Maxim MAX806TMJA, MAX806TCPA, MAX806TCSA, MAX806TEPA, MAX806SCSA Datasheet

19-0243; Rev 1; 9/94

3.0V/3.3V Microprocessor Supervisory Circuits

_______________General Description

These microprocessor (µP) supervisory circuits reduce
the complexity and number of components required for
power-supply monitoring and battery-control functions
in µP systems. They significantly improve system relia­bility and accuracy compared to separate ICs or
discrete components.

These devices are designed for use in systems powered
by 3.0V or 3.3V supplies. See the selector guide in the
back of this data sheet for similar devices designed for
5V systems. The suffixes denote different reset threshold
voltages: 3.075V (T), 2.925V (S), and 2.625V (R) (see

Reset Threshold

section in the

Detailed Description

). All
these parts are available in 8-pin DIP and SO packages.
Functions offered in this series are as follows:

Active-High Reset

Active-Low Reset

Part

MAX690
MAX704
MAX802
MAX804
MAX805
MAX806

Watchdog Input

✓✓ ✓
✓✓✓
✓✓ ✓

✓✓✓

✓✓ ✓
✓✓ ✓

Threshold Accuracy

Backup-Battery

Manual Reset

Switch

Input

Comparator

Power-Fail

Power-Fail

±4%
±4%
±2%
±2%
±4%
±2%

Reset Window

✓

±75mV

✓

±75mV

✓

±2%

✓

±2%

✓

±75mV

✓

±2%

________________________Applications

Battery-Powered Computers and Controllers
Embedded Controllers
Intelligent Instruments
Automotive Systems
Critical µP Power Monitoring
Portable Equipment

__________________Pin Configuration

TOP VIEW

1

V

OUT

MAX690T/S/R

2

MAX704T/S/R

V

CC

MAX802T/S/R

3

GND

MAX804T/S/R
MAX805T/S/R

4

PFI

MAX806T/S/R

( )

ARE FOR MAX804T/S/R, MAX805T/S/R

< > ARE FOR MAX704T/S/R, MAX806T/S/R

DIP/SO

8

VBATT

7

RESET (RESET)

6

WDI

<MR>

5

PFO



____________________________Features

♦–R—E—S—E—T–and RESET Outputs
♦ Manual Reset Input
♦ Precision Supply-Voltage Monitor
♦ 200ms Reset Time Delay
♦ Watchdog Timer (1.6sec timeout)
♦ Battery-Backup Power Switching—

Battery Can Exceed VCCin Normal Operation

♦ 40µA VCCSupply Current
♦ 1µA Battery Supply Current
♦ Voltage Monitor for Power-Fail or

Low-Battery Warning

♦ Guaranteed –R—E—S—E—T– Assertion to VCC= 1V
♦ 8-Pin DIP and SO Packages

______________Ordering Information

PART** TEMP. RANGE

MAX690_CPA

MAX690_CSA 0°C to +70°C
MAX690_C/D 0°C to +70°C Dice*
MAX690_EPA -40°C to +85°C
MAX690_ESA -40°C to +85°C
MAX690_MJA -55°C to +125°C 8 CERDIP

0°C to +70°C

Ordering Information continued on last page.

* Contact factory for dice specifications.
** These parts offer a choice of reset threshold voltage. Select

the letter corresponding to the desired nominal reset threshold
voltage (T = 3.075V, S = 2.925V, R = 2.625V) and insert it into
the blank to complete the part number.

PIN-PACKAGE

8 Plastic DIP
8 SO

8 Plastic DIP
8 SO

_________Typical Operating Circuits

REGULATED +3.3V OR +3.0V

V

UNREGULATED 

DC

0.1µF

R1

3.6V

R2

LITHIUM
BATTERY

( ) ARE FOR MAX804T/S/R, MAX805T/S/R

See last page for MAX704T/S/R, MAX806T/S/R.

PFI

VBATT

0.1µF

V

CC

MAX690T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R

GND

RESET

(RESET)

PFO

V

WDI

OUT

0.1µF

CC

RESET
NMI

I/O LINE

BUS

V

CC

CMOS RAM

µP

GND

GND

MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

________________________________________________________________

Maxim Integrated Products

Call toll free 1-800-998-8800 for free samples or literature.

1

3.0V/3.3V Microprocessor Supervisory Circuits

ABSOLUTE MAXIMUM RATINGS

Terminal Voltage (with respect to GND)

.........................................................................-0.3V to 6.0V

V

CC

VBATT....................................................................-0.3V to 6.0V

All Other Inputs ...................-0.3V to the higher of V

Continuous Input Current

..................................................................................100mA

V

CC

VBATT...............................................................................18mA

or VBATT

CC

GND..................................................................................18mA

Output Current

–R—E—S—E—T–, –P—F—O–

V

OUT

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.

