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I would like to use a watchdog timer as a way to do a proper power cycle in last resort, that is: power down for 1 second, then power up. I have come up with the following design:

MAX6746, FDC6330

The watchdog used here is a MAX6746, the load switch is a FDC6330. +5V_DCIN is plugged to a 5V DC, +5V goes to the rest of the circuit. The capacitors set the timers at 1s active reset, 30s watchdog timeout.

The problem is it is stuck in a loop where every 1s the FDC6330 enables the power to +5V then instantly back to 0V. Any idea? I could not find such use cases on google, watchdogs are usually used to directly control a reset pin for a mcu.

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  • \$\begingroup\$ Have you verified the connections on C8 and C10? \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 25 '14 at 7:38
  • \$\begingroup\$ Yes, actually when I bypass the switch by directly connecting +5v_DCIN to +5V for 1s, then disconnect, everything works as expected, i.e. stays up until the watchdog is not asserted for 30s, then power down and back to power loop. \$\endgroup\$ – tfjgeorge Apr 25 '14 at 8:08
  • \$\begingroup\$ Have you tried using 2 separate supplies? \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 25 '14 at 8:12
  • \$\begingroup\$ I have not yet, do you mean the sudden load could create a voltage drop that would reset the watchdog ? \$\endgroup\$ – tfjgeorge Apr 25 '14 at 8:31
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    \$\begingroup\$ Also, where's the decoupling capacitor on the '6746? \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 25 '14 at 8:37
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Solved using a resistor between 5V_DCIN and Vcc of the watchdog. The reset pulse was triggered by a power glitch on Vcc rather than MR.

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