TPS55340: Shutdowns intermittently occurring during temperature transitions

David Bayer1

Part Number: TPS55340

We are using the TPS55340 for a 8.0V -> 16V boost regulator. Schematic is attached below.

Several boards are exhibiting an issue where as the board temperature transitions from ~52C to 55C, the 16.0V drops out to the Vin of 8.0V.

Sometimes this recovers and boosts back to 16V, and sometimes it does not and remains at Vout = VIN.

The EN line remains high, and the SYNC = 700KHz remains stable.

The TPS55340 device itself does not appear to get getting significantly hotter than 55C.

Could you review the schematic below, and recommend what else to look at?

Also attached is the waveform showing the switching node and the Vout, zoomed in at the point it stopped switching.

over 5 years ago

0 Yinsong Cai1 over 5 years ago

TI__Expert 7450 points

Hi David,

Thank you for your interest in TPS55340.

What is your load? And could you check the FREQ and SS pin see if they are stable at the nominal range?

Thanks,
Yinsong

0 David Bayer1 over 5 years ago in reply to Yinsong Cai1

Prodigy 50 points

Hi Yinsong,

Load is variable between 50mA and 250mA.

FREQ and SS appear normal.

If the SYNC pin was AC coupled to the 700KHz clock, could that cause a shutdown if the DC level is floating?

0 Yinsong Cai1 over 5 years ago in reply to David Bayer1

TI__Expert 7450 points

Do we have the waveform for COMP and FB? Also, what does the external SYNC looks like?

Thanks,
Yinsong

0 Yinsong Cai1 over 5 years ago in reply to David Bayer1

TI__Expert 7450 points

Yes, I want to make sure the high/low threshold for SYNC is always met. So it would be nice to have the SYNC waveform while it shuts down.

Thanks,

Yinsong

0 David Bayer1 over 5 years ago in reply to Yinsong Cai1

Prodigy 50 points

Please see attached waveforms for Vfb, Vcomp, and SYNC

0 David Bayer1 over 5 years ago in reply to David Bayer1

Prodigy 50 points

Also, we do not have pin 10 or 14 (NC's) tied to ground. The datasheet shows these tied to ground. Is it necessary? What could happen if they were left floating?

0 Yinsong Cai1 over 5 years ago in reply to David Bayer1

TI__Expert 7450 points

Hi David,

Do you have the COMP waveform during the shut down transient?

I will check with other engineer about the NC pin and get back to you.

Thanks,
Yinsong

0 Yinsong Cai1 over 5 years ago in reply to David Bayer1

TI__Expert 7450 points

Hi David,

I have just asked our designer. NC pins must be tied to ground, otherwise the chip won't work properly. So please modify the circuit based on this.

Thanks,
Yinsong

0 David Bayer1 over 5 years ago in reply to Yinsong Cai1

Prodigy 50 points

I have not been able to capture a COMP waveform during the shutdown.

Is it possible the NC pins are the culprit? I will have them tied to GND.

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TPS55340: Shutdowns intermittently occurring during temperature transitions