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Original question:

BQ25792: "Charge Termination Done" not reached

BQ25792: shutdown of the system

Rodrigo Blanke Lambrecht
Prodigy 40 points
Part Number: BQ25792
Other Parts Discussed in Thread: BQ25798

(Please refer to the related topic for project information)

When the VBAT is very low the BQ starts the charge in the TRICKLE CHARGE mode. At this moment the VSYS is 8.88 V, below the VSYSMIN = 9.0 V and the status of VSYS is "In Regulation" (REG1E_Charger_Status_3 Register - bit4).

This condition causes the shutdown of the system and we can't see the status of registers after this problem. Is it possible that the BQ is cutting-off the VSYS in the TRICKLE CHARGE?

Similarly, it also happens if you don't have a battery connected, in this case the VSYS = 9.27V and NOT CHARGING status but the system still shuts down completely.

Register/Description

Value

REG20_FAULT_Status_0

0x00

REG21_FAULT_Status_1

0x00

REG1B_Charger_Status_0

0x0F

REG1C_Charger_Status_1

0x2A

REG1D_Charger_Status_2

0x00

REG1E_Charger_Status_3

0x30

REG1F_Charger_Status_4

0x10

REG1C_Charger_Status_1.CHG_STAT

Trickle Charge

REG33_IBAT_ADC

0 mA

REG35_VBUS_ADC

11.71 V

REG37_VAC1_ADC

11.71 V

REG39_VAC2_ADC

11.75 V

REG3B_VBAT_ADC

1.98 V

REG3D_VSYS_ADC

8.86 V

REG1B_Charger_Status_0.VBUS_PRESENT_STAT

1

REG1B_Charger_Status_0.AC1_PRESENT_STAT

1

REG1B_Charger_Status_0.AC2_PRESENT_STAT

1

REG1B_Charger_Status_0.POORSRC_STAT

0

REG1E_Charger_Status_3.VSYS_STAT

1

REG1F_Charger_Status_4.VBATOTG_LOW_STAT

1
  • 0
    TI__Guru**** 165886 points

    HI Rodrigo,

    The battery not connected case is a known deficiency.  If you add 470uF on BAT pin, it will prevent the small battery capacitors from over-voltaging, which causes a BATOVP and then a SYSOVP fault.  The SYSOVP fault turns off the converter for short time.  The pin2pin BQ25798 with additional features does not require the additional 470uF on BAT.

    I am not aware of any ICs with SYSMIN being out of regulation (which for CELLS=3S defaults to 9.0V-9.4V) but I will check a few on the bench.  If your system requires 9.0V, I suggest setting SYSMIN slightly higher than 9V minimum.  Alternatively, you might try turning of PFM mode as the ripple gets quite large in PFM mode. 

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hi Jeff,

    I put the additional capacitor in VBAT but it didn't work. I also tested with a 1000uF capacitor.

    I would like you to send us some samples of the BQ25798 for us to test.

    Regards.

  • 0 in reply to Rodrigo Blanke Lambrecht
    TI__Guru**** 165886 points

    Hi Rodrigo,

    That's odd.  Adding 1000uF prevents BAT and SYS OVP and the subsequent SYS shutdown.  Also, I should have mentioned that if charge is disabled either by CE bit or pin or from TS fault due to missing thermistor at TS pin, BAT and SYS do not OVP.

    Unfortunately, I do not have any BQ25798 samples to send.  I suggest using samples.ti.com to place an order and sign up to be notified when they are back in stock.

    Regards,

    Jeff