MAX16815 데이터 시트보기 (PDF) - Maxim Integrated

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MAX16815

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

Maxim Integrated 

MAX16815/MAX16828

High-Voltage, 100mA/200mA Adjustable Linear

High-Brightness LED Drivers with PWM Dimming

D1

STOP

D2

TAIL

R1

R2

D3

C1

DIS

IN

OUT

R3

ICM7555

TH

TRG

GND

C2

D4

R4*

IN

OUT

MAX16815

MAX16828

+5V REG

V5

C2

DIM

CS+

GND

CS-

LEDs

RSENSE

*R4 < 300k

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 exter-

nal 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 disabled and the

LEDs light up to full brightness. See the ICM7555 data

sheet for formulas to calculate the dimming frequency and

the duty cycle.

LED Current Thermal Foldback

With a minimum number of external components, the

MAX16815/MAX16828 provide LED current thermal fold-

back using a negative temperature coefficient (NTC)

thermistor. Figure 2 shows a thermistor connected to V5

and the CS+ of the MAX16815/MAX16828. As the tem-

perature 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-

C2

RT

R2

LEDs

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.

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