How to use
the design tool (Ver 1.0) for FAN7631
www.fairchildsemi.com
1
Contents
 Motivations
 Design Example
 Single output for LCD TV
2
Motivations
 It is modified from conventional Fairchild LLC design tool of
version 1.3
 It is suitable for FAN7631 in the control parameter design point of
view
 It can be used for high frequency design with resonant frequency
up to 300kHz and softstart frequency up to 600kHz
3
Design Example
Single Output Application for LCD TV
4
Design Example
 Single output application for LCD TV
 Specifications
p
 Output: 24V/8A
 Input: 360Vdc ~ 400Vdc (nominal 380Vdc)
 Let’s
L t’ start
t t to
t design
d i using
i “LLC d
design
i ttooll for
f FAN7631 Ver
V 1.0
1 0”
5
Step 1: Fill out the input/output specifications
Multi-output could be possible up to three.
Specification & Parameter
Output Voltage 1
Output Current 1
Output Voltage 2
Output Current 2
O t t Voltage
Output
V lt
3
1 O
1.
Output
t t Specifications
S ifi ti
Output Current 3
Output Power
Select Configuration of Output Rectifier
Input
24
8
0
0
0
0
Output
Dim.
192.0
W
1
Maximum VF of Output Diode
Maximum Input Voltage
Nominal Input Voltage
Estimated Efficiency
2. Input Specifications Expected Input Power
DC-Link Capacitor
Frequency & Ripple voltage @ Nominal
Minimum Input Voltage
If the PFC circuit is used,
then these two rows have
no meaning.
meaning
Dim.
V
A
V
A
V
A
1
V
400
380
0.95
V
V
680
0
360
uF
Hz
V
202.1
W
0
V
If this is larger than the
gap between Vin,nom
and Vin,mim, increase
the DC-Link Capacitor.
If the secondary side configuration is a center tapped, input “1”.
If the secondary side configuration is a bridge type, input “2”.
6
Step 2-1: Select m (Lp/Lr)
It is recommended to choose 4~8 of m.
The conduction loss would be decreased as m increases.
3 G
3.
Gain
i & Turn
T
ratio
ti
m=
Boundary Voltage
Gain @ Resonant Freq. of Lr & Cr
Margin
g of Maximum Gain
Required Maximum Gain
Turn-ratio (Np/Ns1)
Turn-ratio (Np/Ns2)
6
411
V
1.10
15
%
1.44
9.00
-
Turn-ratio (Np/Ns3)
-
Gain
Below region
(fs<fo)
1. To make all switching frequencies depending
on the input voltage below the resonant
frequency (fs<fo), let the Boundary Voltage
higher than the maximum input voltage.
If Boundary Voltage is less than Vin,max,
above region operation could be with Vin,max.
Above region
(fs>fo)
Gmax @ Vin,min
Gmin @ Vin,max
2. To make turns ratio be an integer, tune the
Boundary Voltage up.
Virtual Gain
@ Boundary Voltage
fs
@ Vin,min
fs
@ Vin,max
fo
fs
7
Step 2-2: Select m (Lp/Lr)
3. Gain & Turn ratio
m=
Boundary Voltage
Gain @ Resonant Freq. of Lr & Cr
Margin of Maximum Gain
Required Maximum Gain
Turn-ratio (Np/Ns1)
Turn-ratio (Np/Ns2)
6
411
1.10
15
Im
-
(I) fs < fo
To respond properly to load changes, there
should be an enough margin. 15~20% is
recommended.
d d
ID
Ip
ID
%
1.44
9.00
-
Turn-ratio (Np/Ns3)
Ip
V
IO
Im
The p
peak gain
g
in the gain
g
curve must exceed
the Required Maximum Gain at full load
condition.
(II) fs > fo
IO
8
Step 3-1: Select Q factor
This graph is obtained when m is selected.
Find out an appropriate Q factor guaranteeing the
Required Maximum Gain
G
on the red curve.
In p
previous page:
p g
1) m is selected to be m=6
2) required peak gain is calculated to be 1.44
Action items:
1) find the curve with m=6 which is highlighted
with red
2) @ m=6 curve, find a pint of gain=1.44
3) read the Q value @ the point of gain=1.44
and find the Q is around 0.35
9
Step 3-2: Select Q factor
Automatically
calculated.
AC Resistor
214.2
ohm
DC Resistor
3.3
ohm
10.6
nF
59.7
uH
630
V
360.0
uH
Q factor
0.350
Expected Resonant Frequency
4. Resonant Parameters
200
kHz
Recommended Cr
Recommended Lr
Selected Cr / Recomm. Voltage Rating
12.0
nF
Selected Lr
60.0
uH
Estimated Lp
Lr and Cr could be calculated
using;
Lr
1
fO 
2 Lr C r Q  C r
R AC
To guarantee the Required Maximum Gain,
Q factor has to be small satisfactorily.
Put the desired resonant frequency down.
Choose Lr and Cr referring to the
Recommended Values including the
voltage rating of Cr.
10
Step 4: Check the peak gain with the gain curve
G
Gain
Gain Curve depending on the load condition.
Check whether the peak gain @ full load > Required Maximum Gain
If not, go back to Step 3 and reduce Q factor.
LLC resonant Converter
2.5
2.4
2.3
2.2
2.1
20
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
Load of 100%
80%
60%
40%
20%
50
100
150
200
250
freq (kHz)
11
300
350
400
450
Step 5: Just check out Section 5 and 6
Section 5 is only for the reference.
