The TLD5542-1QV has a fast discharge feature that allows to quickly discharge the output capacitor. During a fast discharge phase the ouput capacitor is getting discharged to the input capacitor and therefore causing a small reverse input current.

The figure below shows the switching pattern and waveforms during this fast discharge phase.

Read more on fast discharge in the datasheet https://www.infineon.com/dgdl/Infineon-TLD5542-1QV-DataSheet-v01_10-EN.pdf?fileId=5546d4626fc1ce0b016ff1ac705d4601 on pages 27 and 28.

The TLD509x mainly differ in maximum output voltage, output current accuracy, analog dimming, short-to-ground protection and capability to drive an external NMOS for dimming purpose from each other: 

The status functionality of the TLE4242 is unlatched.

When a fault is detected by one of the devices, this one pulls down the ST pin using an open collector circuit. This pulls down the connected PWM pin of the second device and brings it into sleep mode.

When the fault condition is removed the device which has detected the fault releases the ST pin (open collector output off) and the ST pin voltage rises again. The second device connected with its PWM pin to this ST pin is then activated again and both devices are back in normal operation.

In case of a resistive load (e.g. 50 Ohm) is connected to the output of an linear current source instead of real LEDs and the supply voltages increases slowly the output channel may not turn on.

Basic and Basic+ LED drivers are not designed for driving pure resistive loads. In case the output voltage VOUT is below the required output voltage for current control VOUT(CC) (see parameter 7.2.7 in the datasheet) the  main power stage is operating with the short circuit protection mechanism integrated in our LED drivers. At start-up when VOUT < VOUT(CC) the device uses a startup current of a few 100 µA to rise the output voltage. Once the output voltage is above VOUT(CC) the main current control loop is starting to work and the target current is flowing.

Recommendation would be change the load to add diodes in series to the resistor to achieve a forward voltage threshold greater than VOUT(CC) at the start-up current. Further details on the diagnostic features in LITIX Basic+ can be found in LITIX Basic+ Diagnostic features

An external temperature derating can be achieved by placing a PTC type resistor at the IN_SET pin. A short trace length (few cm) to place the PTC resistor closer to the LEDs is uncritical. For extended trace length PCB ground shifts and potential disturbance may impact the current regulation accuracy.

As the voltage in the IN_SET pin is kept constant at 1.22V the change of the resistance directly correlates to the change in output current. The customer can select the PTC type resistor based on the required derating curve and nominal output current. Often also a normal fixed resistor is placed in series to the PTC to set a max current when the system is at low temperature. PTC resistors with nonlinear resistance curves allow to achieve a derating only from a certain temperature onwards (e.g. current constant up to 75°C and then derating). See for example EPCOS B5960x B59701.

General recommendation: no additional capacitance should be placed at the IN_SET pin.

When the TLD1114-1EP is used without the MOSFET no PWM dimming over PWMI, EN or IN_SET pin is possible. PWM operation over supply VS is possible as there the current path to the LEDs is disconnected by the switch supplying the module.

The reason is that the LEDs are always connected to the Power Shift resistor without an active switching element to disconnect. Please have a look on the attached figure.

The current path (shown in green) is always closed as there is no switch to open it.

This means even if you deactivate by EN/PWMI or INSET some current is flowing depending on the power shift resistor.

The current can be estimated with IOUT ~(VS - VLED)/(Rpowershift + Rshunt), where

   - Rshunt = 750mOhm if OUTH is used

   - Rshunt = 1500mOhm if OUTL is used.

This means that the only way to turn off the LEDs is to deactivate the power supply (as done e.g. in a fog light).

In case you want to do the wiping animation you will have to use the Power shift feature WITH mosfet.

See TLD1114-1EP Powershift appnote for further details:

https://www.infineon.com/cms/en/product/power/lighting-ics/litix-automotive-led-driver-ic/litix-basic-plus/tld1114-1ep/#!documents

For all LITIX Basic variants with "Open Load" detection functions the following recommendation applies: 

• LITIX Basic ICs with integrated Open Load functions require a capacitive divider on the OUT. This means CVS2OUT and COUT2GND should be implemented to achieve a robust EMC design. This has been evaluated during our EMC investigations. The reason for this is to increase filter capacitance on the OUT. If it is only done via increasing the COUT2GND capacitor, the open load detection is not working properly anymore. To avoid this the CVS2GND has been recommended as well. 

