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BQ25790: cannot start charge

Howard Zou
Genius 12365 points
Part Number: BQ25790

Hi,

we have build a board based on BQ25790, CE pin is enabled, and 5V is plugged in. We are trying to charge 2 cell battery pack.

But we find that when battery pack is lower than Vbat_uvloz, the charger is not charging at all.

Below is the registers we read, we don't see any fault report, but [0x1c] register shows that it's not charging and the charge current read is really 0. But according to the datasheet, it should be charging with 100mA trickle charge current. Could you please tell me what may be wrong?

            [0x01]=0x348

            [0x03]=0x64

            [0x05]=0x2c

            [0x06]=0xc8

            [0x0B]=0xdc

            [0x0D]=0x4b

            [0x0E]=0x3d

            [0x0F]=0xa2

            [0x10]=0x80

            [0x11]=0x20

            [0x12]=0x0

            [0x13]=0x41

            [0x14]=0x16

            [0x15]=0xaa

            [0x16]=0xc0

            [0x17]=0x7a

            [0x18]=0x55

            [0x19]=0xc8

            [0x1B]=0x0b

            [0x1C]=0x0a

            [0x1D]=0x00

            [0x1E]=0xd0

            [0x1F]=0x10

            [0x20]=0x00

            [0x21]=0x00

            [0x22]=0x00

            [0x23]=0x00

            [0x24]=0x00

            [0x25]=0x00

            [0x26]=0x00

            [0x27]=0x00

            [0x28]=0x00

            [0x29]=0x00

            [0x2A]=0x00

            [0x2B]=0x00

            [0x2C]=0x00

            [0x2D]=0x00

            [0x2E]=0xb0

            [0x2F]=0x00

            [0x30]=0x00

            [0x31]=0x00d1

            [0x33]=0x0000

            [0x35]=0x1366

            [0x37]=0x1366

            [0x39]=0x0000

            [0x3B]=0x006a

            [0x3D]=0x1e66

            [0x3F]=0x01f7

            [0x41]=0x0059

  • 0
    TI__Guru**** 153986 points

    Hi Howard,

    Is your customer relying on the ADC to report trickle charge?  Since the 100mA trickle charge current is provided by a current source that is outside the current sense amplifier, the ADC cannot report trickle charge current.  IBUS ADC is reporting ~200mA.  Where is that 200mA going, to the SYS load?  If not, then it is going to trickle charge.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Genius 12365 points

    Yes there is SYS load in the system.

    And according to REG1C value, it shows not charging, not trickle charge.

    Besides, what do you mean by trickle charge current is provided by a current source outside the current sense amplifier? Isn't all charge current go through the BATFET and the current is sensed through BATFET?

  • 0 in reply to Howard Zou
    TI__Guru**** 153986 points

    HI Howard,

    I just tried on the bench with customer settings and it works for my EVM.

    Trickle charge does not flow from SYS to BAT like pre and fast charge current.  It is a current source injection at the BAT pin.  There is a brief period of no current flow when V(BAT)= VBATUVLO point where trickle charge turns off and before precharge turns on.  Could that be the issue?  Also, in your register list above, register 0x08 isn't shown.  That sets VBAT_LOWV level and precharge current.  What is that register?

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    TI__Guru**** 153986 points

    Howard,

    Can you ask the customer to toggle HiZ? Does that return to trickle charge?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Genius 12365 points

    Jeff, I would like to add one thing.

    The battery connected to BATP is 2 cell battery pack and it's protected by a protector. During the test, the protector is enabled and the charging path is in fact cut off. 

    But according to my knowledge, at this situation, the device should charge the capacitor at BAT pin, and the voltage on BAT pin will gradually rise to the Vreg(for example 8.2V for 2cell setting), right? But we find that the voltage on BAT pin stays at 100mV, that's strange.

  • +1 in reply to Howard Zou
    TI__Guru**** 153986 points

    Hi Howard,

    The protector still allows a small current path in order to charge up the cells enough for the protector to close.  Usually the allowed current is <<100mA.  Maybe not for this one?  Can you confirm through other measurement than ADC that the charger is outputting 100mA?

    Regards,

    Jeff