TL4242QKTTRQ1 Datasheet, PDF (9/21 Pages) Texas Instruments – ADJUSTABLE LED DRIVER

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V_PWM
V_PWM,H
V_PWM,L
I_Q
I_Q,nom
t_PWM,ON
70%
V_D
t_PWM,OFF
30%
V_LD
V_ST
Open
Load
TL4242-Q1
SLVS732E – JULY 2010 – REVISED JULY 2013
Open
Load
t
t
t_STHL
t
t
Figure 8. Function and Timing Diagram
Stoplight and Taillight Application
For many automobiles, the same set of LEDs illuminates both taillights and stoplights. Thus, the LEDs must
operate at two different brightness levels, full brightness for the stoplight and 10% to 25% brightness for the
taillight. The easiest way to achieve the different brightness is dimming by pulse-width modulation (PWM), which
holds the color spectrum of the LED over its whole brightness range. The maximum current that passes through
the LED is programmable by sense resistor R_REF.
Obtain the maximum current, I_Qmax, that passes through the LEDs by the following expression:
I_{Q max}
=
V_REF
R _REF
For example, if R_REF equals 1 Ω, as V_REF is a fixed value range from 168 mV to 185 mV, I_Qmax should be 168 mA
to 185 mA.
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