Total power dissipation for the device consists of three main components: quiescent supply current dissipation (P_VM), the power MOSFET switching losses (P_SW), and the power MOSFET R_DS(on) (conduction) losses (P_RDS). While other factors may contribute additional power losses, they are typically insignificant compared to the three main items.

P_VM can be calculated from the nominal motor supply voltage (V_VM) and the I_VM active mode current specification.

P_SW can be calculated from the nominal motor supply voltage (V_VM), average output current (I_AVG), switching frequency (f_PWM) and the device output rise (t_RISE) and fall (t_FALL) time specifications.

P_RDS can be calculated from the device R_DS(on) and average output current (I_AVG).

R_DS(ON) has a strong correlation with the device temperature. Assuming a device junction temperature of 85 °C, R_DS(on) could increase ~1.5x based on the normalized temperature data. The calculation below shows this derating factor. Alternatively, Section 7.6 shows curves that plot how R_DS(on) changes with temperature.

Based on the example calculations above, the expressions below calculate the total expected power dissipation for the device.

The driver's junction temperature can be estimated using P_TOT, device ambient temperature (T_A), and package thermal resistance (R_θJA). The value for R_θJA depends heavily on the PCB design and copper heat sinking around the device. Section 9.3.2 describes this dependence in greater detail.

The device junction temperature should remain below its absolute maximum rating for all system operating conditions. The calculations in this section provide reasonable estimates for junction temperature. However, other methods based on temperature measurements taken during system operation are more realistic and reliable. Additional information on motor driver current ratings and power dissipation can be found in Section 9.3.2 and Section 12.1.1.