MAX16814_15 Datasheet, PDF (14/25 Pages) Maxim Integrated Products – Integrated, 4-Channel, High-Brightness LED Driver with High-Voltage DC-DC Controller

MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
where RT is in Ω.
The pulse width for the synchronization pulse should
satisfy the following relations:
t _PW
t _CLK
V_S
<
0.5

^0.8

−
t _PW
t _CLK
V_S



+
V_S
>
3.4
t _PW
<
t _CLK
t _CI
(t _CI − 1.05 ×t _CLK )
where tPW is the synchronization source pulse width,
tCLK is the synchronization clock time period, tCI is the
programmed clock period, and VS is the synchronization
pulse voltage level.
5V LDO Regulator (VCC)
The internal LDO regulator converts the input voltage
at IN to a 5V output voltage at VCC. The LDO regulator
supplies up to 50mA current to provide power to internal
control circuitry and the gate driver. Connect a resistor
between VCC 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 VCC 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
function of the average current sourced to drive the
external MOSFET (IDRV) if there are no additional loads
on VCC. IDRV depends on the total gate charge (QG)
and operating frequency of the converter. Connect DRV
to VCC 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
current through each one of the four channels is adjust-
able between 20mA and 150mA using an external
resistor (RSETI) connected between SETI and SGND.
Select RSETI using the following formula:
R_SETI = 1500 I_{OUT_}
where IOUT_ 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
duration of the PWM signal is less than or equal to 5
oscillator 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 threshold 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
BOOST CONVERTER
OUTPUT
OUT1
MAX16814
OUT2
OUT3
OUT4
40mA TO 300mA
PER STRING
Figure 4. Configuration for Higher LED String Current
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