High-Voltage, 3-Channel Linear High-Brightness

LED Driver with Open LED Detection

6

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Detailed Description

The MAX16823 three-channel current regulator operates

from a 5.5V to 40V input voltage range and delivers up

to 100mA per channel to one or more strings of

HBLEDs. The output currents are programmable using

external current-sense resistors in series with the LEDs.

Three DIM inputs allow a wide range of independent

pulsed dimming in addition to providing the on and off

control of the outputs. The MAX16823 offers an LED-

GOOD output that indicates an open-circuit condition

when one or more LED channels are open.

Integrated pass elements minimize external compo-

nents while providing

±5% output current accuracy.

Additional features include a 3.4V (±5%) voltage regula-

tor with 4mA output current capability, short-circuit and

thermal protection.

The MAX16823 uses a feedback loop to linearly control

the current from each output. The voltage across each

sense resistor is compared to a fixed reference voltage

and the error is amplified to drive the internal power

pass device for a particular channel. See the

Block

Diagram. The regulation point is factory-set at 203mV.

The regulated current is adjusted by the value of

The MAX16823 is a constant-current LED driver inter-

nally optimized for driving the impedance range

expected from one or more HBLEDs.

3.4V Regulator (REG)

The MAX16823 includes a fixed 3.4V voltage regulator

that delivers up to 4mA of load current for auxiliary

applications throughout the 5.5V to 40V input voltage

range. Connect a 0.1µF compensation capacitor from

REG to ground. Shorting REG to ground disables the

thermal shutdown.

Thermal Protection

The MAX16823 enters a thermal-shutdown mode in the

event of overheating. This typically occurs in overload or

output short-circuit conditions. When the junction temper-

tion circuitry turns off the series pass elements. The

MAX16823 recovers from thermal-shutdown mode once

the junction temperature drops by 23°C. The part will

therefore protect itself by low-frequency thermal cycling

in the event of a short-circuit or overload condition.

Applications Information

Programming the LED Current

The MAX16823 uses sense resistors to set the output

current for each channel. To set the LED current for a

particular channel, connect a sense resistor across the

corresponding current-sense input (CS_) and GND. For

optimal accuracy, connect the low-side of the current-

sense resistors to the IC’s ground pin with short traces.

The value needed for the sense resistor for a given cur-

rent can be calculated with the equation below:

Input-Voltage Considerations

For proper operation, the minimum input voltage must

always be:

connected LEDs. The minimum operating voltage of

the device is 5.5V.

LEDGOOD

The MAX16823 features an active-low, open-drain

LEDGOOD output that goes low either when one or

more LED channels are open or when a signal at any of

the dimming inputs remains low for a period greater

LGC and ground. The LEDGOOD output goes low after

the following formula to set the delay period:

and ground. The LEDGOOD output goes low during

the thermal shutdown.

tC

F

DELAY

LGC

=×

257 900

,( )

( )

Ω

VV

V

V

IN MIN

CS MAX

FT MAX

DO MAX

()

_(

)

(

)

(

)

≥+

+

R

VV

IA

CS

CS

OUT

_

_

_

()

()

()

Ω=