Features

• Guaranteed Reset Assertion at V_CC = 1V
• 1.5mA Maximum Supply Current
• Fast (35ns Max.) Onboard Gating of RAM Chip Enable Signals
• Conditional Battery Backup Extends Battery Life
• 4.65V Precision Voltage Monitor
• Power OK/Reset Time Delay: 200ms
• External Reset Control
• Minimum External Component Count
• 1µA Maximum Standby Current
• Voltage Monitor for Power Fail or Low Battery Warning
• Thermal Limiting
• Performance Specified Over Temperature
• All the LTC695 Features Plus Conditional Battery Backup and External Reset Control

Typical Application

Description

The LTC1235 provides complete power supply monitoring and battery control functions for microprocessor reset, battery backup, RAM write protection, power failure warning and watchdog timing. The LTC1235 has all the LTC695 features plus conditional battery backup and external reset control. When an out-of-tolerance power supply condition occurs, the reset outputs are forced to active states and the Chip Enable output write-protects external memory. The RESET output is guaranteed to remain logic low with V_CC as low as 1V. External reset control is provided by a debounced push-button reset input.

The LTC1235 powers the active CMOS RAMs with a charge pumped NMOS power switch to achieve low dropout and low supply current. When primary power is lost, auxiliary power, connected to the battery input pin, provides backup power to the RAMs. The LTC1235 can be programmed by a µP signal to either back up the RAMs or not. This extends the battery life in situations where RAM data need not always be saved when power goes down.

For an early warning of impending power failure, the LTC1235 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 the time-out period.