LTC1235 Microprocessor Supervisory Circuit FEATURES DESCRIPTION The LTC 1235 provides complete power supply monitoring n Guaranteed Reset Assertion at V = 1V CC and battery control functions for microprocessor reset, n 1.5mA Maximum Supply Current battery backup, RAM write protection, power failure warn- n Fast (35ns Max.) Onboard Gating of RAM Chip ing and watchdog timing. The LTC1235 has all the LTC695 Enable Signals features plus conditional battery backup and external reset n Conditional Battery Backup Extends Battery Life control. When an out-of-tolerance power supply condition n 4.65V Precision Voltage Monitor occurs, the reset outputs are forced to active states and n Power OK/Reset Time Delay: 200ms the Chip Enable output write-protects external memory. n External Reset Control The RESET output is guaranteed to remain logic low with n Minimum External Component Count V as low as 1V. External reset control is provided by a n 1A Maximum Standby Current CC debounced pushbutton reset input. n Voltage Monitor for Power Fail or Low Battery Warning The LTC1235 powers the active CMOS RAMs with a charge n Thermal Limiting pumped NMOS power switch to achieve low dropout and n Performance Specified Over Temperature low supply current. When primary power is lost, auxiliary n 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 P signal to either back up the RAMs or not. This extends APPLICATIONS the battery life in situations where RAM data need not always be saved when power goes down. n Critical P Power Monitoring n Intelligent Instruments For an early warning of impending power failure, the n Battery-Powered Computers and Controllers LTC1235 provides an internal comparator with a user- n Automotive Systems de ned threshold. An internal watchdog timer is also L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other available, which forces the reset pins to active states when trademarks are the property of their respective owners. the watchdog input is not toggled prior to the time-out period. TYPICAL APPLICATION Battery Life vs Backup Duty Cycle 10 LT1086-5 V 7.5V IN +5V 9 V V POWER TO P V V IN OUT CC OUT LTC1235 + + CMOS RAM POWER 8 0.1F 0.1F 100F 10F ADJ LTC1235 7 I/O LINE V BACKUP BATT 6 +3V RESET PRESET 51k 5 LTC695 P NMI P (WITHOUT PFO 4 PFI SYSTEM CONDITIONAL I/O LINE WDI BATTERY PB RST 3 10k BACKUP) 2 1235 TA1 1 0 THE LTC1235 EXTENDS BATTERY LIFE BY PROVIDING BATTERY POWER ONLY WHEN REQUIRED TO BACK UP RAM DATA. 0 20 40 60 80 100 IT SAVES THE BATTERY WHEN NO DATA BACKUP IS NEEDED. THE P REQUESTS BACKUP WITH THE BACKUP PIN. BACKUP DUTY CYCLE (%) 1235 TA02 1235fa 1 BATTERY LIFE (NORMALIZED)LTC1235 ABSOLUTE MAXIMUM RATINGS (Notes 1 and 2) Terminal Voltage V Output Current ................... Short Circuit Protected OUT V ....................................................... 0.3V to 6.0V Power Dissipation ...............................................500mW CC V .................................................... 0.3V to 6.0V Operating Temperature Range BATT All Other Inputs ........................0.3V to (V + 0.3V) LTC1235C ................................................ 0C to 70C CC Input Current Storage Temperature Range ................... 65C to 150C V ..................................................................200mA Lead Temperature (Soldering, 10 sec.) ................. 300C CC V .................................................................50mA BATT PIN CONFIGURATION TOP VIEW TOP VIEW V V 1 1 BATT 16 PRESET BATT 16 RESET V 2 V 2 15 15 PRESET OUT RESET OUT V 3 V 14 WDO 3 14 WDO CC CC 4 13 13 GND CE IN GND 4 CE IN LTC1235 LTC1235 BATT ON 5 12 BATT ON 5 12 CE OUT CE OUT LOW LINE 6 11 WDI LOW LINE 6 11 WDI PFO PFO 10 PB RST 7 10 PB RST 7 9 PFI 9 PFI BACKUP BACKUP 8 8 N PACKAGE SW PACKAGE 16-LEAD PLASTIC DIP 16-LEAD PLASTIC SOL T = 110C, = 130C/W T = 110C, = 130C/W JMAX JA JMAX JA CONDITIONS:PCB MOUNT ON FR4 MATERIAL, STILL AIR AT 25C COPPER TRACE ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC1235CN PBF LTC1235CN TRPBF LTC1235CN 16-Lead Plastic DIP 0C to 70C LTC1235CSW PBF LTC1235CSW TRPBF LTC1235CSW 16-Lead Plastic SOL 0C to 70C Consult LTC Marketing for parts speci ed with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based nish parts. For more information on lead free part marking, go to: