LM3424_0910 Datasheet, PDF (33/50 Pages) National Semiconductor (TI) – Constant Current N-Channel Controller with Thermal Foldback for Driving LEDs

10. INPUT CAPACITANCE
Solve for the minimum C_IN:
13. INPUT UVLO
Solve for R_UV2:
To minimize power supply interaction a 200% larger capaci-
tance of approximately 20 µF is used, therefore the actual
Δv_IN-PP is much lower. Since high voltage ceramic capacitor
selection is limited, four 4.7 µF X7R capacitors are chosen.
Determine minimum allowable RMS current rating:
The closest standard resistor is 150 kΩ therefore V_HYS is:
Solve for R_UV1:
The chosen components from step 10 are:
11. NFET
Determine minimum Q1 voltage rating and current rating:
The closest standard resistor is 21 kΩ making V_TURN-ON:
The chosen components from step 13 are:
A 100V NFET is chosen with a current rating of 32A due to
the low R_DS-ON = 50 mΩ. Determine I_T-RMS and P_T:
14. OUTPUT OVLO
Solve for R_OV2:
The chosen component from step 11 is:
12. DIODE
Determine minimum D1 voltage rating and current rating:
The closest standard resistor is 499 kΩ therefore V_HYSO is:
Solve for R_OV1:
The closest standard resistor is 15.8 kΩ making V_TURN-OFF:
A 100V diode is chosen with a current rating of 12A and V_D =
600 mV. Determine P_D:
The chosen component from step 12 is:
The chosen components from step 14 are:
33
www.national.com