MAX16838ATP/V+ Maxim Integrated, MAX16838ATP/V+ Datasheet - Page 16

• Manufacturer Part Number: MAX16838ATP/V+
• Description: LED Lighting Drivers Integrated 2-Channel High-Brightness LED Drivers with High-Voltage DC-DC Controller
• Manufacturer: Maxim Integrated

Specifications of MAX16838ATP/V+

• Input Voltage: 4.75 V to 40 V
• Maximum Supply Current: 3.1 mA
• Power Dissipation: 2051 mW

Integrated, 2-Channel, High-Brightness LED Driver
with High-Voltage Boost and SEPIC Controller
For the boost converter, the output capacitor
supplies 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 compensa-
tion for stable operation. This is done by connecting
a resistor (R
from COMP to SGND. R
frequency integrator gain for fast transient response,
while C
tain loop stability. 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
is the current-sense resistor in series with the
/5.
COMP
from above, the crossover frequency is at
MAX
=
C
COMP
is chosen to set the integrator zero to main-
COMP
5 FP1 GM
f
ZRHP
FP1
×
LED
is the maximum duty cycle that occurs
) and capacitor (C
=
=
×
2
is the output voltage of the boost
=
× ×
f
2
ZRHP
π
COMP
V
π
LED
COMP
COMP
2
×
V
π
I
R
LED
LED
(1 D
Feedback Compensation
× ×
×
COMP
COMP
is chosen to set the high-
−
L I
R
×
CS
50
×
and C
V
MAX
C
LED
LED
×
OUT
is the transconduc-
×
I
LED
f
ZRHP
)
COMP
× −
COMP
2
(1 D
LED
) in series
MAX
is the total
a decade
)