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Damaged TPS62160?

alex pabouctsidis
Prodigy 140 points

Hello again,

Reminder: We are currently using the TPS62160 in our designs for both 5V and 3.3V. You can find the schematics and layouts in a previous post here:  

e2e.ti.com/.../481722

We've come across another strange issue with our 3.3V power supply on one of our boards.

When powered with a 12V power supply, the 3.3V DC/DC fails to output the correct voltage. Instead i measured 5.50V. Furthermore, if i reduce the input voltage, the output voltage also reduces. There seems to be a linear relation between Input->output voltage. Some measurements:

Vin -> Vout

12V -> 5.5V

10V ->5.25

8V ->  4.4V

6.5V -> 3.38V

6V down to 3.3V -> 3.3V

What is even more surprising, is that once i reach ~6V, the DC/DC Starts to switch, and the output voltage is the correct. Furthermore, in the "operating region" (6V to 3.3V), the switching signal, output voltage, feedback voltage, all look correct.

Once the voltage was at the correct 3.3V, i could flash the MCU (i was supprised to see that it still works..) on our board. Doing so increases the load current by about 40mA. after doing so, the DC/DC would work for the entire input voltage range 12.5V to 3.3V.

I'm not sure what to make of this. I'm assuming that the DC/DC is damaged, but cannot understand why or how.

Any help would be most appreciated!

Thanks,

Alex 

  • 0
    TI__Guru**** 150900 points
    So, with the higher voltages what was the SW node doing? Can you post a waveform of Vin, SW, Vout, and EN at 12Vin?

    Does this happen on more than 1 PCB? Sometimes manufacturing errors (too much solder) can short things.
  • 0 in reply to Chris Glaser
    Prodigy 140 points
    Chris,

    This has only occurred on one PCB.

    At higher input voltages, the SW node is flat with a constant voltage, which is the same as the output voltage.

    At Vin = 12V, i get 6V on the SW and Vout. EN directly connected to Vin, so it's at 12V as well. All these voltages are flat and clean. There is no switching anywhere.

    An assembly problem would make sense, but visually it looks fine. I also look for a potential short circuit under the chip with a multi meter, but didnt find anything either.

    Regards.
    Alex
  • 0 in reply to alex pabouctsidis
    TI__Guru**** 150900 points
    Since SW is not switching and is just following Vout, the higher output voltage is coming from outside the IC--it is being applied to the output somehow. Since it is just 1 PCB, there is likely a short somewhere.