• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 534 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

TPS43060: VIN Brownout behavior

SteeVeeDee
Intellectual 700 points
Part Number: TPS43060
Other Parts Discussed in Thread: TPS43061, LM5069

We have a scenario where the TPS43060 is on a fully biased, operating properly.

Vin = 28V, Vout = 51V, up to 5A of output current.  The TPS43061 is powered separately by 12V bias rail, i.e. pin 7 = 12V.

Vin is momentarily glitched due to an erroneous cut-out of an up-stream hot-swap controller (LM5069), and afterward we find that the TPS43060 is dead.

I suspect that the glitch is lasting only a few milli seconds, and during the glitch the EN of TPS43060 is held high constantly. 
This glitch is related to the bouncing of a switch, and may not be a single event, and not consistent.

Under these conditions, the output capacitance (~50 uF) is probably not fully discharging, and when Vin comes back, the regulator is now facing a pre-biased but browned-out output voltage.
I imagine that the error amp is likely railed high trying to compensate, the SS is not reset, and when Vin comes back it takes some time to close the loop again. 

Can you provide any insight into how the TPS43060 will behave under these circumstances?

I would think that cycle-by-cycle current limiting would protect the device? 

We will update the design to clean up any bouncing, but we would like to better understand what happened that blew up the device.
Also, upon reviewing the design, I see that we are missing the required Rcharge = 2 Ohm resistor in series with the bootstrap diode.

We will fix this as well, but I mention it in case it is important to this issue.

Thanks, Best, Steve

  • 0
    TI__Guru* 78440 points
    Hello SteeVeeDee,

    Thank you for using the LM43060. The TPS43060 has zero crossing detection circuit built in, that prevents negative current from flowing backwards. Hence the output prebias condition should not be a concern.

    Not seeing your circuit so we cannot easily tell what is really the root cause for the damage. The 2 Ohm Rcharge is recommended to prevent overcharge of the BOOT capacitor, but it is not always necessary for a clean layout. Reserve a position on PCB is a good practice.

    Thanks,
    Youhao
  • 0 in reply to Youhao Xi
    Intellectual 700 points
    After further consideration, I think what is happening is that since the TPS43060 is powered from a separate bias supply, when VIN drops out it increases the duty cycle accordingly, and may be maxing out the error amplifier and compensation and duty cycle. When VIN suddenly comes back on, it takes time for the loop to respond and reduce the duty cycle. During the transient the output voltage is probably over-shooting its target value, and we end up exceeding the 65V maximum rating on the bootstrap pin.