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BQ25890: why charge current is smaller than expectation

liping pan
Intellectual 650 points
Part Number: BQ25890

history case:

BQ25890: Input current limit setting - Power management forum - Power management - TI E2E support forums

Actual test result:

1) set REG00 = 0x7F (resistor connect to ILIM pin is 100ohm)
2) set REG02 = 0x9D
3) set REG03 = 0x50
//step 1) ~3) will be repeated every 1.6s to feed watchodg
4) connect VBUS = 5V (D+ and D- short)
5) read REG0B = 0x76 (why bit1 = 1?)
6) read REG12 = 0x09 (why charge current is only reach 450mA? Should be close to default setting ICHG = 2048mA ?)
7) read REG11 = 0x98 (read VBUS, no issue)
8) read REG13 = 0x13 (why input current limit = 1050mA? The REG00 setting is much higher than it)
9) read REG0E = 0x5F
10) read REG0D = 0x12
11) read REG01 = 0x06
12) read REG04 = 0x20
13) read REG06 = 0x5E
14) read REG0F = 0x5F

  • 0
    TI__Mastermind 31140 points

    Hello, 

    Thank you for reaching out via E2E. Please see my comments regarding your observations below. 

    Firstly, You observe charge current at 450mA instead of closer to the ICHG setting because your battery is almost fully charged. If you refer to the Battery Charging Profile (figure 9-5 on page 26 of datasheet) you will see that when battery voltage reaches the VREG threshold charge current reduces until termination threshold is reached. 

    liping pan said:
    why input current limit = 1050mA?

    The input current is likely being reduced from 3.25A setting in REG00 to 1.05A due to the ICO feature. I recommend you check if your input supply can actually supply 3.25A. The ICO (input current optimizer) feature can also be disabled by setting REG02 bit 4 = 0b. 

    liping pan said:
    why bit1 = 1?

    bit1 in reg0b is a reserved bit. The datasheet has a typo saying it will always read 0. No matter if the bit reads 0 or 1 it will not effect device operation. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Intellectual 650 points

    1) I measured the battery voltage is 3.68V (removed external adapter from VBUS). Based on below charge curve, it only reaches about 50%. So it's far away from fully charged.  

    2) After 9 hours charge, battery voltage reaches 3.94V and the charge current drops to 250mA. Anyway, it's too slow.

    3) Additionally, I also check external VBUS input supply limit is 4A, which is much higher than 3.25A.  So the input has enough current capacity to charge.

  • 0 in reply to liping pan
    TI__Mastermind 31140 points

    Hello, 

    Are you performing you test on our EVM or a custom board? 

    Your chart appears to show that battery voltage reaches approximately 4.2V during charge and the read for REG0E matches this. You may have a large amount of parasitic resistance between the BAT pin and your actual battery terminal. The BQ25890 is only able to measure battery voltage at the BAT pin. If during charging that pin reaches VREG the device will reduce charge current until termination is reached. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Intellectual 650 points

    I am using my board, not EVM.

    1) The system current is about 200mA. Even you consider it, it's still far away from 2A.

    2) I also tried with non-host mode and cut off system load, it's the same charge current.

  • 0 in reply to Garrett Kreger
    Intellectual 650 points

    Here is the schematic

  • 0 in reply to liping pan
    TI__Mastermind 31140 points

    Hello, 

    Thank you for providing information on SYS current draw. I have also reviewed your schematic and all looks okay. 

    Please help to share a waveform capture of VBUS, VBAT(measured as close to BAT pin as possible), and IBAT when you observe charge current lower than expected. In the test please cut off system load to eliminate that variable. Please also provide a full register read when you observe the low charge current. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Intellectual 650 points

    I just find the root cause. 

    The wire between battery package and charge IC is too long.

    When I make it short, it works.

  • +1 in reply to liping pan
    TI__Mastermind 31140 points

    Hello, 

    Great to hear the issue is resolved. This is what I was attempting to explain in my first response. The long wire between the charger IC and the battery creates a large amount of parasitic resistance causing a voltage drop between the BAT pin and the battery package when current is flowing. 

    Best Regards,

    Garrett