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BQ24157: BQ24157 initialization..

Marat G96
Prodigy 60 points
Part Number: BQ24157


Hello.
I'm trying to configure the BQ24157 chip - but it still does not work. The charge current does not rise above 30 mA. Writing data to the register 0x06 does not work - I read its contents after writing, but it does not change, it always has a default value. I tried to write data to this register immediately after the reset, as it is written in the datasheet, but it still did not work.

I want to configure BQ24157 for the following conditions:
Rsense = 68 mOm, Icharge = 550 mA, BatteryRegVolt = 4 V.
My battery has a capacity of 860 mAh, voltage 3.7 V.

Please tell me in which sequence you need to write data to the registers and which data you need to write.
Thanks!

  • 0
    TI__Guru**** 171436 points
    Hi Marat,

    So sorry for the trouble. The safety limit register must be the first register written too after V(BAT) rises above ~ 2V. This is documented in the footnotes until the 0x06 register table on page 29. This includes writes to the watchdog timer. Please note that you must continually write to the watchdog timer or all registers revert to default values, including BATREG which is default 3.54V.

    Regards,
    Jeff
  • 0 in reply to Jeff F
    Prodigy 60 points
    Jeff, thanks.
    1) Write to the register 0x06 really should be immediately after power. I recorded after the reset, so nothing worked.
    But there is one caveat - I write 0xFF in the 0x06 register, but I get 0x7C when reading. Why?

    2) In the first message I asked, if possible, to give an example of configuring BQ 24157. I repeat my request :)
  • 0 in reply to Marat G96
    TI__Guru**** 171436 points
    Hi Marat,

    Regarding 1, as mentioned in the footnotes to the register table on page 29, the safety limit register values limit charge current to 1.25 A for 68mohm resistor (37.4mV offset+13.6mV+54.5mV=105.4mV) and charge voltage to 4.44 V (additional 160mV+80mV on top of default 4.2V). This corresponds to 0x7C.

    Regarding 2, I don't have an example but can suggest the following:
    1. Immediately after CSOUT rises above 2.0V (either battery plug in or VBUS plug in), write your desired maximum charge current and charge voltage to 0x06.
    2. write the watchdog timer bit
    3. write register 0x05 bit5 = 1 to set to normal charging per register 0x04
    4. write input current limit setting in register 0x01 bits 6:7
    5. write battery regulation voltage in register 0x02 (clamps to setting in register 0x06)
    6. write battery charge and termination current in register 0x04 (clamps to setting in register 0x06)

    Repeat 2 above at least every 30 seconds. If large transients are expected that could result in in V(CSOUT) dipping below 2.0V, thereby resetting the safety limit register, many customers repeat 1 above just before the watchdog timer write.

    Regards,
    Jeff
  • 0 in reply to Jeff F
    Prodigy 60 points
    Thanks, Jeff, your example helped. Now the battery is charging, but so far I have not managed to ensure that the charge current was above 1.1 Amperes. Jeff, do I understand correctly that I can not regulate the charge current directly? Can I set only the upper limit (the maximum possible current) and the lower limit?
  • 0 in reply to Marat G96
    TI__Guru**** 171436 points

    You can regulate charge current as long as:

    Input current hasn’t been reached

    Input voltage at charger input pin hasn’t dropped to the VinDPM threshold

    Battery voltage at the charger hasn’t reached the battery regulation voltage

    The last two can happen due to resistive connections to the IC.  The data sheet calls VinDPM special charge voltage.

  • 0 in reply to Jeff F
    Prodigy 60 points

    Jeff, thanks for the help.

    I already understand better how to configure BQ4157.

    There is another question - in paragraph 9.5.3 of the datasheet, the process of charging the battery is described and it says: "If termination is enabled, during the normal charging process with HOST control, once the voltage at the CSOUT pin is above the battery recharge threshold, VOREG - VRCH for the 32-ms (typical) deglitch period, and the termination charge current ITERM is detected, the IC turns off the PWM charge and enables a discharge current, IDETECT, for a period of tDETECT (262-ms typical), then checks the battery voltage."

    Is the Voreg voltage the value in register 0x02?
    What is Vrch?

    I did not fully understand the condition under which the battery charge should stop.
  • 0 in reply to Marat G96
    TI__Guru**** 171436 points
    Hi Marat,

    Yes, VOREG is the value in register 0x02. VRCH is a fixed voltage amount (100mV-150mV) to which battery must discharge (relative to VOREG) before the charger will automatically start to recharge. For termination to occur the charger's CSOUT pin = VOREG-VRCH and the current sensed across the RSNS must be below the ITERM setting. If you have system load in parallel with the battery that is drawing current in excess of ITERM, the charger may never terminate.

    Regards,
    Jeff