WS9822B datasheet(6/11 Pages) ETC2

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WS9822B Product Description

WINSEMI MICROELECTRONICS

Function Description

The WS9822B is a three-stage dimming constant

current LED driver with high precision and is applied to

non-isolated buck LED power system. The WS9822B

integrates a switcher dimming circuit and can change the

output current through shifting external switcher ON/OFF to

perform the dimming function.

The WS9822B is compatible the PCB board with

mainstream non-dimming products in the markets, such as

WS3442, thus it can achieve the seamless upgrades from

non-dimming to ON/OFF dimming.

Switcher Dimming Control

The switcher is opened first and closed again when the

dimming is required, and the output current changes in

accordance with the presetted current. The switching time

should be more than 500mS. The dimming current cyclically

varies in the sequence of 100% to 40% to15%. The reset

time is 5S. So it is a normal dimming if the time interval of the

switch from turn-off to turn-on is less than 5s; otherwise it will

be considered as a reset signal. The output current reaches

up to 100% after the switch is on again whatever the output

stage of the preceding current is.

Start Up

The VCC capacitor will be charged through the start-up

resistor when the system is powered on. When the VCC pin

voltage reaches the turn on threshold, the internal circuits

start operating. The WS9822B integrates the 16V ZENER for

clamping the VCC.

The typical value of the start-up current is 130uA (the

maximum value is 195 uA). For the application of 176VAC—

264VAC, the start-up resistor can be calculated by the

equation（

1）:

_ min

_ max

1.414 176

1.414

1.27M

195









 （1）

The start-up resistor can be chosen from 720K Ω to

1.2MΩ. Two resistors in 1206 size SMD or 1/4W metal film

resistors can be used in series.

Due to the ultra-low operating current, the auxiliary

winding is not needed to supply the IC.

VCC Capacitor Selection

The Vcc capacitor is used to bypass noise to IC, so that

to assure its stable operation, and should be as close as

possible to the chip.

A 4.7uF/25V electrolytic capacitor can be used to Vcc Pin.

If selecting MLCC, the material of X7R will be used to satisfy

the stability of the capacity under high temperature. Due to

external damage resulted from small volume and brittle texture

of MLCC, it is easy to cause Vcc currents leakage, which will

make the WS9822B unable to start. Strict control measures

are taken in the layout and productive process.

In order to avoid the return flickering and the disorder time,

the Vcc capacitor should be in parallel with discharge resistor,

which value should be chosen from 150KΩ to 240KΩ.

Constant Current Control

Utilizing

proprietary

current

control

method,

the

WS9822B can achieve precise LED output current with a few

external components. Cycle by Cycle current sense is adopted

in WS9822B, the CS pin is connected to the current sense

comparator, and the voltage on CS pin is compared with the

internal 400mV reference voltage. The MOSFET will be

switched off when the voltage on CS pin reaches the threshold.

The CS comparator includes a 350ns leading edge blanking

time.

The peak inductor current is calculated by the equation

（

2）:

)

(

PK 

（

2）

Where, RCS is the current sense resistor value.

The current in LED can be calculated by the equation（

3）:

)

(

LED 

（

3）

Where, IPK is the peak current of the inductor.

Freewheeling Diode

The diode will b

ear the reverse voltage equal to the

input voltage when the MOSFET is on. A 600V diode was

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