LMZ10501: Faulty regulators overheat, problem fixed by replacing the component.

user5202449

Part Number: LMZ10501

Tool/software:

Hello,

We are using two LMZ10501 on one PCB. Both are supplied by a 5V Boost.
One LMZ is providing 1V8 and the other 3V3.

We are facing a big issue on this board related to these components. We have around 30% of board failing due to these regulators.
The failure appears on both regulators. The failure can always be fixed by manually replacing the regulator.
When we got a faulty regulator, it usually regulates output as expected but overheat and quickly go off with thermal protection. When the regulator is replaced, the temperature of the regulator does not exceed 40°C at ambient room temperature.

We are not strictly respecting the layout guidelines but yet it does not explain why the issue disappears when we replace the regulators by new one.

I measured impedances between pins to see if there was any short but I did not see any. There are some differences but I don't know if we can learn something from them:

	Impedances between pins for a faulty LMZ10501 1V8 (kΩ)
	Vin	Ground	Vcon	Vout	EN	Vref
Vin		200	80	460	490	250
Ground			70	46	470	136
Vcon				160	600	123
Vout					500	200
EN						630
Vref

	Impedances between pins for a working LMZ10501 1V8 (kΩ)
	Vin	Ground	Vcon	Vout	EN	Vref
Vin		600	490	500	760	424
Ground			70	60	790	141
Vcon				205	777	125
Vout					830	280
EN						810
Vref

We also send some PCB the X-Rays to ensure that the soldering beneath is fine. On both regulators they were fine whereas all PCB sent had issues with at least one of the two regulators.
On the X-Ray though, we discovered that we had two different versions of the regulators. We can see that the IC inside is very different: