GENERAL DESCRIPTION FEATURES The EC4304 is a high-efficiency continuous mode inductive step-down converter which drives N-channel MOSFET and it is designed for driving single or multiple series connected LEDs from a voltage source higher than the LED voltage. It operates from input supply between 7V and 40V and provides and externally adjustable output current to 1A which is depending on supply voltage and external components. This EC4304 includes the output switch and high-side output current sensing circuit, which uses an external resistor to set the output current. The ADJ pin will accept either a DC voltage or a PWM waveform. This will provide either a continuous or gated output current depending upon the control frequency. The PWM filter components contains a soft-start rising time setting. The soft-start time can be increased by using an external capacitor from the ADJ pin to ground. Applying a 0.2V or lower to the ADJ pin turns the output off and switches the device into a low current standby state.  Operates from 7V to 40V Supply Voltage  Internal 40V NDMOS Switch  Output Current 1A  Single Pin On/Off and Brightness Control Using DC Voltage or PWM  EC4304 to 95% Efficiency  Typical +/-5% LED Current Accuracy  Input Under Voltage Lockout  SOT23-5L,DFN 3x3 8L,SOT89-5L Package  RoHS Compliant and Halogen-Free Applications  Automotive LED Lighting  High Power LED Lighting  Indicator and Emergency Lighting  Architectural Lighting  Low Voltage Industrial Lighting  Signage and Decorative LED Lighting

Functional Description The EC4304 is a simple high-efficiency, continuous mode inductive step-down converter. The device operates with an input voltage range from 7V to 40V and delivers output current 1A. A high- side current-sense resistor sets the output current and a dedicated PWM dimming input enables pulsed LED dimming over a wide range of brightness levels. A highside current-sensing scheme and an on-board current- setting circuitry minimize the number of external components which is required while delivering LED current with +5% accuracy, using a 1% sense resistor. Adjusting Output Current The device contains a low pass filter between the ADJ pin and the threshold comparator and an internal current limiting resistor between ADJ and the internal reference voltage. This allows the ADJ pin to be overdriven with either DC or pulse signals to change the VSENSE switching threshold and adjust the output current. Details of the different modes of adjusting output current are given in the applications section by: The value of the output current is 1A at 0.1Ω (0.5A at 0.2Ω) and this is a calculated output current when the ADJ terminal is 1.25V floating. Shutdown Mode Taking the ADJ pin to a voltage below 0.2V for more than approximately 100μs will turn off the output, and supply current will fall to a low standby level of 20μA nominal. Soft-Start The device has inbuilt soft-start action due to the delay through the PWM filter. An external capacitor from the ADJ pin to ground will provide additional soft-start delay, by increasing the time taken for the voltage on this pin to rise to the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the comparator. With no external capacitor, the time taken for the output to reach 90% of its final value is approximately 500μs. Adding capacitance increases this delay by approximately 0.5ms/ nF. Inherent open-circuit LED protection If the connection to the LED(s) is open-circuited, the coil is isolated from the LX pin of the chip, so the chip will not be damaged. Unlike in many boost converters, where the back EMF may damage the internal switch by forcing the drain above its breakdown voltage.