High-Voltage, 350mA, High-Brightness LED

Driver with PWM Dimming and 5V Regulator

6

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Functional Diagram

MAX16803

ENABLE

EN

REFERENCE

GENERATOR

REGULATOR

IN

V5

DIFFERENTIAL

SENSE

AMPLIFIER

THERMAL

SHUTDOWN

DIM

IN

OUT

CS+

CS-

Detailed Description

The MAX16803 is a high-current regulator capable of

providing up to a total of 350mA of current to one or

more strings of HB LEDs. A wide operating input volt-

age range of +6.5V to +40V makes the MAX16803

ideal for automotive applications. A +5V regulated out-

put provides up to 4mA of current to power external cir-

cuitry. In addition, the MAX16803 features thermal and

output short-circuit protection. The wide operating volt-

age range helps protect the MAX16803 against large

transients such as those found in load-dump situations

up to 40V.

The MAX16803 uses a feedback loop to control the out-

put current. The differential voltage across the sense

resistor is compared to a fixed reference voltage, and

the error is amplified to serve as the drive to the internal

power series pass device (see the

Functional

The MAX16803 is a current controller internally opti-

mized for driving the impedance range expected from

one or more HB LEDs.

+5V Regulator

The MAX16803 includes a fixed +5V output regulator

that delivers up to 4mA of load current throughout the

+6.5V to +40V input voltage range. Connect a 0.1µF

compensation capacitor from V5 to ground. Shorting

V5 to ground disables the thermal shutdown. When EN

is low, V5 is off. V5 stays on during PWM dimming.

Thermal Protection

The MAX16803 enters a thermal-shutdown mode in the

event of overheating. This typically occurs in overload or

output short-circuit conditions. If the junction tempera-

tection circuitry turns off the series pass device. The

MAX16803 recovers from thermal-shutdown mode once

the junction temperature drops by 23°C (typ). The part

therefore protects itself by thermally cycling in the event

of a short-circuit or overload condition.

Applications Information

Programming the LED Current

The MAX16803 uses a sense resistor across CS+ and

CS- to set the LED current. The differential sense ampli-

immunity and low-frequency noise rejection. The LED

current is given by