Soft-start allows a gradual increase of the internal current-limit level for the step-up converter during

power-up to reduce input surge currents. As the internal current source charges the internal soft-start

capacitor, the peak N-MOS current is limited by the voltage on the capacitor. In another story, when

toggle or a logic-level transition on EN pin from low to high, soft-start function must work to enable

constant current charging internal capacitor. When soft-start process has finished or appeared falling

edge of PWM signal on EN pin , soft-start capacitor must be discharged to ground level.

The KB4313 provides cycle-by-cycle over-current protection. Current limit is accomplished using a

separate dedicated comparator. The cycle-by-cycle current limit abbreviates the on-time of the N-MOS

in event that the current of flowing N-MOS is greater than the current limit value. The current-limit

feature protection against a hard short or over-current fault at the output.

ground with a sense resistor. This will cause N-MOS to switch with a maximum duty cycle and come

out output over-voltage. This may cause the LX pin voltage to exceed its maximum voltage rating to

damage built-in N-MOS. In the state, the OVLO protection circuitry stops the internal N-MOS . When

The KB4313 maximum power dissipation depends on the thermal resistance of the IC package and

circuit board, the temperature difference between the die junction and ambient air, and the rate of any

airflow. The power dissipation in the device depends on the operating conditions of the regulator.

The step-up converter dissipates power across the internal N-MOS as the controller ramps up the

inductor current. In continuous condition, the power dissipated internally can be approximated by :

D

R

L

f

D

V

V

V

I

P

ON

DS

OSC

in

in

O

O

boost

)

(

2

2

]

)

(

12

1

)

[(

w

here

High Efficiency, Constant Current

8

KB4313

Kingbor Technology Co.,Ltd

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

Soft-Start

Cycle-by-Cycle Over-Current Protection

Over-Voltage Protection

Power dissipation consideration

REV: 2.0

12 Watt Boost White-LED Driver