19-0486; Rev 3; 12/05

8/14/2019 19-0486; Rev 3; 12/05

1/16

General Description

The MAX817/MAX818/MAX819 microprocessor (P)supervisory circuits simplify power-supply monitoring,battery control, and chip-enable gating in P systemsby reducing the number of components required.These devices are designed for use in +5V-poweredsystems. Low supply current (11A typical) and smallpackage size make these devices ideal for portableapplications. The MAX817/MAX818/MAX819 are specif-ically designed to ignore fast transients on VCC. Othersupervisory functions include active-low reset, backup-battery switchover, watchdog input, battery freshnessseal, and chip-enable gating. The Selector Guidebelowlists the specific functions available from each device.

These devices offer two pretrimmed reset threshold volt-

ages for 5% or 10% power supplies: 4.65V for the Lversions and 4.40V for the M versions. The MAX817/MAX818/MAX819 are available in space-saving MAXpackages, as well as 8-pin DIP/SO.

________________________ApplicationsBattery-Powered Computers and Controllers

Embedded Controllers

Intelligent InstrumentsCritical P Monitoring

Portable Equipment

____________________________Features

Precision Supply-Voltage Monitor:4.65V (MAX81_L)4.40V (MAX81_M)

11A Quiescent Supply Current

200ms Reset Time Delay

Watchdog Timer with 1.6sec Timeout(MAX817/MAX818)

Battery-Backup Power Switching; Battery VoltageCan Exceed VCC

Battery Freshness Seal

On-Board, 3ns Gating of Chip-Enable Signals(MAX818)

Uncommitted Voltage Monitor for Power-Fail orLow-Battery Warning (MAX817/MAX819)

Manual Reset Input (MAX819)

MAX817L/M,MAX818L/M,MAX819L/M

+5V Microprocessor Supervisory Circuits

________________________________________________________________ Maxim Integrated Products 1

WDIGND

PFOPFI

1

2

8

7

BATT

RESETVCC

OUT

MAX817

DIP/SO/MAX

TOP VIEW

3

4

6

5

_________________Pin Configurations

19-0486; Rev 3; 12/05

PART

MAX817_CPA

MAX817_CSA

MAX817_CUA 0C to +70C

0C to +70C

0C to +70C

TEMP. RANGE PIN-PACKAGE

8 Plastic DIP

8 SO

8 MAX

______________Ordering Information_____________________Selector Guide

Ordering Information continued on last page.These parts offer a choice of reset threshold voltage. From thetable below, select the suffix corresponding to the desired

threshold and insert it into the blank to complete the part number.Devices are available in both leaded and lead-free packaging.Specify lead free by adding the + symbol at the end of the partnumber when ordering.

SUFFIX RESET THRESHOLD (V)

L 4.65

M 4.40

FEATUREMAX817

L/M

Active-Low Reset

Backup-Battery Switchover

MAX818L/M

MAX819L/M

Power-Fail Comparator

Watchdog Input

Battery Freshness Seal

Manual Reset Input

Chip-Enable Gating

Pin-Package8-DIP/SO/

MAX

8-DIP/SO/

MAX

8-DIP/SO/

MAX

Low-Power, Pin-

Compatible Upgrades for:

MAX690A/

MAX692A

MAX703/

MAX704

Typical Operating Circuit appears at end of data sheet.

Pin Configurations continued at end of data sheet.*Patents Pending

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at1-888-629-4642, or visit Maxims website at www.maxim-ic.com.

8/14/2019 19-0486; Rev 3; 12/05

2/16

MAX817

L/M,MAX818L/M,MAX819L/M

*


2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS(VCC = +4.75V to +5.5V for MAX81_L, VCC = +4.5V to +5.5V for MAX81_M, VBATT = 2.8V, TA = TMIN to TMAX, unless otherwisenoted. Typical values are at TA = +25C.)

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 toabsolute maximum rating conditions for extended periods may affect device reliability.

Note 1: The input voltage limits on PFI and WDI may be exceeded (up to 12V V IN) if the current into these pins is limited to less

than 10mA.

