WS9822B datasheet(8/11 Pages) ETC2

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WS9822B Product Description

WINSEMI MICROELECTRONICS

Vovp is the open circuit protection voltage.

And then the Rovp resistor value can be calculated by the

equation （8）:

)

(







OVP

（

8）

In normal application, the value of Tovp cannot be lower

than 4us, or in other words, the value of Rovp cannot be

lower than 20K, with its recommended range from 20K to

50K. The resistance of Rovp with 1% accuracy should be

used to assure the accuracy of OVP.

Line Voltage Compensation

The WS9822B integrates line voltage compensation

function, which makes LED current remain unchanged in the

range of full voltage, thus has good line regulation and

current accuracy.

Thermal Regulation

The WS9822B integrates thermal regulation function.

When the system is under higher temperature, the output

current is gradually reduced; the output power and thermal

dissipation are also reduced. The system temperature is

regulated and the system reliability is improved. The thermal

regulation temperature is set at 150℃ internally.

Protection Function

The WS9822B offers full protection functions to improve

the system reliability, including LED open/short protection,

CS resistor short protection, VCC under voltage protection,

thermal regulation. When the LED is open circuit, the system

will trigger the over voltage protection and stop switching.

When the LED short circuit is detected, the system works at

lowest frequency. So the system power consumption is very

low.

At some abnormal fault condition, such as CS resistor

shorted or inductor saturation, the internal fast fault detection

circuit will be triggered, the system stops switching

immediately.

After the system enters into faulty condition, the VCC

voltage will decrease until it reaches the UVLO threshold, then

the system will restart again. If the fault condition is removed,

the system will recover to normal operation.

PCB Layout

The following rules should be followed in WS9822B PCB

layout:

VCC Capacitor: The VCC capacitor should be as close

as possible to the VCC Pin and GND pin.

Ground Path: The power ground path for current sense

resistor should be as short as possible, and the power ground

path should be separated from small signal ground path

before connecting to the negative node of the bulk capacitor.

The Area of Power Loop: The area of main current loop

should be as small as possible to reduce EMI radiation, and it

should be away from diodes and other heating components.

DRAIN PIN: The copper area of DRAIN pin can be

increased for better thermal dissipation. And it should be away

from CS / VCC and ROVP Pin.

ROVP PIN: The ROVP resistor should be as close as

possible to the ROVP Pin to prevent from the interference.

The material of PCB: Avoid choosing the material that is

easy to absorb the moisture, just like paper copper-clad

laminates.

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