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TPS564208 problems

Giuseppe Scarpi
Prodigy 110 points
Other Parts Discussed in Thread: TPS564208, TPS564201

I asked this question before, with no answer. I will try and reformulate it more clearly and with more details.

We are experiencing a strange and so far unexplained behaviour with TPS564208.

Our customer uses it to supply a Raspberry PI 3 and a 7" LCD with a 5V, 2.5A. Input voltage is either 12V from external supply, or 7.4V from a battery.

As an emergency measure, in case the RP3 hangs, he put a "reset" microswitch in series with the supply, to disconnect/reconnect both devices (I know... using the ENABLE pin would be more logical).
In several cases, this "reset" destroys the TPS and not always in the same way: short circuit between SW and VIN, or between SW and GND, or SW floating near 0V.

We performed many tests attempting to reproduce the problem, with no success. Among the tests we simulated the "reset" procedure cutting an external 2 Ohm load with a relay, but after 500 cycles the TPS was still very alive.
We also tried with inductive and capacitive loads, or short-circuiting the output... and TPS was still alive.

The external supply is (in my opinion) underpowered. When the loads are connected, VIN may drop a few Volt. The input voltage is still enough to produce 5V output, yet I wonder if such a suddenly drop can cause problems.

Can you suggest something?

  • 0
    TI__Prodigy 575 points

    Hi,

    what do you mean by disconnect/reconnect both devices?

    do you mean there might be a certain period of time that the TPS's input is floating while Vout still remains?

    if that's the case, we met some issue before that when Vin is floating, and Vout exists, the IC won't shut down, and it functions as a step up (boost) converter, and Vin will exceeds max Vin and damage the IC.

    Best Regards,

  • 0
    TI__Prodigy 575 points
    I suggest you to use TPS564201 and try it again, the reason behind is TPS564208 is FCCM mode, which means reverse current can flow, so when the IC is configured as a boost, ouput is new Vin, input is new Vout, current can flow from output pin (new Vin) to input pin (new Vout);

    but for TPS564201, it's eco-mode, won't allow reverse current.