Specs. for parameters dVF and VF_SLS in LITIX™ Basic+ SLS dimensioning tool?
*dVF* is the temperature gradient, meaning the linearized temperature dependency of the LED forward voltage over Tj.
It can be calculated from the curve ΔVf over Tj, which is usually provided in the LEDs datasheet.
Based on the OSRAM LS E6SF, below is an example
From Tj = -20° C to Tj = -10° C, the forward voltage changes by ~40 mV. This means that the forward voltage of the LED changes approximately by 4 mV for each °C of Tj.
The temperature gradient is then 4 mV.
*VF_SLS* is the percentage of typical forward voltage remaining in a shorted LED. This parameter is not included in the datasheet of the LEDs.
It is an assumed percentage in order to add an extra margin to the evaluation of the SLS (Single LED Short) performance. It results in an assumption of residual voltage at the LED which is shorted.
The maximum allowed value for this parameter, 50% (minimum and maximum limits provided in the popup window), indicates the maximum typical forward voltage remaining at the shorted LED and not an overtemperature condition.
A short description of the dVF and VF_SLS parameters is present in the SLS dimensioning tool. In order to access it, click on the question mark icon on the right top corner
For more information on LITIX™ Basic+ Single LED Short detection feature refer to the application note Diagnosis and fault management.