1

LTC690/LTC691

LTC694/LTC695

Microprocessor

Supervisory Circuits

ADJ

10

µF

5V

100

µF

0.1

µF

µP NMI

µP

POWER

POWER TO

CMOS RAM

I/O LINE

µP RESET

µP

SYSTEM

0.1

µF

3V

51k

10k

690 TA01

LT

MICROPROCESSOR RESET, BATTERY BACK-UP, POWER FAILURE

WARNING AND WATCHDOG TIMING ARE ALL IN A SINGLE CHIP

FOR MICROPROCESSOR SYSTEMS

LTC690/LTC691

LTC694/LTC695

PFI

WDI

RESET

PFO

GND

0.1

µF

100

Ω

+

+

RESET Output Voltage vs

Supply Voltage

s

UL Recognized

File # E145770

s

s

1.5mA Maximum Supply Current

s

Fast (35ns Max) Onboard Gating of RAM Chip

Enable Signals

s

SO-8 and S16 Packaging

s

4.65V Precision Voltage Monitor

s

Power OK/Reset Time Delay: 50ms, 200ms

or Adjustable

s

Minimum External Component Count

s

1

µA Maximum Standby Current

s

Voltage Monitor for Power-Fail

or Low-Battery Warning

s

Thermal Limiting

s

Performance Specified Over Temperature

s

Superior Upgrade for MAX690 Family

The LTC

monitoring and battery control functions for microproces-

sor reset, battery back-up, CMOS RAM write protection,

power failure warning and watchdog timing. A precise

internal voltage reference and comparator circuit monitor

the power supply line. When an out-of-tolerance condition

occurs, the reset outputs are forced to active states and the

chip enable output unconditionally write-protects external

memory. In addition, the RESET output is guaranteed to

The LTC690 family powers the active CMOS RAMs with a

charge pumped NMOS power switch to achieve low drop-

out and low supply current. When primary power is lost,

auxiliary power, connected to the battery input pin, powers

the RAMs in standby through an efficient PMOS switch.

For an early warning of impending power failure, the

LTC690 family provides an internal comparator with a

user-defined threshold. An internal watchdog timer is also

available, which forces the reset pins to active states when

the watchdog input is not toggled prior to a preset time-out

period.

®

s

Critical

µP Power Monitoring

s

Intelligent Instruments

s

Battery-Powered Computers and Controllers

s

Automotive Systems

SUPPLY VOLTAGE (V)

0

3

4

5

4

2

1

0

1

2

3

5

EXTERNAL PULL-UP = 10

µA

690 TA02

, LTC and LT are registered trademarks of Linear Technology Corporation.

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO