TPS65400: VDDD issue

Francis Kimpel1

Prodigy 170 points

Part Number: TPS65400

Have built 5 boards that use the TPS65400QRGZRQ1 part

The TPS65400 provides power to an FPGA and on board logic.

4 of the 5 boards power up correctly on all 4 outputs

The TPS65400 on the 5th board does not power up.

Issue:

Observed that the RCCLOCK(Pin 40) input was not oscillating

RCLOCK Resistor = 402K

Capacitor across Resistor = 4.7 pF

VDDD(Pin 20) = 0V during operation. Measured 2.3 ohm to ground with the output capacitor removed.

VDDA(Pin 19) = 6V (within data sheet spec)

VDDG(Pin 18) = 0V during operation. No low resistance to ground

Is the RCLOCK circuit powered by VDDD?

Used 4.7uF part instead of the data sheet recommendation of 3.3uF - Could this have caused the failure?

Is there an ESR requirement for VDDA, VDDD, VDDG regulator capacitors? I didn't see this in the data sheet.

Should the capacitors be rated 2x-3x the output regulator voltage to allow for DC bias effects?

thanks,

over 5 years ago

0 Zhao Ma over 5 years ago

TI__Genius 15135 points

Hi, Francis

1. Could you send me the schematic and layout files?

2. In normal working, the voltage on RCCLOCK pin is a stable voltage, it will not oscillating.

3. Before you remove 4.7uF cap from VDDD pin, during operation, what is the impedance of VDDD pin?

And in good board, during operation, what is the impedance of VDDD pin?

4. RCLOCK circuit is powered by VDDA.

5. 4.7uF instead of 3.3uF will not cause failure.

6. No esr requirement for caps, MLCC is ok.

7. Yes, TI suggests capacitors be rated 2x above the output regulator voltage.

Have you checked the CE, RST_N, ENSW1/2/3/4 pin voltage after power on?

0 Francis Kimpel1 over 5 years ago in reply to Zhao Ma

Prodigy 170 points

I checked CE, RST_N, ENSW1, PV1, VIN pins

CE = 2.2V

RST_N = 2.2V (after RC charge)

ENSW1 = 2.2V

SS1 = 4.5V (after charge)

VIN = 12V

PV1 = 12V

VDDD = 0V

VDDG = 0V

VDDA = 6V

Attached is schematic

Thanks

0 Francis Kimpel1 over 5 years ago in reply to Francis Kimpel1

Prodigy 170 points

Zhao Ma

How do I send you a schematic. I don't see an option to do this?

0 Zhao Ma over 5 years ago in reply to Francis Kimpel1

TI__Genius 15135 points

You can use insert files function, see below.

0 Francis Kimpel1 over 5 years ago in reply to Zhao Ma

Prodigy 170 points

870-000023_PMICONLY.pdf

0 Francis Kimpel1 over 5 years ago in reply to Zhao Ma

Prodigy 170 points

0083.870-000023_PMICONLY.pdf

0 Francis Kimpel1 over 5 years ago in reply to Francis Kimpel1

Prodigy 170 points

Zhao,

Keep in mind that 4 of the 5 boards received worked properly.

0 Zhao Ma over 5 years ago in reply to Francis Kimpel1

TI__Genius 15135 points

Hi, Francis

I have reviewed the schematic, find one weakness point:

Soft start cap C513~C516 are DNP, which means there are no soft start for Buck1/2/3/4, which might cause big inrush current and trigger OCP, so suggest setting C513~C516 to 4.7nF.

However, i don't think this will cause VDDD pin failed.

Maybe VDDD failure is caused by ESD event, suggest changing a new TPS65400 on failed board and test again.

0 Francis Kimpel1 over 5 years ago in reply to Zhao Ma

Prodigy 170 points

Thanks Zhao,

I had actually installed .1 uF soft start capacitors on all 5 boards.

I had the IC replaced at our contract mfg today.

Will look at it tomorrow.

I think it is a handling/soldering/ESD issue considering the other 4 boards worked well.

Just wanted a second set of eyes to look at the design and see if I missed something.

thanks,

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TPS65400: VDDD issue