Input VoltageVCC, BATT .............................. ............................-0.3V to +6.0VAll Other Pins (Note 1).............................-0.3V to (VCC + 0.3V)

Input CurrentVCC Peak ........................... ............................... ....................1AVCC Continuous ............................ .............................. ...250mABATT Peak .............................. ............................... ........250mABATT Continuous ............................... ..............................50mAGND .............................. ............................... ....................25mA

Output CurrentOUT................................................................................250mAAll Other Outputs ............................... ..............................25mA

OUT Short-Circuit Duration.................................................10sec

Continuous Power Dissipation (TA = +70C)Plastic DIP (derate 9.09mW/C above +70C) .............727mWSO (derate 5.88mW/C above +70C)..........................471mWMAX (derate 4.10mW/C above +70C) .....................330mW

Operating Temperature RangesMAX81_ _C_A ............................ ..........................0C to +70CMAX81_ _E_A ............................... ....................-40C to +85C

Storage Temperature Range .............................-65C to +160CLead Temperature (soldering, 10sec) .......................... ...+300C

As applicable; CE IN = 0V,

WDI and MRunconnected

VCC < VRST

IOUT = 50mA

IOUT = 5mA

VCC = 0V, VOUT = 0V

IOUT = 250A, VCC < (VBATT - 0.2V)

CONDITIONS

mV40Battery Switchover Hysteresis

mV-20

Battery Switch Threshold

(VCC - VBATT)

20

VVBATT - VBATT -

0.1 0.02VOUT in Battery-Backup Mode

A11 60

ISUPPLYSupply Current (excluding IOUT)11 45

V0 5.5Operating Voltage Range, VCC,

VBATT (Note 2)

100BATT to OUT On-Resistance5 10VCC to OUT On-Resistance

VVCC - VCC -

0.5 0.25

VOUT Output

VCC - VCC -

0.05 0.025

A5.0

A1BATT Leakage Current,

Freshness Seal Enabled

UNITSMIN TYP MAXSYMBOLPARAMETER

VCC = 0VSupply Current in Battery-Backup Mode (excluding IOUT)

0.05 1.0

MAX81_ _C

MAX81_ _E

TA

= +25C

TA = TMIN to

TMAX

Power-up

Power-down

TA = +25C

TA = TMIN to

TMAX

5.5V > VCC > (VBATT + 0.2V)BATT Standby Current (Note 3)

-0.10 0.02

A-1.00 0.02

8/14/2019 19-0486; Rev 3; 12/05

3/16

ELECTRICAL CHARACTERISTICS (continued)

(VCC = +4.75V to +5.5V for MAX81_L, VCC = +4.5V to +5.5V for MAX81_M, VBATT = 2.8V, TA = TMIN to TMAX, unless otherwisenoted. Typical values are at TA = +25C.)



_______________________________________________________________________________________ 3

VPFO= 0V

VPFI > 1.30V, ISOURCE = 40A, VCC > 4.5V

MAX81_M

VPFI < 1.20V, ISINK = 3.2mA, VCC > 4.50V

MAX81_L

WDI = GND, time average

From VRST, VCC falling at 10V/ms

WDI = VCC, time average

VCC = 5V

MAX81_ _C, VCC = 1V, VCC falling,

VBATT = 0V, ISINK = 50A

VCC > VRST(MAX), ISOURCE = 800A

VCC < VRST(MIN), ISINK = 3.2mA

VIL = 0.4V, VIH = 0.8VCC

CONDITIONS

A250 500PFOShort-Circuit Current

VCC - 1.5VOHPFOOutput Voltage V

0.4VOL

nA-25 0.01 25IPFIPFI Input CurrentmV4PFI Input Hysteresis

V1.20 1.25 1.30VPFTPFI Input Threshold

A-20 -15

WDI Input Current (Note 5)120 160

V3.5VIH

WDI Input Threshold (Note 4)0.8VIL

ns50tWDIWDI Pulse Width

V4.25 4.40 4.50

VRSTReset Threshold4.50 4.65 4.75

sec1.00 1.60 2.25tWDWatchdog Timeout Period

s100VCC to RESETDelay

0.3

mV25Reset Threshold Hysteresis

ms140 200 280tRPReset Timeout Period

VCC - 1.5VOH

0.4

VOL


MAX81_ _E, VCC = 1.2V, VCC falling,

VBATT = 0V, ISINK = 100A

V

0.3

RESETOutput Voltage

0.8V

2.0

VILMR Input Threshold

s1MRPulse Width

VIH

ns100MRPulse that Would Not Cause

a Reset

ns120MR to Reset Delay

k45 63 85MRPull-Up Resistance

RESET AND WATCHDOG TIMER

POWER-FAIL COMPARATOR (MAX817/MAX819 only)

MANUAL RESET INPUT (MAX819 only)

8/14/2019 19-0486; Rev 3; 12/05

4/16

MAX817


*


4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VCC = +4.75V to +5.5V for MAX81_L, VCC = +4.5V to +5.5V for MAX81_M, VBATT = 2.8V, TA = TMIN to TMAX, unless otherwisenoted. Typical values are at TA = +25C.)

