TPS51225C: The output voltage increase with temperature

Edward Lee

Intellectual 1655 points

Part Number: TPS51225C

Hi Sir,

My customer recently encountered a problem with TPS51225C (generating 3.3V and 5V from 12V).

The output voltage increases about 0.8~1V as the temperature rises from 25 degree to 60 degree.

They have checked the following items but found nothing anomaly.

1. The voltage level at VFB1 and VFB2 - > Stable and no deviation

2. The voltage at VIN of IC and synchronous mosfet -> Stable

3. The phases at SW1 and SW2 -> Stable and no obvious jitters as temperature rises.

4. The voltage at VREG3 and VREG5 ->

As the output voltage increases with temperature, the voltage at VREG5 rises too (switchover) while the voltage at VREG3 does not change too much (about 3.4V)

It would be kind of you to give us some directions.

Thanks

Sincerely,

Edward

over 4 years ago

0 Gerold Dhanabalan - Online Design Tools over 4 years ago

TI__Genius 14455 points

Hi Edward,

What is the temperature grade of the feedback resistors used? If the feed resistors change too much, then Vout will also change but you will not see anything change with Vfb. That does not explain why Vreg5 changes. Can you please share some more information on how much change in Vreg 5 you see?

Regards,

Gerold

0 Yuchang Zhang over 4 years ago in reply to Gerold Dhanabalan - Online Design Tools

TI__Mastermind 18510 points

Hi Edward,

Check PGOOD is high or not while the output gets 0.8V~1V increase, I suppose the Vout is set 5V, and if Vout get 0.8V~1V higher, it may trigger PG rising fault or even OV protection. but if the reason is caused by feedback resistor change as Gerold mentioned, which will cause the target Vout change, Vout OV will not happen and PG should keep high. you can check FB resistors based on this.

Vreg5 will switchover from 5Vout, so it makes sense 5Vout higher cause Vre5 higher, and Vreg3 is linear regulated from VO1, so it will not be changed.

BTW, you said SW jitter is stable, Did you compare the duty cycle between 25C and 60C? is it match with the corresponding Vout value?

Upload your schematic and waveforms for review.

Yuchang

0 Yuchang Zhang over 4 years ago in reply to Yuchang Zhang

TI__Mastermind 18510 points

Edward,

Since we are discussing this question with Email, this thread will be closed now.

Yuchang

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TPS51225C: The output voltage increase with temperature