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KB4314
High Efficiency, Constant Current
1 Watt Boost White-LED Driver
Function Description
The KB4314 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
30V 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. KB4314 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.
Enable Control
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.
Dimming Control
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:
I
LED
Where:
105
mV T
ON PWM
R
SENSE
T
S PWM
T
ON-PWM
: On time of PWM signal
T
S-PWM
: A cycle time of PWM signal
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.
REV: 1.0
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KINGBOR [ KINGBOR TECHNOLOGY CO ]
