TPS3851: Strange reset behavior

Per Be

Part Number: TPS3851

Hi.

We are using a TPS3851 connected as:

During power on when reset is deactivated and also when we stop kicking when reset is released it's not consistant:
Picture below shows the reset pulse when kicks has been turned off:

I would have expected a nice high pulse for ~13ms

The power-on reset looks the same (with the difference that it stays high in the end)

How can this be?

over 3 years ago

0 Per Be over 3 years ago

Prodigy 10 points

Noticed I missed to add the PU resistor in the reset/WDO pin. there is a resistor of 10k with a 100nF capacitor to ground near MCU .
Like this:

0 Jesse Villanueva over 3 years ago in reply to Per Be

TI__Mastermind 20420 points

Hi Per,

Happy to answer your question. What kind of signal does the WDI_DISABLE input provides? Also why are you using both pull up and the adjustable configuration for the CWD pin?

Jesse

0 Per Be over 3 years ago in reply to Jesse Villanueva

Prodigy 10 points

Hi.

Sorry failed to mention. The resistor is not mounted, this is alternative assembly where resistor can be mounted instead of capacitor, so please ignore R7.

WDI_DISABLE comes from MCU and I have measured this it's high while reset is released (it's actually high always, just with test software we can command disable of watchdog).

Update:

The "problem" is the MCU. During boot (after reset) the pin is default configured as output and drives reset_n low...

I've cut the trace and the reset now behaves as expected.

0 Jesse Villanueva over 3 years ago in reply to Per Be

TI__Mastermind 20420 points

Hi Per,

Thank you for the update. Please ask if you have anymore questions.

Jesse

Power management

Power management forum

TPS3851: Strange reset behavior