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Original question:

BQ24780S: BQ24780S

BQ24780S: bq24780 work with ACIN only and automatically turn on the ACFET?

user3680879
Intellectual 390 points
Part Number: BQ24780S
Other Parts Discussed in Thread: BQ24780,

Dear SIr,

1. Can the bq24780 work without the battery? We are planning to make the battery as a customer choice. 

2. Can the bq24780 automatically  turn on the ACFET without the host comtrol when just powering with ACIN? As the host were powering by the VSYS, we need the VSYS setup before the host can run and take the control. On the test board, we found the ACFET were turn off when without the host control, so the VSYS were zero when no battery plug in.

Best Regards,

  • 0
    TI__Expert 5330 points
    1. Yes, the bq24780s can be used without a battery. Please use the \BATPRES input pin to indicate to the device if the battery is present or removed.
    2. If you have valid power on VCC (> UVLO = 2.4-2.8V, < ACOV = 24-28V) and ACDET is above the ACOK rising threshold (2.375-2.475V), and VCC is above SRN (battery voltage), then ACOK will be driven high and the ACDRV will be charge pumped to 6V above CMSRC which will enable the ACFET and RBFET. This is done automatically by BQ24780s without host control.

    Regards,
    Steve
  • 0
    Intellectual 390 points

    findDear SIr,

    For more information, the battery FET can turn on when plug in the battery and I can find +6v DC between the BATDRV and BATSRC pin. But there have no such voltage between ACDRV and CMSRC pin ,so the ACFET is always turn off. The ACDET is +1.5v dc , the REGN is +6v dc and the . BATPRES is biased to 3.3v dc.

    Please give me some advice!

    Best Regards,

  • 0 in reply to Steve Preissig
    Intellectual 390 points
    Dear Steve,
    Thanks a lot!
    The issue is on the voltage feed to ACDET. It should be above 2.4v as your suggested. Now it is working.
    BTW , it seems that bq24780 can't automatically charge the battery when the battery is shut down in the case of discharge protection. The charging could only be enable by the host ,right?
    Further more, is there any posible to implement the discharge protection by bq24780 itself? Thus the battery will shut down when reaching the lower threshold without external proection circuit.

    Best Regards,
  • 0 in reply to user3680879
    TI__Expert 5330 points
    Glad the ACDET is now working as expected. For your questions:

    BTW , it seems that bq24780 can't automatically charge the battery when the battery is shut down in the case of discharge protection. The charging could only be enable by the host ,right?
    >> I would need to know more about the gauge/protection IC at the battery to answer this fully. If the protection device blocks both charging and discharging current under this condition, then that would prevent the BQ24780s from charging and then, as you say, the host would have to go into the protection IC and re-enable charging current flow into the battery before the BQ24780s could resume charging.

    Further more, is there any posible to implement the discharge protection by bq24780 itself? Thus the battery will shut down when reaching the lower threshold without external proection circuit.
    >> It depends on what you mean by discharge protection. The BQ24780s has a configurable discharge current limit (Reg 0x39.) This current limit is only applied during Turbo Boost mode, however.
    >> When you mention the lower threshold, however, this makes me think that you are thinking more in terms of halting battery discharge if the battery reaches a fully depleted lower voltage level. This will happen automatically according to the battery depletion threshold level set in Reg 0x3B, bits [15:14], but also is only applied during Turbo Boost mode.
    >> For discharging the battery when no adapter is present, neither the discharge current limit nor the battery depletion threshold is applied. This is because battery discharge can only be controlled in Turbo Boost mode. When the adapter is not present and the battery is discharging across the BATFET, the backgate diode of this FET can always conduct current from the battery into Sys, regardless of how BQ24780s drives the gate. For this condition, you would need to block discharge at the gauge/protection IC if desired.

    Regards,
    Steve
  • 0 in reply to Steve Preissig
    Intellectual 390 points

    Dear Steve,
    Thanks for so detail advice!

    For my 1st question, the protect IC on the battery side only block the discharge direction when reaching the lower threshold ,thus the battery will have no output voltage ,like no battery plugin. It is often in the case of powering only by the battery and the system will turn off when battery is blocked.  I just wonder if bq24780 can try to pre-charge the battery when the battery has been blocked or even no battery and ACIN pluging in. If can not , we have to control the bq24780 to go to the charge mode by the host,and so the host must be turned to the power on mode in that case.

    Many Thanks and Best Regards,

  • 0 in reply to user3680879
    TI__Genius 10240 points
    Hi there,

    Your understanding is correct that bq24780 can't automatically charge the battery when the battery is shut down in the case of discharge protection. The charging could only be enable by the host .