FAN302HL Fairchild Semiconductor, FAN302HL Datasheet - Page 12

• Manufacturer Part Number: FAN302HL
• Description: This highly integrated PWM controller, FAN302HL, provides several features to enhance the performance of general flyback converters
• Manufacturer: Fairchild Semiconductor

© 2010 Fairchild Semiconductor Corporation
FAN302HL • Rev. 1.0.1
Burst-Mode Operation
The power supply enters “Burst-Mode” at no-load
conditions. As shown in Figure 31, when V
below V
voltage drops at a rate dependent on load current. This
causes the feedback voltage to rise. Once V
V
pulse. The feedback voltage then falls and the process
repeats. Burst Mode operation alternately enables and
disables switching of the MOSFET, reducing the
switching losses in Standby Mode.
Operating Current
The typical operating current is 3.5mA. This low
operating current results in higher efficiency and
reduces the V
FAN302HL enters Burst Mode, the operating current is
reduced to 200μA, allowing the power supply to meet
power conservation requirements.
Gate Output
The FAN302HL BiCMOS output stage is a fast totem-
pole gate driver. Cross conduction has been avoided to
minimize heat dissipation, increase efficiency, and
enhance reliability. The output driver is clamped by an
internal Zener diode to protect the power MOSFET
transistors against over-voltage gate signals.
Slope Compensation
The sensed voltage across the current-sense resistor is
used for Current-Mode control and pulse-by-pulse
current
synchronized positively-sloped ramp built-in at each
switching cycle, improves stability and prevents sub-
harmonic oscillations due to Peak-Current Mode control.
Constant Power Mode Control
When V
Constant-Power-Mode control, the primary-side current
limit voltage (V
mis-sampling V
(ZCD). Once V
to V
FBH
STH
, the internal circuit starts to provide switching
.
FBL
S
limiting.
Figure 31. Burst-Mode Operation
, the PWM output shuts off and the output
is lower than V
DD
CS
S
S
hold-up capacitance requirement. Once
is higher than V
) changes from V
through the Zero Current Detection
Built-in
S-CM-MIN
slope
S-CM-MAX
STH
, FAN302HL enters
compensation,
to V
, the V
STH-VA
FB
CS
FB
exceeds
to avoid
returns
drops
a
12
Protections
The FAN302HL self-protection functions include V
Over-Voltage Protection (V
Temperature
Protection (V
pulse current limit.
The V
Mode. Once an abnormal condition occurs, switching is
terminated and the MOSFET remains off, causing V
to drop. When V
5V, the internal startup circuit is enabled, and the supply
current drawn from HV pin charges the hold-up
capacitor. When V
16V, FAN302HL resumes normal operation. In this
manner, the auto-restart alternately enables and
disables the switching of the MOSFET until the
abnormal condition is eliminated (see Figure 32).
The V
implemented as Latch Mode. If abnormal conditions
occur, PWM switching is terminated and the MOSFET
remains off. In this scenario, V
working as auto-restart (V
trigger PWM pulses). FAN302HL enters Latch Mode,
disables PWM switching of the MOSFET until V
lower than V
again, then resumes normal operation (see Figure 33).
DD
Figure 32. Auto-Restart Mode Operation
S
OVP protection is implemented as Auto-Restart
OVP and internal OTP protections are
S
DD-LH
OVP), brownout protection, and pulse-by-
Protection
DD
(AC power is removed), powers on
DD
drops to the V
reaches the turn-on voltage of
DD
auto-restart behavior doesn’t
(OTP),
DD
OVP), internal Over-
DD
DD
V
turn-off voltage of
drops, but keeps
S
Over-Voltage
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DD
DD
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