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BQ25703AEVM-732: BQ25703A

Babar Khan
Prodigy 205 points
Part Number: BQ25703AEVM-732
Other Parts Discussed in Thread: BQ25703A, BQ25703

Currently i am evaluating BQ25703A for our application. i have the demo board BQ25703AEVM. i have few question related to the part.

1)  The datasheet says “Charge 1- to 4-Cell Battery from Wide Range of Input Sources and Battery voltage regulation 1.024 - 19.2 V”. our design spec for 5 * AA NiMH (1.5V per cell) so, the Battery voltage would be 7.5V in total. would it be ok to use this part for our product.

2) i have set the BQ25703A for 1 cell 4.2V Li-ion but i can not read the charge and discharge register on Battery Management Studio v1.3.72 . i could read Vbus, Psys,VBat etc

3) whats the purpose of ILIM_HIZ pin.

regards 

Babar

  • 0
    TI__Guru 56650 points

    1. 7.5V battery voltage should be OK. Please set CELL_BATPRES to 2S setting to avoid one cell setting SYSOVP.

    2. If the communication is normal, you should be able to read 0x02H  charge current register. To read charge or discharge current read back register 0x28H, please also check the charge option 2 (0x32H register): IBAT_SEL bit.

    3. ILIM_HIZ:

    a. Limit input current (See datasheet: 8.6.6.1 Input Current Registers).

    b. HIZ mode  (See datasheet: 8.3.2.4 Device Hi-Z State)

  • 0 in reply to Wang5577
    Prodigy 205 points
    1: so you mean having 7.5V Vbat is fine even with 5 cells - AA batteries (1.5V each)?
    - setting it to 2S setting would be fine in term of the charge voltage requirements for 7.5 V cell pack ?
  • 0 in reply to Babar Khan
    TI__Guru 56650 points
    I mean if CELL pin is one CELL setting, the SYSOVP is around 5V. So, it cannot charge the output voltage to 7.5V.
    With 2S setting, the default charge voltage is 8.4V. You can change it to 7.5V before enable charge.
  • 0 in reply to Wang5577
    Prodigy 205 points

    Thanks

    i am still unable to read the Input, charge and discharge currents. i am able to read the voltages but not currents.

    on ADC Option i did enabled the ADC_ICHG and IDCHG but still unable to read it.

  • 0 in reply to Babar Khan
    TI__Guru 56650 points
    bq25703 converts all ADC channels to the register value at one time. If you are able to read the voltage, you should be able to get the current value.
    Would you check the IBAT and IADPT voltage? The charger runs into PFM mode at light load. But, the ADC converter doesn't take the average current value. When ADC convert starts, the charger switching FETs may be off and the current could be zero.
    Would you increase the system load to make the converter run at PWM? And then, read the voltage and current again.
  • 0 in reply to Wang5577
    Prodigy 205 points
    i have increase the System load and started to read the Input current.
    i tried to set higher charge current (Charge Current Register) but it doesn't change. its goes back to the default setting 128mA.
    i am getting
    IBAT = 0mV
    IADPT = 29mV
    thanks
  • 0 in reply to Babar Khan
    TI__Guru 56650 points
    That answers why you can read out charge current or input current issue because they are zero or almost zero.
    The issue is a not ADC issue. It is charger current register reset issue. So, when you read the current, please check the charge current is reset or not. Also, please read the charger status register to help us find out the issue.
  • 0 in reply to Wang5577
    Prodigy 205 points

    i have got another issue.

    When main supply is disconnected (Powered from Batteries) i am unable to read the registers and the Biasing voltage 3V3 is not regulating if VBAT is below 4V.

    thanks for the support 

  • 0 in reply to Babar Khan
    TI__Guru 56650 points

    Let us start a new threat with this new issue. Please send me the SCL and  SDA waveform. And  then, we can debug where the issue comes from.

  • 0 in reply to Wang5577
    Prodigy 205 points
    do you want just the read waveform of the SCL and SDA lines?