WS9225 Datasheet, PDF (5/8 Pages) Shenzhen Winsemi Microelectronics Co., Ltd – High Precision PSR Constant Current LED Driver

WS9225ProductDescription
Application Information
The WS9225 is a high performance power switch
specially designed for LED lighting, with patent constant
current control technology. The WS9225integrates a 650V
power MOSFET. The accurate LED current can be realized
without opto-coupler, TL431 feedback circuit and auxiliary
winding while minimizing the external component count,
lowering the total bill of material cost.
Start Up
The start-up current inWS9225 is designed to as low as
205uA. The VCC capacitor will be charged through the
start-up resistor when the system is powered on. Once the
VCC voltage reaches the start-up threshold, the WS9225
will start to switch. TheWS9225 integrates a 19V zener for
VCC clamping. Due to the ultra-low operating current, the
auxiliary winding is not needed to supply the IC.
Operating Switching Frequency
The WS9225 is designed to work in discontinuous
conduction mode and no external loop compensation
component is required while maintaining stability. The
maximum duty cycle is limited to 42%. The maximum
switching frequency at normal operation is suggested to set
around 65KHz~70KHz. If the maximum frequency is set too
high, it will affect the number of maximum series LED lamps.
If set too low, the LED open circuit voltage will be too high.
The maximum and minimum switching frequency is
limited in WS9225 to ensure the stability of system.
The switching frequency can be set by the formula:
f

Np² V_LED
8 Ns²  Lp  I_LED
Where, LP is the primary winding inductance of
transformer.
Constant Current Control
Cycle-by-Cycle current sense is adopted in WS9225,
the CS is connected to the current sense comparator, and
the voltage on CS will be compared with the internal 400mV
reference voltage, the MOSFET will be switched off when
the voltage on CS reaches the threshold. The output of the
comparator includes a 350ns leading edge blanking time.
The primary peak current is given by:
I _{P_PK}

400
(mA)
R_CS
The current in LED can be calculated by the equation:
I _OUT

I _{P_PK}
4

N_P
N_S
Protection Function
The WS9225 has integrated rich protection functions,
LED open/short protection, CS resistor shortcircuit
protection, VCC under voltage protection,over temperature
protection, and so on. When the LED is open circuit, it will
trigger over-voltage protection logic and latch, the system
stops switching immediately.
When the LED short circuit is detected the system
works at low frequency (Fop=3KHz), so the power
consumption is low. After the system enters into fault latch
condition, the VCC voltage will fall until it reaches UVLO
threshold. Then the system will re-start again. If the fault
condition is removed, the system will recover to normal
operation.
Where,
PCB Layouts
NP: primary winding turns of transformer
The following rules should be followed in WS9225 PCB
NS: secondary winding turns of transformer
layout.
IP_PK: peak current in MOSFET
Bypass Capacitor
The bypass capacitor on VCC should be as close as
Power MOSFET
possible to the VCC pin and GND pin.
The WS9225integrates a 650V power N-MOSFET. It
Ground Path
can minimize the external component count and reduce the
The power ground path for current sense should be
BOM cost and PCB size.
short, and the power ground path should be separated from
The WS9225 uses DIP-8 package. The recommended
small signal ground path before the negative of the bulk
system output power is below 24W in universal input
capacitor.
(90Vac~265Vac) application.
The Area of Power Loop
The area of main current loop should be as small as
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
www.winsemi.com Tel : [phone] Fax : [phone]
WINSEMI MICROELECTRONICS
WINSEMI MICROELECTRONICS
5/8