Document
October 2003
rev 1.0
ASM690A / 692A ASM802L / 802M ASM805L
µP Power Supply Supervisor With Battery Backup Switch
Applications
• • • • • • • • Embedded control systems Portable/Battery operated systems Intelligent instruments Wireless instruments Wireless communication systems PDAs and hand-held equipments µP / µC power supply monitoring Safety system
General Description
The AS690A / AS692A / AS802L / AS802M / AS805L offers complete single chip solutions for power supply monitoring and control battery functions in microprocessor systems. Each device implements four functions: Reset control, watchdog monitoring, battery-backup switching and power-failure monitoring. In addition to microprocessor reset under power-up and power-down conditions, these devices provide batterybackup switching to maintain control in power loss and brownout situations. Additional monitoring capabilities can provide an early warning of unregulated power supply loss before the voltage regulator drops out. The important features of these four functions are: • • • •
Typical Operating Circuit
Unregulated DC Regulated +5V VCC RESET PFI R2 VBATT PFO WDI VOUT RESET NMI VCC
www.DataSheet4U.com
R1
0.1 µF
1.6 second watchdog timer to keep microprocessor responsive 4.40V or 4.65V VCC threshold for microprocessor reset at power-up and power-down SPDT (Single-pole, Double-throw) PMOS switch connects backup power to RAM if VCC fails 1.25V threshold detector for power loss or general purpose voltage monitoring
I/O LINE
GND
+
_
ASM690A
VCC
CMOS RAM
GND
These features are pin-compatible with the industry standard power-supply supervisors. Short-circuit and thermal protection have also been added. The AS690A / AS802L / 4.65V and the AS692A / AS802M AS805L generate a reset pulse when the supply voltage drops below generate a reset below
VBATT VCC
Block Diagram
8 2 Reset Generator
+ |+ -
1 Battery-Switchover Circuit VOUT 7 RESET (RESET)
4.40V. The ASM802L / ASM802M have power-fail accuracy to ± 2%. The ASM805L is the same as the ASM690A except that RESET is provided instead of RESET.
Features
• Two precision supply-voltage monitor options •4.65V (AS690A / AS802L / AS805L) •4.40V (AS692A / AS802M ) • • • • • • • Battery-backup power switch on-chip Watchdog timer: 1.6 second timeout Power failure / low battery detection Short circuit protection and thermal limiting Small 8-pin SO package No external components Specified over full temperature range
WDI 6
1.25V 3.5V
|+ + |+ +
Watchdog Timer
0.8V PFI 4
1.25V
|+ +
5 PFO
ASM690A, ASM692A, ASM802L, ASM802M, (ASM805L)
3
GND
Alliance Semiconductor 2575 Augustine Drive . Santa Clara, CA 95054 . Tel: 408.855.4900 . Fax: 408.855.4999 . www.alsc.com
Notice: The information in this document is subject to change without notice
BUS
3.6 V Lithium Battery
GND
October 2003
rev 1.0
ASM690A / 692A ASM802L / 802M ASM805L
Pin Configuration
Plastic/CerDip/SO
VOUT VCC GND PFI
1 2 3 4
ASM690A ASM692A ASM802L ASM802M (ASM805L)
8 7 6 5
VBATT RESET (RESET) WDI PFO
Pin Description
Pin Number
www.DataSheet4U.com ASM692A
ASM802L / ASM802M
ASM690A /
Name ASM805L
Function
Voltage supply for RAM. When VCC is above the reset threshold, VOUT connects to 1 1 VOUT VCC through a P-Channel MOS device. If VCC falls below the reset threshold, this output will be connected to the backup supply at VBATT (or VCC, whichever is higher) through the MOS switch to provide continuous power to the CMOS RAM. 2 3 2 3 VCC GND +5V power supply input. Ground Power failure monitor input. PFI is connected to the internal power fail comparator which is referenced to 1.25V. The power fail output (PFO) is active LOW but remains HIGH if PFI is above 1.25V. If this feature is unused, the PFI pin should be connected to GND or VOUT. Power-fail output. PFO is active LOW whenever the PFI pin is less than 1.25V. Watchdog input. The WDI input monitors microprocessor activity. An internal timer is reset with each transition of the WDI input. If the WDI is held HIGH or LOW for longer than the watchdog timeout period, typically 1.6 seconds, RESET (or RESET) is asserted for the reset pulse width time, tRS, of 140ms, minimum. Active-LOW reset output. When triggered by VCC falling below the reset threshold 7 RESET or by watchdog timer timeout, RESET (or RESET) pulses low for the reset pulse width tRS, typically 200ms. It will remain low if VCC is below the reset threshold (4.65V in ASM690A / ASM802L and 4.4V in the ASM692A / ASM802L) and remains low for 200ms after VCC rises above the reset threshold. 7 RESET VBATT Active-HIGH reset output. The inverse of RESET. Auxiliary power or backup-battery input. VBATT should be connected to GND if the 8 8 function is not used. The input has about 40mV of hysteresis to prevent rapid toggling between VCC and VBATT.
4
4
PFI
5
5
PFO
6
6
WDI
µP Power Supply Supervisor With Battery Backup Switch
Notice: The information in this document is subject to change without notice
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October 2003
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