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BQ25750: 48V battery charging circuit

Ben
Intellectual 400 points
Part Number: BQ25750

Tool/software:

Hi TI team,

I'd like to request of schematic review for 48V battery case from your team.

1. Battery type (Pack/Charging voltage)

48V : Li-ion(14S6P/58.1V), Li-ion(13S2P/54.6V), Li-ion(14S5P/58.8V)

2. System load

- Max 300~500W

- typical 150W

2. Design parameter

- Input source(VAC) : 48V typical

- Fsw : 373kHz

- Charging voltage : 57.24V

- Inductance : 10uH

- Input current max : 7A

- Charging current max : 7A

3. Schematic

Schematic


For your information

1. AL-caps(C100&C132) are option (no SMT)

2. To protect inrush current, I will add R-C components to gate of BATDRV&ACDRV.

- R : 10ohm , C : 10nF

Please design review for 48V battery charging case and advise to protect IC from battery voltage and inrush.

Thank you.

  • 0
    TI__Mastermind 30865 points

    Hello Ben,

    Thanks for being patient with this. I'm sorry for the delay in response.

    I'll look into this and get back to you by the end of the week.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    TI__Mastermind 30865 points

    Hello Ben,

    Thanks for being patient with this. I'll get back to you on Monday.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    TI__Mastermind 30865 points

    Hello Ben,

    Thanks for being patient. The schematic looks good.

    We'll get back to you on the power path later on. How soon will you need a response on this?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Intellectual 400 points

    Hello Ethan,

    I recognized the schematic looks no good Today... I already manufactured board as this schematic.

    It doesn't work to Buck-boost due to BTST no connect from DRV_SUP. I guessed the BTST connecting to DRV_SUP via the device inside.

    I added diode between DRV_SUP and BTST, It works well.

    Anyway, I will try to 48V battery charging with 57~58V. Does you have any advise except to R-C Filter at gate?

    I'm ready to test your comment for 48V battery charging. I don't want to the device damage.

    Thanks.

  • +1 in reply to Ben
    TI__Mastermind 30865 points

    Hello Ben,

    Thanks for being patient with this. I was on vacation Sep 17th to Sep 27th. I'm back in the office now though.

    To use the BATFETs at a battery voltage of 58V, we recommend using a FET like the NTMFSC4D2N10MC.This FET has a high threshold voltage. For the RC values, we recommend C=6.8nF and R=169kΩ. The high threshold voltage and RC values will slow down the FET turn-on time. Please note that we are still working on validating this solution.

    We also recommend to reduce the VSYS and VBAT capacitance to 80µF.

    Let me know if you have any questions about this setup.

    There is an alternative to using the BATFETs to provide power to the system though. You can also use auto reverse mode to supply the system load when VAC is removed. To use auto reverse mode, I recommend setting ACUV to just below the min input voltage, setting SYS_REV to the minimum system load voltage, and setting EN_AUTO_REV=1. You'll also need to remove the BATFETs.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Intellectual 400 points

    Hello Ethan

    Thanks your comment.

    I think "inrush current" has two case in the BQ25750 circuit. 

    Case1 is the AL-cap that is directly located to the battery connector. At the VSYS and VBAT line Total capacitance is AL-CAP(68uFx2=136uF) + MLCC(25uF) = 161uF approximately. I can remove a one AL-cap, and the capacitance can be around 80uF with MLCC DC-bias. In that case, I will remove AL-cap placed as close as connector directly. It can be decrease Inrush current from battery to AL-cap. (Remark :Link)

    Could there be a problem such as AL-cap burnt or IC damage by SRP, SRN port in the case1? Because, Case1 inrush current has the higher than Case2.

    Case2 is at the moment when the BATFET turn on. The BATFET ISC030N10NM6 what I used my board has a similar spec as your comment. It didn't fault when I connect 48V battery to board yet. And I used C=10nF, R=10Ohm without any system load connection. It looks to work well miller effect at the turn-on time. Also I think If R value is more higher as your comment 169kOhm, the current is decreasing for sinking to the capacitor, means miller effect has decreasing too, and Inrush can be higher.

    What would you reason to apply high value resistor?

    Thank you.

  • 0 in reply to Ben
    TI__Mastermind 30865 points

    Hello Ben,

    Thanks for your comments about this. I'll need time to write up answer for this. I'll get back to you before the end of the week.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    TI__Mastermind 30865 points

    Hello Ben,

    Thanks for being patient with this and thanks for providing us with your test data.

    1. We are thinking about reducing the total capacitance of the BQ25750. It only needs 80uF on both the input and output to function.

    2. We are still working on validating this solution. I think a lower resistance would be better here. I should have more information later next week.

    Best Regards,
    Ethan Galloway

  • +1 in reply to Ethan Galloway
    TI__Mastermind 30865 points

    Hello Ben,

    Thanks for being patient with this.

    From our testing, a lower resistance is better and a capacitance of 8nF to 20nF works well for the circuit.

    Also, it looks like the power path function of your circuit is working well. Let me know if you have any more questions about this. If not, I can marked this thread as resolved.

    Best Regards,
    Ethan Galloway