SNVS603D August 2009 – July 2019 LM3424
PRODUCTION DATA.
Peak current mode control is used by the LM3424 to regulate the average LED current through an array of HBLEDs. This method of control uses a series resistor in the LED path to sense LED current and can use either a series resistor in the MOSFET path or the MOSFET RDS-ON for both cycle-by-cycle current limit and input voltage feed forward. The controller has a fixed switching frequency set by an internal programmable oscillator which means current mode instability can occur at duty cycles higher than 50%. To mitigate this standard problem, an artificial ramp is added to the control signal internally. The slope of this ramp is programmable to allow for a wider range of component choices for a given design. A detailed explanation of this control method is presented in the following sections.