sg6901asz-f116 Fairchild Semiconductor, sg6901asz-f116 Datasheet - Page 15

• Manufacturer Part Number: sg6901asz-f116
• Description: Pfc/flyback-pwm Controller
• Manufacturer: Fairchild Semiconductor

PFC / Flyback PWM Controller
Multi-Vector Error Amplifier
Although the PFC stage has a low bandwidth voltage loop
for better input power factor, the innovative multi-vector
error amplifier provides a fast transient response to clamp
the overshoot and undershoot of the PFC output voltage.
Figure 5 shows the block diagram of the multi-vector
error amplifier. When the variation of the feedback
voltage exceeds ±5% of the reference voltage, the
transconductance error amplifier adjusts its output
impedance to increase the loop response.
© System General Corp.
Version 1.0.1 (IAO33.0062.B0)
FIG. 5 Multi-Vector Error Amplifier
FIG.4 Average-Current-Mode Control Loop
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PFC Over-Voltage Protection
Using a voltage divider from the output of PFC to the
OVP pin, the PFC output voltage can be safely protected.
Once the voltage on the OVP pin is over OVP
OPFC is disabled. THE OPFC is not enabled again until
the OVP voltage falls below OVP
Cycle-by-Cycle Current Limiting
SG6901A provides cycle-by-cycle current limiting for
both PFC and PWM stages. Figure 6 shows the peak
current limit for the PFC stage. The PFC gate drive is
terminated once the voltage on the ISENSE pin goes
below V
The voltage of V
relationship between V
The amplitude of the constant current, I
the internal current reference according to the equation:
I
P
=
2
×
1.2V
PK
R
.
I
www.sg.com.tw • www.fairchildsemi.com
---------------------
RMS
determines the voltage of V
PK
and V
Product Specification
RMS
PFC
is shown in Figure 6.
.
September 26, 2007
P
, is determined by
SG6901A
PFC
PK
(8)
. The
, the