Datasheet

17Maxim Integrated
Integrated, 2-Channel, High-Brightness LED Driver
with High-Voltage Boost and SEPIC Controller
MAX16838
SEPIC Operation
Figure 4 shows a SEPIC application circuit using the
MAX16838. The SEPIC topology is necessary to keep
the output voltage of the DC-DC converter regulated
when the input voltage can rise above and drop below
the output voltage.
Boost-Buck Configuration
Figure 5 shows a boost-buck configuration with the
MAX16838 and MAX15054.
PCB Layout Considerations
LED driver circuits based on the MAX16838 device use
a high-frequency switching converter to generate the
voltage for LED strings. Take proper care while laying
out the circuit to ensure proper operation. The switching-
converter part of the circuit has nodes with very fast volt-
age changes that could lead to undesirable effects on
the sensitive parts of the circuit. Follow these guidelines
to reduce noise as much as possible:
1) Connect the bypass capacitor on V
CC
and DRV as
close as possible to the device, and connect the
capacitor ground to the analog ground plane using
vias close to the capacitor terminal. Connect SGND
of the device to the analog ground plane using a via
close to SGND. Lay the analog ground plane on the
inner layer, preferably next to the top layer. Use the
analog ground plane to cover the entire area under
critical signal components for the power converter.
2) Have a power ground plane for the switching-
converter power circuit under the power compo-
nents (input filter capacitor, output filter capacitor,
inductor, MOSFET, rectifier diode, and current-
sense resistor). Connect PGND to the power ground
plane as close to PGND as possible. Connect all
other ground connections to the power ground
plane using vias close to the terminals.
Figure 4. SEPIC Configuration
R
ISET
R2
OV
R1
OV
C
OUT
LED
STRINGS
R
RT
R
CS
R2
EN
R1
EN
C
VCC
C
DRV
R
DRV
IN DRAIN OV
NDRV
GATE
OUT1
OUT2
ISET
CS
RT
LEDGNDPGNDSGND
COMP
DIM
DRV
CFB
EN
C
IN
C
s
4.75V TO 40V
L
1
L
2
D
V
CC
R
COMP
C
COMP
FLT
MAX16838