MAX16814AUP+T【PDF 15/25 页】IC LED DVR HI-BRIGHT 4CH 20TSSOP

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MAX16814

Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

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

detected, a shorted LED string is detected, and during

thermal shutdown. FLT is cleared when the fault condi-

tion is removed during thermal shutdown and shorted

LEDs. FLT is latched low for an open-LED condition

and can be reset by cycling power or toggling the EN

pin. The thermal shutdown threshold is +165 N C and has

15 N C hysteresis.

Open-LED Management and Overvoltage Protection

On power-up, the MAX16814 detects and disconnects

any unused current-sink channels before entering soft-

start. Disable the unused current-sink channels by

connecting the corresponding OUT_ to LEDGND. This

avoids asserting the FLT output for the unused chan-

nels. After soft-start, the MAX16814 detects open LED

and disconnects any strings with an open LED from the

internal minimum OUT_ voltage detector. This keeps the

DC-DC converter output voltage within safe limits and

maintains high efficiency. During normal operation, the

DC-DC converter output regulation loop uses the mini-

mum OUT_ voltage as the feedback input. If any LED

string is open, the voltage at the opened OUT_ goes

to V LEDGND . The DC-DC converter output voltage then

increases to the overvoltage protection threshold set by

the voltage-divider network connected between the con-

verter output, OVP input, SGND. The overvoltage protec-

tion threshold at the DC-DC converter output (V OVP ) is

determined using the following formula:

Short LED Detection

The MAX16814 checks for shorted LEDs at each rising

edge of DIM. An LED short is detected at OUT_ if the

following condition is met:

V OUT_ > V MINSTR + 3 x V RSDT

where V OUT_ is the voltage at OUT_, V MINSTR is the

minimum current-sink voltage, and V RSDT is the pro-

grammable LED short detection threshold set at the

RSDT input. Adjust V RSDT using a voltage-divider resis-

tive network connected at the V CC output, RSDT input,

and SGND.

Once a short is detected on any of the strings, the LED

strings with the short are disconnected and the FLT out-

put flag asserts until the device detects that the shorts

are removed on any of the following rising edges of DIM.

Connect RSDT directly to V CC to always disable LED

short detection.

Applications Information

DC-DC Converter

Three different converter topologies are possible with

the DC-DC controller in the MAX16814, which has the

ground-referenced outputs necessary to use the con-

stant current-sink drivers. If the LED string forward volt-

age is always more than the input supply voltage range,

use the boost converter topology. If the LED string for-

ward voltage falls within the supply voltage range, use

the boost-buck converter topology. Boost-buck topology

V OVP = 1.23 × ? 1 +

R1 ?

R2 ? ?

(see the Typical Operating Circuit)

is implemented using either a conventional SEPIC con-

figuration or a coupled-inductor boost-buck configura-

tion. The latter is basically a flyback converter with 1:1

where 1.23V (typ) is the OVP threshold. Select R1 and

R2 such that the voltage at OUT_ does not exceed the

absolute maximum rating. As soon as the DC-DC con-

verter output reaches the overvoltage protection thresh-

old, the PWM controller is switched off setting NDRV

low. Any current-sink output with V OUT_ < 300mV (typ) is

disconnected from the minimum voltage detector.

Connect the OUT_ of all channels without LED connec-

tions to LEDGND before power-up to avoid OVP trigger-

ing at startup. When an open-LED overvoltage condition

occurs, FLT is latched low.

Maxim Integrated

turns ratio. 1:1 coupled inductors are available with tight

coupling suitable for this application. Figure 6 shows

the coupled-inductor boost-buck configuration. It is also

possible to implement a single inductor boost-buck con-

verter using the MAX15054 high-side FET driver.

The boost converter topology provides the highest

efficiency among the above mentioned topologies. The

coupled-inductor boost-buck topology has the advan-

tage of not using a coupling capacitor over the SEPIC

configuration. Also, the feedback loop compensation for

SEPIC becomes complex if the coupling capacitor is not

large enough. A coupled-inductor boost-buck is not suit-

able for cases where the coupled-inductor windings are

not tightly coupled. Considerable leakage inductance

requires additional snubber components and degrades

the efficiency.

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MAX16814BEUP+ 功能描述:LED照明驱动器 4Ch HB Drvr w/High-V DC/DC Controller RoHS:否制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N

MAX16814BEUP+T 功能描述:LED照明驱动器 4Ch HB Drvr w/High-V DC/DC Controller RoHS:否制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N

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