SLUAB05 April 2025 BQ25856-Q1

2 ACUV and ACOV Settings

The BQ25856-Q1's VAC undervoltage threshold is set by the ACOV/ACUV voltage divider. The BQ25856-Q1 enters into auto reverse mode as soon as the power drops below the ACUV setting with the EN_AUTO_REV set to 1. The ACUV setting is set by a resistor voltage divider on the VAC, ACUV, and ACOV pins. These pins also control the ACOV setting and ACUV_DPM voltage. The ACOV pin detects when the VAC voltage is above a certain value. The ACUV_DPM voltage limits the output charge current of the BQ25856-Q1 to prevent the input power supply from being overwhelmed. The resistor divider is shown in Figure 2-1.

Figure 2-1 ACOV and ACUV Resistor Divider

The ACUV/ACOV settings are set by the following equations.

Equation 1.

V_{V A C O V P} = \frac{1.2 (R_{A C 1} + R_{A C 2} + R_{A C 3})}{R_{A C 3}}

Equation 2.

V_{A C U V_D P M} = \frac{1.2 (R_{A C 1} + R_{A C 2} + R_{A C 3})}{R_{A C 2} + R_{A C 3}}

Equation 3.

V_{V A C U V P} = \frac{1.1 (R_{A C 1} + R_{A C 2} + R_{A C 3})}{R_{A C 2} + R_{A C 3}}

Setting the ACUV voltage correctly is critical for a fast transition time. A smaller difference between the minimum VAC voltage and the ACUVP threshold results in the reverse mode being triggered faster. A faster transition time gives less time for the system voltage to drop below critical levels.