The BQ25756 Design Calculator can be used for all of the BQ2575X and BQ2585X-Q1 families of devices. This calculator can help with resistor programming, IC set-up, and the BOM selection process. The calculator can also take user inputs about the operating conditions, BOM, and system requirements to estimate the power loss and efficiency. Note that the calculator does not take into account power losses from other sources, like magnetic core losses, or copper trace losses.

This calculator also includes a thermistor qualification tab to estimate the minimum/typical/maximum temperature falling and rising thresholds for the various temperature charging windows. This tab can be used to select a thermistor for the application of interest, but this section focuses on the inductor calculation steps in the design calculator.

To use this calculator, skip over the warning about circular references and fill in the yellow cells. The cells with red tabs contain additional information about the adjacent cell. Red cells highlight the cells that can have an issue.

First, enter the input voltage range, output voltage, and maximum output current into the calculator

Second, enter the desired switching frequency. The calculator can be quickly used to find the resistor value for a given frequency. The Buck Voltage Limitation row lists the maximum possible output voltage for a buck-only part.

Third, enter in the proposed inductor. This section can be used to calculate the ripple current and ripple current percentage.

The BQ2575X and BQ2585X-Q1 ICs can support an inductor of 2.2µH to 15µH and a DCR of 1.75mΩ to 60mΩ. The max possible time constant for the ICs is 1.26µH/mΩ.