TPS54332 output unexpectedly low

Vincent Chang

Other Parts Discussed in Thread: TPS54332, TPS54232

Hi,

I designed a power circuit based on TPS54332, which takes a 17VDC input, generating a 6VDC output, which is further converted to 4VDC, 3.3VDC, etc through other TPS54332-based voltage converting modules. However, the problem is: for the output which is expected to be 6VDC, only 0.128V is measured. Voltages for the various pins for the TPS54332 are measured as follows:

1. Boot 5.22V

2. Vin 17.44V

3. EN 2.04V

4. SS 0V

5. VSNS: 0.016V

6. COMP: 0.572V

7. GND: 0V

8. PH: 0.128V

the schematics and layout are shown below. I would be very grateful if you can help solve the problem.

Thanks!

Vincent

over 11 years ago

0 JohnTucker over 11 years ago

TI__Guru**** 191445 points

That schemetic is too tiny to read. Can you provide a larger one, preferably PDF? Also waveforms are better than dc voltages.

0 Vincent Chang over 11 years ago in reply to JohnTucker

Prodigy 160 points

2112.test.pdf

Thanks for the reply! Here is the enlarged schematics. Since I have only multimeter with me now, Dc voltages are the only things I can measure. Sorry about that!

Vincent

0 JohnTucker over 11 years ago in reply to Vincent Chang

TI__Guru**** 191445 points

You measure 0 V at SS so there won't be any output. Try removing the 10 k resistors from SS to GND. Let me know if that fixes your issue.

0 Vincent Chang over 11 years ago in reply to JohnTucker

Prodigy 160 points

That solved the problem! Many Thanks! But I just cannot understand why--- the resistor is what is suggested by the datasheet.

Vincent

0 JohnTucker over 11 years ago in reply to Vincent Chang

TI__Guru**** 191445 points

The datasheet schematic uses a 1 M resistor, 10 k is to low a value.

0 Vincent Chang over 11 years ago in reply to JohnTucker

Prodigy 160 points

I just re-checked the datasheet of TPS54232 (sorry, I mis-typed it as TPS54332 previously), and in Table I of page 9, it was stated that R3 (the resistor we were talking about) is 10K, not 1M.

Vincent

0 JohnTucker over 11 years ago in reply to Vincent Chang

TI__Guru**** 191445 points

No, the R3 in that table corresponds to the schematic on the front page. R3 is the compensation resistor. There is no resistor shown in parallel with the slow start cap.

0 Vincent Chang over 11 years ago in reply to JohnTucker

Prodigy 160 points

Oh, I see. I have mistaken it with Fig. 12 (typical application), where there is also a R3.

Thanks! You have been a great help!

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TPS54332 output unexpectedly low