TLV62130A: Step-down converter seems to continously restart.

Jed Althouse

Part Number: TLV62130A
Other Parts Discussed in Thread: TLV62130

I am trying to bring-up a TLV62130 12V to 3.3V regulator circuit, but it seems to restart continuously. The scope shot below shows the ENABLE, VOUT/VOS and SS/TR signals. I assume that the SS/TR signal going low means that a failure condition has occurred. From the datasheet, I see that one of these conditions occur: (1) a shutdown (EN=GND), (2) an undervoltage lockout or (3) a thermal shutdown. The condition causes an internal resistor to pull the SS/TR pin down. Returning from those states causes a new startup sequence as set by the SS/TR connection. Is this what I am seeing here?

(1) As can be seen, the enable signal stays high. (2) While VIN is not shown, it isn't going undervoltage - it is around 12V. (3) The time frame is too short to have a thermal shutdown, right?

What might be causing this shutdown to occur? Are there other conditions not mentioned in the datasheet that would cause a shutdown?

Here is the schematic:

There is a 1KΩ pull-down resistor for the DEF pin, but this isn't shown.

The layout is not optimal. For instance there isn't a separate trace from the VOUT to the VOS input. It is all part of the same copper fill.

over 5 years ago

0 Chris Glaser over 5 years ago

TI__Guru*** 142880 points

Hi Jain,

The SS/TR pin waveform does not look normal. It should be a linear ramp up from a current source charging a capacitor. Can you replace the SS/TR cap and retest? Is there anything else connected to that pin besides the cap? What part number are you using for the cap?

Did you confirm that the boards were build correctly, with no open/shorted pins, solder on the thermal pad, etc.?

0 Jed Althouse over 5 years ago in reply to Chris Glaser

Prodigy 160 points

Chris, thank you for the reply. Looking at my layout, I see that the vias in thermal pad area are not filled and plated as was expected. It's likely there wasn't a ground connection on the exposed pad.

0 Chris Glaser over 5 years ago in reply to Jed Althouse

TI__Guru*** 142880 points

Thanks for confirming. You might try reworking 1 IC with enough solder there and see if you have different startup results.

As well, you could measure the IC with a thermal camera or a finger to see if it is too hot and reaching thermal shutdown.

0 Chris Glaser over 5 years ago in reply to Chris Glaser

TI__Guru*** 142880 points

Hi Jain,

Were you able to resolve this?

0 Jed Althouse over 5 years ago in reply to Chris Glaser

Prodigy 160 points

Chris,

Thanks for checking back. I haven't done any more with this issue. Our current thinking is that it is a soldering issue - either with the thermal pad or the pins on the periphery.

One of our manufacturing engineers said he would look at it, but I haven't heard back from him yet.

I'll post more information as I get it.

Thanks.
J.A.

0 Chris Glaser over 5 years ago in reply to Jed Althouse

TI__Guru*** 142880 points

Thanks for the update. Just reply back if you need additional help.

0 Jed Althouse over 5 years ago in reply to Chris Glaser

Prodigy 160 points

Found the culprit. The 4-pad output inductor was rotated 90° and was simply passing the output switch node (SW) to VOUT.

0 Chris Glaser over 5 years ago in reply to Jed Althouse

TI__Guru*** 142880 points

Thanks for sharing. Yes, that would produce undesirable results :)

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TLV62130A: Step-down converter seems to continously restart.