SLUSF12 Data sheet

SLUSF12A april 2023 – august 2023 UCC14131-Q1

PRODUCTION DATA

Package Options

Mechanical Data (Package|Pins)

DWN|36
- MPSS132

Thermal pad, mechanical data (Package|Pins)

Orderable Information

slusf12a_oa

12.2.2.3 RDR Circuit Component Selection

R_LIM1 value is chosen by

Equation 14.

R_{L I M 1} = \frac{(V_{V D D - V E E} - V_{C O M - V E E})}{(C_{O U T 3} \times (1 + {∆ C}_{O U T 3_P O S}) \times (\frac{0.1 \times V_{C O M - V E E}}{0.003}) + {∆ I}_{C O M_S O U R C E})} - R_{L I M_I N T}

where

∆I_{COM_SOURCE}=I_COM-VEE-I_VDD-COM, when I_COM-VEE>I_VDD-COM. Otherwise, ∆I_{COM_SOURCE}=0A

When the calculated R_LIM1 value is higher than 3kΩ, we suggest to use a 3kΩ resistor for R_LIM1. The reason is that the extra power loss saving with a >3kΩ resistor is very limited, and a maximum 3kΩ resistor is recommended to reserve enough sourcing capability through R_LIM1 for transient event.

R_LIM2 value is chosen by

Equation 15.

R_{L I M 2} = \frac{V_{C O M - V E E} - 0.5}{V_{C O M - V E E} ∙ (\frac{1}{R_{L I M_M A X_L}} - \frac{1}{R_{L I M_M A X_H}})}

where R_{LIM_MAX_L} is the smallest value between R_{LIM_MAX_L1} and R_{LIM_MAX_L2} in the Single R_LIM Resistor Selection Section, and 0.5V represents the diode forward voltage drop of D_LIM.

When the calculated R_LIM1 and R_LIM2 values have large enough difference, the RDR improvement on efficiency will be significant. If R_LIM1 and R_LIM2 values are close, then single R_LIM resistor can be considered to reduce the external components.

The power loss of R_LIM1 can be derived as

Equation 16.

P_{R L I M 1} = \frac{{V_{V D D - C O M}}^{2}}{R_{L I M 1}} {D u t y}_{R L I M} + {(I_{S I N K} \times \frac{V_{C O M - V E E} {\times R}_{L I M 2}}{V_{C O M - V E E} {\times R}_{L I M 2} + (V_{C O M - V E E} - 0.5) {\times R}_{L I M 1}})}^{2} {\times R}_{L I M 1}

where

Equation 17.

I_{S I N K} = {[\frac{C_{O U T 2} \times (1 - {∆ C}_{O U T 2})}{C_{O U T 2} \times (1 - {∆ C}_{O U T 2}) + C_{O U T 3} \times (1 - {∆ C}_{O U T 3})} - \frac{C_{O U T 2}}{C_{O U T 2} + C_{O U T 3}}] \times Q}_{G_{T o t a l}} \times f_{S W} + {∆ I}_{C O M_{S I N K}}

The power loss of R_LIM2 can be approximated as

Equation 18.

P_{R L I M 2} = {(I_{S I N K} \times \frac{(V_{C O M - V E E} - 0.5) {\times R}_{L I M 1}}{V_{C O M - V E E} {\times R}_{L I M 2} + (V_{C O M - V E E} - 0.5) {\times R}_{L I M 1}})}^{2} {\times R}_{L I M 2}

The maximum voltage rating of diode D_LIM needs to consider the highest V_VDD-to-VEE. The maximum current rating of D_LIM can be chosen based on the derating from the worst-case continuous current, (V_COM-to-VEE – V_{F_DLIM}) / R_LIM2, where V_{F_DLIM} is the forward voltage of D_LIM. The diode package size is determined based on the power loss in forward conduction, P_{Loss_DLIM} = V_{F_DLIM} x ((V_COM-to-VEE – V_{F_DLIM}) / R_LIM2). A Schottky diode is recommended to reduce the power loss.