TLD1114-1EP: Possibility of digital dimming without MOSFET in power shift circuit
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: