MAX16814_10 Datasheet, PDF(14/25 Page) Maxim Integrated Products – Integrated, 4-Channel, High-Brightness LED Driver with High-Voltage DC-DC Controller

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Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

The pulse width for the synchronization pulse should

satisfy the following relations:

t PW

t CLK

0.5

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t PW

t CLK

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3.4

t PW

t CLK

t CI

(t CI â 1.05 Ãt 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 func-

tion 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 operat-

ing 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 cur-

rent through each one of the four channels is adjustable

between 20mA and 150mA using an external resistor

(RSETI) connected between SETI and SGND. Select

RSETI using the following formula:

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 converterâs output voltage. If the turn-on duration

of the PWM signal is less than 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

overtemperature shutdown. An open-drain LED fault

flag output (FLT) goes low when an open-LED string is

detected, a shorted LED string is detected, and during

BOOST CONVERTER

OUTPUT

OUT1

MAX16814

OUT2

OUT3

OUT4

40mA TO 300mA

PER STRING

RSETI = 1500 IOUT_

Figure 4. Configuration for Higher LED String Current

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