Power-down

VCC = 5V

IOUT = -1A, VCC = 0V, VBATT = 2.8V

IOUT = -100A, VCC = 0V

Enable mode

Disable mode

CONDITIONS

s15RESET to CEOUT Delay

3.5VILCEOUT Input Threshold V

0.8VIH

V2.7

VOH

CEOUT OutputVCC - 1V

40 150CE IN to CEOUT Resistance

(Note 6)

A0.005 1CE IN Leakage Current


Note 2: Either VCC or VBATT can go to 0V if the other is greater than 2.0V.

Note 3: - = battery-charging current, + = battery-discharging current.

Note 4: WDI is internally serviced within the watchdog timeout period if WDI is left unconnected.

Note 5: WDI input is designed to be driven by a three-stated output device. To float WDI, the high-impedance mode of the output

device must have a maximum leakage current of 10A and a maximum output capacitance of 200pF. The output device

must also be able to source and sink at least 200A when active.

Note 6: The chip-enable resistance is tested with VCC = +4.75V for the MAX818L and VCC = +4.5V for the MAX818M.

VCE IN = VCEOUT = VCC/2.

Note 7:The chip-enable propagation delay is measured from the 50% point at CE IN to the 50% point at CEOUT.

Disable mode, CEOUT = 0V mA0.1 0.75 2.0CEOUT Short-Circuit Current

(Reset Active)

50 source impedance driver, CLOAD = 50pF ns3 8CE IN to CEOUT Propagation

Delay (Note 7)

CHIP-ENABLE GATING (MAX818 only)

8/14/2019 19-0486; Rev 3; 12/05

5/16



_______________________________________________________________________________________ 5

8-40 40

SUPPLY CURRENTvs. TEMPERATURE (NO LOAD)

12

MAX817/18/19-01

TEMPERATURE (C)

SUPPLYCURRENT(A)

-20 0 20 80 10060

16

14

10

0

-40 40

BATTERY SUPPLY CURRENT(BACKUP MODE) vs. TEMPERATURE

20

80

100

120

140

160

MAX817/18/19-02

TEMPERATURE (C)

BATTERYSUPPLYCURRENT(nA)

-20 0 20 80 10060

60

40

VCC = 0V

VBATT = 5.0V

VBATT = 2.8V

VBATT = 2.0V

0-40 40

CE IN TO CE OUT ON-RESISTANCEvs. TEMPERATURE

20

80 MAX817/18/19-03

TEMPERATURE (C)

CEINTOCEOUTON-R

ESISTANCE()

-20 0 20 80 10060

60

40

90

100

10

70

50

30

VCE IN = 4V

VCE IN = 3V

VCE IN = 2V

0-40 40

BATT TO OUT ON-RESISTANCEvs. TEMPERATURE

MAX817/18/19-04

TEMPERATURE (C)

BATTTOOUTON-R

ESISTANCE()

-20 0 20 80 10060

50

100

150

200

250

300

VBATT = 2.0V

VBATT = 2.8V

VBATT = 5.0V

VCC = 0V

0

-40 40

VCC TO RESET PROPAGATION DELAYvs. TEMPERATURE

200

MAX817/18/19-07

TEMPERATURE (C)

VCCTORESETPROPAGA

TIONDELAY(ms)

-20 0 20 80 10060

300

400

500

100

VCC FALLING AT:0.25V/ms

1V/ms

10V/ms

3-40 40

VCC TO OUT ON-RESISTANCEvs. TEMPERATURE

MAX817/18/19-05

TEMPERATURE (C)

VCCTOOUT

ON-R

ESISTANCE()

-20 0 20 80 10060

4

5

6

7

180-40 40

RESET TIMEOUT PERIODvs. TEMPERATURE

MAX817/18/19-06

TEMPERATURE (C)

RESETTIM

EOUTPERIOD(ms)

-20 0 20 80 10060

190

200

210

220

1.50-40 40

WATCHDOG TIMEOUT PERIODvs. TEMPERATURE

1.60

MAX817/18/19-08

TEMPERATURE (C)

WATCHDOGTIMEOUT

PERIOD(sec)

-20 0 20 80 10060

1.65

1.70

1.55

0-40 40

BATTERY FRESHNESS SEALLEAKAGE CURRENT vs. TEMPERATURE

10

MAX817/18/19-09

TEMPERATURE (C)

LEAKAGECURRENT(nA)

-20 0 20 80 10060

15

20

5

__________________________________________Typical Operating Characteristics

(VCC = +5V, VBATT = 3.0V, TA = +25C, unless otherwise noted.)

