MAX16814ATP+T Maxim Integrated Products, MAX16814ATP+T Datasheet - Page 16

• Manufacturer Part Number: MAX16814ATP+T
• Description: LED Drivers Integrated 4-Channel High-Brightness LED
• Manufacturer: Maxim Integrated Products

Specifications of MAX16814ATP+T

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
First select a converter topology based on the above
factors. Determine the required input supply voltage
range, the maximum voltage needed to drive the LED
strings including the minimum 1V across the constant
LED current sink (V
needed to drive the LED strings (I
where I
and N
Calculate the maximum duty cycle (D
lowing equations:
For boost configuration:
For SEPIC and coupled-inductor boost-buck-configura-
tions:
where V
volts (approximately 0.6V), V
supply voltage in volts, and V
voltage of the external MOSFET in volts when it is on,
and 0.3V is the peak current-sense voltage. Initially, use
an approximate value of 0.2V for V
Calculate a more accurate value of D
MOSFET is selected based on the maximum inductor
current. Select the switching frequency (f
on the space, noise, and efficiency constraints.
In all the three converter configurations, the average
inductor current varies with the line voltage and the
maximum average current occurs at the lowest line
voltage. For the boost converter, the average inductor
current is equal to the input current. Select the maximum
peak-to-peak ripple on the inductor current (DIL). The
recommended peak-to-peak ripple is 60% of the aver-
age inductor current.
16
_____________________________________________________________________________________
STRING
D
STRING
MAX
D1
D
is the forward drop of the rectifier diode in
MAX
=
is the number of strings used.
(V
I
is the LED current per string in amperes
LED
IN_MIN
=
(V
(V
=
LED
LED
I
LED
STRING
−
), and the total output current
+
V
Boost and Coupled-Inductor
(V
+
V
DS
Boost-Buck Configurations
D1
V
LED
IN_MIN
Power-Circuit Design
D1
×
−
DS
−
N
0.3V V
Inductor Selection
−
V
+
STRING
LED
DS
V
is the drain-to-source
DS
V
IN_MIN
is the minimum input
D1
MAX
+
MAX
−
to calculate D
) as follows:
)
0.3V)
LED
SW
after the power
) using the fol-
)
) depending
+
V )
D1
MAX
.
Use the following equations to calculate the maximum
average inductor current (IL
rent (IL
Allowing the peak-to-peak inductor ripple DIL to be
+30% of the average inductor current:
and:
Calculate the minimum inductance value, L
ries with the inductor current ripple set to the maximum
value:
where 0.3V is the peak current-sense voltage. Choose
an inductor that has a minimum inductance greater
than the calculated L
IL
selected inductor is 10% higher than the inductor peak
current for boost configuration. For the coupled-inductor
boost-buck, the saturation limit of the inductor with only
one winding conducting should be 10% higher than IL
Power circuit design for the SEPIC configuration is very
similar to a conventional boost-buck design with the
output voltage referenced to the input supply voltage.
For SEPIC, the output is referenced to ground and the
inductor is split into two parts (see Figure 5 for the SEPIC
configuration). One of the inductors (L2) takes LED cur-
rent as the average current and the other (L1) takes
input current as the average current.
Use the following equations to calculate the average
inductor currents (IL1
currents (IL1
P
. The recommended saturation current limit of the
P
) in amperes:
L
MIN
P,
IL1
IL2
=
AVG
(VIN
P
IL
∆
IL
) in amperes:
IL IL
AVG
P
MIN
=
MIN
AVG
=
=
I
IL
LED
AVG
=
and current rating greater than
−
, IL2
AVG
1 D
AVG
V
f
1 D
−
SW
×
DS
I
×
−
LED
SEPIC Configuration
D
0.3 2
AVG
+
MAX
) and peak inductor cur-
MAX
× ∆
−
MAX
∆
×
0.3V) D
2
IL
IL
) and peak inductor
×
1.1
×
MAX
MIN
, in hen-
P
.