Rainbow-electronics MAX16803 Manual do Utilizador descarregar pdf (Página 8)

MAX16803

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

ICM7555. When V

STOP

is present, DIM is pulled up to

STOP

. The PWM dimming operation is disabled and

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.

LED

= [V

SENSE

- [R2 / (R2 + RT)] x V5] / R1

High-Voltage, 350mA, High-Brightness LED

Driver with PWM Dimming and 5V Regulator

8 _______________________________________________________________________________________

DIM

CS-

CS+

OUT

GND

OUT

TRG

DIS

ICM7555

TAIL

STOP

SENSE

MAX16803

+5V REG

LEDs

Figure 4. PWM Dimming Operation with ICM7555 Timer

DIM

CS-

CS+

OUT

GND

LEDs

PWM DIMMING

MAX16803

Figure 5. LED Current Thermal Foldback with an NTC Thermistor

1 2 3 4 5 6 7 8 9 10 11 12

MAX16803 1
PACKAGE OUTLINE 12

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