TPS3420: Back drive on VCC with logic high on PBx

Shiv Agarwal

Part Number: TPS3420

Hello,

My circuit has an initial condition of PBx powered logic high and VCC floating.
For above situation, I see potential appear on VCC.

Could you comment if this is expected behavior?

Thanks!

over 1 year ago

0 Jesse Villanueva over 1 year ago

TI__Genius 12400 points

Hi Shiv,

Thank you for your question, I just want to clarify, You are detecting voltage on the VCC while the pin floating and a HIGH on PBx? If this is the case, what is the voltage on PBx and the voltage detected on the floating VCC? I will have to check with our design team if there is a path from PBx to VCC to cause this behavior.

Jesse

0 Shiv Agarwal over 1 year ago in reply to Jesse Villanueva

Prodigy 40 points

Hello Jesse,
I have the PBx tied together. On system turn on from battery, the MCU pulls the PBx to 1.5V while the VCC is not powered at all (VCC is powered from external USB). At this point I see the 1.5V on PBx drop to less than 1V and VCC is at ~0.5V.

Thanks,
Shiv

0 Jesse Villanueva over 1 year ago in reply to Shiv Agarwal

TI__Genius 12400 points

Hi Shiv,

Thank you for the additional details, I will convey it to our design team and I will update you once I hear back from them.

Jesse

0 Shiv Agarwal over 1 year ago in reply to Jesse Villanueva

Prodigy 40 points

Checking in.

+1 Jesse Villanueva over 1 year ago in reply to Shiv Agarwal

TI__Genius 12400 points

Hi Shiv,

According to our design team this is an expected behavior. When PB is high and VCC is floating, there is a forward bias path through an internal transistor from PD to VCC.

Jesse

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TPS3420: Back drive on VCC with logic high on PBx