MAX16803 Maxim Integrated Products, MAX16803 Datasheet - Page 8

• Manufacturer Part Number: MAX16803
• Description: High-Brightness LED Driver
• Manufacturer: Maxim Integrated Products

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
V
the LEDs light up to full brightness. See the ICM7555
data sheet for formulas to calculate the dimming fre-
quency and the duty cycle.
High-Voltage, 350mA, High-Brightness LED
Driver with PWM Dimming and 5V Regulator
Figure 4. PWM Dimming Operation with ICM7555 Timer
Figure 5. LED Current Thermal Foldback with an NTC Thermistor
8
STOP
_______________________________________________________________________________________
. The PWM dimming operation is disabled and
C3
R3
DIS
TH
TRG
STOP
R2
STOP
TAIL
V
ICM7555
IN
Two Brightness Levels for
C1
IN
is present, DIM is pulled up to
GND
OUT
D3
PWM DIMMING
R1
TAIL/STOP Lights
D4
IN
EN
DIM
GND
D1
D2
C1
MAX16803
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.
IN
EN
DIM
GND
OUT
CS+
CS-
V5
I
LED
MAX16803
= [V
C2
SENSE
LED Current Thermal Foldback
OUT
CS+
RT
CS-
V5
- [R2 / (R2 + RT)] x V5] / R1
+5V REG
R2
C2
LEDs
R1
www.DataSheet4U.com
LEDs
R
SENSE