....................................................................18mA

................................................................................100mA

ELECTRICAL CHARACTERISTICS

(VCC= 3.17V to 5.5V for the MAX690T/MAX704T/MAX80_T, VCC= 3.02V to 5.5V for the MAX690S/MAX704S/MAX80_S, VCC= 2.72V to

5.5V for the MAX690R/MAX704R/MAX80_R; VBATT = 3.6V; T

Operating Voltage Range,

, VBATT (Note 1)

V

CC

MAX690_C, MAX704_C, MAX80_ _C
MAX690_E/M, MAX704_E/M, MAX80_ _E/M

–M—R–
VCCSupply Current
(excluding I

OUT

)

I

SUPPLY

(MAX704_/

MAX806_)

–M—R–
VCCSupply Current in Battery­Backup Mode (excluding I

OUT

)

VBATT Supply Current, Any Mode
(excluding I

OUT

) (Note 2)

Battery Leakage Current
(Note 3)

(MAX704_/

MAX806_)

MAX690_C/E, MAX704_C/E, MAX80_ _C/E

MAX690_M, MAX704_M, MAX80_ _M

MAX690_C/E, MAX704_C/E, MAX80_ _C/E

MAX690_M, MAX704_M, MAX80_ _M

MAX690_C/E, MAX704_C/E, MAX80_ _C/E,

I

OUT

MAX690_C/E, MAX704_C/E, MAX80_ _C/E

I

OUT

V

Output Voltage V

OUT

MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

MAX690_M, MAX704_M, MAX80_ _M

I

OUT

MAX690_M, MAX704_M, MAX80_ _M

I

OUT

I

OUT

A

= V

CC

= V

CC

= 5mA (Note 4)

= 50mA

= 5mA (Note 4)

= 50mA

= 250µA, VCC> 2.5V (Note 4)

Continuous Power Dissipation (T

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

= +70°C)

A

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

CERDIP (derate 8.00mW/°C above +70°C)...................640mW

Operating Temperature Ranges

MAX690_C_ _/MAX704_C_ _/MAX80_ _C_ _........0°C to +70°C

MAX690_E_ _/MAX704_E_ _/MAX80_ _E_ _......-40°C to +85°C

MAX690_M_ _/MAX704_M_ _/MAX80_ _M_ _...-55°C to +125°C

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

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

= T

to T

MIN

; unless otherwise noted. Typical values are at TA= +25°C.)

MAX

CONDITIONS

1.0 5.5

1.1 5.5

MAX690_C/E, MAX704_C/E,
MAX80_ _C/E, VCC< 3.6V

MAX690_C/E, MAX704_C/E,
MAX80_ _C/E, VCC< 5.5V

MAX690_M, MAX704_M,
MAX80_ _M, VCC< 3.6V

MAX690_M, MAX704_M,
MAX80_ _M, V

CC

< 5.5V

40 50

50 65

40 55

50 70

VCC= 2.0V, VBATT = 2.3V

0.4 1

0.4 10

0.01 0.5

0.01 5

V

-V

CC

CC

0.03 0.015

V

-V

CC

CC

0.3 0.15

V

-V

CC

CC

0.035 0.015
V

-V

CC

CC

0.35 0.15

V

-V

CC

CC

0.0015 0.0006

UNITSMIN TYP MAXSYMBOLPARAMETER

V

µA

µA25 50

µA

µA

-

-

-

-

-

2 _______________________________________________________________________________________

3.0V/3.3V Microprocessor Supervisory Circuits

ELECTRICAL CHARACTERISTICS (continued)

(VCC= 3.17V to 5.5V for the MAX690T/MAX704T/MAX80_T, VCC= 3.02V to 5.5V for the MAX690S/MAX704S/MAX80_S, VCC= 2.72V to

5.5V for the MAX690R/MAX704R/MAX80_R; VBATT = 3.6V; T

I

V

in Battery-Backup Mode

OUT

Battery Switch Threshold,
VCCFalling

Battery Switch Threshold,
VCCRising (Note 7)

OUT

I

OUT

VBATT - V
VBATT > VCC(Note 6)

SW

This value is identical to the reset threshold,
VCCrising

MAX690T/704T/805T

MAX802T/804T/806T

MAX690S/704S/805S

Reset Threshold (Note 8)

V

RST

MAX802S/804S/806S

MAX690R/704R/805R

MAX802R/804R/806S

Reset Timeout Period
–P—F—O–, –R—E—S—E—T–

–P—F—O–, –R—E—S—E—T–

Output Voltage

Output Short to

GND Current (Note 4)
–P—F—O–, –R—E—S—E—T–

, RESET

Output Voltage

VCC< 3.6V

WP

V

I

OH

SOURCE

VCC= 3.3V, VOH= 0V

OS

I

SINK

MAX690_/704_/802_/806_, VCC= V

OL

MAX804_/805_, VCC= V
VBATT = 0V, VCC= 1.0V, I

–P—F—O–, –R—E—S—E—T–

Output Voltage

MAX690_C, MAX704_C, MAX80_ _C

V

OL

VBATT = 0V, VCC= 1.2V, I
MAX690_E/M, MAX704_E/M, MAX80_ _E/M

RESET Output Leakage Current
(Note 9)

VBATT = 0V,
VCC= V
V

RESET

= T

to T

A

MIN

MAX

CONDITIONS

= 250µA, VBATT = 2.3V

= 1mA, VBATT = 2.3V

> VCC> 1.75V (Note 5)

CC,VSW

= 50µA

= 1.2mA;

RST

MAX804_C,

min;

RST

= 0V, V

CC

MAX805_C
MAX804_E/M,

MAX805_E/M

; unless otherwise noted. Typical values are at TA= +25˚C.)

