TPS5450: Back feeding the regulator in shutdown

Michael Rourke

Part Number: TPS5450

I have a TPS5450 that regulates 14V from a 24V input. When input power fails, the TPS5450 shutdown pin is pulled low. As the 14V output decays, a power path FET switches to a 9V battery to feed the downstream system. However, the battery will also put voltage on the PH pin (through the inductor).

Will this cause any internal issues?

over 3 years ago

0 Jimmy Hua over 3 years ago

TI__Guru 50120 points

Hi,

Can you provide a schematic / block diagram drawing of your application? If there is a voltage on the output when the input supply is off, then there may be some reverse current that flows back into the regulator and could potentially bias the high-side FET. In order to prevent this from happening, you can place a diode between VOUT to VIN such that when this reverse current occurs, the current will take the path through the diode instead of through the PH of the device.

Regards,

Jimmy

0 Michael Rourke over 3 years ago in reply to Jimmy Hua

Intellectual 350 points

Jimmy -

Thank you for your quick response. I have attached a copy of the input power schematic.Input Power.pdf

Mike

0 Jimmy Hua over 3 years ago in reply to Michael Rourke

TI__Guru 50120 points

Hi Mike,

Thanks for the schematic.
I''ll take a look at it and get back to you with some feedback.

Regards,

Jimmy

0 Jimmy Hua over 3 years ago in reply to Jimmy Hua

TI__Guru 50120 points

Hi Mike,

As suggested earlier, I think having a reverse current Schottky diode will help with backfeed from the 9V battery. This way, if VOUT >>VIN in the event the TPS5450 is disabled, the current path will bypass the TPS5450 device and not cause damage to the IC. With this diode, there is a potential for reverse current to flow from VOUT to PH to VIN (through the internal high-side FET) and damage the part.

Regards,

Jimmy

0 Michael Rourke over 3 years ago in reply to Jimmy Hua

Intellectual 350 points

Jimmy -

Thanks for the input. Perhaps it would be better to put a FET (Ideal Diode) on Vout.

Mike

+1 Jimmy Hua over 3 years ago in reply to Michael Rourke

TI__Guru 50120 points

Hi Mike,

I believe that would work as well. You would just need turn the FET on when you want VOUT connected downstream and off if disconnected downstream.

Regards,

Jimmy

Power management

Power management forum

TPS5450: Back feeding the regulator in shutdown