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TPS61073 SW pin frequently broken short to GND

Other Parts Discussed in Thread: TPS61073, TPS62261

hi,

After weeks of test, the 5.5V output TPS61073 used in my PCB design is indeed having big problem. I already got dozens of dead TPS61073, all of them having the same problem, SW pin short to GND. This death could happen when VBAT of TPS61073 is just powered up (about 4.1V) by USB 5V with a reverse protection Schottky Barrier Rectifier Diode MSE1PJ, could also happen when it's just enabled. I also got two semi-broken TPS61073, one with a SW pin with just 45ohm to GND (so it gets quite hot), and another one only output about 5V. I think most of the death is with USB powered ones. But I also remember having battery powered death. I don't know if this problem is caused by bad layout, you can check it below.

My design has power from either 5V USB, or a external power 3.3V to 5.5V (for example battery). The 5.5V output is used to power 5V voltage reference for sensors and ADCs. the current load is normally <5mA. So i think most of the time TPS61073 works in power save mode.

Here is the schematic of the power supply module.

My PCB is 4 layer, and here is the layout part for TPS61073:

top layer with via: (what is shown here is PGND for TPS61073 and TPS62261)

 

top components: (The 2Mohm feedback resistor is at left side of TPS61073 connecting VOUT and FB pins)

layer2:

layer3:

bottom layer:

bottom component: (a 0603 0ohm resistor is placed at bottom layer to connect PGND to GND. The 200Kohm feedback resistor is also at bottom layer and it connected to GND pin of TPS61073)

 

I have tried to reduce either input capacitor number or output capacitor number, and put 100Kohm pulldown resistor between EN and GND pins, and also tried to put a 0402 5V zenor diode between SW and GND pins. But after all these, the TPS61073 SW pin could still short to GND sometimes.

So I'm really hopeless now........

 

Anyone has idea why?