LM3423 Datasheet, PDF (6/10 Pages) National Semiconductor (TI) – The boost circuit can be easily redesigned for different

5. OUTPUT CAPACITANCE
Solve for C_O:
T_U0 is approximated:
To ensure stability, calculate ω_P2:
A total value of 40 µF (using 4 10 µF ceramic capacitors) is
chosen to improve PWM dimming response therefore the ac-
tual Δi_LED-PP is:
Solve for C8:
Determine minimum allowable RMS current rating:
To attenuate switching noise, calculate ω_P3:
The chosen components from step 5 are:
6. PEAK CURRENT LIMIT
Solve for R6:
The closest standard resistor is 0.06 Ω therefore I_LIM is:
Assume R20 = 10Ω and solve for C12:
Since PWM dimming can be evaluated with this board, a
much larger compensation capacitor C8 = 1.0 µF is chosen
and a smaller high frequency capacitor C12 = 0.1 µF is cho-
sen.
The chosen components from step 7 are:
The chosen component from step 6 is:
7. LOOP COMPENSATION
ω_P1 is approximated:
ω_Z1 is approximated:
8. INPUT CAPACITANCE
Solve for the minimum C_IN:
To minimize power supply interaction a much larger capaci-
tance of 100 µF is used, therefore the actual Δv_IN-PP is much
lower.
Determine minimum allowable RMS current rating:
The chosen components from step 8 are:
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