TPS65400: One of the outputs is wrong

Rajat Rao

Part Number: TPS65400

Hello,

I am using TPS65400 PMIC in an FPGA board. The schematic is attached. It is similar to the circuit used by Diligent in the ArtyZ7 board.

I find that the output of SW3 is wrong. The output is 3.3V whereas it should be 1.8V according to the resistors connected.

The other three outputs are correct. This seems quite weird! Any idea what could be wrong?

I measured the enable signals to be at 1.6V while they have actually been pulled up to VDDD which is equal to 3.3V.

In the ArtyZ7 board, I measured the enable signals to be at 2.7V while they are actually pulled up to 3.3V (but not VDDD).

In the data sheet, I found that 1.28V on the enable pins is treated as a high. What is the correct way of enabling the PMIC and why is there a significant voltage drop?

More importantly, why is only SW3 giving a wrong output?

Thanks,

Rajat Rao

over 7 years ago

0 Gavin Wang (Zejing) over 7 years ago

TI__Expert 3480 points

Can you help probe the voltage of FB3 and SW3?

0 Rajat Rao over 7 years ago in reply to Gavin Wang (Zejing)

Intellectual 760 points

The voltage at SW3 output is 3.3V and the voltage at FB3 pin is 1.46V.

So, the ratio of resistors in the feedback seems correct.

0 Gavin Wang (Zejing) over 7 years ago in reply to Rajat Rao

TI__Expert 3480 points

Because Vef is default 0.8V. And the VREF_COMMAND command can also set VREF. Did you do any setup to change the ref for SW3?

0 Rajat Rao over 7 years ago in reply to Gavin Wang (Zejing)

Intellectual 760 points

No, the VREF has not been changed. We are using the default settings.
However, we have identified a board defect and I'll get back after checking on this issue.

Thanks,
Rajat Rao

0 Zhao Ma over 7 years ago in reply to Gavin Wang (Zejing)

TI__Genius 15135 points

Hi, sir

1. EN1, EN2, EN3, EN4 cannot be connected to VDDD, because only when EN1-4 is high, the VDDD regulator will work up to 3.3V.

Please set EN1, EN2, EN3, EN4 floating, and test again.

2. I saw the compensation circuit for SW3 channel is not correct, i guess the SW3 converter maybe is not stable.

R55=180k is too big, suggest to reduce it to 51kohm.

C91 is too small, suggest to increase it to 1.2nF.

With same reason, suggest to reduce R57 to 51kohm.

Besides, could you probe SW3 switching node and VCC1V8 waveform?

0 Rajat Rao over 7 years ago in reply to Zhao Ma

Intellectual 760 points

Hi Zhao Ma,

Thanks for your insightful reply.
We floated all enable signals. We also solved a hardware problem and the PMIC outputs now seem correct.
Your second suggestion seems interesting and we shall try to implement that also soon.

Thanks,
Rajat Rao

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TPS65400: One of the outputs is wrong