MAX16815/MAX16828
High-Voltage, 100mA/200mA Adjustable Linear
High-Brightness LED Drivers with PWM Dimming
8 _______________________________________________________________________________________
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 V
STOP
is present, DIM is
pulled up to V
STOP
. 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.
I
LED
= [V
RSNS
- (R2 / R
T
) (V
V5
- V
RSNS
)]/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
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:
V
IN(MIN)
> V
CESAT(MAX)
+ V
FT(MAX)
+ V
RSNS
where V
CESAT(MAX)
is the maximum saturation voltage
of the external BJT and V
FT(MAX)
is the total forward
voltage of all series connected LEDs.
