WS3252
Function Description
WS3252 is a high-integrated offline PWM controller,
optemized for high poformance low power AC/DC
charger and adapter adapter application. WS3252
operates
in
primary-side
opto-coupler
sensing
and
and
regulation.
could
be
Consequently,
TL431
winding. During MOSFET turn-on time, the load current
is supplied from the output filter capacitor Co. The
current in the primary winding ramps up. When MOSFET
turns off, the primary current transfers to the secondary
at the amplitude of
eliminated, thus reduce the cost. High presicion CC/CV
control can meet most adapter and charger application
requirements.
I
s
=
N
P
*
I
p
N
s
The auxiliary voltage reflects the output voltage, given by
V
AUX
=
Startup Current and Startup Control
Startup current of WS3252 is designed to be extremely
low at 5uA, so that VCC could be charged up above
UVLO threshold level and device starts up quickly. A
large value startup resistor can therefore be used to
minimize the power loss, predigest the design of startup
circuit and provides reliable startup in application.
N
AUX
* (
V
o
+ ∆
V
)
N
S
Where
△
V indicates the drop voltage of the output
Diode.
Via a resistor divider connectrd between the auxiliary
winding and INV, the auxiliary voltage is sampled at the
end of the demagnetization and it is hold until the next
sampling. The sampled voltage is compared with
Vref(2V) and the error is amplified. The error amplifier
output COMP reflects the load condition and controls the
PWM switching frequency to regulate the output voltage,
thus the constant output current can be achieved.
When sampled voltage is below Vref and error amplifier
output COMP reaches its maximum, the switching
frequency is controlled by the sampled voltage thus the
output voltage to regulate the output current, thus the
constant output current can be achieved.
Operating Current
The operating current of WS3252 is low at 2mA.
Excellent efficiency is achieved with low operating
current together and multi-mode control circuit.
CC/CV Operation
WS3252 is designed to produce good CC/CV control
characteristic as shown in the fig.1. In charger
applications, a discharged battery charging starts in the
CC portion of the curve until it is nearly full charged and
smoothly switches to operate in CV portion of the curve.
In an AC/DC adapter, the normal operation occurs only
on the CV portion of the curve. The CC portion provides
output current limiting. In CV operation, the output
voltage is regulated through the primary side control. In
CC operation mode, WS3252 will regulate the output
current constant regardless of the output voltage drop.
Adjustable CC point and Output Power
In WS3252, the CC point and maximum output power
can be externally adjusted by eaternal current sense
resistor Rs at CS pin. The output power is adjusted
through CC point change. The larger Rs, the smaller CC
point is, and the smaller output power becomes, and
vice versa.
V o
Large R s
Sm all R s
Principle of Operation
To achieve high precision CC/CV control, system needs
to be designed in DCM mode for flyback system. In DCM
mode, the output voltage can be sensed via the auxiliary
Fig.2 Adjustable output power by changing Rs
6/8
I o
Steady, keep you advance
WINSEMI [ SHENZHEN WINSEMI MICROELECTRONICS CO., LTD ]
