SLUAAX5 August   2024 BQ25750 , BQ40Z80 , MSPM0L1306

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2The Role of MCU in Smart Battery System
  6. 3Application Example Using BQ25750, BQ40z80, and MSPM0L1306
    1. 3.1 Gauge Setup
    2. 3.2 Charger Setup
    3. 3.3 MCU Setup
    4. 3.4 Communication Protocol
    5. 3.5 MCU Code Example
    6. 3.6 Data Collected
  7. 4Summary
  8. 5References

Charger Setup


 Typical
                                        Application Block Diagram of the BQ25750

Figure 3-2 Typical Application Block Diagram of the BQ25750

TI provides a wide portfolio of chargers which are I2C only, and SMBus only. Table 3-2 is the typical application of using the BQ25750 which is an I2C based charger. For this application note, the only configuration changed from the above-mentioned block diagram is the bottom resistor (RBOTTOM) of the voltage divider that determines the feedback voltage. The feedback voltage is then scaled to determine the desired battery regulation voltage. The resistor divider must be chosen such that the divider covers the different ranges of charging voltage requested from the gauge. In BQ25750, the resistor divider first sets the desired target battery voltage and then feedback voltage can be changed (through register 0x00).

For this example, the range of charging voltages from the gauge is 6×Voltage at different temperature ranges per cell. Depending on the temperature ranges, the low voltage, medium voltage, high voltage, and max charge voltage changes (set by user). Using the value in Table 3-1, users can determine the highest requested charging voltage is 6×4.1 V. After determining the range of charging voltage of the gauge, 16.7kΩ resistor is chosen for RBOTTOM to cover 23.97V to 24.96V (3.995/cell to 4.16/cell) following the BQ25756 Design Calculator. If the range requested by the gauge is below the minimum value, then set to the lowest feedback voltage by the MCU. For more information on the BQ25750 or other charger setup and configuration, refer to the data sheet and user guide.

The charging current must be written to the Charge_Current_Limit 16 bit register at 0x02 address. The register has a range from 400mA-20000mA, the bitstep of 50mA, and only 9 bits out of the 16 bits are read by the charger to represent the charging current (only bits 10:2, the rest of the bits are reserved). See the Charge Charge_Current_Limit register section of the BQ25750: Standalone/I2C Controlled, 1- to 14-Cell Bidirectional Buck-Boost Battery Charge Controller with Direct Power Path Control data sheet for more information on the details and refer to Section 3.5 for the exact formatting of the charging current.

Table 3-2 Charging Current Register Settings in BQ25750
Bit Field Type Reset Notes Description
15:11 RESERVED R 0x0 Reserved
10:2 ICHG_REG R/W 0x190

Reset by:

REG_RESET

WATCHDOG

Fast Charge Current Regulation Limit with 5mΩ

RBAT_SNS:

Actual charge current is the lower of ICHG_REG and ICHG pin

POR: 20000mA (190h)

Range: 400mA-20000mA (8h-190h)

Clamped Low

Clamped High

Bit Step: 50mA

The charging voltage must be written to the Charge_Voltage_Limit 16 bit register at 0x00 address. The register has a range from 1504mV-1566mV, the offset of 1504mV, the bit step of 2mV, and the only the last 5 bits are read by the charger to represent the charging voltage. See the Charge Charge_Voltage_Limit register section of the BQ25750: Standalone/I2C Controlled, 1- to 14-Cell Bidirectional Buck-Boost Battery Charge Controller with Direct Power Path Control data sheet for more information on the details and refer to Section 3.5 for the exact formatting of the charging voltage.

Table 3-3 Charging Voltage Register Settings in BQ25750
Bit Field Type Reset Notes Description
15:5 RESERVED R 0x0 Reserved
4:2 VFB_REG R/W 0x10

Reset by:

REG_RESET

FB voltage regulation limit:

POR: 1536mV (10h)

Range: 1504mV-1566mV (0h-1Fh)

Bit Step: 2mV

Offset: 1054mV


 Resistor
                                        Divider Setting Feedback Voltage

Figure 3-3 Resistor Divider Setting Feedback Voltage
Note: The charge voltage written to the register is the feedback voltage. The battery regulation voltage is the set by feedback voltage divided by the resistor divider.
Equation 1. V B A T = F B × R B O T T O M + R 28 R B O T T O M