WS9822B Product Description
Vovp is the open circuit protection voltage.
And then the Rovp resistor value can be calculated by the
equation （8）:
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.
ROVP 5TOVP 106
(K) （8）
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.
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.
PCB Layout
Line Voltage Compensation
The following rules should be followed in WS9822B PCB
layout:
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.
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.
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.
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.
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
www.winsemi.com
Tel : +86-755-8250 6288
Fax : +86-755-8250 6299
8/11
WINSEMI [ SHENZHEN WINSEMI MICROELECTRONICS CO., LTD ]
