
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
The factor 1.1 provides a 10% margin to account for the
converter losses:
IL2 AVG = I LED
For simplifying further calculations, consider L1 and
L2 as a single inductor with L1 and L2 connected in
parallel. The combined inductance value and current is
calculated as follows:
Assuming the peak-to-peak inductor ripple D IL is Q 30%
of the average inductor current:
L MIN =
L1 MIN × L2 MIN
L1 MIN + L2 MIN
and:
IL1
?= IL1 AVG × 0.3 × 2
and:
IL AVG
= IL1 AVG + IL2 AVG
IL1 P
= IL1 AVG +
? IL1
2
where IL AVG represents the total average current through
both the inductors together for SEPIC configuration. Use
these values in the calculations for SEPIC configuration
= IL2 AVG +
IL2 P
L1 MIN =
L2 MIN =
C S ≥
IL2
? = IL2 AVG × 0.3 × 2
and:
? IL2
2
Calculate the minimum inductance values L1 MIN and
L2 MIN in henries with the inductor current ripples set to
the maximum value as follows:
(VIN MIN ? V DS ? 0.3V) × D MAX
f SW × ? IL1
(VIN MIN ? V DS ? 0.3V) × D MAX
f SW × ? IL2
where 0.3V is the peak current-sense voltage. Choose
inductors that have a minimum inductance greater than
the calculated L1 MIN and L2 MIN and current rating
greater than IL1 P and IL2 P , respectively. The recom-
mended saturation current limit of the selected inductor
is 10% higher than the inductor peak current:
Maxim Integrated
in the following sections.
Select coupling capacitor C S so that the peak-to-peak
ripple on it is less than 2% of the minimum input sup-
ply voltage. This ensures that the second-order effects
created by the series resonant circuit comprising L1,
C S , and L2 does not affect the normal operation of the
converter. Use the following equation to calculate the
minimum value of C S :
I LED × D MAX
V IN_MIN × 0.02 × f SW
where C S is the minimum value of the coupling capacitor
in farads, I LED is the LED current in amperes, and the
factor 0.02 accounts for 2% ripple.
Slope Compensation
The MAX16814 generates a current ramp for slope com-
pensation. This ramp current is in sync with the switch-
ing frequency and starts from zero at the beginning of
every clock cycle and rises linearly to reach 50 F A at the
end of the clock cycle. The slope-compensating resistor,
R SCOMP , is connected between the CS input and the
source of the external MOSFET. This adds a program-
mable ramp voltage to the CS input voltage to provide
slope compensation.
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