Remind Lp and Lr are not Lm and Llkg.
Magnetizing Inductance
328.6
Leakage Inductance of Primary-side
31.37
uH
4.05
uH
0.39
uH
-
uH
Inductance of Secondary-side 1
5. Transformer Parameters Leakage Inductance of Secondary-side 1
for Simulation
Inductance of Secondary-side
y
2
uH
Leakage Inductance of Secondary-side 2
-
uH
Inductance of Secondary-side 3
-
uH
-
uH
Leakage Inductance of Secondary-side 3
Phase Angle of Lr & Cr
1178.5 krad/s
Phase Angle of Lp & Cr
481.1 krad/s
Resonant Freq. of Lr & Cr (fr)
187.7 kHz
6. Operating Parameters Resonant Freq. of Lp & Cr
Operating Freq. @ Max. Input Voltage
76.6
kHz
175.8
kHz
Operating Freq. @ Nom. Input Voltage
159.4 kHz
Operation Freq. @ Min. Input Voltage
141.9
kHz
The real value of resonant frequency.
Estimated operating frequency
depending on the input voltage.
Check out all are below resonant frequency.
12
Step 6: Obtain components’ values of control part
Referring to the gain curve, put down the minimum operating frequency.
Keep it in your mind that the set must do not enter the ZCS mode.
Minimum
Mi
i
Operating
O
i Frequency
F
off IC
Maximum Operating Frequency of IC
fss
Rmin
Rmax
450.0 kHz
7.7 kohm
4.2 kohm
Soft-start Time(tSS)
7. Parameter of
Control Part
It is set for burst
operation
75 kHz
kH
200 kHz
30.00 msec
Css
0.35
uF
Auto Restart Time(tAR)
243
ms
40
ms
OLP Time(tOLP)
Recommended Sensing Resistor(RCS)
0.13 ohm
Input Voltage for disabling Brownout Protection
Input Voltage for enabling Brownout Protection
Vin, hysteresis
Rupper_LUVP
Rlower_LUVP
Dead Time(DT)
380
280
V
Dead Time Capacitor (CDT)
Dead time section
Brownout protection
section
13
360.00
360
00
20.00
2.00
16.8
V
V
MΩ
kΩ
9.9
kΩ
10.0
nF
ns
Dead Time Resistor(RDT)
To avoid triggering of OCP
at startup, there is 50%
margin of the estimated
peak primary current.
It is 6fmin and upper
limit is 600kHz
Css related section
(tSS, tAR, TOLP)
Step 7: Just check out Section 8
The estimated rms value of the primary current.
The more m, the smaller Irms.
If the transformer is too hot, there are two solutions;
First, go back to Step 2 and increase m.
Second, increase wire gauge as large as possible.
8. Current on
Input & Output Stage
IRMS of Primary-side @ Nominal Input
1.16 Arms
IPEAK of Primary-side @ Nominal Input
1.64
IRMS of Output 1
9.59 Arms
IRMS of Output 2
- Arms
IRMS of Output 3
- Arms
A
It will be used to select the sense resistor.
To avoid triggering of OCP at startup, there is 50% margin of the
estimated peak primary current.
14
Step 8: Select the secondary diode
Margin of Rated Voltage
50
%
Margin of Rated Current
100
%
Rated Current & Voltage of Output 1 Diode
9. Secondary-Side
Diode Specification
Rated Current & Voltage of Output 2 Diode
Rated Current & Voltage of Output 3 Diode
The voltage rating is (2*Vo)*150% as your input.
The current rating has 100% margin.
15
72.0
V
8.60
A
-
V
-
A
-
V
-
A
Step 9: Transformer Design
To guarantee safe operation, recommended BMAX when integrated transformer
1) 0.2~0.26 for fr=100kHz
2) 0.15~0.2 for fr=200kHz
3) 0.1~0.15 for fr=300kHzis recommended.
Used core information
Expected BMAX
0.2 Tesla
Ae of Core
150
㎟
Min. Number of Primary Winding Turns(Np,min)
25.0 Turns
Number of Output 1 Winding Turns(Ns1)
3 02 Turns
3.02
Number of Expected Primary Winding Turns(Np)
27.2 Turns
Number of Output 2 Winding Turns(Ns2)
10. Transformer
Specifications
Minimum Np. Np must
be greater than this.
- Turns
Number of Output 3 Winding Turns
- Turns
Primary-side Inductance (Lp)
360.0
uH
60.0
uH
Area of Primary Winding Wire
0.23
㎟
Area of Output 1 Winding Wire
1.25
㎟
Area of Output 2 Winding Wire
-
㎟
Area of Output 3 Winding Wire
-
㎟
Resonant Inductance (Lr)
Current Density
5 A/㎟
Among multi-outputs, fill in the blank with
the lowest output.
If Np<Np,min, error message is like below, so
please increase Ns1
Select the current density and the adequate wire.
If the window area of the used core is insufficient
with the recommended winding wire,
increase the current density.
16
Considerations







4~8 of m is recommended.
Let Boundary Voltage above Vin,max.
Select Q factor for “Peak Gain > Required Maximum Gain.”
Set fs,min to avoid ZCS region operation.
Set the voltage margin for selecting the secondary diode
diode.
Np must be greater than Minimum Np.
If the temperature of transformer is too high,
 Go
G back
b k to
t Step
St 2,
2 and
d increase
i
m.
 Go back to Step 9, and decrease Current Density.
17
Thank you !
18