FSEZ1216B Fairchild Semiconductor, FSEZ1216B Datasheet - Page 11

• Manufacturer Part Number: FSEZ1216B
• Description: This highly integrated PWM controller provides several features to enhance the performance of low-power flyback converters
• Manufacturer: Fairchild Semiconductor

© 2008 Fairchild Semiconductor Corporation
FSEZ1216B Rev. 1.0.0
Functional Description
The proprietary topology of FSEZ1216B enables most
simplified circuit design especially for battery charger
applications. Without secondary feedback circuitry, the
CV and CC control can still be achieved accurately. As
shown in Figure 24, with the frequency-hopping, PWM
operation, EMI problem can be solved by using
minimized filter components. FSEZ1216B also provides
many protection functions. The VDD pin is equipped
with over-voltage protection (OVP) and under-voltage
lockout (UVLO). Pulse-by-pulse current limiting and CC
control ensure over-current protection (OCP) at heavy
loads. The GATE output is clamped at 15V to protect
the external MOSFET from over-voltage damage. Also,
the internal over-temperature-protection (OTP) function
shuts down the controller with latch when over heated.
Startup Current
The startup current is only 10μA. Low startup current
allows a startup resistor with a high resistance and a low
wattage to supply the starup power for the controller. A
1.5MΩ, 0.25W, startup resistor and a 10μF/25V V
hold-up capacitor is sufficient for an AC-to-DC power
adapter with a wide input range (100V
Operating Current
The operating current has been reduced to 3.5mA. The
low operating current results in higher efficiency and
reduces the V
FSEZ1216B enters deep-green mode, the operating
current is reduced to 1mA, assisting the power supply to
easily meet the power conservation requirement.
Green-Mode Operation
Figure 25 shows the characteristics of the PWM
frequency vs. the output voltage of the error amplifier
(V
proportional, output load parameter (V
indication of the output load for modulating the PWM
frequency.
frequency is fixed at 50KHz. Once V
V
50KHz to 500Hz, thus providing further power savings
and easily meeting international power-conservation
requirements.
N
COMV
, the PWM frequency starts to linearly decrease from
).
The
Figure 24. Frequency Hopping
In
DD
hold-up capacitance requirement. Once
heavy-load
FSEZ1216B
conditions,
uses
COMV
AC
to 240V
the
COMV
is lower than
the
) as an
positive,
AC
).
PWM
DD
11
Constant Voltage (CV) and Constant
Current (CC) Operation
An innovative technique of the FSEZ1216B can
accurately achieve CV/CC characteristic output without
secondary-side voltage or current-feedback circuitry.
There is a feedback signal from the reflected voltage
across the primary auxiliary winding for CV/CC
operation. This voltage signal is proportional to
secondary winding, so it provides the controller the
feedback signal from secondary side and achieves
constant-voltage-output property. In constant-current-
output operation, this voltage signal is detected and
examined by the precise constant-current-regulation
controller, then determines the on-time of the MOSFET
to control input power and provide constant-current-
output property. With feedback voltage V
current-sense resistor, the controller can obtain the
input power of the power supply. Therefore, the region
of constant-current-output operation can be adjusted by
the current sense resistor.
Temperature Compensation
The
compensation, in order to get better CV regulation at
different
compensation
coefficient (PTC) current that can compensate the
forward-voltage drop of the secondary diode varying
with temperature. This variation causes output-voltage
rising at high temperature.
Leading-Edge Blanking (LEB)
Each time the power MOSFET is switched on, a turn-on
spike occurs at the sense resistor. To avoid premature
termination of the switching pulse, a leading-edge
blanking time is built in. Conventional RC filtering can
therefore be omitted. During this blanking period, the
current-limit comparator is disabled and it cannot switch
off the gate driver.
Figure 25. Green-Mode Operation Frequency
FSEZ1216B
ambient
current
temperatures.
has
is
vs. V
a
built-in
COMV
positive-temperature-
This
CS
temperature
www.fairchildsemi.com
across the
internal