TPS65131-Q1: TPS65131 Vref question

Gary Teng

Part Number: TPS65131-Q1
Other Parts Discussed in Thread: TPS65131

Hi all,

My customer use TPS65131 in their panel design. In their first board TPS65131 works good. But in second version, its Vref become to 0.85V so the output voltage is lower than first version board. Except the Vref issue, all other function looks good. It can boost, invert, and adjust voltage. Is there any reason the Vref become lower? Thanks for your kindly help. (No schematic change... where do we have to check in layout?)

Best regards,

Gary Teng

over 7 years ago

0 Aaron Goodson over 7 years ago

TI__Expert 6330 points

Hi gary,

I have notified our expert regarding this issue. Please expect a response by 2/27/19.

Thanks,

Aaron

0 Liaqat Khan over 7 years ago

TI__Mastermind 18550 points

Hello,

The likely reason for Vref being low will be some kind of loading on Vref voltage/pin. If the first version of the board had correct Vref and the second version has significantly lower Vref voltage while the two schematics /BOM are same, this sounds like a board assembly issue not a layout issue. Please double check component values on the second board version to ensure that they are same as on first version.

Kind Regards,
Liaqat

0 Gary Teng over 7 years ago in reply to Liaqat Khan

Genius 5990 points

Hi Liaqat,

In my understand, Vref is genearted from TPS65131 itself. It means TPS65131 receive power from Vin(?) and generate a 1.2V voltage out. And I can remove all boost and invert circuit and I'll see 1.2V on Vref pin right?

Gary

5315.tps65131.pdf

0 Liaqat Khan over 7 years ago in reply to Gary Teng

TI__Mastermind 18550 points

Hi Gary,

It is correct that Vref is generated internally within TPS65131 but if it gets loaded by some external component, such as smaller than expected value for resistor R4 in the schematics below or a resistor assembled on the board instead of a capacitor at C8, it can lower the VREF voltage. Since you mentioned that there is no change between two versions of the board, I was guessing that some board assembly issue where a wrong component value got assembled on the board may be the cause of this issue.

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TPS65131-Q1: TPS65131 Vref question