WS3232 datasheet(5/7 Pages) WINSEMI

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WS3232

3232

Function

unction

unction Description

Description

WS3232 is a high PF offline QR PSR controller, optimized

for

low

power

LED

driver.

WS3232

operates

primary-side

sensing

and

regulation.

Consequently,

opto-coupler and TL431 could be eliminated, thus reduce

the cost.

Startup

Startup Current

Current

Startup current of WS3232 is designed to as low as 60uA.

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 WS3232 will

start to switch. The WS3232 integrates a 15V zener for

VCC clamping. Due to the ultra-low operating current, the

auxiliary winding is not need to supply the IC.

Quasi-Resonant

Quasi-Resonant Operation

Operation

Quasi-Resonant switching mode is applied in WS3232.

When the voltage across drain and source of the primary

MOSFET is at voltage valley, the MOSFET would be

turned on, reducing the switching losses and improving

EMI performance.

CC Operation

Operation

WS3232 is designed to

produce good CC control

characteristic. In DCM mode, the output current Io can be

represented b y,

Io=0.5*Ips*Tons/T

Where Ips is the peak current of the secondary side; Tons

is the turn on time of secondary side; T is the switching

period.

Ips=Ipp*Nps=(Vcs/Rcs)*Nps

Where Ipp is the primary peak current; Vcs is the voltage

on CS resistor; Rcs is primary current detection resistor;

Nps is the turns ratio of primary to secondary of the

flyback transformer. The relationship of Vcs, To ns and T is

controlled

constant

internal

circuit,

3*Vcs*Tons/T=0.5V. Thus, Io can be represented b y,

Io=0.5*(Vcs/Rcs)*Nps*Tons/T

=(Vcs*Tons/T)*0.5*（Nps/Rcs）

=0.083*（Nps/Rcs）

Once the parameters of the transformer and the current

sense resistor Rcs is determined, so is the output current.

And the output current can be set by adjusting the current

sense resistor Rcs.

Internal

Internal pre-charge

pre-charge

pre-charge design

design

design for

for

for quick

quick

quick start

start

start up

After VCC exceeds UVLO_ON, Vcomp is pre-charged by

an internal current source. The PWM block will not start to

output PWM signals until Vcomp is over 0.45V. Such

design is meant to reduce the start up time. The voltage

pre-charged Vcomp

start-up

procedure

can be

programmed b y,

Vcomp=0.4V-300uA*Rcomp

Where Rcomp is the series resistor of Comp pin.

Operation

Operation switching

switching

switching frequency

frequency

The frequency of WS3232 is decided by load condition

and QR mode. When the output power decreases, the

switching frequency can become rather high. The

maximum switching frequency in WS3232 is internally

limited to 120Khz.

Current

Current Sensing

Sensing

Sensing and

and

and Leading

Leading

Leading Edge

Edge

Edge Blanking

Blanking

Cycle-by-Cycle current limiting is offered in WS3232. The

switch current is detected by a sense resistor into the

sense pin. An internal leading edge blanking circuit chops

off the sense voltage spike at initial MOSFET on state due

to snubber diode reverse recovery so that the external RC

filtering on sense input is no longer required. The current

limit comparator is disabled and thus cannot turn off the

external MOSFET during the blanking period.

Protection

Protection Controls

Controls

Excellent

system

stability

achieved

the

comprehensive protection of WS3232. Including

WS3232 Datasheet(PDF) 5 Page - Shenzhen Winsemi Microelectronics Co., Ltd

WS3232 Datasheet(HTML) 5 Page - Shenzhen Winsemi Microelectronics Co., Ltd

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