8/14/2019 19-0486; Rev 3; 12/05

6/16

MAX817


*


6 _______________________________________________________________________________________

00 4

BATTERY SUPPLY CURRENTvs. SUPPLY VOLTAGE

MAX817/18/19-12

VCC (V)

BA

TTERYSUPPLYCURRENT(A)

1 2 3 5 6

1

2

3

4

5

6

7

8

0-40 40

CE IN TO CE OUT PROPAGATION DELAYvs. TEMPERATURE

MAX817/18/19-13

TEMPERATURE (C)

CEINTOCEOUTPROPAGATIONDELAY(ns)

-20 0 20

tPD-

tPD+

80 10060

1

2

3

4

5

6

7

20

MAX817/MAX819 PFI THRESHOLDvs. TEMPERATURE

M

AX817/18/19-14

TEMPERATURE (C)

THRESHOLD(V)

-40 -20 0 60 80 10040

1.244

1.242

1.240

1.246

1.248

1.250

1.252

1.254

4.3

-40 40

RESET THRESHOLDvs. TEMPERATURE

4.5

MAX817/18/19-10

TEMPERATURE (C)

RESETTHRESHOLD(V)

-20 0 20 8060

4.6

4.7

4.4

MAX81_L

MAX81_M

1000

1200

1400

1600

01 10 100 1000 10,000

MAXIMUM TRANSIENT DURATIONvs. RESET THRESHOLD OVERDRIVE

200

MAX817/18/19-11

RESET COMPARATOR OVERDRIVE, VTH-VCC (mV)

MAX

IMUM

TRANSIENTDURATION(s)

400

600

800RESET OCCURSABOVE CURVE

20

MAX817/MAX819 PFI TO PFO PROPAGATIONDELAY vs. TEMPERATURE

M

AX817/18/19-15

TEMPERATURE (C)

PROPAGATIONDELAY(s)

-40 -20 0 60 80 1004028

29

30

31

32

33

____________________________Typical Operating Characteristics (continued)

(VCC = +5V, VBATT = 3.0V, TA = +25C, unless otherwise noted.)

8/14/2019 19-0486; Rev 3; 12/05

7/16



_______________________________________________________________________________________ 7

______________________________________________________________Pin Description

Ground. 0V reference for all signals.33

Input Supply Voltage, +5V input.22

Supply Output for CMOS RAM. When VCC rises above the reset threshold

or above VBATT, OUT is connected to VCC through an internal P-channel

MOSFET switch. When VCC falls below VBATT, BATT connects to OUT.

11

GND3

VCC2

OUT1

Power-Fail Comparator Output. When PFI is less than VPFT or when VCC is

below VBATT, PFOgoes low; otherwise PFOremains high. PFO is also used to

enable the battery freshness seal (see Battery Freshness Sealand Power-Fail

Comparatorsections).

5

Chip-Enable Input. The input to the chip-enable gating circuit. Connect toground if unused.

4

Power-Fail Comparator Input. When VPFI is below VPFT or when VCC is below

VBATT, PFOgoes low; otherwise, PFO remains high (see Power-Fail Comparator

section). Connect to ground if unused.

4

PFO5

CE IN

PFI4

Backup-Battery Input. When VCC falls below VBATT, OUT switches from VCC to

BATT. When VCC rises above VBATT, OUT reconnects to VCC.88

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

low whenever VCC is below the reset threshold or whenMR

is a logic low. Itremains low for 200ms after VCC rises above the reset threshold, the watchdog

triggers a reset, or MRgoes low to high.

77

BATT8

RESET7

Manual Reset Input. A logic low on MRasserts reset. Reset remains asserted

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

low input has an internal 63k pull-up resistor. It can be driven from a TTL- or

CMOS-logic line or shorted to ground with a switch. Leave open, or connect to

VCC if unused.

