TOSHIBA

T B 6 2 7 3 2 F U

27, Feb 2002 (Ver.04)

6

Fig 4 : burst control wave form

THE STAE OF THE PEAK CURRENT CONTROL

The peak current control is repeat in the control the waveform which showed it in the Fig 3.

The current pulse of the Fig 3 is a charging current on the output capacitor C2.

It is supplied to LED as a discharge current on the output side capacitor, and it through the R_sens to GND.

And, as for the charging voltage waveform of the output capacitor C2, it returns in the IC from the K terminal.

The internal circuit which the K terminal should be input from controls the current pulses so that the

average voltage value of the voltage wave form which it could get may become 53 mV (typ).

The constant current is controlled as a result as an average electric current value. Therefore, when R_sens = 2.7

ohm is connected, the average current value of (53 mV /2.7 ohms) = 19.6 mA can get it.

This IC is designed for the purpose of supplying the power 320 mW (min).

Generally it is a step up inductance 6.8 uH to the load power 320 mW. And, when the load electric power is small, it

can be done small for the inductance.

As a condition about the LED load between the generator terminal and the K terminal,

Please keep the condition in Vin (Vcc) < LED VF total.

There are no relations with the control of the IC, and LED is always turned on.

STANDBY MODE OPERATION

The SHDN terminal set-up the normal operation and the standby operation. The lighting operation is possible in

the "L" level in the stop (at the standby mode), the "H" level. Still, consumption supply current in the standby mode

is 1.2uA (max).

A-terminal voltage

A-terminal current

(External inductor current)

K-terminal voltage

(Waveform of current for cap. charge)

Maximum On pulse

width = 85%

I A( peak )

LED Vf

Switching frequency fOSC = 1MHz

It stabilizes it in the set Io

with lowering IA (peak).

It stabilizes it in the set Io

with lowering IA (peak).