一、General Description

The TX5121 is a step-up DC/DC converter specifically designed to drive up to 6 series white LEDs with constant current. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminates the need for ballast resistors. The TX5121 switches at 1.4MH z, allowing the use of tiny external components. A low 0.25V feedback voltage minimizes power loss in the current setting resistor for high efficiency. The OVP pin monitors the output voltage and turns off the converter whenever the LEDs are open. The TX5121 is available in low profile SOT-23-6 package.

二、Pin Assignment

三、Electrical Characteristics

四、Function Description

The TX5121 uses a constant frequency control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the block diagram. At the start of each oscillator cycle, the SR latch is set, w hich turns on the pow er switch M1. An artificial ramp is generated to the positive terminal of the PWM comparator A2. When this voltage exceeds the level at the negative input of A2, the SR latch is reset turning off the power switch. The level at the

negative input of A2 is set by the error amplifier A1, and is simply an amplified version of the diff erence between the feedback voltage and the reference voltage of 0.254V. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier’s output increases, more current is delivered to the output, if it decreases, less current is delivered.

Application Information