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

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

gered. If WDI is left unconnected or is connected to a high-impedancethree-state buffer, the watchdog feature is disabled. The internal watchdog

timer clears whenever reset is asserted, WDI is three-stated, or WDI sees a ris-

ing or falling edge. The WDI input is designed to be driven by a three-stated-

output device with a maximum high-impedance leakage current of 10A and a

maximum output capacitance of 200pF. The output device must also be capa-

ble of sinking and sourcing 200A when active.

66

Chip-Enable Output. CEOUT goes low only if CE IN is low while reset is not

asserted. If CEIN is low when reset is asserted, CEOUT will remain low for

15s or until CE IN goes high, whichever occurs first. CEOUT is pulled up to

OUT in battery-backup mode. CEOUT is also used to enable the battery

freshness seal (see Battery Freshness Sealsection).

5

MR6

WDI

CEOUT

FUNCTIONNAMEMAX817 MAX818 MAX819

PIN

8/14/2019 19-0486; Rev 3; 12/05

8/16

MAX817


*


8 _______________________________________________________________________________________

MAX817

MAX818

MAX819

VCC

BATT

WDI

PFI

CE IN

1.25V

CE OUT

GND

OUT

RESET

THIS PINFOR MAX819ONLY.

THIS SECTIONFOR MAX817/MAX818 ONLY.

THIS SECTIONFOR MAX817/MAX819 ONLY.

THIS SECTIONFOR MAX818ONLY.

MR

PFO

CHIP-ENABLEOUTPUT

CONTROL

1.25V

RESETGENERATOR

BATTERYFRESHNESS

SEAL CIRCUITRY

BATTERY SWITCHOVERCIRCUITRY

WATCHDOGTIMER

Figure 1. Functional Diagram

8/14/2019 19-0486; Rev 3; 12/05

9/16



_______________________________________________________________________________________ 9

_______________Detailed Description

General Timing CharacteristicsDesigned for 5V systems, the MAX817/MAX818/MAX819 provide a number of microprocessor (P)supervisory functions (see the Selector Guide on thefirst page). Figure 2 shows the typical timing relation-ships of the various outputs during power-up andpower-down with typical VCC rise and fall times.

RESET OutputA Ps reset input starts the P in a known state. TheMAX817/MAX818/MAX819 P supervisory circuitsassert a reset to prevent code-execution errors duringpower-up, power-down, and brownout conditions.RESET is guaranteed to be a logic low for 0V < VCC Reset Threshold Open Closed

ClosedOpen

OpenClosed

VCC < Reset Threshold and

VCC > VBATT

VCC < Reset Threshold andVCC < VBATT

RESET THRESHOLD = 4.65V IN MAX81_LRESET THRESHOLD = 4.4V IN MAX81_M

OUT

D3

SUBSTRATE

D1 D2SW2SW1 SW4SW3

BATT VCC

MAX817MAX818MAX819

8/14/2019 19-0486; Rev 3; 12/05

13/16



______________________________________________________________________________________ 13

Watchdog Input CurrentThe MAX817/MAX818 WDI inputs are internally driven

through a buffer and series resistor from the watchdogcounter (Figure 1). When WDI is left unconnected, thewatchdog timer is serviced within the watchdog timeoutperiod by a low-high-low pulse from the counter chain.For minimum watchdog input current (minimum overallpower consumption), leave WDI low for the majority of thewatchdog timeout period, pulsing it low-high-low oncewithin 7/8 of the watchdog timeout period to reset thewatchdog timer. If instead WDI is externally driven high forthe majority of the timeout period, up to 150A can flowinto WDI.

Using a SuperCap as aBackup Power Source

SuperCaps are capacitors with extremely high capaci-tance values (on the order of 0.47F) for their size. SinceBATT has the same operating voltage range as VCC, andthe battery switchover threshold voltages are typically30mV centered at VBATT, a SuperCap and simplecharging circuit can be used as a backup power source.Figure 11 shows a SuperCap used as a backup source.

If VCC is above the reset threshold and VBATT is 0.5Vabove VCC, current flows to OUT and VCC from BATTuntil the voltage at BATT is less than 0.5V above VCC.For example, if a SuperCap is connected to BATTthrough a diode to VCC, and VCC quickly changes from5.4V to 4.9V, the capacitor discharges through OUTand VCC until VBATT reaches 5.1V typical. Leakage cur-

rent through the SuperCap charging diode and theinternal power diode eventually discharges theSuperCap to VCC. Also, if VCC and VBATT start from0.1V above the reset threshold and power is lost at

VCC, the SuperCap on BATT discharges through VCCuntil VBATT reaches the reset threshold. Battery-backup

mode is then initiated and the current through VCCgoes to zero.