UNITSMIN TYP MAXSYMBOLPARAMETER

VBATT VBATT

- 0.1 - 0.034
VBATT

- 0.14
mV65 25

VCCfalling
VCCrising
VCCfalling
VCCrising
VCCfalling
VCCrising
VCCfalling
VCCrising
VCCfalling
VCCrising
VCCfalling
VCCrising

3.00 3.075 3.15

3.00 3.085 3.17

3.00 3.075 3.12

3.00 3.085 3.14

2.85 2.925 3.00

2.85 2.935 3.02

2.88 2.925 3.00

2.88 2.935 3.02

2.55 2.625 2.70

2.55 2.635 2.72

2.59 2.625 2.70

2.59 2.635 2.72
ms140 200 280t

V

V

CC

CC

- 0.3 - 0.05

µV180 500I

min;

RST

max

= 40µA,

SINK

SINK

= 200µA,

0.13 0.3

0.17 0.3

-1 1
µA

-10 10

V

V2.30 2.40 2.50V
V

V

V

V0.06 0.3V

V

MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

_______________________________________________________________________________________ 3

3.0V/3.3V Microprocessor Supervisory Circuits

ELECTRICAL CHARACTERISTICS (continued)

(VCC= 3.17V to 5.5V for the MAX690T/MAX704T/MAX80_T, VCC= 3.02V to 5.5V for the MAX690S/MAX704S/MAX80_S, VCC= 2.72V to

5.5V for the MAX690R/MAX704R/MAX80_R; VBATT = 3.6V; T

SYMBOLPARAMETER UNITS

VCC< 3.6V

PFI Input Threshold

PFI Input Current

PFI Hysteresis, PFI Rising

PFI Input Current

–M—R–

Input Threshold

–M—R–

Pulse Width

–M—R–

to Reset Delay

–M—R–

Pull-Up Current

WDI Input Threshold

V

PFT

V

falling

PFI

MAX690_C/E, MAX704_C/E, MAX80_ _C/E
MAX690_M, MAX704_M, MAX80_ _M

V

VCC< 3.6V

PFH

MAX690_C/E, MAX704_C/E, MAX80_ _C/E
MAX690_M, MAX704_M, MAX80_ _M

V

IH

MAX704_/MAX806_ only

V

IL

MAX704_/MAX806_ only

MR

MAX704_/MAX806_ only

MD

MAX704_/MAX806_ only, –M—R–= 0V, VCC= 3V

V

IH

MAX690_/MAX802_/MAX804_/MAX805_ only

V

IL

0V< VCC< 5.5V

Watchdog Timeout Period

WD

VCC< 3.6V
MAX690_/MAX802_/MAX804_/MAX805_ only

Note 1: VCCsupply current, logic input leakage, watchdog functionality (MAX690_/802_/805_/804_), –M—R–functionality

(MAX704_/806_), PFI functionality, state of –R—E—S—E—T–(MAX690_/704_/802_/806_), and RESET (MAX804_/805_) tested at
VBATT = 3.6V, and V

Note 2: Tested at VBATT = 3.6V, V

= 1.9V.

V

Note 3: Leakage current into the battery is tested under the worst-case conditions at V

CC

= 5.5V. The state of –R—E—S—E—T–or RESET and –P—F—O–is tested at VCC= VCCmin.

CC

= 3.5V and 0V. The battery current will rise to 10µA over a narrow transition window around

CC

VBATT= 1.0V.

Note 4: Guaranteed by design.
Note 5: When V

has a small 25mV typical hysteresis to prevent oscillation. For V

MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

voltage on VBATT.

Note 6: When VBATT > V
Note 7: V

V
switchover occurs 200ms prior to reset.

> VCC> VBATT, V

SW

> VSW, V

switches from VBATT to VCCwhen VCCrises above the reset threshold, independent of VBATT. Switchover back to

OUT

occurs at the exact voltage that causes –R—E—S—E—T–to go high (on the MAX804_/805_, RESET goes low); however

CC

CC

remains connected to VCCuntil VCCdrops below VBATT. The VCC-to-VBATT comparator

OUT

remains connected to VCCuntil VCCdrops below the battery switch threshold (VSW).

OUT

Note 8: The reset threshold tolerance is wider for V

prevents internal oscillation.

Note 9: The leakage current into or out of the RESET pin is tested with RESET asserted (RESET output high impedance).

= T

to T

A

MIN

CONDITIONS

MAX802_C/E, MAX804_C/E,
MAX806_C/E

MAX690_/MAX704_/MAX805_

; unless otherwise noted. Typical values are at TA= +25˚C.)

