Q: TPS3828-33 watchdog failed by 1170817

Hi,

I have a customer using the TPS3828-33 and he have a problem that the reset is not activated when the WDI pin is LOW.

There are two cases:

1. If WDI stops toggle and stays HIGH then RESET will go active after 1,2 sec.

2. If WDI stops toggle and stays LOW then RESET will NOT go active after 1,2 sec.

In both cases WDI will be held low during RESET. 


A: Re: TPS3828-33 watchdog failed by 10449

It is confirmed that the microprocessor watchdog output did not have enough drive strength to properly pull the TPS3828 WDI pin high and low.  The TPS3828 will not generate a reset if the WDI pin is open or driven with a high impedance.  This is proper operation and is how the IC was designed to function.

If the microprocessor does not have enough drive strength to drive the WDI pin directly, connect a pullup resistor from WDI to VCC.  Connect an N-CH FET from WDI to ground with source connected to ground and the drain connected to WDI. Connect the uP output to the gate.  When the uP output is high impedance or low, the FET is off and the WDI input is pulled high which will generate a reset.  When the uP output is high, the WDI pin is pulled to ground.