Operation Without aBackup Power Source

The MAX817/MAX818/MAX819 were designed for bat-tery-backed applications. If a backup battery is notused, connect VCC to OUT, and connect BATT toground.

Replacing the Backup BatteryThe backup power source can be removed while VCCremains valid, without danger of triggering a resetpulse, if BATT is decoupled with a 0.1F capacitor to

ground. As long as VCC stays above the reset thresh-old, battery-backup mode cannot be entered.

Adding Hysteresis to the Power-FailComparator (MAX817/MAX819)

The power-fail comparator has a typical input hystere-sis of 4mV. This is sufficient for most applications wherea power-supply line is being monitored through anexternal voltage divider (see Monitoring an AdditionalSupply).

For additional noise margin, connect a resistor betweenPFOand PFI, as shown in Figure 12. Select the ratio ofR1 and R2 such that PFI sees VPFT when VIN falls to the

Figure 11. Using a SuperCap as a Backup Power Sourcewith a +5V 10% Supply

SuperCap is a trademark of Baknor Industries.

BATT

VCC OUT

RESET

GND

TO STATIC RAM

TO P

0.1F

MAX817MAX818MAX819

+5V

100k

Figure 12. Adding Hysteresis to the Power-Fail Comparator

VCC

GND

TO P

PFI

PFO

R1

R2 R3

*OPTIONAL

C1*

VIN

+5V

R1+ R2

R2

VH = 1.25V

VTRIP = 1.25V

+

+

||

||R2 R3

R1 R2 R3

MAX817MAX819

PFO

0V

+5V

VHVL0V VTRIPVIN

( )

R1

VL - 1.25

R3

5- 1.25=

R2

1.25

( )

8/14/2019 19-0486; Rev 3; 12/05

14/16

MAX817


*


14 ______________________________________________________________________________________

desired trip point (VTRIP). Resistor R3 adds hysteresis.It will typically be an order of magnitude greater than R1

or R2. The current through R1 and R2 should be at least1A to ensure that the 25nA (max) PFI input leakagecurrent does not shift the trip point. R3 should be largerthan 200k to prevent it from loading down the PFOpin.Capacitor C1 adds additional noise rejection.

Monitoring an Additional Supply(MAX817/MAX819)

The MAX817/MAX819 P supervisors can monitor eitherpositive or negative supplies using a resistor voltagedivider to PFI. PFOcan be used to generate an interruptto the P or to trigger a reset (Figures 9 and 13).

Interfacing to Ps with

Bidirectional Reset PinsPs with bidirectional reset pins, such as the Motorola68HC11 series, can contend with the MAX817/MAX818/MAX819 RESET output. If, for example, the RESET out-put is driven high and the P wants to pull it low, inde-terminate logic levels may result. To correct this,connect a 4.7k resistor between the RESET outputand the P reset I/O, as in Figure 14. Buffer the RESEToutput to other system components.

Negative-Going VCCTransientsThese supervisors are relatively immune to short-dura-tion, negative-going VCC transients (glitches) whileissuing a reset to the P during power-up, power-down,and brownout conditions. Therefore, resetting the P

when VCC experiences only small glitches is usually notdesirable.

The Typical Operating Characteristicsshow a graph ofMaximum Transient Duration vs. Reset ThresholdOverdrive for which reset pulses are not generated. Thegraph was produced using negative-going VCC pulses,starting at 3.3V and ending below the reset threshold bythe magnitude indicated (reset threshold overdrive). Thegraph shows the maximum pulse width that a negative-going VCC transient can typically have without triggeringa reset pulse. As the amplitude of the transient increases(i.e., goes farther below the reset threshold), the maxi-mum allowable pulse width decreases. Typically, a VCCtransient that goes 100mV below the reset threshold andlasts for 135s will not trigger a reset pulse.

A 0.1F bypass capacitor mounted close to the VCCpin provides additional transient immunity.

