High-Voltage, 350mA LED Driver with
Analog and PWM Dimming Control
LED Current Thermal Foldback
With a minimum number of external components, the
MAX16804 provides LED current thermal foldback
using a negative temperature coefficient (NTC) thermis-
tor. Figure 3 shows a thermistor connected to V5 and
the CS+ of the MAX16804. As the temperature increas-
es, the voltage drop across R2 increases causing the
LED current to decrease.
I LED = [V SENSE - [R2/(R2 + RT)] x V5]/R1 (4)
Other Applications
Figure 4 shows an application circuit with the
MAX16804 using a single BJT to provide high output
current. For proper operation:
V IN(MIN) > V CESAT(MAX) + V FT(MAX) + V RSENSE (5)
where V CESAT(MAX) is the maximum saturation voltage
of the external BJT.
V IN
C1
IN
OUT
PWM DIMMING
EN
DIM
GND
MAX16804
V5
CS+
CS-
C2
RT
R2
LEDs
R1
Figure 3. LED Current Thermal Foldback Operation with an NTC Thermistor
LEDs
V IN
IN
OUT
Q1
C1
EN
V5
C2
MAX16804
PWM DIMMING
DIM
GND
Figure 4. Increased Output Current (Ampere Range) with a Single BJT
CS+
CS-
R SENSE
8
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