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TPS57160-Q1: Power sequencing requirements?

Leong
Expert 1070 points
Part Number: TPS57160-Q1

Hi, we have a new board built with TPS57160-Q1 for buck operation. In the initial test bypassed the input but directly applied 30V on the PH output (at the load side, so there is an inductor between the 30V and PH pin) to test later stages. right after the 30V is applied, the chip failed by shorting to ground (later measured 7 ohm between ph to gnd). 

we looked at the circuit (pretty much the same as the datasheet figure 51, with more capacitors on the input and higher inductance) and the internal diagram but we could not see how there could be a path to short to ground.

after removing the part, we shorted the PH with Vin and tested the voltage rise and current there was no overshoot (<31V) or high current pulse (very short 25ns pulse on current to back charge the input caps). 

Can anyone point out if there is power sequencing requirements for this part? if possible how it might fail if voltage is applied on PH pin without other pins or inputs being powered?

thanks

  • 0
    TI__Mastermind 22301 points

    Leong,

    There is a parasitic diode  from PH to VIN on the high side MOSFET, so if the PH voltage is higher than the VIN voltage it will conduct uncontrollable reverse current and blow that FET.

    I suspect when you applied 30V to the output and left VIN pin floating, reverse current started flowing to charge up the input capacitors.

    I dont know why it would short PH to ground, but definitely the VIN to PH FET was destroyed and it could have damaged surrounding circuitry.

    Hope this helps,

    -Orlando

  • 0 in reply to Orlando Murray
    Expert 1070 points

    Orlando,

    thanks for the hint. yes we were suspecting the diode too.. but the input caps are fairly small totaling 7uF. The power supply was a linear supply not that fast when turning on. it was measured like 1ms to 30V. given I=C dv/dt it would be on the order of hundred mA. and this is a 1.5A part.. 

    another question mark is on the boot strap. since there is no input voltage, the voltage between boot and PH would be reversed.. is the internal circuitry capable of handling this? i see an 8V max voltage between boot pin and PH pin in the max electrical rating table but it does not say about reverse. 

    I've ordered a few more parts to do some experiments.. will report later.. any ways, is there suggestion to protect under such operation?

    thanks

    regards

    Leong

  • 0 in reply to Leong
    TI__Mastermind 22301 points

    Leong,

    It could also be damage to the gate driver push-pull (BOOT-SW) output.

    I'm still not sure how that would short PH to gnd.

    If you have tolerance to blow up more boards maybe you can run the test again and tying BOOT and SW together?

    -Orlando

  • 0 in reply to Orlando Murray
    Expert 1070 points

    thanks Orlando, it might be the combination of a few parts blown that affects the rest since it is such a small package..