LINEAR TECHNOLOGY LTC1235 User Guide
Summary
The LTC1235 is an advanced microprocessor supervisory circuit designed for robust power management in critical, battery-powered applications. It ensures data integrity by providing complete power supply monitoring, intelligent conditional battery backup to protect RAM data, and reliable reset control. This manual details the comprehensive features, including precision voltage monitoring, system watchdog timing, and external reset mechanisms. It is essential documentation for engineers designing complex embedded controllers, portable computer systems, or automotive electronics that demand high reliability during low or fluctuating power conditions.
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LTC1235
Microprocessor Supervisory Circuit
ESCRIPTIOSFEATURE Guaranteed Reset Assertion at VCC = 1V The LTC1235 provides complete power supply monitoring 1.5m A Maximum Supply Current and battery control functions for microprocessor reset, Fast (35ns Max.) Onboard Gating of RAM Chip battery backup, RAM write protection, power failure warn- Enable Signals ing and watchdog timing. The LTC1235 has all the LTC695 Conditional Battery Backup Extends Battery Life features plus conditional battery backup and external reset 4.65V Precision Voltage Monitor control. When an out-of-tolerance power supply condition Power OK/Reset Time Delay: 200ms occurs, the reset outputs are forced to active states and the External Reset Control Chip Enable output write-protects external memory. The Minimum External Component Count RESET output is guaranteed to remain logic low with VCC as 1µA Maximum Standby Current low as 1V. External reset control is provided by a debounced Voltage Monitor for Power Fail or Low Battery push-button reset input.
Warning
The LTC1235 powers the active CMOS RAMs with a charge
Thermal Limiting
pumped NMOS power switch to achieve low dropout and
Performance Specified Over Temperature
low supply current. When primary power is lost, auxiliary
All the LTC695 Features Plus Conditional Battery
power, connected to the battery input pin, provides backup
Backup and External Reset Control
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
PPLICATI SA always be saved when power goes down.
BA TT ER LI FE (N OR AL IZ ED
Critical µP Power Monitoring For an early warning of impending power failure, the Intelligent Instruments LTC1235 provides an internal comparator with a user- Battery-Powered Computers and Controllers defined threshold. An internal watchdog timer is also avail- Automotive Systems able, which forces the reset pins to active states when the watchdog input is not toggled prior to the time-out period.
PPLICATITYPICAL Battery Life vs
Backup Duty Cycle
LT1086-5
VIN ≥ 7.5V
POWER TO µP LTC1235
VIN VOUT VOUTVCC
0.1µF CMOS RAM POWER 10µF 100µF 0.1µF
ADJ LTC1235
VBATT I/O LINEBACKUP
+3V LTC695
RESET µP RESET
51k (WITHOUT
CONDITIONAL
PFO µP NMI µP
PFI BATTERY
SYSTEM
BACKUP)
PB RST WDI I/O LINE
LTC1235 TA1
BACKUP DUTY CYCLE (%)
THE LTC1235 EXTENDS BATTERY LIFE BY PROVIDING BATTERY POWER ONLY WHEN REQUIRED TO BACK UP RAM DATA.
LTC1235 TA02
IT SAVES THE BATTERY WHEN NO DATA BACKUP IS NEEDED. THE µP REQUESTS BACKUP WITH THE BACKUP PIN.
Page Summary Contents For LINEAR TECHNOLOGY LTC1235 User Guide
Manual Details
| Brand | Linear |
|---|---|
| Pages | 16 |
| File Size | 252.35 KB |
| Published | May 30, 2026 |
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Frequently Asked Questions
How does the LTC1235 extend battery life?
It extends battery life by using conditional battery backup, providing power only when required to back up RAM data.
What monitors can trigger a reset or warning condition?
The device monitors for primary power loss (PFO), low battery voltage thresholds (via internal comparator), and watchdog timer expiration.
What is the maximum standby current draw of the reset output?
The minimum external component count RESET output has a guaranteed maximum standby current of n1μA.
Does the unit protect RAM data during power loss?
Yes, connected auxiliary battery power can provide backup power to the RAMs, allowing key data to be retained.