WS2259
Function Description
At very light load or no load condition, the IC operates in
Burst Mode. In this condition, the voltage at FB is below
burst mode threshold level, thus system goes into burst
mode. The gate dive output switches only when VCC
voltage drops below a preset level or FB input is active to
output an on state. Otherwise the gate drive remains at off
state to minimize the switching loss thus reduce the
standby power consumption. The standby current of
WS2259 is low as 800uA, Thus the standby of WS2259
can be low than 100mW. The frequency control also
eliminates the audio noise at any loading conditions.
WS2259 is a highly integrated current mode PWM control
IC which is optimized for high performance. It is applied
for switch power of the small-sized and medium-sized for
example the power adaptor. The low startup current,
operation current and burst mode function at the condition
of no load and low load can decrease the standby power
of the system, and improve the power convert efficiency.
The internal synchronous slope compensation, the
leading edge blanking function of the Sense pin not only
decrease the component number, but also improve the
stability of the system and avoid the harmonics generation.
WS2259 also have multiform general recovery protection
mode. The main function is described as below.
Oscillator Operation
A resistor connected between RI and GND sets the
charge/discharge time of the constant current source to
the internal cap and thus the PWM oscillator frequency is
determined. The relationship between RI and switching
frequency follows the below equation:
Startup Current and Startup Control
Startup current of WS2259 is designed to be very low
（4uA） so that VDD could be charged up above UVLO
threshold level and 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. For the design of AC/DC
adaptor with universal input range, a startup resistor of 2
MΩ, 1/8 W could be used together with a VDD capacitor
to provide a fast startup and low power dissipation
solution.
6500
FOSC
=
(Khz)
RI(Kohm)
If RI floating, the frequency will be internal set at 50 KHz
Current Sensing and Leading Edge Blanking
Cycle-by-Cycle current limiting is offered in WS2259. The
switch current is detected by a sense resistor into the
SENSE pin. The internal Leading-edge blanking chops off
the sense voltage spike at initial MOSFET on state due to
snubber diode circuit reverse recovery and thus reduce
the external RC filter circuit. The current limit comparator
is disabled and cannot turn off the external MOSFET
during the blanking period. PWM duty cycle is determined
by voltage level into SENSE pin and FB pin.
Operating Current
The operating current of WS2259 is very low .Good
efficiency is achieved with low operating current together
with extended burst mode control circuit which can easy
the design of VDD capacitor.
Soft-start
As soon as VDD reaches UVLO(on), the soft-start
function operates, the peak current is then gradually
increased from zero. Every restart attempt is followed by
4ms soft-start.
Internal Synchronized Slope Compensation
Built-in slope compensation circuit adds slope voltage
onto the current sense input voltage for PWM generation.
This greatly improves the close loop stability at CCM and
prevents the sub-harmonic oscillation and thus reduces
the output ripple voltage.
Burst Mode
Rev.A Apr.2011
7/11
Steady, keep you advance
WINSEMI [ SHENZHEN WINSEMI MICROELECTRONICS CO., LTD ]
