TL4242QKTTRQ1 Datasheet, PDF (8/21 Pages) Texas Instruments – ADJUSTABLE LED DRIVER

TL4242-Q1
SLVS732E – JULY 2010 – REVISED JULY 2013
APPLICATION INFORMATION
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Figure 7 shows a typical application with the TL4242-Q1 LED driver. A supply current adjusted by the R_REF
resistor drives the three LEDs, preventing brightness variations due to forward voltage spread of the LEDs. An
appropriate duty cycle applied to the PWM pin can compensate through software for the luminosity spread
arising from the LED production process. Therefore, it is not necessary to select LEDs for forward voltage or
luminosity classes. The minimum supply voltage calculates as the sum of the LED forward voltages, the TL4242-
Q1 drop voltage (maximum 0.7 V at an LED current of 300 mA), and the maximum voltage drop at the shunt
resistor R_REF of 185 mV.
V_BAT
I
RADJ GND
RO
SI
Q
D
100 nF
Microcontroller
10 µF 10 kW
ST
PWM
I
Q
TL4242-Q1
REF
GND D
LED
Dragon
47 nF
0.47 W
0.25 W
R_REF
Figure 7. Application Circuit
The status output of the LED driver (ST) detects an open-load condition, enabling supervision of correct LED
operation. A voltage drop at the shunt resistor (R_REF) below 25 mV (typical) detects an LED failure. In this case,
the status output pin (ST) goes low after a delay time adjustable by an optional capacitor connected to pin D.
Figure 8 shows the functionality and timing of ST and PWM. One can adjust the status delay through the
capacitor connected to pin D. Delay time scales linearly with the capacitance, C_D:
t _STHL,typ
+
C_D
47 nF
10 ms
t _STLH,typ
+
C_D
47 nF
10 ms
8
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