TPS62291: Blowing internal MOSFET

Hello Wladimir,
To support you, I need some info. Is it possible to have the schematic and layout of your application? Which kind of test you did? Also know the conditions and environment of your test can help me.

Hello Alfonso,

here is the part with the TPS62291. The whole schematic is much bigger. The inductor (L5) is Taiyo Yuden  CKP32162R2M-T. There are several 1µF capacitors around the PCB on the 3.3V net. The parts marked with "DNP" are not populated.

Hello,
we are looking at your schematic and layout, and I will back to you soon. Can you please give details about the test you did and the relative conditions? Can you provide the measurements data? It helps to understand the behavior of the device.

Dear Alfonso,

what exactly do you mean by test equipment?

When I build the devices, I test them for function with battery and USB input.

There is no dedicated test equipment in my lab, just a scope and some multimeters. When the two devices came back, I measured the 3.3V net against ground with a multimeter set up for diode testing. Usually (on working devices) the reading is not less than about 0.7V. This two devices had 7.5mV - almost a short circuit. After desoldering I can confirm about 7mV between ground and switch output. Between VIN and SW I can measure the body diode of the high side FET (480mV). So I think, the high side FET is OK, the low side FET is blown. After soldering a new TPS62291 the devices work properly. This means that the rest of the device is OK.

Hello Wladimir,
Your schematic and layout seem ok. Usually, this problem is caused by an overvoltage at the switching node (SW) due to an overvoltage at the supply or attaching measurement equipment. With USB there is the risk of overvoltage generation by plugging in/ unplugging.

Dear Alfonso,

There is a 5.6V zener diode (ON Semi 1SMB5919BT3G) between VBUS and GND near the USB connector. There is a bus protector (ST Micro ESDALCL62SC6) which also protects VBUS.

And finally there is a 1.5A PPTC fuse (Bel Fuse 0ZCJ0075AF2E) in the VBUS net.

Could ESD cause this failure?

Thank You.

Hello Wladimir,
ESD is anyway a risk. An overvoltage damaged the low-side switch. That could happen during operation at different operating conditions or during changing of the operative/test conditions. It is also possible generate overvoltage stress by handling the device.

Dear Alfonso,
Do You have any suggestions for the next batch? Maybe other part or more protection?
Thank You.

Hello,
typically zener diode or tvs diode are used as protection. I am trying to understand well your problem but I did not figure out anything relevant. Maybe the handling of the device or problem during the soldering cause this failure. Are you working in a lab with proper esd protection like floor, bench and shoes?