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Help needed: UCD9240 READ_IOUT reading is not stable

Dimitry Kloper
Prodigy 20 points
Other Parts Discussed in Thread: UCD9240, UCD7230

Hello

I am trying to play with UCD9240 on PR662F prototype board.

I am able to connect and configure the device via TI I2C dongle and TI Fusion Designer. 

The only problem I have is unstable READ_IOUT values.

I connect one of the rails to 20Ohm load, and configure VOUT to be at 2.5V.

My IOUT_CAL_GAIN is set 129mOhm  and IOUT_CAL_OFFSET is set at approximately -4.8A.

While the real current on the load is stable around 128.9mA TI Fusion Monitoring shows the current value

varying randomly from 0 to 0.2A. I tried to set higher load values (up to 1KOhm) and behavior is similar.

I am guessing that I am missing another configuration parameter, can anybody help?

Thanks

--

 Dima

  • 0
    TI__Intellectual 815 points

    Hi Dima,

    Which Power Stage are you using?  Are you using Inductor DCR or R_series for current monitoring?

    I can give an example to show how to calculate the IOUT_CAL_GAIN  and IOUT_CAL_OFFSET.

    Let's take UCD9240+UCD7230 as an example.

    [1] For R_series current sensing.

    I set the series resistor as 2.8mohm and GUI automatically give the results:

    From UCD7230 datasheet, you can see the gate driver's Current sense amplifier GAIN= 48, OFFSET=0.6V

    So The Iout Cal Gain = 2.8*48=134 mohm 

    The Iout Cal Offset = 0.6V/134mohm = 4.4A

    [2] For inductor DCR current sensing

    The calculation methods will be the same, and you just replace R_series with DCR value.

    For this example, my DCR=1.2mohm. And GUI gave the correct results.

    Hope it be useful.

    Best,

    Luke

  • 0 in reply to Luke Lu
    Prodigy 20 points

    Luke,

    Thanks for your answer, it is much appreciated.

    I guess I was not clear about the exact type of the board I am using. It is quite old and I am not able to find a direct link on TI site, but the schematics can be found here. The board has UCD9240 controlling a pair of PTD08A010 on page 3 and 4 and four R2J20602NP devices controlled by pages 1 and 2. I am experimenting with PTD08A010 that sits on rail 4 (tried the one one 3 with same results).

    I have put a screen capture on youtube  trying to demonstrate my problem.

    Thanks

    --

     Dima

  • 0 in reply to Dimitry Kloper
    TI__Intellectual 815 points
    Dima,

    Good to Know which devices you are using. So what is your current sense resistor value? Just as my last reply, We need to know both the device you are using and the current sense resistor value to determine Iout_Cal_gain.
    It seems that no sound from your video on youtube. Have you solved the problem?

    Thanks,
    Luke
  • 0 in reply to Dimitry Kloper
    TI__Intellectual 815 points
    Hi Dima,

    I will suspect your load current is too Low. At such small load, it is difficult to read accurate current. Reading will be more accurate once you add load to 10A or 20A.

    Thanks,
    Luke