C(RX): Choose C(RX) between 200 pF and 600 pF. A 560 pF, 50 V, ±5% COG/NPO ceramic is recommended for both CC1 and CC2 pins.
Q1: For a 3 A application, an N-Channel MOSFET with RDS(on) in the 10 mΩ range is sufficient. BV(DSS) should be rated for 30 V for applications delivering 20 V, and 25 V for 15 V applications. For this application, the TI CSD17579Q3A (SLPS527) NexFET™ is suitable.
RS: TPS25740B OCP set point thresholds are targeted towards a 5 mΩ, ±1% sense resistor. Power dissipation for RS at 3 A load is approximately 45 mW.
R(DSCG): The minimum value of R(DSCG) is chosen based on the application VBUS (max) and I(DSCGT). For VBUS (max) = 15 V and I(DSCGT) = 350 mA, RDS(CG(min)) = 42.9 Ω. The size of the external resistor can then be chosen based on the capacitive load that needs to be discharged and the maximum allowed discharge time of 265 ms. Typically, a 120 Ω, 0.5 W resistor provides suitable performance.
RF/CF: Not used
C(PDIN): The requirement for C(PDIN) is 10 µF maximum. A 6.8 µF, 25 V, ±10% X5R or X7R ceramic capacitor is suitable for most applications.
D(VBUS): D(VBUS) provides reverse transient protection during large transient conditions when inductive loads are present. A Schottky diode with a V(RRM) rating of 30 V in a SMA package such as the B340A-13-F provides suitable reverse voltage clamping performance.
C(SLEW): To achieve a slew rate from zero to 5 V of less than 30 mV / µs using the typical GDNG current of 20 µA then C(SLEW) (nF) > 20 µA / 30 mV / µs = 0.67 nF be used. Choosing C(SLEW) = 10 nF yields a ramp rate of 2 mV / µs.
R(FBL1)/R(FBL2)/R(FBL3): In this design example, R(FBU) = 49.9 kΩ and R(FBL) = 9.53 kΩ. The feedback error amplifier VREF = 0.8 V. Using the equations for R(FBL2) (Equation 5 and Equation 6) provide a calculated value of 9.9 kΩ and a selected value of 9.76 kΩ. In similar fashion for R(FBL1), a calculated value of 6.74 kΩ and a selected value of 6.65 kΩ is provided. Lastly for R(FBL3), the calculated value is 8.1 kΩ with a selected value of 8.06 kΩ.
C(SLU)/C(SLL): The value of C(SLU) is calculated based on the desired 95% slew rate using Equation 13 and Equation 14. Choose a 22 nF capacitor for C(SLU). Choose a 100 nF capacitor for C(SLL).