9.3.1.1 Power Dissipation Due to Device On-State Resistance (R_DS(ON))

The current path for a motor connected in full-bridge is through the high-side FET of one half-bridge and low-side FET of other half-bridge. The power dissipation of DRV89XX-Q1 depends on the amount of current flowing through the full-bridge and the number of such full-bridges which are operating together. The power dissipation (P_{FB_CONT}) in a single full-bridge configuration for continuous mode depends on the motor rms current (I_RMS) and high-side (R_{DS(ON)_HS}) and low-side (R_{DS(ON)_LS}) on-state resistance as shown in Equation 1.

The power dissipation (P_{FB_STALL}) in a single full-bridge configuration for motor is a stall condition depends on the motor peak current (I_PEAK) and high-side (R_{DS(ON)_HS}) and low-side (R_{DS(ON)_LS}) on-state resistance as shown in Equation 2.

Now, the power dissipation for operating mode and stall mode in single full-bridge for the typical application as shown in Table 92 is calculated in Equation 3 and Equation 4 respectively.

For N_F-full bridges in operating condition and N_S-full bridges in stall condition, the total driver power (P_DRV) is expressed and calculated as shown in Equation 5.