TLD5097EL_15 Datasheet, PDF (27/41 Pages) Infineon Technologies AG – Multitopology LITIX Power DC/DC Controller IC

Infineon® LITIX™ Power
TLD5097EL
Analog Dimming
10
Analog Dimming
This pin is influencing the Feedback Voltage Error Amplifier by generating an internal current accordingly to
an external reference voltage (VSET). If the analog dimming feature is not needed this pin must be connected
to IVCC or external > 1.6V supply. Different application scenarios are described in Figure 10-3. This pin can
also go outside of the ECU for instance if a thermistor is connected on a separated LED Module and the Analog
Dimming Input is used to thermally protect the LEDs. For reverse battery protection of this pin an external
series resistor should be placed to limit the current.
10.1 Purpose of Analog Dimming
1. It is difficult for LED manufacturers to deliver LEDs which have the same Brightness, Colorpoint and
Forward Voltage Class. Due to this relatively wide spread of the crucial LED parameters automotive
customers order LEDs from one or maximum two different colorpoint classes. The LED manufacturer must
preselect the LEDs to deliver the requested colorpoint class. Those preselected LEDs are matched in terms
of the colorpoint but a variation of the brightness remains. To correct the brightness deviation an analog
dimming feature is needed. The mean LED current can be adjusted by applying an external voltage VSET
at the SET pin.
2. If the DC/DC application is separated from the LED loads the ECU manufacturers aim is to develop one
hardware which should be able to handle different load current conditions (e.g. 80mA to 400mA) to cover
different applications. To achieve this average LED current adjustment the analog dimming is a crucial
feature.
10.2 Description
Application Example
Desired LED current = 400mA. For the calculation of the correct Feedback Resistor R_FB the following equation can
be used: This formula is valid if the analog dimming feature is disabled and V_SET > 1.6V.
(10.1)
I _LED
= ^VREF
R_FB
→ R_FB
= ^VREF
I _LED
→ R_FB
=
0.3V _{= 750mΩ}
400mA
A decrease of the average LED current can be achieved by controlling the voltage at the SET pin (V_SET) between
0V and 1.6V. The mathematical relation is given in the formula below:
(10.2)
I _LED
=
V_SET − 0.1V
5 ⋅ R_FB
If V_SET is 100mV the LED current is only determined by the internal offset voltages of the comparators. For this
example I_LED = 0A if V_SET < 100mV. Refer to the concept drawing in Figure 10-2.
Data Sheet
27
Revision 1.0
2015-03-12