TPS55165-Q1: Not regulating over input range

John

Prodigy 40 points

Part Number: TPS55165-Q1

Tool/software:

I am using the TPS55165QPWPRQ1 in the fixed 12V out configuration.

This is a copy of my schematic:

Here is also the relevant portion of my layout:

I am using the same exact part number inductor that was identified in the EVM board for this part.

I had three boards prototyped. One works correctly. The output is always 12V when input ranges from 12 to 24V. However, the other two boards do not regulate the output voltage at 12V when the input is below 15 V.

This is a screen capture of the output voltage of the board that is working correctly when the input voltage is 12 V.

This is a scope capture of the output of one of the bad boards when the input voltage is at 12 V.

In both situations there was no load.

I'm not sure if there was an assembly error or if there is something marginal with the board design that is causing one board to work and two boards to not work. I verified all of the components are correct. I can't seem to figure out what could be different among the boards that I have. I would appreciate any help with troubleshooting this. Thank you.

8 months ago

0 Bryce Xun 8 months ago

TI__Mastermind 27950 points

Hi John,

Thanks for reaching out.

From the schematic, the IGN_PWRL shows floating, have you tried to connect this pin with GND to see if any difference?

BRs,

Bryce

0 John 8 months ago in reply to Bryce Xun

Prodigy 40 points

Yes, I had tried connecting this pin to GND but it made no difference.

0 Mulin Yuan 8 months ago in reply to John

TI__Genius 15400 points

Hi John,

Bryce is OoO until 5th/Feb. Please expect a delayed response.

Regards,

Mulin

0 John 8 months ago

Prodigy 40 points

I noticed that when I ramp the input voltage slowly, the regulator works fine. I'm not sure as to what might be the root cause.

0 Mulin Yuan 8 months ago in reply to John

TI__Genius 15400 points

Hi John,

Can you share the waveforms of Vin,Vout, SW1, SW2 and inductor current?

Regards,

Mulin

0 John 8 months ago in reply to Mulin Yuan

Prodigy 40 points

This is a waveform showing Vin and Vout:

This is voltage on one side of the inductor:

A zoomed in view:

This is the voltage on the other side of the inductor:

When I ramp the input voltage slowly and the output is at a steady 12 V, either side of the inductor looks like this:

0 Mulin Yuan 8 months ago in reply to John

TI__Genius 15400 points

Hi Josh,

Thank you for sharing the waveforms. Expert for this device is OoO and will come back on 5th/Feb. He will give you feedback at that time. Thanks.

Regards,

Mulin

0 John 7 months ago in reply to Mulin Yuan

Prodigy 40 points

Has your expert returned to the office? I would need this part to work with a faster input voltage ramp. Are there any other recommended component values I should be using?

0 Bryce Xun 7 months ago in reply to John

TI__Mastermind 27950 points

Hi John,

Thanks for your patience, we are just back from holiday.

With your experiments, the three boards can all operate normally if you use slower Vin ramp rate, right?

Can you also check the VREG waveforms with Vin and Vout together at NG board?

BRs,

Bryce

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TPS55165-Q1: Not regulating over input range