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BQ76940: BQ76940

mohd imran khan
Intellectual 510 points
Part Number: BQ76940

Hi,

When is read SYS_STAT register from BQ76940 AFE i am continuously getting SCD bit high. Even Though there is no load connected to Shunt register. Can any body Help me with tihs!

Thanks

Imran

  • 0
    Intellectual 510 points
    hi
    I tried after placing 0.1uF disc type ceramic capacitor.
    Now I am able to get discharge voltages at discharge pin of AFE of 11volts. But after 4ms voltage is becoming zero. Since there is no load connected to SRP-SRN pin or to shunt resistor but discharge pin voltage is becoming zero.

    Please help me with suggestions.

    Thanks
    Imran
  • 0 in reply to mohd imran khan
    Intellectual 510 points
    hi
    please find below ripples scan and output scan after filter.
    Still after placing filter relatively near to IC, output is going low after 4ms once discharge bit is enable in control register.

    Thanks
    Imran
  • 0 in reply to mohd imran khan
    TI__Guru 54715 points
    Hi Imran,
    SRN and SRP are inputs and should be connected to GND (VSS) through the filter and through the sense resistor. When current flows through the sense resistor the pins get a signal which is compared to the threshold and converted by the CC if enabled. Be sure the pins are properly connected. Part behavior is uncertain if the inputs are floating.
    Connect the pins and see if the problem goes away. If not you might try changing the threshold or delay for the Protect 2 register to see if there is some influence, although you may notice that 4 ms is not a delay setting.
    You might also check the pins with an oscilloscope to see if they change, and check that power is stable.
    If the part has been damaged due to improper connection, it will need to be replaced.
  • 0 in reply to mohd imran khan
    Intellectual 510 points
    Hi,

    To make current to flow through the shunt resistor, i have to turn on discharge mosfet. for that i need to make discharge pin high. i am able to make volt at dis pin high but it is becoming low after 4 ms. let me check after connecting with battery -ve and +ve with some load.

    Thanks
    Imran
  • 0 in reply to mohd imran khan
    Intellectual 510 points
    Hi,

    I tried connecting -ve to battery -ve and +ve to battery +ve. I converter 48v to 12 v using step down converter and gave bd bulb as load. Still i am facing same problem.
    i tried with different capacitor values at SRP and SRN. At one trial i was able to get the output but it was not repeatable.
    Can you give me some input on this?

    Thanks
    Imran
  • 0 in reply to mohd imran khan
    TI__Guru 54715 points
    Hi Imran,
    The high frequency mV signal does not look good. The capacitor on the sense input should not be as important as the resistor connections. SRN and SRP should look like GND.
    After DSG goes low read the status register to see what fault was registered.
    You can simulate a current by applying a few mV to SRP or SRN. You can leave the filter resistor attached. If you apply positive mV to SRN and cross the thresholds you have set you should see the OCD and SCD bits. SRP must remain at GND.
    You might get a colleague to look at the circuit, sometimes a local consultant very helpful