TLE4242EJ_15 Datasheet, PDF (8/17 Pages) Infineon Technologies AG – 1 Channel High Side Current Source up to 500mA

Infineon® LITIX™ Linear
TLE4242EJ
Product Description
5
Product Description
The TLE4242EJ is an adjustable constant current source providing currents up to 500 mA. The product is
optimized for automotive applications, but is suitable for industrial applications as well, where high currents
are required.
5.1
Output Current Setting
An external shunt resistor in the ground path of the connected LEDs is used to sense the LED current. A
regulation loop regulates the voltage drop at the shunt resistor R_REF on a constant level of typ. 175 mV.
Selecting the appropriate shunt resistance allows to adjust the desired constant current level. The typical
output current is calculated according to Equation (5.1).
I_Q(typ)
=
V_{-----R----E---F-}
R_REF
(5.1)
V_REF is the reference voltage with a typical value of 175 mV, details at Reference voltage. The equation applies
in a range of 0.39 Ω ≤ R_REF ≤ 1.8 Ω.
The output current is shown as a function of the reference resistance in Chapter 5.3.1. With the PWM input
the LED brightness can be regulated via duty cycle. Also PWM = 0 V sets the TLE4242EJ in sleep mode resulting
in a very low current consumption I_I(off) Current consumption at Input-pin during off-state. Due to the high
impedance of the PWM input the PWM pin can also be used as an enable input.
The application example in Figure 6-1 shows a typical application with the TLE4242EJ LED driver. The three
LEDs are driven with an adequate supply current adjusted by the resistor R_REF. Thus brightness variations due
to forward voltage spread of the LEDs are prevented. The luminosity spread arising from the LED production
process can be compensated via software by an appropriate duty cycle applied to the PWM pin. Therefore,
selection of the LEDs to forward voltage as well as to luminosity classes can be spared. The minimum supply
voltage for the application is the sum of the LED forward voltages, the TLE4242EJ drop voltage Minimum drop
voltage Vdr = VI - VQ and the max. voltage drop at the shunt resistor R_REF of V_REF(max) according to Reference
voltage.
The status output of the LED driver (ST) detects an open load condition enabling to supervise correct LED
function. A LED failure is detected, if the voltage drop at the shunt resistor R_REF falls below typ. 25 mV. In this
case the status output pin ST is set low after a delay time, which is adjustable via an optional capacitor
connected to the pin D.
The functionality of the status ST and PWM-pin as well as their timings are shown in Figure 5-1. The pull up
resistor value at the ST-pin is recommended with R_{ST_pu} ≥ 4.7 kΩ. The status delay can be adjusted via the
capacitor connected to the timing pin D. The delay time t_ST(HL) and t_ST(LH) scales linearly with the capacitance
C_D:
t_{ST(HL, typ)}
=
---^C-----^D---- ⋅ 10ms
47nF
(5.2)
t_{ST(LH, typ)}
=
---^C-----^D---- ⋅ 10μs
47nF
(5.3)
Data Sheet
8
Revision 1.0
2015-03-13