (continued)(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline informationgo to www.maxim-ic.com/packages.)

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Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses areimplied. 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 408-737-7600 ____________________ 19

© 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.

SO

T23,

8L

.EP

S

REV.DOCUMENT CONTROL NO.APPROVAL

PROPRIETARY INFORMATION

TITLE:

3.002.60EC E1E

BETWEEN 0.08mm AND 0.15mm FROM LEAD TIP.8. MEETS JEDEC MO178.

8∞

0.60

1.75

0.30

L2

0∞e1

e

L

1.50E1

0.65 BSC.

1.95 REF.

0.25 BSC.

GAUGE PLANE

SEATING PLANE C

C

L

PIN 1I.D. DOT

(SEE NOTE 6)

LC

LC

A2

e1

D

DETAIL "A"

5. COPLANARITY 4 MILS. MAX.

NOTE:

7. SOLDER THICKNESS MEASURED AT FLAT SECTION OF LEAD

6. PIN 1 I.D. DOT IS 0.3 MM ÿ MIN. LOCATED ABOVE PIN 1.

4. PACKAGE OUTLINE INCLUSIVE OF SOLDER PLATING.

3. PACKAGE OUTLINE EXCLUSIVE OF MOLD FLASH & METAL BURR.

HEEL OF THE LEAD PARALLEL TO SEATING PLANE C.2. FOOT LENGTH MEASURED FROM LEAD TIP TO UPPER RADIUS OF

1. ALL DIMENSIONS ARE IN MILLIMETERS.

L2

L

A1A

0.45

1.30

0.15

1.45

MAX

0.28b

0.90A2

0.00A1

0.90A

MINSYMBOL

3.00

0.20

2.80D

0.09C

SEE DETAIL "A"

LCb e

D 121-00781

PACKAGE OUTLINE, SOT-23, 8L BODY

0

0

Package Information (continued)(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline informationgo to www.maxim-ic.com/packages.)

dual/triple ultra-low-voltage sot23 µp supervisory …€“max6729 dual/triple ultra-low-voltage...

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