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  • TI Thinks Resolved

TPS73201-EP: The overcurrent limit is over spec

Prodigy 430 points

Replies: 20

Views: 5895

Part Number: TPS73201-EP

Hi expert,

      I got a feedback from customer talking about overcurrent limit of TPS73201-EP.

      In the datasheet, there is a range of it, which is 250mA ~ 600mA.

      You can see the waveform captured by customer, it is limited by 634mA which is over spec.

      Can you explain how does it happen? It is a 5V to 3.3V design.

      Thanks a lot.

Best regards, Cage.

  • Hello Cage,

    The 250 - 600mA limit is tested for Vout at 90% of intended value. It sounds like this is only a maximum spec under these specific conditions. The short circuit current value only gives a typical value of 300mA (i.e. no max short circuit current).

    Can you describe the waveform to me a little more to better help me understand? It looks like Vout is at 2V when it should be set to 3.3V (as per your comments about the design). What is the output load at this time? Also, what causes Vout to drop to 0V? Any help understanding the circuit and what's changing during the waveform would be useful.

    Thanks,
    Kyle
  • In reply to Kyle Rakos:

    Hi Kyle,

         It is tested by EVM. As below picture.

         And the Vout was 3.3V until customer applied a load on it.

        And Vout went down to 0V when the current increased to 634mA.

        Ch1 is Vout, and Ch4 is Iout.

        Thank you.

    Best regards, Cage.

  • In reply to Cage Chen:

    Hi Cage,

    So to clarify, the waveform shows Vout sometime after the load has already been applied that causes too much current? Are you able to upload a waveform the first time the load is applied? In other words, can we see Vout at 3.3V and what happens after the load is applied.

    Thanks,
    Kyle
  • In reply to Kyle Rakos:

    Hi Kyle,

         Here is the waveform at beginning of load increasing.

         For your reference.

    Best regards, Cage.

    CH1: Vout, CH4: Iout.

  • In reply to Cage Chen:

    Hi Kyle,

    Sorry that the Vin should be 3.3V, and Vout is 3V.
    Customer is asking how do we specify the range of Over current limit in datasheet?
    In the datasheet, it shows Vout=0.9*Vout(normal), in this case, the Vout normal is 3V, so it should be limited when Vout drops to 2.7V.
    But in this case, Vout dropped to 2V to cause protection.
    Could you explain it?
    Thanks a lot for your help always.

    Best regards, Cage.
  • In reply to Cage Chen:

    Hi Kyle,

    Do you have any update for this issue?
    Customer is pushing hard!
    Thank you.

    Best regards, Cage.
  • In reply to Cage Chen:

    Hello Cage,

    Sorry for the delay. I'm still looking into this and I hope to have a response by tomorrow.

    Thanks,
    Kyle
  • In reply to Kyle Rakos:

    Hello Cage,

    I would like to clarify what I previously said about the output voltage. The output current limit was tested with Vout set to 90% of Vout(nom). This is just a test condition, not something that will occur (i.e. Vout won't necessarily go to 90% of its nominal value).

    So the only potential concern we see in the waveforms is that the current is above 600mA at some point. Could you clarify how the customer is measuring it? Sometimes current probes have offsets that cause inaccurate measurements . Also where is the current being measured? Ideally it would be the current out of the device, not the device plus output capacitor. The capacitor could be adding current to the output that the IC doesn't sense.

    Thanks,
    Kyle
  • In reply to Kyle Rakos:

    Hi Kyle,

         Customer use a current probe to measure the current after capacitors.

         It is a 3.3V to 3V design, which means the current limit should at 3V*0.9=2.7V.

         But from the below waveform, you can see the Vout didn't drop to 0 immediately when Iout is over 600mA.

         The current limit behavior of TPS73201-EP is latch or what kind of action when TPS73201-EP is at current limit condition?

         Thank you.

    Best regards, Cage.

    ps, I will also ask customer to remove capacitor to see if it improves or not.

    ps, if it is possible you can also take an EVM to duplicate it?

  • In reply to Cage Chen:

    Hello Cage,

    Could you make sure that the current probe is properly calibrated? Oftentimes these probes have offsets and this could account for the current difference from 600mA.

    The current limit will not be set to 90%. That is just a test measurement condition. In other words, the current limit test was done when Vout is 90% of its nominal value. When current limit is hit Vout will drop to whatever it needs to in order to stay under 600mA.

    Unfortunately I do not believe there is an EVM for this device.

    Thanks,
    Kyle

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