MAX16838AUP/V+T Maxim Integrated Products, MAX16838AUP/V+T Datasheet - Page 16

• Manufacturer Part Number: MAX16838AUP/V+T
• Description: LED Drivers Integrated 2-Channel High-Brightness LED
• Manufacturer: Maxim Integrated Products

Specifications of MAX16838AUP/V+T

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

Integrated, 2-Channel, High-Brightness LED Driver
with High-Voltage Boost and SEPIC Controller
For the boost converter, the output capacitor sup-
plies the load current when the main switch is on. The
required output capacitance is high, especially at higher
duty cycles.
Calculate the output capacitor (C
ing equation:
where V
supply voltage. Use a combination of low-ESR and high-
capacitance ceramic capacitors for lower output ripple
and noise.
The input current for the boost converter is continuous
and the RMS ripple current at the input capacitor is low.
Calculate the minimum input capacitor C
lowing equation:
where V
This equation assumes that input capacitors supply
most of the input ripple current.
Using a Schottky rectifier diode produces less forward drop
and puts the least burden on the MOSFET during reverse
recovery. A diode with considerable reverse-recovery time
increases the MOSFET switching loss. Select a Schottky
diode with a voltage rating 20% higher than the maximum
boost-converter output voltage and current rating greater
than that calculated in the following equation:
16
Input Capacitor Selection in Boost Configuration
_____________________________________________________________________________________
C
IN_P-P
LED_P-P
OUT
C
> (D
IN
is the peak-to-peak input ripple voltage.
I
D
= IL
is the peak-to-peak ripple in the LED
=
MAX
1.2
P-P
× 
x I
/(8 x f



Output Capacitor Selection in
LED
1 D
IL
-
AVG
SW
Rectifier Diode Selection
)/(V
MAX
LED_P-P
x V
OUT
Boost Configuration




IN_P-P
( )
) using the follow-
A
IN
x f
)
using the fol-
SW
)
The voltage feedback loop needs proper compensation
for stable operation. This is done by connecting a resis-
tor R
SGND. R
grator gain for fast transient response while C
chosen to set the integrator zero to maintain loop stabil-
ity. For optimum performance, choose the components
using the following equations:
where
is the right half plane zero for the boost regulator.
R
source of the internal switching MOSFET. I
LED current that is the sum of the LED currents in both
the channels. V
regulator. D
at minimum input voltage. GM
tance of the error amplifier.
is the output pole formed by the boost regulator.
Set the zero formed by R
below the crossover frequency. Using the value of
R
f
ZRHP
CS
COMP
R
COMP
COMP
is the current-sense resistor in series with the
/5.
from above, the crossover frequency is at
COMP
and capacitor C
MAX
=
C
COMP
5 FP1 GM
f
ZRHP
FP1
is chosen to set the high-frequency inte-
×
LED
is the maximum duty cycle that occurs
=
=
×
is the output voltage of the boost
2
=
× ×
f
2
ZRHP
π
V
π
LED
COMP
COMP
2
COMP
×
π
V
I
R
LED
LED
(1 D
Feedback Compensation
× ×
×
COMP
COMP
−
L I
R
×
CS
50
×
and C
in series from COMP to
V
MAX
C
LED
LED
×
OUT
is the transconduc-
×
I
LED
f
ZRHP
)
× −
COMP
2
(1 D
LED
MAX
is the total
a decade
COMP
)
is