LP2981: Can I bias the GND pin to bring the output up?

Mike Nudelman

Part Number: LP2981
Other Parts Discussed in Thread: TPS7A24

Say I have the LP2981-50DBVR, the 5V part. Can I bias up the GND pin (say use a Schottky with 0.5V Vf between it and GND) and make it 5.5V? Will the performance be degraded?

3 months ago

0 Hannah Grace 3 months ago

TI__Expert 6470 points

Hello,

Thank you for your question.

Please allow me 2-3 business days to reply to your question.

Best Regards,

Hannah

0 Hannah Grace 3 months ago in reply to Hannah Grace

TI__Expert 6470 points

Just to clarify, are you asking if you can use a Schottky diode between OUT and GND?

0 Mike Nudelman 3 months ago in reply to Hannah Grace

Intellectual 265 points

Yes. Schottky (with a resistor, like 20K or so, to provide extra current from Vin to the diode's A; the diode, again, is between the GND pin and the GND)

0 Hannah Grace 3 months ago in reply to Mike Nudelman

TI__Expert 6470 points

Thank you for the clarification. Please allow me a couple business days to clarify with peers.

Best Regards,

Hannah

0 Mike Nudelman 3 months ago in reply to Hannah Grace

Intellectual 265 points

Something like this.

+1 Hannah Grace 3 months ago in reply to Mike Nudelman

TI__Expert 6470 points

I believe the voltage on the GND pin is allowed to move in the circuit. I believe any noise at the GND pin would show up in the output voltage, because the reference is moving. As a result, the noise shouldn't be any lower than Vin noise except from what you are filtering out. If noise is mandatory for your application, we do not recommend moving forward with this design. If too much current tries to enter the GND pin, but your voltage exceeds the threshold voltage on the diodes, then this design should reroute the excess current through the diodes. In turn, this could save the part from damage. If you are intending for the GND pin to be RC filtered, you may be able to put the filter on the input instead.

I think a voltage divider with a potentiometer on the GND pin may be easier to set the output voltage to your desired output. This is not a standard way of how we use our LDOs, but these are my thoughts on the matter.

The TPS7A24 device is a pin for pin device with the same functionality as the LP2981: TPS7A24 data sheet, product information and support | TI.com

This device also has a FB resistor network, which allows for an adjustable output. This device would allow you to meet the 5.5V requirement for your project.

Best Regards,

Hannah

0 Mike Nudelman 3 months ago in reply to Hannah Grace

Intellectual 265 points

Thanks, Hannah.

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LP2981: Can I bias the GND pin to bring the output up?