This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS7A49: Thermal shutdown at warm ambient temperatures (20C-50C) with high humidity?

Part Number: TPS7A49

I've run into an interesting problem with a design where this chip appears to be going into thermal shutdown at warmer ambient temperatures (20C-50C) in humid weather (boards are conformal coated).

Haven't been able to confirm if they have been able to come out of this failure mode by themselves, but I can confirm that cycling the input voltage to this chip will reset the fault in most cases.

I've been able to repeat the same fault in the lab by spraying failed circuits (that have been reset by cycling the input power) with freeze spray, but not using heat, which is what I would expect, so I'm kind of at a loss at what the issue is. When sprayed with freeze spray the circuits will be coming up to temperature again (usually around 0C-20C, but sometimes lower) and the chip will start cycling on and off on the output. Sometimes this leads to the output permanently turning off, and sometimes it stays on after a few on/off cycles. This to me suggests the thermal shutdown is happening.

Does this sound like a poor soldering issue to the ground pad? Or is there something I'm missing.

The power draw is quite low, about 4mW across the device, and there should be adequate heatsinking for the device. The PowerPad under the device is connected and has multiple vias going to the ground planes. Any thoughts or ideas based on the circuit below? Has anyone else experienced these kinds of issues?

  • Hi Sophia,

    In order to help debug, can you provide a scope shot with Vin, Vout, and if possible Iout? Thermal shutdown will look like a square wave on the output.

    At 4mW dissipation in the LDO and using your nominal voltages your load current is only 800uA. Is this correct?

    Very Respectfully,
    Ryan