• State TI Thinks Resolved
  • Locked Locked
  • Replies 10 replies
  • Answers 6 answers
  • Subscribers 63 subscribers
  • Views 1005 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25792: Query on Charging Lifepo4(4s, 12.8V) battery

Yashwanth S N
Prodigy 110 points
Part Number: BQ25792
Other Parts Discussed in Thread: BQ25798, BQ4050, BQ25730, BQ25720

Hi,

In our project we are using 4s Lifepo4(12.8V) battery for back up supply. The requirement mentioned below.

We have 2 input (Need dual input selector option)

1) 9-18V input from Vehicle battery

2) 12V input from solar panel.

The solar panel will be primary supply.

Output Requirement:

Voltage : 10V to 14V

current  : 2.2 A

The output of BQ25792(SYS) is directly connected to 12V loads.

Can we use BQ25792 for above mentioned application. 

If no could please suggest suitable BMS Part.

Thanks

Yashwanth S N

  • 0
    TI__Guru**** 169546 points

    Hi Yashwanth,

    The BQ2579X family has dual input selection and buck-boost operation so it the best choice for your input power.  I recommend BQ25798 because it has a MPPT feature that might be helpful for solar panel.  As with all of our NVDC chargers, the SYS output has a minimum value setting for when the battery is discharged.  But, once the battery voltage exceeds that minimum setting, V(SYS)=V(BAT)+~150mV until V(BAT)=BATREG.  So, V(SYS) will eventually be slightly higher than 12.8V.  

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Prodigy 110 points

    Hi Jeff,

    Thanks for your inputs.

    The max cutoff voltage of 4s Lifepo4 battery pack is 14.4V and discharge cut-off voltage 10V.

    So in the BQ25792/BQ25798

    a)Can i use 4s setting with Vreg =14.4V and VSYSMIN=10V?.

    b) But once power on reset, the default 4s setting is Vreg=16.8V and VSYSMIN=12V, his this will effect my battery pack?

    Thanks

    Yashwanth 

  • 0 in reply to Yashwanth S N
    TI__Guru**** 169546 points

    Hi Yashwanth,

    Regarding A), I suggest using the PROG resistor to set for 3S (MINSYS=9V, BATREG=12.6V and ICHRG=1A) and then use I2C to change the MINSYS, BATREG and ICHG default register settings after the host comes up to 12V, 12.8V and 2.2A.

    Regarding B) please see A. 

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 110 points

    Hi Jeff,

    I understood that for 4s Lifepo4 battery pack we can set 3S setting in the PROG pin(Default: MINSYS=9V, BATREG=12.6V and ICHRG=1A) and then we can change MINSYS, BATREG and ICHG value through I2C by writing in the respective register  .

    As per your suggestion if we set BATREG=12.8V the battery will not charge fully right?. In the 3S setting BATREG range can set from 10 to 13.99V so we can set BATREG =13.99V(In this case also we are not charging fully but charging nearer to 100%) since fully charged voltage is 14.4V.

    The 2.2A mentioned in the above question is load on the SYS pin and planning to charge battery in 1A so total input current requirement will be 3.2A (The recommended part is satisfying).

    The recommended part BQ25798(MPPT feature) will test with existing design board since it has same package.

    We have requirement on the SOC(State of charge), SOH(state of Health) read through I2C, Is this algorithm is available in the existing setup?.

    Thanks

    Yashwanth S N

  • 0 in reply to Yashwanth S N
    TI__Guru**** 169546 points

    Hi Yashwanth,

    4S config on PROG pin sets the BATREG to 16.8V at startup.  So, you can use that setting but then I recommend pulling /CE pin high until the host can lower the BATREG to 14.4V to prevent overvoltage on the 4S batteries.  The charger only has an instantaneous ADC with no memory.  So it cannot report SOC or SOH like a gauge.  However, host software and memory could be used with the ADC measurements of battery voltage and current to compute SOC and SOH.  Or you could add a TI gas gauge.

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Prodigy 110 points

    Hi Jeff,

    Thanks for the inputs.

    I understood that i can use it in 2 settings for my application.

    1. 3S setting with BATREG(13.99V)

    or

    2. 4S setting with BATREG(14.4V), (By pulling CE pin high(charging disable) the changes needs to be done)

    Could you please suggest TI gas gauge for my application.

    Thanks

    Yashwanth S N

  • 0 in reply to Yashwanth S N
    TI__Intellectual 2025 points

    For 4S LFP, please consider BQ4050.

    Thanks,

    Rushi

  • 0 in reply to Rushi_Dalal
    Prodigy 110 points

    Hi Jeff,

    Do we have any other battery charger with all functionality of BQ25798 with higher input current rating(5A)

    Thanks

    Yashwanth S N

  • 0 in reply to Yashwanth S N
    TI__Guru**** 169546 points

    Hi Yashwanth,

    Not with integrated FETs. For higher input current, I recommend BQ25720 or BQ25730 charge controller families with external FETs.

    Regards,

    Jeff