FAN302HL Fairchild Semiconductor, FAN302HL Datasheet - Page 10

• 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
Operation Description
Constant-Voltage Regulation Operation
FAN302HL is the high-frequency and ultra-low standby
power IC with Constant Voltage (CV) / Constant Current
(CC) regulation.
When FAN302HL operates in CV regulation, the
feedback voltage (V
modulates the PWM duty, as shown in Figure 24,
causing fixed switching frequency (85kHz). Once the
V
disabled and operation current decreases.
Constant-Current Regulation Operation
During CC operation, the proprietary Primary-Side
Regulation (PSR) topology simplifies circuit design
without secondary feedback circuitry for battery-charger
applications. The CC regulation achieved through PSR
technique uses a mixed-signal algorithm to detect the
primary-side current and to sample the voltage through
primary-side auxiliary winding and calculate the average
current on secondary side.
Figure 25 shows the basic circuit diagram of a flyback
converter, with typical waveforms shown in Figure 26.
Generally, Discontinuous Conduction Mode (DCM)
operation is preferred for constant-current control since
it allows better output regulation. The operation
principles of DCM flyback converter are:
During the MOSFET on time (t
applied across the primary-side inductor (L
MOSFET current (I
FB
f
decreases below V
OSC
Figure 24. f
Burst mode
V
FB-L
V
CV Regulation
FB-H
ds
Green mode
) increases linearly from zero to the
OSC
FB
FB (V)
) works as output load and
I
V
O
Frequency Hopping
vs. V
FB-G
FB-G
, frequency hopping is
FB
ON
CC Regulation
in CV Regulation
), input voltage (V
m
). Then,
DL
) is
10
peak value (I
from the input and stored in the inductor.
When the MOSFET is turned off, the energy stored in
the inductor forces the rectifier diode (D) to be turned
on. While the diode is conducting, the output voltage
(V
applied across the secondary-side inductor (L
N
the peak value (I
current discharge time (t
inductor has been delivered to the output.
When the diode current reaches zero, V
quickly: if it is greater than the V
the IC gets the t
During the inductor current discharge time, the sum of
output voltage and diode forward-voltage drop is
reflected to the auxiliary winding side as (V
N
secondary winding. In constant-current output operation,
this voltage signal is detected and examined by the
precise constant-current regulation controller. The on
time of the MOSFET is determined to control input
power and provide constant-current output property.
With feedback voltage V
resistor, the controller can obtain the input power of
power supply. Therefore, the region of constant-current
output operation can be adjusted by the current-sense
resistor, as shown in Equation (1).
During CC regulation, the V
output voltage decreases. The switching frequency
reduces linearly from f
changes from V
relationship between frequency and V
28 shows the output V-I curve and V
I
O
p
a
O
2
/N

) and the diode current (I
), together with diode forward voltage drop (V
1
2
s
Figure 25. Simplified Flyback Converter Circuit
. This voltage signal is proportional to the

i
PK

N
N
P
S
pk

t
). During this time, the energy is drawn
DIS
t
DIS
s
p
SN-CC
kN

for CC regulation.
1
2
p

/N
N
N
to V
P
S
OSC
s
DIS
) to zero. At the end of inductor

CS
V
R
), all the energy stored in the
SG-CC
CS
CS
to f
D
across the current-sense
) decreases linearly from

S
t
DIS
t
. Figure 27 shows the
s
OSC-CCM
voltage decreases as
VS-OFFSET
S
voltage.
S
S
voltage. Figure
as V
voltage drops
www.fairchildsemi.com
drop voltage,
S
(1)
O
voltage
+V
F
m
), are
N
F
) 
s
2
/