Figure 13. Monitoring a Negative Voltage

MAX817MAX819

VCC

GND

PFI PFO

R1

R2

V-

NOTE: VTRIP IS NEGATIVE

0V

PFO

0VVTRIP

V-

+5V

+5V

R1

5- 1.25

R2

1.25 - VTRIP=

Figure 14. Interfacing to Ps with Bidirectional Reset I/O

MAX817MAX818MAX819

BUFFERED RESET TO OTHER SYSTEM COMPONENTS

4.7k

VCC

GND

VCC

GND

RESETRESET

8/14/2019 19-0486; Rev 3; 12/05

15/16



______________________________________________________________________________________ 15

____Pin Configurations (continued)__________Typical Operating Circuit

WDIGND

CE OUTCE IN

1

2

8

7

BATT

RESETVCC

OUT

MAX818

DIP/SO/MAX

TOP VIEW

3

4

6

5

MRGND

PFOPFI

1

2

8

7

BATT

RESETVCC

OUT

MAX819

DIP/SO/MAX

3

4

6

5

CE IN*

*CE IN AND CE OUT APPLY TO MAX818 ONLY.**WDI APPLIES TO MAX817/MAX818 ONLY.

BATT

RESET

I/O

OUT

CMOSRAM

RESET

WDI**

CE OUT*

0.1F

0.1F 0.1F

GND

MAX817MAX818MAX819

VCC

ADDRESSDECODE

REAL-TIME

CLOCK

A0A15

P

+5V

Watchdog Software Considerations(MAX817/MAX818)

To help the watchdog timer monitor software executionmore closely, set and reset the watchdog input at differentpoints in the program, rather than pulsing the watchdoginput high-low-high or low-high-low. This technique avoidsa stuck loop, in which the watchdog timer would contin-ue to be reset within the loop, keeping the watchdog fromtiming out. Figure 15 shows an example of a flow diagramwhere the I/O driving the watchdog input is set high at thebeginning of the program, set low at the beginning ofevery subroutine or loop, then set high again when theprogram returns to the beginning. If the program shouldhang in any subroutine, the problem would quickly becorrected, since the I/O is continually set low and thewatchdog timer is allowed to time out, triggering a reset or

an interrupt. As described in the Watchdog Input Currentsection, this scheme results in higher average WDI inputcurrent than does the method of leaving WDI low for themajority of the timeout period and periodically pulsing itlow-high-low. Figure 15. Watchdog Flow Diagram

START

SETWDILOW

SUBROUTINEOR PROGRAM LOOP,

SET WDIHIGH

RETURN

END

8/14/2019 19-0486; Rev 3; 12/05

16/16

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.

16 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600

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

MAX817


*


Ordering Information (continued) Chip Information

TRANSISTOR COUNT: 719

These parts offer a choice of reset threshold voltage. From thetable below, select the suffix corresponding to the desiredthreshold and insert it into the blank to complete the part number.

Devices are available in both leaded and lead-free packaging.Specify lead free by adding the + symbol at the end of the partnumber when ordering.

PART

MAX817_EPA

MAX817_ESA

MAX818_CPA 0C to +70C

-40C to +85C

-40C to +85C

TEMP. RANGE PIN-PACKAGE

8 Plastic DIP

8 SO

8 Plastic DIP

MAX818_CSA

MAX818_CUA

MAX818_EPA -40C to +85C

0C to +70C

0C to +70C 8 SO

8 MAX

8 Plastic DIP

MAX818_ESA -40C to +85C 8 SO

MAX819_CPA

MAX819_CSA

MAX819_CUA 0C to +70C

0C to +70C

0C to +70C 8 Plastic DIP

8 SO

8 MAX

MAX819_EPA

MAX819_ESA -40C to +85C

-40C to +85C 8 Plastic DIP

8 SO

SUFFIX RESET THRESHOLD (V)

L 4.65

M 4.40

L

C

A1B

DIM

A

A1

B

C

D

E

e

H

L

MIN

0.036

0.004

0.010

0.005

0.116

0.116

0.188

0.016

0

MAX

0.044

0.008

0.014

0.007

0.120

0.120

0.198

0.026

6

MIN

0.91

0.10

0.25

0.13

2.95

2.95

4.78

0.41

0

MAX

1.11

0.20

0.36

0.18

3.05

3.05

5.03

0.66

6

INCHES MILLIMETERS

8-PIN MAXMICROMAX SMALL-OUTLINE

PACKAGE

0.650.0256

A

e

E H

D

0.101mm

0.004 in

21-0036D

Package Information(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

Documents

19-0486; Rev 3; 12/05