SLUAAH0 Application note

SLUAAH0 February 2022 UCC14130-Q1 , UCC14131-Q1 , UCC14140-Q1 , UCC14141-Q1 , UCC14240-Q1 , UCC14241-Q1 , UCC14340-Q1 , UCC14341-Q1 , UCC15240-Q1 , UCC15241-Q1

8.2.5 C_VEE Above Nominal Value C_VDD Below Nominal Value: I_{Q_VEE} > I_{Q_VDD}

Finally, consider the ILIM contribution for the combined effect of C_VDD to C_VEE capacitor value mismatch and gate driver I_Q variation. The case shown in Figure 8-5 is the combination of case 1 (Figure 8-1) and case 3 (Figure 8-3) where the RLIM regulator is sourcing current into the gate driver COM pin. This is the worst case where the voltage across C_VEE (COM-VEE) drifts lower resulting in ILIM sourcing additional compensating current through R_LIM to restore equal capacitor charge balance.

Figure 8-5 Case 1 and Case 3: C_VEE Higher, C_VDD Lower, I_{Q_VEE} > I_{Q_VDD}

The additional compensated charge, Δ_{QC_UP}, as a result of the worst case expected capacitor variation ΔC_VDD and ΔC_VEE is given by Equation 29 which is Equation 21 repeated here for completeness.

Equation 29.

{∆ Q}_{C_U P} = Q_{G} \times (\frac{C_{V E E} \times (1 - ∆ C_{V E E})}{C_{V D D} \times (1 - ∆ C_{V D D}) + C_{V E E} \times (1 - ∆ C_{V E E})} - \frac{C_{V E E}}{C_{V D D} + C_{V E E}})

R_LIM is calculated from Equation 30 and the power dissipated is given from Equation 31 where the total ILIM now consists of ΔQ_{C_UP} derived from the total capacitor variation and I_Q variation for the case that I_{Q_VEE} > I_{Q_VDD}.

Equation 30.

R_{L I M} = \frac{V D D - C O M}{I L I M} - R_{I N T_U P} = \frac{V D D - C O M}{{∆ Q}_{C_U P} \times F_{S W} + (I_{Q_V E E} - I_{Q_V D D})} - R_{I N T_U P}

Equation 31.

P_{R L I M} = {I L I M}^{2} {\times R}_{L I M} = {({∆ Q}_{C_U P} \times F_{S W} + (I_{Q_V E E} - I_{Q_V D D}))}^{2} \times R_{L I M}

8.2.5 CVEE Above Nominal Value CVDD Below Nominal Value: IQ_VEE > IQ_VDD

8.2.5 C_VEE Above Nominal Value C_VDD Below Nominal Value: I_{Q_VEE} > I_{Q_VDD}