FAN9612 Fairchild Semiconductor, FAN9612 Datasheet - Page 22

• Manufacturer Part Number: FAN9612
• Manufacturer: Fairchild Semiconductor

© 2008 Fairchild Semiconductor Corporation
FAN9611 / FAN9612 • Rev. 1.1.4
Quick Setup Guide
The FAN9611/12 can be configured following the next
steps outlined in this section. This Quick Setup Guide
refers to the schematic diagram and component
references of Figure 33. It uses the equations derived
and explained in Application Note AN-6086.
In preparation to calculate the setup component values,
the power supply specification must be known.
Furthermore, a few power stage components must be
pre-calculated before the controller design begins as
their values determine the component selections. An
Excel design tool is also available to ease calculations.
From Power Supply Specification:
Minimum AC RMS Input (Turn-On)
Minimum AC RMS Input (Turn-Off)
Minimum Line Frequency
Nominal DC Output
Output Voltage Ripple (2 · f
Latching Output OVP
Nominal Output Power (to Load)
Desired Hold-Up Time
Minimum DC Output (End of t
Minimum Switching Frequency
Maximum DC Bias (for FAN9611/12)
Pre-Calculated Power Stage Parameters:
Estimated Conversion Efficiency
Maximum Output Power per Channel
Output Capacitance
Boost Inductance per Channel
Maximum On-Time per Channel
Turns Ratio (N
Other Variables Used During the Calculations:
Peak Inductor Current
Maximum DC Output Current (to Load)
Calculated Component Values:
Zero Current Detect Resistor
Bypass Capacitor for 5V Bias
Maximum On-Time Set
Soft-Start Capacitor
Compensation Capacitor
Compensation Resistor
Compensation Capacitor
Feedback Divider
Feedback Divider
Over Voltage Sense Divider
Over Voltage Sense Divider
Input Voltage Sense Divider
Description
BOOST
/ N
AUX
)
LINE
HOLD
)
)
V
V
C
C
Name
V
V
V
P
f
OUT,RIPPLE
V
OUT,LATCH
t
f
R
R
LINE,MIN
R
I
LINE.OFF
ON,MAX
R
COMP,HF
V
P
t
OUT,MIN
SW,MIN
C
COMP,LF
R
R
LINE.ON
C
R
R
MAX,CH
O,MAX
R
DDMAX
I
C
HOLD
L,PK
ZCD1
COMP
ZCD2
N
MOT
OUT
OUT
η
OUT
L
OV1
OV2
5VB
FB1
FB2
IN1
SS
,
Value
0.15μ
0.95
10
22
Input Voltage Sense Divider
Brownout Hysteresis Set
Gate Drive Resistor
Gate Drive Speed-Up Diode
Bypass Capacitor for VDD_HF
Startup Energy Storage for V
Current Sense Resistor
Step 1: Input Voltage Range
FAN9611/12 utilizes a single pin (VIN) for input voltage
sensing. The VIN pin must be above 0.925V (V
enable operation. The converter turns on at a higher
VIN voltage (V
The input voltage information is used for feedforward in
the control algorithm as well. The input-voltage
feedforward operates over a four-to-one range from
0.925V (V
pin.
At V
voltage feedforward is not possible. The input voltage-
sense circuitry saturates at this point and the PWM
ramp is modulated any longer. Above V
converter’s output power becomes a function of the
input voltage as shown in Figure 32. It can also be
expressed analytically as:
where VIN is the voltage at the VIN pin and P
desired maximum output power of the converter which
will be maintained constant while the input voltage
feedforward circuit is operational.
As can be seen, the converter’s output power capability
will follow a square function above V
P
OUT_NO_FF
Figure 31. VIN Turn-on and Turn-off Thresholds
IN
voltages above the 3.7V upper limit (V
Figure 32. VIN Feedforward Range
IN_BO

) to 3.7V (V
IN_ON
P
MAX
) set independently by the designer.




VIN
3.7
DD
FF_UL



2
), as measured at the VIN
FF_UL
R
R
D
R
CS1
C
C
G1
G1
R
INHYST
VDD1
VDD2
.
, R
, D
, R
IN2
G2
G2
CS2
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FF_UL
FF_UL
MAX
IN_BO
), input
2.2μ
47μ
, the
is the
) to
(5)