• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 62 subscribers
  • Views 178 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TPS73701DRVEVM-529: TPS73701 Over current behavior

Hank Wang3
Prodigy 40 points
Part Number: TPS73701DRVEVM-529

Hi 

I have a question about TPS73701 current limit.

When I was testing TPS73701 OCP, the output current retried as red below.

Is this normal behavior?

Ch1: Vin

Ch2: Vout

Ch3: En

Ch4: Iout

 

schematic:

Thanks

BR,

Hank

  • 0
    TI__Mastermind 33055 points

    Hi Hank,

    The LDO may be unstable.  It looks like the output capacitors are low ESR variants and the design is not following the datasheet guidance.  Please note that there is a typo in the datasheet, it should read "the product of Cout and total ESR drops below 50nF-ohms".

    If it is unstable, you may be able to stabilize it by removing all output capacitors except one 10uF cap.  For 10uF capacitance, this assumes that the ESR of the capacitor is greater than 5 milliohms.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 40 points

    Hi Stephen

    But I had made transient test as below, it seem be stable.

    Ch2: Vout

    Ch4: Iout

    Thanks

    BR,

    Hank

  • 0 in reply to Hank Wang3
    TI__Mastermind 33055 points

    Hi Hank,

    It looks to me like the current limit circuit may be oscillating.  Can you try the same test but with just one 10uF on Vout?  The load transient test is not stressing the current limit loop as that loop is not engaged with the level of current applied in the load transient test data (I'm reading the oscilloscope data as max 280mA current which does not engage the current limit).

    If using just one 10uF capacitor on Cout does not improve these results, then I would also short the L372 ferrite bead on the input, as this looks like a lossy inductor at low frequencies and I want to be sure this is not impacting the stability of the LDO.

    Please respond with your findings.  I will be regularly monitoring this thread.

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 40 points

    Hi Stephen

    I had only used one 22uF cap, but the output current still retried.

    But I tried CCL mode for E-load, the OCP is as below.

    Is this normal behavior? or What will be normal behavior when OCP happens?

     Is current limit of TPS73701 retry or latch mode?

    Thanks

    BR,

    Hank

  • 0 in reply to Hank Wang3
    TI__Mastermind 33055 points

    Hi Hank,

    Are you using an electronic load?  If so, I would recommend retesting with a physical resistor that is switched on using a switch (relay, MOSFET, BJT, etc).  Electronic loads can interfere with the measurement as the control loop of the e-load reacts with the control loop of the LDO.  So what you may have been seeing is the electronic load oscillating, and not the LDO.

    Thanks,

    Stephen