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TPS54233: Low current operation

AmundF
Prodigy 50 points
Part Number: TPS54233
Other Parts Discussed in Thread: TPS54332

Hi, I'm currently using your converter in an 18V battery power application that needs to be able to enter a UVLO state. With the current implementation, an MCU will disable all components connected to the output of the converter (at 3V). The 3V rail will therefore only be loaded with about 70 µA. Is the TPS54233 able to deliver a steady voltage at such low currents? How do I best determine this?

If the TPS54233 is not able to deliver for such small loads: Using the enable pin of the converter to turn it off has been considered, but is not ideal as this would either cause a large hysteresis or have an overly large current consumption from the battery. Are there some circuit that can be added here to avoid these issues.

Best Regards

  • 0
    TI__Guru 53815 points

     

    When the TPS54233 detects a switching cycle with a peak inductor current less than 100mA, the TPS54233 will enter into pulse skipping mode to reduce switching frequency and losses.  The high-side driver is design to operate at 100% duty cycle with BOOT to PH as low as 2.1V.  The internal 6-V gate-drive voltage regulator of 6V should maintain sufficient BOOT voltage even at 100% duty cycle with VOUT = 3V.

    The ripple voltage in ECO mode will typically be higher than that at steady-state, so if the output is sensitive to AC ripple voltage, you'll want to check that with your design to minimize bursting when operating at extremely light load.

    Disabling the TPS54233 and using it's 1μA shutdown would be preferred if the 3V output does not need to be maintained   For the lowest possible shutdown, a P-channel MOSFET can be connected in series with the VIN to EN resistor, with it's gate pulled low to turn it on and pull up on EN and it's gate allowed to float to VIN when OFF.  This generally adds an N-channel MOSFET, P-channel MOSFET and two biasing resistors, but it prevents the EN divider from sinking current when placing the TPS54233 into disable.

  • 0 in reply to Peter James Miller
    Prodigy 50 points

    Hi, thanks for the rapid and great reply!

    I would like to use the 1µA shutdown, as you mention, but I was a bit imprecise regarding the MCU in my original question. The MCU in my design is powered by the TPS54233, which means the system will, as far as I understand, not be able to reboot after turning off. It would be preferable if the system is able to turn back on when the battery voltage rises above a certain threshold. 

  • 0 in reply to AmundF
    TI__Expert 7520 points

     

    I would like to add some comments from my side here:

    1. What is the input of the TPS54233? Is it battery/adapter? What is the lowest input of TPS54233?

    2. Since the TPS54332 is supplied to the MCU, you may check the operation voltage of the MCU. Just as Peter said, the ripple voltage in ECO mode will typically be higher than that at steady-state, an EVM of TPS54233 will help you check the AC ripple. What is also important is that, when MCU turns off all the other components, there would be a load transient here. When the load of TPS54233 changes from heavy to light, there should be overshoot and undershoot on the output voltage. If the the overvoltage is above the absolute operation voltage of the MCU, it would damage the part. If the under voltage is below the operation voltage of the MCU, the MCU won't work normally.

    Hope this helps. 

    BR

    Ruby