MAX16828ASA(2009) 查看數據表（PDF） - Maxim Integrated

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MAX16828ASA
(Rev.:2009)

High-Voltage, 100mA/200mA Adjustable Linear High-Brightness LED Drivers with PWM Dimming

Maxim Integrated 

High-Voltage, 100mA/200mA Adjustable Linear

High-Brightness LED Drivers with PWM Dimming

D1

STOP

D2

TAIL

R1

R2

D3

C1

DIS

IN

D4

OUT

R3

ICM7555

R4*

TH

TRG

GND

C2

IN

OUT

MAX16815

MAX16828

+5V REG

V5

C2

DIM

CS+

GND

CS-

LEDs

RSENSE

*R4 < 300kΩ

Figure 1. PWM Dimming Operation with ICM7555 Timer

Two Brightness Levels for

TAIL/STOP Lights

Figure 1 shows PWM dimming operation for the

MAX16815/MAX16828 with an ICM7555 timer. The

ICM7555 provides 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 VSTOP is present, DIM is

pulled up to VSTOP. The PWM dimming operation is dis-

abled and the LEDs light up to full brightness. See the

ICM7555 data sheet for formulas to calculate the dim-

ming frequency and the duty cycle.

LED Current Thermal Foldback

With a minimum number of external components, the

MAX16815/MAX16828 provide LED current thermal

foldback using a negative temperature coefficient

(NTC) thermistor. Figure 2 shows a thermistor connect-

ed to V5 and the CS+ of the MAX16815/MAX16828. As

the temperature increases, the voltage drop across R2

increases, causing the LED current to decrease.

ILED = [VRSNS - (R2 / RT) (VV5 - VRSNS)]/R1

Other Applications

The application circuit in Figure 3 implements a two-

level brightness current for TAIL/STOP lights. In TAIL

operation, Q1 is off and R1 sets the output current. In

VIN

C1

PWM

DIMMING

IN

OUT

MAX16815

MAX16828

V5

DIM

CS+

GND

CS-

LEDs

C2

RT

R2

R1

Figure 2. LED Current Thermal Foldback with an NTC

Thermistor

STOP operation, Q1 turns on and the output current is

set by a parallel combination of R1 and R2. Figure 4

shows an application circuit with the MAX16815/

MAX16828 using a single BJT to provide high output

current. For proper operation:

VIN(MIN) > VCESAT(MAX) + VFT(MAX) + VRSNS

where VCESAT(MAX) is the maximum saturation voltage

of the external BJT and VFT(MAX) is the total forward

voltage of all series connected LEDs.

8 _______________________________________________________________________________________

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