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TPS65023B: How to best measure current on each PMIC rail?

Bob C
Intellectual 615 points
Part Number: TPS65023B
Other Parts Discussed in Thread: INA3221,

Hello,

We have the TPS65023B designed into a board and need to determine current on the three VDCDC rails. 

I don't see an I2C register to do this.  I know there have been undocumented registers with other TI parts.  Is there a way to determine current by reading the I2C registers?

If we can't use I2C to determine current, then what's the TI recommended way to measure current with a scope & voltage probes using  measurements across the inductor and cap? We're using the same topology as shown in the first page of the datasheet and used on the TPS65023B EVM.

Thank you,

Bob

  • 0
    TI__Mastermind 30280 points

    Bob,

    There are no I2C registers to measure load current for the TPS65023B. The load current is typically measured using a 5mOhm resistor placed after the output capacitors, and the measurement is typically taken with an INA3221 or similar current sensing device.

    Since this is not possible on your board, it may be possible to lift one end of the inductor to place a short blue-wire. This would allow you to use a current probe.

  • 0 in reply to Brian Berner
    Intellectual 615 points

    Thank you Brian.  I was hoping I could estimate / determine the load current by measuring the duty cycle and inductor voltage waveform (or something like this).  However, I may not have enough information to do so due to the internal transistors in the PMIC.

    Please let me know if you have any advice or ideas on how this might be done

    Thanks again,

    Bob

  • 0 in reply to Bob C
    TI__Mastermind 30280 points

    Bob,

    In order to do what you are suggesting, you would need to first perform these measurements on a TPS65023BEVM-664 using a controlled load current (electronic load or power decade resistor box).

    First, you would need to find out the PFM-to-PWM transition point for each DC-DC under the same input/output voltage conditions.

    Then, in PWM mode you would need to carefully monitor the pulse-width (duty cycle) vs. load current. Using these measurements from a control test, you could loosely apply these to your own circuit to estimate the load current.

    In fPWM mode it would be very difficult at low currents (<100mA) to estimate the load current because some of the current is being sunk through the low-side FET.