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BQ24773: questions on default setting

Vincenzo Pizzolante
Mastermind 22746 points
Part Number: BQ24773

hi,

we are considering the bq24773 for a 2S Li-Ion charger.

As far as I understood, at power up default settings are (CELL is left floating for a 2S config.):

ChargeVoltage() = 8400mV

ChargeCurrent() = 2944mA

MaxChargeVoltage() = 9008mV

MinChargeVoltage() = 6144mV

What I didn't understand is what is the SYS level after soft-start is over.

8.4V?

Vbat + little Drop-out?

thansk a lot in advance

KR

Vincenzo

  • 0
    TI__Genius 11850 points

    Hi Vincenzo,

    Here are the default register settings after POR. Some of the values you gave (such as the charge current) are incorrect, so please take note of that.

    To answer your question, VSYS should be around 9.2 V after POR for a 2-cell configuration. I confirmed this on an EVM and got the same result.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    TI__Mastermind 22746 points

    hi Angelo,

    a very last question.

    the VSYS is 9.2V regardless if battery is connected or not, right?

    as this will supply the rest of circuitry, i want to be sure it is always there even if battery is removed

    KR

    Vincenzo

  • 0 in reply to Vincenzo Pizzolante
    TI__Mastermind 22746 points
    PS: I also need the source/gerber files of the EVM (SLUUAO3C)
    Where could I find them?
  • 0 in reply to Vincenzo Pizzolante
    TI__Genius 11850 points
    Hi Vincenzo,

    Here's what I'm seeing on the BQ24773 EVM after plugging in the 20 V adapter. Keep in mind that my EVM is configured for 2-cell charging, and I didn't change any of the register values. There are 3 cases:

    1) No battery connected, then plug in 20 V adapter. VSYS = 9.09 V (due to MaxChargeVoltage register).
    2) Low voltage battery connected (VBAT < SYS_MIN), then plug in 20 V adapter. VSYS = 6.18 V (due to MinSystemVoltage register).
    3) High voltage battery connected (VBAT > SYS_MIN), then plug in 20 V adapter. VSYS = 9.09 V (due to MaxChargeVoltage register).

    Even with no battery connected, VSYS will still be regulated above SYS_MIN due to the NVDC architecture.

    Regarding the PCB files for the EVM, we're working on getting those to you. I will email the files to you when we're ready.

    Best regards,
    Angelo
  • 0 in reply to Angelo Zhang87
    TI__Mastermind 22746 points
    thanks a lot Angelo...
    a very last question: do you know why TPS38x (U2) is there?
    no mention in the evm doc... debugging purpose?

    KR
    Vincenzo
  • 0 in reply to Vincenzo Pizzolante
    TI__Mastermind 22746 points
    PS: we plan to pull down to GND the /BATPRES input as we don't need the feature (users can't access the battery at all).
    this should not create any problem/drawback, correct?
  • 0 in reply to Vincenzo Pizzolante
    TI__Genius 11850 points
    Hi Vincenzo,

    I just emailed you the PCB files. Regarding your other questions:

    1) Yes, if the battery is always present, then it should be fine to ground /BATPRES. One small consequence of doing this is that you will not be able to exit LEARN mode by pulling /BATPRES high, as described in Section 8.3.8 of the datasheet, but I'm not sure how relevant this is to your application.

    2) U2 behaves like a comparator to determine whether or not the battery is present. Based on your description, it sounds like U2 is unnecessary for your application since the battery is always present, so you can leave it out.

    Best regards,
    Angelo