SLUAAT5 December   2023 BQ25756

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2LiFePO4 Charging Profile
  6. 3BQ25756 Settings For LiFePO4
    1. 3.1 Set Charging Voltages
      1. 3.1.1 Regulation Voltage
      2. 3.1.2 Recharge Voltage
      3. 3.1.3 Battery Low Voltage
    2. 3.2 Set Charging Current
      1. 3.2.1 Charging Current
        1. 3.2.1.1 ICHG Pin Pull Down Resistor
        2. 3.2.1.2 ICHG_REG Register Bits
      2. 3.2.2 Pre-Charge Current
      3. 3.2.3 Termination Current
    3. 3.3 TS Pin Setting
      1. 3.3.1 JEITA Enabled
      2. 3.3.2 JEITA Disabled
      3. 3.3.3 NTC Monitoring Disabled
  7. 4Supercapacitor Charging Profile
  8. 5SBQ25756 Settings For Supercapacitor
    1. 5.1 Charge Current Setting
    2. 5.2 Charge Voltage Setting
    3. 5.3 TS Pin Setting
  9. 6Test Results From EVM
    1. 6.1 Charging LiFePO4 Battery
    2. 6.2 Charging Supercapacitor
  10. 7Summary
  11. 8References

3.1.1 Regulation Voltage

Battery regulation voltage is programmed using a resistor divider to the FB pin. The default internal voltage reference is VFB=1.536 V, and can be changed using the VFB_REG register bits. The top of the resistor divider is selected to be 249 kΩ. The bottom resistor is calculated as

Equation 1.
GUID-20231205-SS0I-7BLB-PVWJ-KKFNSRQQX2JK-low.svg

where VFB=1.536 V, RTOP=249 kΩ and RFBG=33 Ω which is the internal FBG pull down resistor. For a 4 S battery, the desired battery regulation voltage VBATREG=4×3.6 V=14.4 V. With these values the bottom resistor is calculated to be RBOT = 29.76 kΩ.


GUID-20231205-SS0I-SB4F-Q1CW-TKMG6XV4PHDF-low.svg

Figure 3-1 Regulation Voltage Setting Using a Resistive Divider to pin FB

If we choose the nearest 0.1% resistor, for example, RBOT = 30.1 kΩ, then effective VBATREG is 14.25 V. We can fine tune VBATREG by adjusting the internal reference VFB via VFB_REG in register REG0x00. In this case, the value can be set to 1.552 V which makes battery regulation voltage VBATREG very close to 14.4 V.