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BQ24071: BQ24071 configuration

Duane Smith
Intellectual 400 points
Part Number: BQ24071
Other Parts Discussed in Thread: BQ25703A, BQ25703, TPS63070, BQ24170

We are looking at using the BQ24071 with a 3.7vdc battery and I have a few questions: http://www.tenergy.com/Tenergy-Lithium-Ion-Polymer-3-7V-3000mAh-6050100-UL-Approved-Rechargeable-Battery

1) Is there a boost regulator in the BQ24071 to give us the 6vdc out?

2) If the 3.7vdc battery has a standard recharge current of 500ma and recharge time of 3hrs, if we set the recharge current to 250ma does that double the recharge time to 6hrs?

3) Is the R_DPPM based on the battery voltage or the output voltage, see equation:

R_DPPM = 4.025 V / (100E-6 A * 1.150) = 35 kohm (we can use a standard 34.8 kohm resistor here)

  • 0
    TI__Genius 10240 points
    Duane,

    1. Please refer to the datasheet, no boost for BQ24071.
    2. The relation is not linear. You can do such estimation for small C-rate charging. What is your recharge definition? If the battery need a full charging cycle, 500mA 3-hr can't be done for this 3000mAh battery as 500mA x 3 hrs = 1500mAh. You can't charger the battery in 3 hrs even if the whole charging is in CC mode.
    3. Please refer to the datasheet 8.3.1.1.3 Dynamic Power-Path Management (DPPM). y. If the voltage on the OUT pin drops to a preset value, V(DPPM) × SF, due to a limited amount of input current, then the battery charging current is reduced until the output voltage stops dropping.
  • 0
    Intellectual 400 points
    Eric,

    Thanks for the information. Because the BQ24071 is not a boost and we need at least 5v out we changed the battery to a 7.4v battery pack. The following are the specs on the Tenergy 7.4V 5200mAh Side By Side Li-Ion Battery Pack with PCB:

    Specifications:
    Item Value
    Capacity 5200 mAh
    Nominal Voltage 7.4 V
    Fully Charged Voltage 8.4 V
    Discharge Cut-off Voltage 6.0 V
    Max Charge Voltage 4.20 ± 0.05 V/cell
    Internal Impedance ≤ 70 mΩ
    Standard Charge Current 0.2C (1.04 A)
    Rapid Charge Current 1C (5.2A)
    Standard Discharge Current 0.2C (1.04 A)
    Max Discharge Current 1C (5.2 A)
    Max Pulse Discharge Current 2C (10.4 A)
    Weight 6.7 ±0.7 oz (190 ±2 g)
    Dimensions 2.83" x 2.76" x 0.79" (72 x 70 x 20 mm)
    Operating Charge Temperature 32 to 113°F (0 to 45°C)
    Operating Discharge Temperature -4 to 140°F (-20 to 60°C)
    1 Month Storage Temperature 23 to 95°F (-5 to 35°C)
    6 Month Storage Temperatures 32 to 95°F (0 to 35°C)
    MPN 31005

    So these are the calculations for bias resistors that I have, let me know if there are correct:

    Value of R_SET (R_205 on the schematic)
     Battery identified can support 1 A charge current
     RSET = V(SET) x K(SET) / IO(BAT) = 2.5 V x 425 / 1 A= 1.06 kohm; we can go with an off-the-shelf resistor at 1 kohm for R205

    Value of R_TMR (R_207 on the schematic)
     The Battery does not identified a fully discharged time due to the integrated battery monitor circuit so I would just set this to what is in the datasheet
     RTMR = t(CHG) / K(TMR) gives 6 hrs x 60 min/hr x 60 s/min / 0.360 s/Ω = 60 kΩ; we can go with an off-the-shelf resistor at 60 kohm for R207

    R_DPPM = V_DPPM-REG / (I_DPPM * SF)
     I_DPPM = 100E-6 A (from datasheet)
     RDPPM = V(DPPM-REG) / (I(DPPM) x SF) = 4.26 V / ( 100 μA x 1.15) = 37.044 kohm (we can use a standard 37 kohm resistor here)

    Appreciate your help!

    Thanks
  • 0 in reply to Duane Smith
    TI__Mastermind 21590 points
    Hello,
    Based on your specifications, i'll suggest going with a buck boost charger since you changed the battery to a 2 cell battery. The BQ24071 which is a single cell linear charger wont work for this application. Please take a look at the BQ25703A which is a NVDC I2C Battery Buck-Boost Charge Controller with System Power Monitor & Processor
  • 0 in reply to Raheem
    Intellectual 400 points
    Thanks, we are looking for a simple battery charge circuit we do not have any supervisory processor, will the BQ25703A need any control functions from the I2C for setup or operation?
  • 0 in reply to Duane Smith
    TI__Mastermind 21590 points
    Hello,
    The BQ25703 does require I2C. Do you plan on using a buck boost after the charger to maintain 5V output when on BAT only power or do you prefer an integrated solution? What is the input voltage of the charger?
  • 0 in reply to Raheem
    Intellectual 400 points
    We would like a simple integrated solution that allowed us to use a Lithium-ion battery (voltage not specified) and a battery recharge circuit, the battery is a backup to a a wall mount DC input. We have no specification on any of the input design just the outputs required.

    Our end goal is to have a simple design that provides a +5vdc output @ 1.5a and a 3.3vdc output @ 500ma.

    If you have a solution that can provide these output with a battery we would be very grateful.

    Thanks
  • 0 in reply to Duane Smith
    Intellectual 400 points
    Can you suggest a battery that will work with the BQ24071 which has a 6vdc output?
  • 0 in reply to Duane Smith
    TI__Mastermind 21590 points
    Hello Duane,
    I'll suggest you use a BQ24170 battery charger along with a buck boost converter like the TPS63070 to maintain the putput at 6V when the battery voltage falls below 6V.