TPS51200: Pin 3 (VO) only gives 37mV out

Alex Silva

Part Number: TPS51200

Hello all,

I got a batch of 5 identical pcbs manufactured with a TPS51200 on each board.

I'm now testing board no. 3 (boards 1 and 2 have passed all the tests), and I'm only getting 38.2mV on pin 3 whereas on boards 1 and 2 I get 0.75V. I get the following readings on this faulty board:

0.739V on pin 1 (REFIN)

1.487V on pin 2 (VLDOIN)

38.2mV on pin 3 (VO) <----- problem here

0.743V on pin 6 (REFOUT)

1.15V on pin 7 (EN)

22mV on pin 9 (PGOOD)

3.3V on pin 10 (VIN)

I'm attaching my schematics and layout and would appreciate if someone could tell me what could be possibly preventing VO to output the correct voltage.

Thanks in advance!

Alex

over 7 years ago

0 Alex Silva over 7 years ago

Prodigy 140 points

I'm sorry that the title says 37mV - it's actually 38.2mV. I couldn't edit after posting.

0 Weidong Zhu over 7 years ago in reply to Alex Silva

TI__Expert 5965 points

Hi Alex, it looks EN voltage is too low. Can you check the EN pin voltage on the other two boards? Thanks.

Regards,
Weidong

0 Alex Silva over 7 years ago in reply to Weidong Zhu

Prodigy 140 points

Hi Weidong, thank you for replying.

All 3 boards have the same voltage on the enable pin:

Is there anything else I could check?

Regards,

Alex

0 Qian Chen over 7 years ago in reply to Alex Silva

TI__Mastermind 24075 points

Hi Alex,

The high-level threshold of EN pin is 1.7V.

Please make EN pin above 1.7V and check again.

R91 value seems too large. Even R91 is connected to 1.8V_PG, due to leakage current of EN, pin, the EN pin voltage could be lower than 1.7V.

I suggest to use a lower value like 1k ohm for R91.

Thanks

Qian

0 Alex Silva over 7 years ago in reply to Qian Chen

Prodigy 140 points

Hi Qian,

Thank you for replying. I can change R91 for 1K and for the next batch I can change the voltage to 1.7V, but why would the other 2 boards work with 1.15V on the EN pin?

Thanks!

0 Qian Chen over 7 years ago in reply to Alex Silva

TI__Mastermind 24075 points

HI Alex,

Part has variatoin. That means the EN high threshold of different parts could be slightly different.

To make every part work, the EN voltage should be higher than the spec listed on datasheet, which is 1.7V.

In next batch, I suggest to make the EN pin voltage higher than 1.7V, like 1.8V or higher.

Thanks

Qian

0 Alex Silva over 7 years ago in reply to Qian Chen

Prodigy 140 points

Hi Qian,

Thank you very much. I'm going to mark this as resolved and if I have problems with the next batch I'll let you know.

Regards,

Alex

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TPS51200: Pin 3 (VO) only gives 37mV out