MAX

MIN TYP MAX

1.212 1.237 1.262

1.187 1.237 1.287

-25 2 25

-500 2 500

MAX690_C/E, MAX704_C/E,
MAX80_ _C/E

MAX690_M, MAX704_M, MAX80_ _M

10 20
10 25

-25 2 25

-500 2 500

0.7 x V

CC

0.3 x V

CC

0.7 x V

CC

0.3 x V

CC

MAX690_C/E, MAX802_C/E,
MAX804_C/E, MAX805_C/E

MAX690_M, MAX802_M,
MAX804_M, MAX805_M

MAX690/MAX802/MAX804/
MAX805 only

CC

< 1.75V (typ), V

CC

rising than for VCCfalling to accommodate the 10mV typical hysteresis, which

CC

-1 0.01 1

-10 0.01 10

1.12 1.60 2.24

= 5.5V, VBATT = 1.8V and at VCC= 1.5V,

switches to VBATT regardless of the

OUT

V

nA

mV

nA

V

ns100 20t
ns60 500t
µA20 60 350

V

µAWDI Input Current

sect

ns100 20WDI Pulse Width

4 _______________________________________________________________________________________

3.0V/3.3V Microprocessor Supervisory Circuits

__________________________________________Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

VCC-to-V

5

VBATT = 3.0V

4

3

ON-RESISTANCE (Ω)

2

OUT

-to-V
1

CC

V

0

–60 –20 60 140

ON-RESISTANCE

OUT

vs. TEMPERATURE

= 2.5V

V

CC

VCC = 5V

20 100–40 0 8040 120

TEMPERATURE (°C)

BATTERY SUPPLY CURRENT

vs. TEMPERATURE

10,000

VCC = 0V
PFI = GND

1000

100

10

1

BATTERY SUPPLY CURRENT (nA)

0.1
–60 –20 60 140

VBATT = 3V

TEMPERATURE (°C)

VBATT = 5V

VBATT = 2V

20 100–40 0 8040 120

1.240

1.238

1.236

1.234

PFI THRESHOLD (V)

1.232

1.230
–60 –20 60 140

_______________________________________________________________________________________

= 3.3V

V

CC

PFI THRESHOLD

vs. TEMPERATURE

= 3.3V

V

CC

V

= 2.5V

CC

VBATT = 3.0V

TEMPERATURE (°C)

VBATT-to-V

180

VCC = 0V

MAX690-806 TOC01

140

100

ON-RESISTANCE (Ω)

OUT

60

VBATT-to-V

20

–60 –20 60 140

216

212

MAX690-806 TOC04

208

VBATT = 3.0V

204

200

RESET TIMEOUT PERIOD (ms)

196

–60 –20 60 140

VCC = 5V

20 100–40 0 8040 120

ON-RESISTANCE

OUT

vs. TEMPERATURE

VBATT = 2V

VBATT = 3V

VBATT = 3.3V

VBATT = 5V

20 100–40 0 8040 120

TEMPERATURE (°C)

RESET TIMEOUT PERIOD

vs. TEMPERATURE

VCC = 5V

= 3.3V

V

CC

20 100–40 0 8040 120

TEMPERATURE (°C)

1.004

MAX690-806 TOC07

1.002

1.000

0.998

0.996

NORMALIZED RESET THRESHOLD (V)

0.994
–60 –20 60 140

SUPPLY CURRENT
vs. TEMPERATURE

50

MAX690-806 TOC02

45

40

VBATT = 3V

35

PFI = GND
MR/WDI FLOATING

SUPPLY CURRENT (µA)

30

25

–60 –20 60 140

RESET-COMPARATOR PROPAGATION 

DELAY vs. TEMPERATURE

30

VBATT = 3.0V
100mV OVERDRIVE

26

MAX690-806 TOC05

22

18

PROPAGATION DELAY (µs)

14

10

–60 –20 60 140

TEMPERATURE (°C)

NORMALIZED RESET THRESHOLD

vs. TEMPERATURE

VBATT = 3.0V

20 100–40 0 8040 120

TEMPERATURE (°C)

VCC = 5V

V

CC

V

CC

20 100–40 0 8040 120

TEMPERATURE (°C)

20 100–40 0 8040 120

MAX690-806 TOC08

= 3.3V

= 2.5V

MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

MAX690-806 TOC03

MAX690-806 TOC06

5

3.0V/3.3V Microprocessor Supervisory Circuits

______________________________________________________________Pin Description

MAX690
MAX802

—

— RESET Active-High, Open-Drain Reset Output is the inverse of –R—E—S—E—T–.

PIN

MAX704
MAX806

1 V

2 V
3 GND Ground

4 PFI

5

6 WDI

7

8 VBATT

MAX804
MAX805

1

2
3

4

5

—

6

7

—

8

_______________Detailed Description

A microprocessor’s (µP’s) reset input starts the µP in a
known state. These µP supervisory circuits assert reset to
prevent code execution errors during power-up, power­down, brownout conditions, or a watchdog timeout.

–R—E—S—E—T–
V

a backup battery,–R—E—S—E—T– is guaranteed valid for V
> 1V. Once VCCexceeds the reset threshold, an
internal timer keeps–R—E—S—E—T– low for the reset timeout
period; after this interval,–R—E—S—E—T– goes high (Figure 2).