For all LITIX BASIC ICs without the "Open Load" detection function implemented the following recommendation applies: 

• LITIX Basic products without Open Load detection functions such as TLD1120 do can skip the CVS2OUT capacitor.
• The GND connection of the LED load can cause a parasitic behavior during the BCI test. The layout of the PCB Board design is also an important factor how many disturbances the IC OUT or in this case the current regulation loop of the IC will see during the BCI test. The COUT2GND will filter eventual disturbances and ensure a more stable output current regulation. 

NOTE: The actual datasheet drawing of the TLD1120 is showing a CVS2OUT capacitor only! This may not solve BCI issues and a COUT2GND filter is recommended. A dedicated AppNote is planned to focus on this topic.

Exceptional error handlings when having multiple devices, e.g. for TAIL/STOP applications, can be implemented with LITIX™ Basic+. This is useful if the light function, where the error occurs, determines which LED driver to turn off and which LED driver to keep on. For example if the LEDs of the TAIL light have an error, only the TAIL light may be turned off and the STOP light may be kept on. On the other hand, if the LEDs of the STOP light fails, all STOP and TAIL shall be turned off.
There are two solutions:

Solution 1:
Connect the ERRN node of the Tail/Stop part to the enable circuit of the Tail part:

Due to the voltage thresholds of the EN/DEN pin (the lowest is 1.4V) there is some margin.
Advantage here is that the devices disabled via EN/DEN consume almost no current (<2µA)
This can be used in case no additional turn off delay via a capacitor at the D-pin is required.

Solution 2:
The ERRN network needs to be split by a diode and place RERRN pull up resistors on either side of the diode:

The resistors and diode have to be designed such that the voltage VERRN goes below 0.8V in an error case. Therefore one also needs to consider the forward voltage of the diode because a small current (e.g. 0.5-1mA) is flowing through it. The remaining ERRN voltage of the device pulling down the node is also depending on the current which is flowing into it. A Schottky diode is beneficial due to the low voltage drop.

LEDs transform only 2/3 of the electrical power to light, while 1/3 are dissipated in heat. When the LED junction temperature reaches the maximum rating the system is no longer reliable. In this case an output power reduction strategy allows to keep the LED turned on while not violating the temperature rating.

To apply an output power derating strategy it is required to estimate the junction temperature of LEDs. To do this, a temperature sensing element is placed on the same PCB close to the LEDs. The sensing position determinates the detected temperature as a function of LED junction temperature. Through thermal simulation or experimentally it is possible to relate the sensed temperature  to the actual junction temperature of the LED.

To keep the overall cost of the system low, the most common sensing elements are NTC or PTC resistors. NTCs and  PTCs can be connected to the analog dimming input of LITIX Power devices (SET pin).

NTC resistors reduce their resistance when the sensed  temperature increases. This characteristic can be used to reduce the voltage on SET pin during the overheating by placing the resistor as illustrated below

Hints to design a power derating with NTC:

1. Define at which temperature T~a~ the system need to degrade the output power
2. Select an NTC with appropriate R/T characteristic and calculate the resistance at temperature T~a~
3. Calculate R that imposes 1.6 V to SET pin at T~a~ temperature by R{~}_NTC~ T~a~)*(5-1.6)/1.6
4. Calculate the overall IVCC current consumption with lowest value of NTC (maximum temperature) and check that it is lower than the maximum allowable.

PTC resistors increase their resistance when the sensed temperature increases. This characteristic can be used to reduce the current on analog dimming network and then the voltage on SET pin. The circuit proposed is the following

Hints to design a power derating with PTC:

1. Define at which temperature T~a~ the system need to degrade the output power
2. Select an PTC with appropriate R/T characteristic curve and calculate the resistance at temperature T~a~
3. Calculate R that imposes 1.6 V to SET pin at T~a~ temperature by R{~}_PTC~ (T~a~)*1.6/(5-1.6)
4. Calculate the overall IVCC current consumption with lowest value of PTC (minimum temperature) and check that is lower than the maximum allowable. 

See https://www.infineon.com/cms/en/product/power/lighting-ics/litix-automotive-led-driver-ic/litix-power/ for datasheets and application notes. 

NTC resistors reduce their resistance when the sensed  temperature increases. This characteristic can be used to reduce the voltage on SET pin during the overheating by placing the resistor as illustrated below