Two Brightness Levels for

TAIL/STOP Lights

Figure 4 shows PWM dimming operation for the

MAX16803 with an ICM7555 timer. The ICM7555 pro-

vides adjustable duty cycle using two external resistors

and a capacitor. In TAIL operation, the output of the

ICM7555 feeds into DIM and lights up the LEDs. The

LED’s brightness depends on the duty cycle of the

the LEDs light up to full brightness. See the ICM7555

data sheet for formulas to calculate the dimming fre-

quency and the duty cycle.

LED Current Thermal Foldback

With a minimum number of external components, the

MAX16803 provides LED current thermal foldback

using a negative temperature coefficient (NTC) thermis-

tor. Figure 5 shows a thermistor connected to V5 and

the CS+ of the MAX16803. As the temperature increas-

es, the voltage drop across R2 increases causing the

LED current to decrease.

High-Voltage, 350mA, High-Brightness LED

Driver with PWM Dimming and 5V Regulator

8

_______________________________________________________________________________________

IN

EN

DIM

CS-

CS+

OUT

GND

GND

OUT

TRG

DIS

IN

R2

ICM7555

C1

D2

TAIL

STOP

V5

TH

MAX16803

C2

+5V REG

D1

D4

D3

R1

LEDs

R3

C3

Figure 4. PWM Dimming Operation with ICM7555 Timer

IN

EN

DIM

CS-

CS+

OUT

GND

R1

LEDs

C1

V5

R2

RT

PWM DIMMING

MAX16803

C2

Figure 5. LED Current Thermal Foldback with an NTC Thermistor