ADM8617 Analog Devices, ADM8617 Datasheet - Page 8

• Manufacturer Part Number: ADM8617
• Description: Low Voltage Supervisory Circuit with Watchdog in 4-Lead SC70 (Active-low with an Open-Drain Output)
• Manufacturer: Analog Devices

Specifications of ADM8617

• Batt-backup-flg: No
• Manual Reset Capability: No
• Package: SC70
• Power Fail Indicator: No
• Reset Threshold Summary: 9 Options--1.58 to 4.63V
• Reset Output-stage: Active-Low/Open-Drain
• Min Reset Timeout (ms): 1,1120,140,20
• Typ Watchdog Timeout (ms): 102,1600,6.3
• Watchdog Timer: Yes

ADM8616/ADM8617
CIRCUIT DESCRIPTION
The ADM8616/ADM8617 provide microprocessor supply
voltage supervision by controlling the microprocessors RESET
input. Code execution errors are avoided during power-up,
power-down, and brownout conditions by asserting a RESET
signal when the supply voltage is below a preset threshold and
by allowing supply voltage stabilization with a fixed timeout
RESET after the supply voltage rises above the threshold. In
addition, problems with microprocessor code execution can be
monitored and corrected with a watchdog timer. By including
watchdog strobe instructions in microprocessor code, a watch-
dog timer can detect if the microprocessor code breaks down or
becomes stuck in an infinite loop. If this happens, the watchdog
timer asserts a RESET pulse that restarts the microprocessor in
a known state.
RESET OUTPUT
The ADM8616 features an active-low, push-pull RESET output,
while the ADM8617 features an active-low, open-drain RESET
output. The RESET signal is guaranteed to be logic low and
logic high, respectively, for V
The RESET output is asserted when V
threshold (V
watchdog timeout period (t
duration of the RESET active timeout period (t
above the RESET threshold or after the watchdog timer times
out. Figure 11 illustrates the behavior of the RESET outputs.
RESET
V
CC
V
V
1V
0V
0V
CC
CC
TH
), or when WDI is not serviced within the
Figure 11. RESET Timing Diagram
V
TH
t
RP
WD
CC
). RESET remains asserted for the
down to 1 V.
CC
is below the RESET
RP
V
) after V
TH
t
RD
CC
rises
Rev. B | Page 8 of 12
WATCHDOG INPUT
The ADM8616/ADM8617 feature a watchdog timer that
monitors microprocessor activity. A timer circuit is cleared with
every low-to-high or high-to-low logic transition on the watch-
dog input pin (WDI), which detects pulses as short as 50 ns.
If the timer counts through the preset watchdog timeout period
(t
toggle the WDI pin to avoid being reset. Failure of the micro-
processor to toggle WDI within the timeout period, therefore,
indicates a code execution error, and the RESET pulse generated
restarts the microprocessor in a known state.
In addition to logic transitions on WDI, the watchdog timer
is also cleared by a RESET assertion due to an undervoltage
condition on V
is cleared and does not begin counting again until RESET deas-
serts. The watchdog timer can be disabled by leaving WDI
floating or by three-stating the WDI driver.
WD
RESET
), RESET is asserted. The microprocessor is required to
WDI
V
CC
V
V
V
1V
0V
0V
0V
CC
CC
CC
CC
Figure 12. Watchdog Timing Diagram
. When RESET is asserted, the watchdog timer
V
t
RP
TH
t
WD
t
RD