Datasheet

14 Maxim Integrated
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
MAX16814
where R
T
is in Ω.
The pulse width for the synchronization pulse should
satisfy the following relations:
( )
PW
S
CLK
PW
SS
CLK
CLK
PW CI CLK
CI
t
V 0.5
t
t
0.8 V V 3.4
t
t
t t 1.05 t
t
<

− +>


< −×
where t
PW
is the synchronization source pulse width,
t
CLK
is the synchronization clock time period, t
CI is the
programmed clock period, and
V
S
is the synchronization
pulse voltage level.
5V LDO Regulator (V
CC
)
The internal LDO regulator converts the input voltage
at IN to a 5V output voltage at V
CC
. The LDO regulator
supplies up to 50mA current to provide power to internal
control circuitry and the gate driver. Connect a resistor
between V
CC
and DRV to power the gate-drive circuitry;
the recommended value is 4.7I. Bypass DRV with a
capacitor to PGND. The external resistor and bypass
capacitor provide noise filtering. Bypass V
CC
to SGND
with a minimum of 1FF ceramic capacitor as close to the
device as possible.
PWM MOSFET Driver
The NDRV output is a push-pull output with the on-resis-
tance of the pMOS typically 1.1I and the on-resistance
of the nMOS typically 0.9I. NDRV swings from PGND to
DRV to drive an external n-channel MOSFET. The driver
typically sources 2.0A and sinks 2.0A allowing for fast
turn-on and turn-off of high gate-charge MOSFETs.
The power dissipation in the MAX16814 is mainly a func-
tion of the average current sourced to drive the external
MOSFET (I
DRV
) if there are no additional loads on V
CC
.
I
DRV
depends on the total gate charge (Q
G
) and operat-
ing frequency of the converter. Connect DRV to V
CC
with
a 4.7I resistor to power the gate driver with the internal
5V regulator.
LED Current Control
The MAX16814 features four identical constant-current
sources used to drive multiple HB LED strings. The cur-
rent through each one of the four channels is adjustable
between 20mA and 150mA using an external resistor
(R
SETI
) connected between SETI and SGND. Select
R
SETI
using the following formula:
SETI OUT_
R 1500 I=
where I
OUT_
is the desired output current for each of the
four channels.
If more than 150mA is required in an LED string, use two
or more of the current source outputs (OUT_) connected
together to drive the string as shown in Figure 4.
LED Dimming Control
The MAX16814 features LED brightness control using an
external PWM signal applied at DIM. A logic-high signal
on the DIM input enables all four LED current sources
and a logic-low signal disables them.
For the MAX16814A_ _ and the MAX16814U_ _, the duty
cycle of the PWM signal applied to DIM also controls the
DC-DC converter’s output voltage. If the turn-on dura-
tion of the PWM signal is less than or equal to 5 oscilla-
tor clock cycles (DIM pulse width decreasing) then the
boost converter regulates its output based on feedback
from the OVP input. During this mode, the converter
output voltage is regulated to 95% of the OVP thresh-
old voltage. If the turn-on duration of the PWM signal is
greater than or equal to 6 oscillator clock cycles (DIM
pulse width increasing), then the converter regulates its
output so that the minimum voltage at OUT_ is 1V.
Fault Protections
Fault protections in the MAX16814 include cycle-by-
cycle current limiting using the PWM controller, DC-DC
converter output overvoltage protection, open-LED
detection, short LED detection and protection, and
overtemperature shutdown. An open-drain LED fault
Figure 4. Configuration for Higher LED String Current
OUT1
40mA TO 300mA
PER STRING
BOOST CONVERTER
OUTPUT
MAX16814
OUT2
OUT3
OUT4