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TPS63900EVM: and TPS63802: Quiescent current much higher than specifications

Part Number: TPS63900EVM
Other Parts Discussed in Thread: TPS63900, , TPS63802, TPS63802EVM

Hello,

I am conducting a basic prototyping test for TPS63900 using the evaluation board TPS63900EVM.

  • The switches on the evaluation board are configured for an output of 3V and unlimited current.
  • Loads I have tried connecting to VOUT: my IoT device, a large resistor, my multimeter set to read current, and an open circuit.
  • Power sources I have tried connecting to VIN: a power supply set to various levels between 2V and 3.5V, and a 3.5V battery.

In all cases, the average current drained from the power source is several hundreds of uA higher than expected. For instance with an open circuit, I would expect to see roughly the specified 1uA iq, but instead 360uA are drained.

Note: The same tests conducted using TPS63802 yield similar results.

What could cause the EVMs to drain so much current regardless of the load? Is it possible that I could have incorrectly set them up in a way that causes a leak? Or is this behavior perhaps normal?

Thanks in advance,

Frank

  • Hello user6375055,

    Please check the topside marking of the EVM.

  • Thanks for your reply,

    Can you elaborate? What exactly should I be looking for in the topside markings that relates to input current?

    Frank

  • Hello user6375055,

    Please check out the caution box on page 4 of the TPS63900 datasheet. I expect that you have X-marked silicon on your EVM of TPS63900. This could be the root cause for the increased input current.

  • Hi Brigitte,

    Thank you, that was helpful. You're correct, there is an X639 marking on the TPS63900 chip itself.

    I think this explains most of the increased input current but not all. There is an additional behavior that occurs not only with the TPS63900EVM but also with the TPS63802EVM.

    Input current spikes periodically in synchonization with the output voltage's sawtooth waveform. Due to this, the average input current is bumped up significantly.
    Please see the attached image showing input current and output voltage over about 150 milliseconds. These measurements were taken using TPS63802EVM with an input voltage of 3.5V and an output current of 1uA.

    Thanks again,

    Frank

  • Hello Frank,

    This is normal behavior with no load. The device is switching only for a few cycles and goes then again to sleep until the output voltage is falling below the minimum level. Then it switches again for some cycles.

    The quiescent current in the datasheet is defined not switching, so thequiescent current in the system is the current at the time when the device does not switch plus the averaged current spikes.

    So the quiescent current on the EVM of TPS63802 is higher than 11uA. The same is valid for the TPS63900 (it is higher than the specified value), but TPS63900 has a very good efficiency for low output currents. Please check out this thread for efficiency from 1uA onwards:

    If you order PTPS63900 samples, you will get the new material.