If a brownout condition occurs (VCCdips below the
reset threshold),–R—E—S—E—T– goes low. Each time–R—E—S—E—T
is asserted, it stays low for the reset timeout period.

MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

Any time VCCgoes below the reset threshold, the
internal timer restarts.

The watchdog timer can also initiate a reset. See the

Watchdog Input

The MAX804_/MAX805_ active-high RESET output is
open drain, and the inverse of the MAX690_/MAX704_/
MAX802_/MAX806_–R—E—S—E—T– output.

6 _______________________________________________________________________________________

is guaranteed to be a logic low for 0V < VCC<

, provided that VBATT is greater than 1V. Without

RST

section.

NAME FUNCTION

Supply Output for CMOS RAM. When VCCis above the reset threshold, V

1

2
3

4

5

6

—

–R—E—S—E—T–

—

7

8

connected to VCCthrough a P-channel MOSFET switch. When VCCfalls below VSWand

OUT

VBATT, VBATT connects to V
Main Supply Input

CC

Power-Fail Input. When PFI is less than V
low; otherwise, –P—F—O–remains high. Connect to ground if unused.

Power-Fail Output. When PFI is less than V

–P—F—O–

otherwise, –P—F—O–remains high. Leave open if unused.
Watchdog Input. If WDI remains high or low for 1.6sec, the internal watchdog timer runs out

and reset is triggered. The internal watchdog timer clears while reset is asserted or when
WDI sees a rising or falling edge. The watchdog function cannot be disabled.

Manual Reset Input. A logic low on –M—R–asserts reset. Reset remains asserted as long as
–M—R–

–M—R–

is low and for 200ms after –M—R–returns high. This active-low input has an internal
70µA pull-up current. It can be driven from a TTL or CMOS logic line, or shorted to
ground with a switch. Leave open if unused.

Active-Low Reset Output. Pulses low for 200ms when triggered, and stays low whenever
VCCis below the reset threshold or when –M—R–is a logic low. It remains low for 200ms after
either VCCrises above the reset threshold, the watchdog triggers a reset, or –M—R–goes
from low to high.

Backup-Battery Input. When VCCfalls below VSWand VBATT, V
VBATT. When VCCrises above the reset threshold, V
exceed VCC. Connect to VCCif no battery is used.

Reset Output

OUT

The MAX690T/MAX704T/MAX805T are intended for

3.3V systems with a ±5% power-supply tolerance and a
10% system tolerance. Except for watchdog faults,
reset will not assert as long as the power supply
remains above 3.15V (3.3V - 5%). Reset is guaranteed
to assert before the power supply falls below 3.0V.

The MAX690S/MAX704S/MAX805S are designed for

3.3V ±10% power supplies. Except for watchdog
faults, they are guaranteed not to assert reset as long

CC

as the supply remains above 3.0V (3.3V - 10%). Reset
is guaranteed to assert before the power supply falls
below 2.85V (VCC- 14%).

The MAX690R/MAX704R/MAX805R are optimized for

–

monitoring 3.0V ±10% power supplies. Reset will not
occur until VCCfalls below 2.7V (3.0V - 10%), but is
guaranteed to occur before the supply falls below

2.59V (3.0V - 14%).
The MAX802R/S/T, MAX804R/S/T, and MAX806R/S/T

are respectively similar to the MAX690R/S/T,
MAX805R/S/T, and MAX704R/S/T, but with tightened
reset and power-fail threshold tolerances.

. Connect to VCCif no battery is used.

or when VCCfalls below VSW, –P—F—O–goes

PFT

, or VCCfalls below VSW, –P—F—O–goes low;

PFT

switches from VCCto

OUT

reconnects to VCC. VBATT may

OUT

Reset Threshold

OUT

is

3.0V/3.3V Microprocessor Supervisory Circuits
MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

VBATT

V

WDI

CC

*
**

MR

PFI

BATTERY
SWITCHOVER
COMPARATOR

1.237V

1.237V

*

WATCHDOG

TIMER

* MAX690T/S/R, MAX802T/S/R, MAX804T/S/R, MAX805T/S/R ONLY
** MAX704T/S/R, MAX806T/S/R ONLY
( ) MAX804T/S/R, MAX805T/S/R ONLY

RESET
COMPARATOR

V

BATTERY

SWITCHOVER

CIRCUITRY

PFT

MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R

GENERATOR

POWER-FAIL
COMPARATOR



RESET

V

OUT

RESET
(RESET)

PFO

3.0V OR 3.3V

V

CC

0V

3.0V OR 3.3V

V

OUT

V

SW

3.0V OR 3.3V

RESET

(RESET)

PFO

( ) MAX804T/S/R, MAX805T/S/R ONLY, RESET EXTERNALLY PULLED UP TO VCC

VBATT = 3.6V

t

WP

VBATT = PFI = 3.6V
I

= 0mA

OUT

V

RST

V

SW

Figure 1. Block Diagram Figure 2. Timing Diagram

Watchdog Input

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

(MAX690_/802_/804_/805_)

does not toggle the watchdog input (WDI) within 1.6sec,
a reset pulse is triggered. The internal 1.6sec timer is
cleared by either a reset pulse or by a transition (low-to­high or high-to-low) at WDI. If WDI is tied high or low, a

–R—E—S—E—T–

pulse is triggered every 1.8sec (tWDplus tRS).

