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BQ25713: Delay time on ILIM setting change

Hardy Xue
Expert 3640 points
Part Number: BQ25713

Hi Team,

Customer found the VSYS will have voltage rise when adapter plug-in and then ILIM pull up. I also can duplicate this phenomenon on EVM. The waveform and test condition as below.

1. Why VSYS rise after adapter plug-in?

2. If the ILIM pin set 0V, does charger can use 0x0E/0Fh to set input current limit after power on?

3. Why does the VSYS change after ILIM pull up and delay about 120ms?

test condition: 

Adapter voltage: 15v

Battery voltage: 8.5v

System loading: 2.5A

Battery charging voltage/current: 8.8A / 1A

Customer's board waveform:

After red line, the register are 

  1. 32h bit 7=0
  2. 0E0Fh =3100

EVM waveform:

Ch3: VSYS

Ch4: VILIM

Best regards,

Hardy

  • 0
    TI__Expert 4780 points

    Hello Hardy,

    Below is the sequence of events after an adapter is plugged in.

    The power-up sequence from DC source is as follows:
    1. 50 ms after VBUS above VVBUS_CONVEN, enable 6 V LDO and CHRG_OK goes HIGH
    2. VBUS qualification is executed 50 ms after VBUS first rises above VVBUS_UVLOZ. If VVBUS_UVLOZ < VBUS < VVBUS_CONVEN then charger fails VBUS qualification, and the charger will re-qualify VBUS every 2s.
    3. Input voltage and current limit setup
    4. Battery CELL configuration
    5. 150 ms after VBUS above VVBUS_CONVEN, converter powers up.

    Before the adapter is plugged in, the System is powered by battery, so VSYS = VBAT - VDS of the BATFET

    • ILIM_HIZ is tied via a resistor divider to VDDA which is connected to REGN. In Step 2 you can see REGN goes to 6V (6V LDO) thus ILIM_HIZ voltage will go to the setting provided by the voltage divider.
    • Based on this and other settings, Step 3 and 4 are executed next
    • After ~150ms total, the converter starts up, which will begin to regulate VSYS at the Minimum System Voltage, which could be different than the previous VSYS which was driven by battery voltage.

    If you set ILIM_HIZ to 0V, the device will be in HIZ mode. If you want to use Reg0F/0E to set the input current instead of the ILIM_HIZ pin, you need to tie the ILIM_HIZ pin > 0.8V to ensure it is not in HIZ mode, and set the EN_EXTILIM bit in ChargeOption2 (Reg32[7]=0) register to 0 to disable the ILIM function on ILIM_HIZ and use the register setting instead. 

    Thanks,

    Khalid