MAX16836_09 Datasheet, PDF (8/11 Pages) Maxim Integrated Products – High-Voltage, 350mA, High-Brightness LED Driver with PWM Dimming and 5V Regulator

High-Voltage, 350mA, High-Brightness LED
Driver with PWM Dimming and 5V Regulator
Two Brightness Levels for
TAIL/STOP Lights
Figure 4 shows PWM dimming operation for the
MAX16836 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
V_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.
D1
STOP
D2
TAIL
R1
R2
D5
C1
D3
IN
DIS
OUT
ICM7555
R3
TH
TRG
GND
C3
D4
R4*
*R4 ≤ 300kΩ
Figure 4. PWM Dimming Operation with ICM7555 Timer
LED Current Thermal Foldback
With a minimum number of external components, the
MAX16836 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 MAX16836. As the temperature increas-
es, the voltage drop across R2 increases causing the
LED current to decrease.
I_LED
=
[V_SENSE
−
[R2 /(R2
+
RT)]
×
V5]
×
⎛
⎝⎜
R_T + R₂
R₁R_T
⎞
⎠⎟
(assuming I_RT < < I_LED).
IN
OUT
EN _MAX16836
+5V REG
V5
LEDs
C2
DIM
CS+
R_SENSE
GND
CS-
VIN
C1
PWM DIMMING
IN
OUT
EN
V5
MAX16836
DIM
CS+
GND
CS-
LEDs
C2
RT
R2
R1
Figure 5. LED Current Thermal Foldback with an NTC Thermistor
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