The KB4312 is a high efficiency and constant current DC-DC converter IC which is designed primarily

for use in LED module applications. The output voltage of the step-up converter can be set from Vin to

28V with external sense resistor. The device suits to drive series-connected LEDs and provides even

illumination by sourcing the same output current through each LED. KB4312 also consists of a logic

shutdown , cycle-by-cycle current-limited , soft-start functions.

Logic control input or PWM duty cycle control allows easy adjustment of LEDs brightness and on/off

control. The average LED current is proportionable the duty-cycle of the PWM signal. Typical PWM

frequency should be between 100Hz and 1kHz.

The boost converter operates in current-mode PWM and a constant frequency of 1.2 MHz. Depending

on duty cycle of each switching cycle can regulate output voltage. On the rising edge of the internal

clock , the control and driver logic block sets internal flip-flop when the output voltage is too low,

which turns on the N-MOS. The external inductor current ramps up linearly, storing energy in a

magnetic filed. Once peak current of inductor over trans-conductance output level , the N-MOS turns

off, the flip-flop resets, and external schottky diode turns on. This forces the current through the

inductor to ramp back down, transferring the energy stored in the magnetic field to the output capacitor

and LEDs. To reduce external component amount , the device will be built-in

internal loop

compensation.

Digital logic of EN provides an electrical ON/OFF control of the power supply. Connecting this pin to

ground or to any voltage less than 0.4V and sustain the level over 4ms will completely turn off the

regulator. In this state, current drain from the input supply is less than 1uA, the internal reference, error

amplifier, comparators, and biasing circuitry turn off . If holding time of low level is less than 3ms on

this pin, then the device only shutdown driver logic block.

Digital logic of EN also provides LEDs brightness control by applying a PWM signal on EN pin. With

this way, the LEDs operate with either zero or full current . The average LED current is proportional to

the duty-cycle of the PWM signal. Typical PWM frequency should be between 100Hz and 1kHz.

Output current is given by:

PWM

S

SENSE

PWM

ON

LED

T

R

T

mV

I

105

Where:

If dimming control is not required , EN works as a simple on/off control. Drive EN high to enable the

device , or drive EN low for shutdown.

6

KB4312

Kingbor Technology Co.,Ltd

TEL:(86)0755-26508846 FAX:(86)0755-26509052

Function Description

Enable Control

Dimming Control