JAJSS91 November 2023 BQ25756E
PRODUCTION DATA
The battery current sense resistor between SRP and SRN is fixed at 5 mΩ; using a different value is not recommended. The input current sense resistor between ACP and ACN is typically 2 mΩ, but can be increased to achieve better accuracy at lower sensed currents. In USB-PD EPR applications, a 5-mΩ sense resistor is recommended to achieve programmability in 50 mA/step. In addition, if input current limit function is not desired, ACP and ACN may be shorted together. For both of these sense resistors, a filter network is recommended as shown in the Typical Application.
For both the input current and the output current, the limits may be programmed using the I2C interface or an external programming resistor on ILIM_HIZ and ICHG pins, respectively.
PARAMETER | FORMULA | VALUE |
---|---|---|
Input Current Hardware Limit | Unused | Pull ILIM_HIZ pin to GND |
Input Current Software Limit | Unused, set by MPPT | REG06 = 0x0640 (20 A with 5-mΩ RAC_SNS) |
Output Current Hardware Limit | Unused | Pull ICHG pin to GND |
Output Current Software Limit | ICHG = 15 A | REG02 = 0x04B0 (15 A) |
The default input sense resistor (RAC_SNS) is 2 mΩ, and the register allows for a range of up-to 50-A input current limit. If lower currents are desired, it is possible to use a higher resistor, such as 5 mΩ. In this case, the IAC_DPM register value should be multiplied by a factor of 2/5 to program the correct current. For example, if a 5-mΩ RAC_SNS is used, and the register is programmed to a value of 0x60, the true maximum current across the RAC_SNS will be: 12A * 2/5 = 4.8 A. Similarly, the KILIM parameter used to set the ILIM_HIZ pull-down resistor should be scaled by 2/5. For example, with a 5-mΩ RAC_SNS resistor, a 6-A current limit would be achieved as: RILIM = KILIM * (2/5) / 6A = 3.3 kΩ.