PT4556F PT4556G PT4556J led lighting driver chip PT4121 is a step-down constant current controller working in continuous inductor current conduction mode, used to drive one or more LEDs

With LEDs in series, the output current accuracy is as high as 3%. The PT4121 input voltage range is from 6V to 50V, and the output current is adjustable. That

The average LED current is set with a high-side current-sampling resistor, and the DIM pin is used for analog dimming and PWM dimming. 2. Typical application circuit

3. Introduction to the working principle

PT4121 and inductor (L), current sampling resistor (RS), MOSFET form a self-oscillating continuous inductor current mode

A step-down constant current LED controller.

When VIN is powered on, the initial current of the inductor (L) and the current sensing resistor (RS) is zero, and the LED output current is also zero.

At this time, the output of the CS comparator is high, the power switch is turned on, and the current flows through the inductor (L), the current sampling resistor (RS),

The LED and power switch flow from VIN to ground, and the slope of the current rise is determined by VIN, the inductor (L), and the LED voltage drop, on RS

A dropout VCSN is generated, when (VIN-VCSN) > 230mV, the output of the CS comparator goes low, the power switch is turned off,

The current flows through the inductor (L), current-sense resistor (RS), LED and Schottky diode (D) with another slope when (VIN-VCSN)

< 170mV, the power switch is turned back on so that the average current on the LED is

The high-end current sampling structure makes the number of external components small, using a sampling resistor with 1% accuracy, LED output current control

Controlled to an accuracy of ±3%.

4.2 Selection of VCC Capacitor

The VCC voltage of PT4121 is 5V, and the typical withstand voltage value is 10V, 1μF, X5R or X7R ceramic capacitor. when losing

When the output current is large, in order to prevent insufficient driving capability due to undervoltage of VCC, the VCC capacitor can be appropriately increased to strengthen the gate

Drive capability

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