As long as reset is asserted, the timer remains cleared
and does not count. As soon as reset is deasserted,
the timer starts counting. Unlike the 5V MAX690 family,
the watchdog function cannot be disabled.

The PFI input is compared to an internal reference. If
PFI is less than V
comparator is intended for use as an undervoltage

PFT

detector to signal a failing power supply. However, the
comparator does not need to be dedicated to this
function because it is completely separate from the rest
of the circuitry.

The power-fail comparator turns off and–P—F—O– goes low
when VCCfalls below VSWon power-down. The power­fail comparator turns on as VCCcrosses VSWon
power-up. If the comparator is not used, connect PFI to
ground and leave–P—F—O– unconnected.–P—F—O–may be
connected to–M—R–on the MAX704_/MAX806_ so that a
low voltage on PFI will generate a reset (Figure 5b).

_______________________________________________________________________________________ 7

Power-Fail Comparator

,–P—F—O– goes low. The power-fail

3.0V/3.3V Microprocessor Supervisory Circuits

In the event of a brownout or power failure, it may be

Backup-Battery Switchover

necessary to preserve the contents of RAM. With a
backup battery installed at VBATT, the devices auto­matically switch RAM to backup power when V
falls.

CC

This family of µP supervisors (designed for 3.3V and 3V
systems) doesn’t always connect VBATT to V
VBATT is greater than VCC. VBATT connects to V
(through a 140Ω switch) when VCCis below VSWand

OUT

when

OUT

VBATT is greater than VCC, or when VCCfalls below

1.75V (typ) regardless of the VBATT voltage. This is
done to allow the backup battery (e.g., a 3.6V lithium
cell) to have a higher voltage than VCC.

Switchover at VSW(2.40V) ensures that battery-backup
mode is entered before V
minimum required to reliably retain data in CMOS RAM.

gets too close to the 2.0V

OUT

Switchover at higher VCCvoltages would decrease
backup-battery life. When VCCrecovers, switchover is
deferred until VCCrises above the reset threshold
(V

) to ensure a stable supply. V

RST

VCCthrough a 3Ω PMOS power switch.

is connected to

OUT

Manual Reset

A logic low on–M—R–asserts reset. Reset remains asserted
while–M—R–is low, and for tWP(200ms) after–M—R–returns
high. This input has an internal 70µA pull-up current, so
it can be left open if it is not used.–M—R–can be driven with
TTL or CMOS logic levels, or with open-drain/collector
outputs. Connect a normally open momentary switch
from–M—R–to GND to create a manual-reset function;
external debounce circuitry is not required.

__________Applications Information

These µP supervisory circuits are not short-circuit
protected. Shorting V
up transients such as charging a decoupling
capacitor—destroys the device. Decouple both V
and VBATT pins to ground by placing 0.1µF capacitors
as close to the device as possible.

SuperCaps™ are capacitors with extremely high
capacitance values (e.g., order of 0.47F) for their size.
Figure 3 shows two ways to use a SuperCap as a
backup power source. The SuperCap may be
connected through a diode to the 3V input (Figure 3a)
or, if a 5V supply is also available, the SuperCap may
be charged up to the 5V supply (Figure 3b) allowing a
longer backup period. Since VBATT can exceed V
while VCCis above the reset threshold, there are no
special precautions when using these µP supervisors
with a SuperCap.

These µP supervisors were designed for battery­backed applications. If a backup battery is not used,
connect both VBATT and V
different µP supervisor such as the MAX706T/S/R or
MAX708T/S/R.

Replacing the Backup Battery

The backup power source can be removed while V
remains valid, if VBATT is decoupled with a 0.1µF

to ground—excluding power-

OUT

Using a SuperCap

as a Backup Power Source

Operation without a Backup

Power Source

to VCC, or use a

OUT

capacitor to ground, without danger of triggering
RESET/–R—E—S—E—T–. As long as VCCstays above VSW,

Table 1. Input and Output Status in
Battery-Backup Mode

PIN NAME STATUS

V

V

–P—F—O–

MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

WDI The watchdog timer is disabled
–M—R–

–R—E—S—E—T–

RESET High impedance
VBATT Connected to V

Connected to VBATT through an internal

OUT

140Ω switch
Disconnected from V

CC

The power-fail comparator is disabled when

PFI

VCC< V

SW

Logic low when VCC< VSWor PFI < V

Disabled
Low logic

OUT

OUT

PFT

battery-backup mode cannot be entered.

Adding Hysteresis

to the Power-Fail Comparator

The power-fail comparator has a typical input
hysteresis of 10mV. This is sufficient for most applica­tions where a power-supply line is being monitored
through an external voltage divider (see the section

Monitoring an Additional Power Supply

).

If additional noise margin is desired, connect a resistor
between–P—F—O– and PFI as shown in Figure 4a. Select
the ratio of R1 and R2 such that PFI sees 1.237V (V
when VINfalls to its trip point (V
hysteresis and will typically be more than 10 times the

). R3 adds the

TRIP

PFT

value of R1 or R2. The hysteresis window extends both
above (VH) and below (VL) the original trip point (V

™ SuperCap is a trademark of Baknor Industries.

