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1. OPERATING POINT
Solve for V
O
and r
D
:
Solve for D, D', D
MAX
, and D
MIN
:
2. SWITCHING FREQUENCY
Solve for R
T
:
The closest standard resistor is 14.3 k
Ω
therefore f
SW
is:
The chosen component from step 2 is:
3. AVERAGE LED CURRENT
Solve for R
SNS
:
Assume R
CSH
= 12.4 k
Ω
and solve for R
HSP
:
The closest standard resistor for R
SNS
is actually 0.1
Ω
and for
R
HSP
is actually 1 k
Ω
therefore I
LED
is:
The chosen components from step 3 are:
4. THERMAL FOLDBACK
Find the resistances corresponding to T
BK
and T
END
(R
NTC-
BK
= 24.3 k
Ω
and R
NTC-END
= 7.15 k
Ω
) from the manufacturer's
datasheet. Assuming R
REF1
= R
REF2
= 49.9 k
Ω
, then R
BIAS
=
R
NTC-BK
= 24.3 k
Ω.
Solve for R
GAIN
:
The chosen components from step 4 are:
5. INDUCTOR RIPPLE CURRENT
Solve for L1:
The closest standard inductor is 33 µH therefore
Δ
i
L-PP
is:
Determine minimum allowable RMS current rating:
The chosen component from step 5 is:
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LM3424