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BQ25703A: BQ25703A charge current

Jonas
Intellectual 540 points
Part Number: BQ25703A

Hi

my customer have used BQ25703A in their new project . but have some question need consult.

1.  at the first, we can not charge normal at the EVM. But after we select the RESET_VINDPM, the charge function is normal. But why ? why this register  is enable or disable charge register ? the charge test discription have  no information is about this ,in EVM user guide

2. After we can charge, we find the real charge current is 200mA higer than setting current, example, we set 1024mA charge current, but we test 1224mA charge current at customer board. below is customer schematic. please help analysis.

3. About the charge efficiency, at customer board, we test the efficiency is only 80%, but we select the EN_IDPM and setting the DPM current, then the efficiency can arrive 85% ? why this register can increase efficiency ?  the MOS Rdson is about 5mohm, what other way we can use to improve the efficiency to 91% as EVM  ? 

thanks a lot

Jonas zhang

  • 0
    TI__Guru 56650 points

    1. BQ25703A check the input voltage For Vindpm setting when the adapter is plug in. If the input voltage is not stabilized after input source plug-in about 40ms, the Vindpm setting could be wrong. The value can be read out from Vindpm register.

    2. Please measure the Vsrp-srn near the charger IC. I want to make sure it is not sensing issue.

    3. BQ25703A doesn’t support 5mohm input current sensing resister. Please use 10mohm sensing resister. The same converter could have different efficiency with different load current, input; output voltage and operation mode (PFM or PWM). Yes, if you set the input current limit, you may change the operation current and get different efficiency number.

  • 0 in reply to Wang5577
    Intellectual 540 points

    Dear Wang:

    Thanks for your reply

    ==>1.  we use DC source as input power, I think it's stablility. I think VINDPM can disable, if we don't want use DPM function, right ? If yes, why RESET_ VINDPM can enable or disable the charger function, I also can not unstand.

    ==>2. VSRP-SRN, we check the sense resistor and the capacitor. we found that they are faraway with IC on the EVM EVM, not near IC, so we not attempt this point at customer board. but we will advice customer place them close to  IC as possible.

    ==>3. we use 10mohm current sensing resister. not 5mohm. And we setting the GUI sofware at the same register, when we test and compare their efficiency. 12V input, 8.4V 1024mA charger output.

    Jonas zhang

  • 0 in reply to Jonas
    TI__Guru 56650 points
    1. If Vin<Vindpm, the converter is off. When you RESET_VINDPM, Vin>Vindpm. Please check the input voltage start up waveform and verify the vindpm register value to confirm it.
    2. Charging current sensing resistor can be put a little bit far from the IC. So, we need Kelvin connection. If any charging current passes the SRP or SRN sensing wire, that may cause the regulation error.
    3. The same converter could have different efficiency with different load current, input; output voltage and operation mode (PFM or PWM). Yes, if you set the input current limit, you may change the operation current and get different efficiency number. What is your test condition with 80% efficiency and 85% efficiency?
  • 0 in reply to Wang5577
    Intellectual 540 points

    Dear Wang:

    ==>3. 80% test condition: 12V input, 8.4Vcharger voltage and 1024mA charge current.no setting IDPM. 85% test condition, 12V input,8.4V charge voltage. And setting IDPM, and IDPM current limit set to 1024mA, and set the charge current>1024mA, but the real charge current to battery is 1024mA for IDPM limit.

    thanks

    Jonas zhang

  • 0 in reply to Jonas
    Intellectual 540 points
    Wang:

    EN_OOA bit is setted to low.
  • 0 in reply to Jonas
    TI__Guru 56650 points
    Jonas:

    The test conditions of "setting IDPM" are not true. 12V 1A input; 85% efficiency and 8.4Vout, what output current should be? You said, "the real charge current to battery is 1A". So, 12V*1A*0.85= 10.2W It does not equal 8.4V*1A=8.4W.
    One of your condition is not true. Please use real meter to measure the input voltage, input current, output voltage and output current. The efficiency number can not use your setting number to do the calculation. Or, you may get efficiency higher than 100%.
  • 0 in reply to Wang5577
    Intellectual 540 points
    Dear Wang

    You're right, I remeber wrong input current data. And now we closed this issue by change the PMOS. they can test 93% efficiency at charger mode.

    thanks for you special reply. thank you.

    Jonas zhang