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TPS7H1111-SEP: Circuit for Bode Plots

David McLaren
Prodigy 50 points
Part Number: TPS7H1111-SEP
Other Parts Discussed in Thread: TPS7H1111EVM-CVAL,

Hello. The TPS7H1111EVM-CVAL board has a 51 ohm resistor between the voltage output and OUTS pin for Bode plot measurements. The TPS7H1111 datasheet (Section 8.3.8) states that any such resistor should be replaced with a 0 ohm shunt during nominal operation. Can you confirm that this is required, rather than leaving the resistor in place during nominal operation? If this is the case, how will the results I see with the evaluation board be affected by the 51 ohm resistor and should I replace this with 0 ohms for my other measurements?

When using two parallel TPS7H1111-SEP devices with current sharing, are there any other considerations to be taken into account when taking Bode plot measurements, or is it sufficient to take the measurements for each device separately using a resistor between OUT and OUTS for each device?

Thanks,

David

  • +1
    TI__Genius 9750 points

    Hi David,

    The main reason we recommend removing the injection resistor or replacing with a 0-Ohm shunt when not collecting Bode plots is because it can introduce noise to the output. The device was designed, tested, and characterized with the intention of no resistor between OUT to OUTS during nominal operation, so it is also generally good practice to use this configuration for testing.

    We have not collected any physical data comparing parallel-device bode plots against bode plots of single devices operating under the equivalent per-device conditions, so I can't make any conclusive statements, but it seems plausible that your idea of testing individual devices to confirm stability could work. We focused on defining and ensuring the stability of a single device and would expect it to extend to parallel devices. You could also perform a load step of the parallel configuration as a sanity check, which would be a little easier to setup.

    Thanks,

    Sarah

  • 0 in reply to Sarah Koch
    Prodigy 50 points

    Hi Sarah,

    Okay, that's all clear. Thanks very much for your help.

    David