High-Voltage, 350mA LED Driver with

Analog and PWM Dimming Control

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7

The dimming feature can be used for LED brightness

adjustment (see the Simplified Diagrams) and theater

dimming. If an external PWM signal is used, the theater-

dimming effect can be achieved by varying the PWM

duty cycle. Figure 1 shows a simple circuit that imple-

ments theater dimming with a DC input signal.

+5V Regulator

The MAX16804 includes a fixed +5V output regulator

that delivers up to 2mA of load current throughout the

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

pensation 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 MAX16804 enters a thermal-shutdown mode in the

event of overheating. This typically occurs in overload or

short-circuit conditions on the output. If the junction tem-

mal-protection circuitry turns off the series pass device.

The MAX16804 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 MAX16804 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

(2)

Input-Voltage Considerations

For proper operation, the minimum input voltage must

always be:

series connected LEDs and

drop output voltage. The minimum operating voltage of

the device is +5.5V.

Two Brightness Levels for

TAIL/STOP Lights

Figure 2 shows two-level brightness adjustment using

the MAX16804 with minimum external components. Set

the dimming level with a resistive divider connected to

DIM. See Equation 1 for details.

MAX16804

IN

OUT

V5

LEDs

VIN

THEATER

DIMMING

SIGNAL

+5V REG

CS+

0.1

μF

CS-

DIM

GND

EN

Figure 1. Theater Dimming

IN

EN

DIM

CS-

CS+

OUT

GND

R1

R2

TAIL

STOP

D1

D2

V5

MAX16804

LEDs

Figure 2. Two-Level Brightness Operation