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TPS62130: after deasserting EN, Vout stays somewhat on

Daniel Schroll
Prodigy 20 points
Part Number: TPS62130
Other Parts Discussed in Thread: TPS62135, TPS63710

The TPS62130 is used for a 3V3 power rail sourced from 12V. A pushbutton-controller drives the EN pin of TPS62130 (internal open-collector, that drives the net down to GND in disabled mode, a 100k resistor pulls the net to 12V. Some other voltage regulators are controlled by the PG output.

On Startup everything looks ok. 12V is applied and all regulators stay of. When the pushbutton is pressed, the EN net is asserted to approx 10.5V. All regulators turn on and generate the correct voltages.

When the Pushbutton is pressed again, the pb-controller correctly deasserts EN to about 40mV. But the PG and Vout are rippeling around 2.1V:

Why doesn't TPS62130 shut down gracefully?

  • 0
    TI__Guru**** 150650 points
    Hi Daniel,

    Can you also look at the SW node on the scope? It probably has the same signal. This indicates that the TPS62130 is indeed off (SW is not going from Vin to GND) and that something else is applying a voltage to its output. This is very common in multi-rail systems. See this app note, which touches on this topic: www.ti.com/.../slyt689.pdf

    In any case, I would recommend the newer TPS62135/6 over the TPS62130. These devices also include output discharge.

    Finally, it looks like you have a negative voltage in your system. Did you already find TPS63710 as a very low noise way to create this directly from the 12Vin?
  • 0 in reply to Chris Glaser
    TI__Guru**** 150650 points
    Hi Daniel,

    Were you able to look at the SW signal and reach a conclusion on this?
  • 0 in reply to Chris Glaser
    Prodigy 20 points

    Hi Chris,

    sorry for not responding on time;)

    The SW signal looked exactly the same, as you thought. In the meantime, i found the problem: a regulator, that has its EN input connected to PG has an internal Pullup. That Pullup induced the Voltage into PG, that has its pullup to VOUT. I found this, because PG had a slightly higher DC offset.

    On the six prototypes, i fixed this with a n-mos, that pulls the PG-line to GND, when the PBC output EN is low.

    Thanks for your tips. They helped a lot!

    greetings Daniel