LTC690/LTC691

LTC694/LTC695

1

690fe

TYPICAL APPLICATION

FEATURES

DESCRIPTION

Microprocessor

Supervisory Circuits

monitoringandbatterycontrolfunctionsformicroprocessor

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.Aninternalwatchdogtimerisalsoavailable,which

forces the reset pins to active states when the watchdog

input is not toggled prior to a preset timeout period.

RESET Output Voltage

vs Supply Voltage

APPLICATIONS

n

Enable Signals

or Adjustable

or Low-Battery Warning

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

ADJ

10μF

5V

100μF

0.1μF

μP NMI

μP

POWER

POWER TO

CMOS RAM

I/O LINE

μP RESET

μP

SYSTEM

0.1μF

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

0.1μF

100Ω

+

+

SUPPLY VOLTAGE (V)

0

3

4

5

4

2

1

0

1

2

3

5

EXTERNAL PULL-UP = 10μA

690 TA02