TRIP

CC

CC

CC

)

).

8 _______________________________________________________________________________________

3.0V/3.3V Microprocessor Supervisory Circuits

3.0V OR 3.3V

MAX690T/S/R

V

CC

1N4148

0.47F

Figure 3. Using a SuperCap as a Backup Power Source

MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R

VBATT

MAX806T/S/R

( ) ARE FOR MAX804T/S/R, MAX805T/S/R ONLY



GND

V

RESET 

(RESET)

TO STATIC

OUT

RAM

TO µP

Connecting an ordinary signal diode in series with R3,
as shown in Figure 4b, causes the lower trip point (VL)
to coincide with the trip point without hysteresis (V
so the entire hysteresis window occurs above V
This method provides additional noise margin without

TRIP

TRIP

compromising the accuracy of the power-fail threshold
when the monitored voltage is falling. It is useful for
accurately detecting when a voltage falls past a
threshold.

The current through R1 and R2 should be at least 1µA to
ensure that the 25nA (max over extended temperature
range) PFI input current does not shift the trip point. R3
should be larger than 10kΩ so it does not load down the

–P—F—O–

pin. Capacitor C1 adds additional noise rejection.

Monitoring an Additional Power Supply

These µP supervisors can monitor either positive or
negative supplies using a resistor voltage divider to
PFI. –P—F—O– can be used to generate an interrupt to the
µP (Figure 5). Connecting–P—F—O– to–M—R–on the MAX704
and MAX806 causes reset to assert when the
monitored supply goes out of tolerance. Reset remains
asserted as long as–P—F—O– holds–M—R–low, and for 200ms
after–P—F—O– goes high.

Interfacing to µPs

with Bidirectional Reset Pins

µPs with bidirectional reset pins, such as the Motorola
68HC11 series, can contend with the MAX690_/
MAX704_/MAX802_/MAX806_–R—E—S—E—T– output. If, for

+5V

3.0V OR 

3.3V

1N4148

0.47F

ba

MAX690T/S/R

V

CC

MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R

VBATT

MAX806T/S/R

( ) ARE FOR MAX804T/S/R, MAX805T/S/R ONLY

GND

V

OUT

RESET 

(RESET)



example, the–R—E—S—E—T– output is driven high and the µP
wants to pull it low, indeterminate logic levels may
result. To correct this, connect a 4.7kΩ resistor

),

between the–R—E—S—E—T– output and the µP reset I/O, as in

.

Figure 6. Buffer the–R—E—S—E—T– output to other system
components.

Negative-Going VCCTransients

While issuing resets to the µP during power-up, power­down, and brownout conditions, these supervisors are
relatively immune to short-duration negative-going V
transients (glitches). It is usually undesirable to reset
the µP when VCCexperiences only small glitches.

Figure 7 shows maximum transient duration vs. reset­comparator overdrive, for which reset pulses are not
generated. The graph was produced using negative­going VCCpulses, starting at 3.3V and ending below
the reset threshold by the magnitude indicated (reset
comparator overdrive). The graph shows the maximum
pulse width a negative-going VCCtransient may
typically have without causing a reset pulse to be
issued. As the amplitude of the transient increases
(i.e., goes farther below the reset threshold), the
maximum allowable pulse width decreases. Typically,
a VCCtransient that goes 100mV below the reset
threshold and lasts for 40µs or less will not cause a
reset pulse to be issued.

A 100nF bypass capacitor mounted close to the V
pin provides additional transient immunity.

TO STATIC
RAM

TO µP

MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

CC

CC

_______________________________________________________________________________________ 9

3.0V/3.3V Microprocessor Supervisory Circuits

V

V

IN

MAX690T/S/R

PFI

MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R

PFO

V

GND

CC



*OPTIONAL

R

1

R

2

R

3

C1*

TO µP

IN

R

1

R

2

R

3

C1*

TO µP

PFI

MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R

PFO

V

GND

CC



*OPTIONAL

PFO

V

CC

V

VH = (V

PFO

TRIP

0V

V

= V

TRIP

VH = R1 (V

WHERE

V

IN

R

1

R

2

=

V

PFT

PFT + VPFH

0V

R1 + R

2

( )

PFT

R

2

1

+ V

( )

PFT

PFH)

R

1

V

= 1.237V

PFT

V

VD

V

(



= 10mV

PFH

= DIODE FORWARD VOLTAGE DROP
= V

L

TRIP

PFI PFO

V

TRIPVH

R

1 + R2

)

R

2

R

1 + R2

)

(

)

R

2

V

TRIP

1

1

+

+

R

R

2

3

V

CC

MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R



GND

V

H

(V

CC - VD

–

R

3

3.0V OR 3.3V

MR

* MAX704T/S/R, 
MAX806T/S/R ONLY

PFT

V

IN

)

*

V

IN

PFO

0V

V

TRIP

VH = (V

V

0V

R1 + R

= V

( )

PFT

+ V

PFT

PFH

= R

( )

L

1 VPFT

V

L

V

TRIP

2

R

2

1

) (R1)

1
R

1

+

+

( )

R

R

1

2

1

1

+

+

–

R

R

1

2

3

V

H

WHERE
1
R

3

V

CC

R

3

V

IN

V

= 1.237V

PFT
PFH

= 10mV



V

ba

Figure 4. a) Adding Additional Hysteresis to the Power-Fail Comparator b) Shifting the Additional Hysteresis above V

3.0V OR 3.3V

V

R

1

R

2

V-

V

CC

PFO

1

V

= R

(V

MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

TRIP

V

+ V

2

PFT

= R

(V

)

L

2

PFT

+

)

PFH

(

R

1

1

1

+

(

)

R

R

1

2

CC

MAX690T/S/R

PFI PFO

MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R



GND

V

V

TRIP

L

1

V

CC

–

)

R

R

2

1

V

CC

–

R

1

WHERE

NOTE: V

0V

V
V

TRIP

PFT
PFH

V-

= 1.237V

= 10mV

IS NEGATIVE



ba

Figure 5. Using the Power-Fail Comparator to Monitor an Additional Power Supply

10 ______________________________________________________________________________________

3.0V/3.3V Microprocessor Supervisory Circuits

BUFFERED RESET TO OTHER SYSTEM COMPONENTS

V

CC

MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX806T/S/R

GND

4.7k

RESET

RESET

V

CC

µP

GND

Figure 6. Interfacing to µPs with Bidirectional Reset I/O

100

80

60

40

20

MAXIMUM TRANSIENT DURATION (µs)

0

10 100 1000

RESET COMPARATOR OVERDRIVE (V

VCC = 3.3V

= +25°C

T

A

RST

DS690-806 fig7

- VCC) (mV)

_Typical Operating Circuits (cont.)

3.0V OR 3.3V

0.1µF 0.1µF

3.6V

0.1µF

V

CC

VBATT

MAX704T/S/R
MAX806T/S/R

MR

GND

PFI

V

RESET

OUT

RAM

µP

MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

Figure 7. Maximum Transient Duration without Causing a
Reset Pulse vs. Reset Comparator Overdrive

______________________________________________________________________________________ 11

3.0V/3.3V Microprocessor Supervisory Circuits

_Ordering Information (continued) ___________________Chip Topography

V

PART** TEMP. RANGE

MAX704_CPA

MAX704_CSA 0°C to +70°C
MAX704_C/D 0°C to +70°C Dice*
MAX704_EPA -40°C to +85°C
MAX704_ESA -40°C to +85°C
MAX704_MJA -55°C to +125°C 8 CERDIP
MAX802_CPA
MAX802_CSA 0°C to +70°C
MAX802_C/D 0°C to +70°C Dice*
MAX802_EPA -40°C to +85°C
MAX802_ESA -40°C to +85°C
MAX802_MJA -55°C to +125°C 8 CERDIP
MAX804_CPA
MAX804_CSA 0°C to +70°C
MAX804_C/D 0°C to +70°C Dice*
MAX804_EPA -40°C to +85°C
MAX804_ESA -40°C to +85°C
MAX804_MJA -55°C to +125°C 8 CERDIP
MAX805_CPA
MAX805_CSA 0°C to +70°C
MAX805_C/D 0°C to +70°C Dice*
MAX805_EPA -40°C to +85°C
MAX805_ESA -40°C to +85°C
MAX805_MJA -55°C to +125°C 8 CERDIP
MAX806_CPA
MAX806_CSA 0°C to +70°C
MAX806_C/D 0°C to +70°C Dice*
MAX806_EPA -40°C to +85°C
MAX806_ESA -40°C to +85°C
MAX806_MJA -55°C to +125°C 8 CERDIP

0°C to +70°C

0°C to +70°C

0°C to +70°C

0°C to +70°C

0°C to +70°C

PIN-PACKAGE

8 Plastic DIP

8 SO

8 Plastic DIP

8 SO

8 Plastic DIP

8 SO

8 Plastic DIP

8 SO

8 Plastic DIP

8 SO

8 Plastic DIP

8 SO

8 Plastic DIP

8 SO

8 Plastic DIP

8 SO

8 Plastic DIP

8 SO

8 Plastic DIP

8 SO

* Contact factory for dice specifications.
** These parts offer a choice of reset threshold voltage. Select

the letter corresponding to the desired nominal reset threshold
voltage (T = 3.075V, S = 2.925V, R = 2.625V) and insert it into
the blank to complete the part number.

V

CC

GND

(2.032mm)

( ) ARE FOR MAX804T/S/R, MAX805T/S/R.
[ ] ARE FOR MAX704T/S/R, MAX806T/S/R.

TRANSISTOR COUNT: 802;
SUBSTRATE IS CONNECTED TO THE HIGHER OF

VCCOR VBATT, AND MUST BE FLOATED IN ANY
HYBRID DESIGN.

OUT

PFI PFO

0.080"

VBATT

(2.794mm)

RESET
(RESET)

WDI
[MR]

0.110"

MAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/R

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.

12

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