Power Supply and Watchdog Timer a Monitoring Circuit ADM9690 FUNCTIONAL BLOCK DIAGRAM FEATURES Precision Voltage Monitor (4.31 V) Watchdog Timeout Monitor V CC Selectable Watchdog Timeout0.75 ms, 1.5 ms, 12.5 ms, 25 ms V MON ADM9690 Two RESET Outputs 4.31V APPLICATIONS Microprocessor Systems RESET(1) RESET(1) OSC SEL1 TIMER WATCHDOG Computers TIMEBASE OSC SEL2 RESET(2) Printers RESET(2) TIMER Controllers Intelligent Instruments WATCHDOG WATCHDOG TRANSITION INPUT (WDI) DETECTOR GND GENERAL DESCRIPTION The watchdog timer monitoring circuit is designed to monitor The ADM9690 contains a voltage monitoring comparator and a the activity on the WDI input. This input is normally connected watchdog timer monitor. It is designed to monitor the 5 V to an output line on the P. Its function is to check that the power supply to a microprocessor and the microprocessor opera- microprocessor has not stalled in an infinite loop. If there is a tion via a watchdog function. period of inactivity for the watchdog timeout period, both reset outputs are activated. As above, RESET(1) remains low for The voltage monitoring comparator monitors the voltage on 50 ms while RESET(2) remains low for an additional 10 ms. V . If it drops outside tolerance, as will happen during a MON The watchdog timer is restarted when RESET(1) goes inactive. power-fail, two reset signals are generated. Both reset signals go The actual watchdog timeout period is adjustable using two active (low) simultaneously. They will remain active while select inputs SEL1 and SEL2. V is below the threshold, and for 50 ms (RESET(1)) or MON 60 ms (RESET(2)) after V climbs above the reset thresh- MON The ADM9690 is available in an 8-lead SOIC package. It is old. RESET(1) is intended to provide a power-on reset signal specified over the industrial temperature range. for the P while RESET(2) is used to hold additional circuitry in a reset state until the P has regained control following a power-up. The voltage monitoring circuitry remains operational with V as low as 2 V. CC REV. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or Tel: 781/329-4700 World Wide Web Site: (V = Full Operating Range. T = T to T unless otherwise noted) ADM9690SPECIFICATIONS CC A MIN MAX Parameter Min Typ Max Units Test Conditions/Comments V OPERATING VOLTAGE RANGE 4.3 5.5 V CC SUPPLY CURRENT 55 100 A RESET AND WATCHDOG TIMER Reset Voltage Threshold 4.2 4.31 4.42 V V Falling T = 0C to +70C MON A Reset Threshold Hysteresis 30 mV Reset Timeout Delay (t ) 50 75 ms Figure 7, 8 1 RESET(2) Timeout Delay (t ) 10 15 ms Figure 7, 8 2 WATCHDOG TIMEOUT PERIOD (TWD) 0.4 0.75 1.28 ms SEL2 = 0, SEL1 = 0 1.0 1.5 2.4 ms SEL2 = 0, SEL1 = 1 9.0 12.5 19 ms SEL2 = 1, SEL1 = 0 18 25 38 ms SEL2 = 1, SEL1 = 1 WDI INPUT PULSEWIDTH 100 ns V = 0.4, V = 3.5 V IL IH RESET(1)/(2) Output Voltage 0.1 0.4 V I = 3.2 mA SINK 0.3 0.4 V I = 10 mA, SINK 0.45 0.7 V I = 15 mA, SINK 3.5 V I = 1 A SOURCE WDI INPUT THRESHOLD Logic Low 0.8 V 150 ns Pulse Logic High 3.5 V 150 ns Pulse WDI Input Current 1.2 5 A WDI = V CC 5 1.2 A WDI = 0 V SEL1/2 Input Current 1 +1 A SEL = V CC 10 5 10 A SEL = 0 V Specifications subject to change without notice. 2 REV. A