### Easy Design a SRC Converter By CM6900G

```CM6900 Application Note A-003A
Easy Design a SRC Converter
By CM6900G
Michael Lee
Introduction
Recently, resonant DC/DC converter has been accepted by the industry, however, the design
of a resonant converter is still foreign to most engineers.
make a good design.
The important topic is how to
Here, we focus on the explanation on how engineers can add simple
mathematical formula to design the procedures needed for a resonant converter.
This
would help engineers to easily and quickly design the product that client request, simplify the
design process and time, and solve the puzzle engineers may have for resonant converter.
In order to easily explain the design concept of the resonant controller and its relationship
with the controller IC, this application note will integrate Champion’s resonant control IC
(CM6900 series) as the controller of switching controller design.
SRC V.S LLC
The resonant controller of AC/DC output mainly uses series resonant as the main structure, it
is categorized into two operating zone for load curve. SRC is operated on the resonant point
(operated in the inductor load area); LLC is operated below the resonant point and between
the second resonant point (operated at the inductor load area). Graph 1 (SRC) and graph 2
(LLC) below gives further explanation.
2008/04/12
Champion Microelectronic Corporation
Page 1
CM6900 Application Note A-003A
20
15
Vp in Transformer
Vs1 ( Fsw )
Vs2 ( Fsw )
Vs3 ( Fsw )
Vs4 ( Fsw )
10
Vs5 ( Fsw )
Vs6 ( Fsw )
5
2 .10
4
4 .10
4
6 .10
4
8 .10
4
1 .10
Fsw
Switch Frequency
5
5
1.2 .10
5
1.4 .10
Fr
5
1.6 .10
5
1.8 .10
2 .10
5
Fmax
Fmin>=Fr
From graph 1 SRC load curve, it can be seen that the resonant controller’s operating zone,
frequency is from Fmin~Fmax. In other words, the switching frequency Fsw operate above
the resonant point Fsw>=Fr.
2008/04/12
Champion Microelectronic Corporation
Page 2
CM6900 Application Note A-003A
20
15
Vp in Transformer
Vs1( Fsw)
Vs2( Fsw)
Vs3( Fsw)
Vs4( Fsw)
10
Vs5( Fsw)
Vs6( Fsw)
5
2 .10
4
4 .10
4
6 .10
4
Fr2
8 .10
4
1 .10
1.2 .10
Fsw
Switch Frequency
5
5
1.4 .10
Fr1
5
1.6 .10
5
1.8 .10
5
2 .10
5
Fmax
Fmin>=Fr2
From graph 1 SRC load curve, it can be seen that the frequency of the resonant controller’s
operating zone is from Fmin~Fmax.
In other words, when operating above the second
resonant point and between Fsw>=Fr2~Fr1, at light load the frequency will be Fsw>Fr1.
Therefore, comparing the advantage and disadvantage when designing SRC and LLC, LLC is
by far more difficult to design compare to SRC.
It is difficult to design if load curve is not
simulated, so SRC is much easier to design because it only needs to design on a single
resonant point.
There will not be design issues even if simulation is not done.
So, as to the serial resonant controller, there are two operating zone. SRC is the one with
switching frequency operated on the resonant frequency while LLC operates between two
resonant points, therefore LLC design is comparatively difficult.
2008/04/12
Champion Microelectronic Corporation
Page 3
CM6900 Application Note A-003A
Design a SRC Converter
1. Design flow and parameter setting
a. Input spec (350Vdc ~ 395Vdc)
b. Output spec (normally 5V or 12V/24V)
c. Decide resonant frequency (Fr: normally set at 50Khz)
d. Decide controller IC (CM6900G) Minimum working frequency (same Fmin
and Fr)/Maximum working frequency (Fmax normally set at 200Khz)
e. Decide the Q value of resonant frequency (normally set between 0.3 ~ 0.5)
f. Structure Choice (below 500W use half bridge CLASS D, above 500W uses
standard half bridge or full bridge).
2. Calculation Example (12V/25A 300W)
Here we use 300W 12V/25A as an example to explain the design and calculation of SRC
resonant converter. Graph 3 is the SRC half bridge circuit; graph 4 is CM6900G circuit
and component values used.
2008/04/12
Champion Microelectronic Corporation
Page 4
CM6900 Application Note A-003A
+VDC
D10 SS16
R43
47Ω
Q12
9A/500V
C30
100pF/1KV
DRVH
R44
47KΩ
C31
PQ-20/16 160uH
47nF/630V
0.8uH/25A
5
7
9A/500V
C35
SYNDRVH
+ C33
+ C33
0.1uF/63V 3300uF/16V 3300uF/16V
75A/50V
C37
100pF/1KV
DRVL
12V
L5
Q13
1
Q14
R45 47KΩ
6
T5
D11 SS16
R46
47Ω
75A/50V
T4
2
6
5
DRVHGND
C32
47nF/630V
SYNDRVL
Lp(1.5mH)
8
Q15
+ C34
C47
3300uF/16V
0.1uF/63V
R47 47KΩ
ERL-35
R49
47KΩ
Graph 3 SRC Half Bridge Circuit
+12V
R53
2KΩ
1
2
3
VREF
R58 430KΩ
C50
4
R37
2MΩ
5
R64
100KΩ
1nF/25V
R57
1KΩ
VREF
U6
R55
1.8KΩ
6
7
SD
C49
R70
1KΩ
1nF/25V
R63
150K
R65
100KΩ
C58
0.1uF/16V
RSET
47KΩ
8
R59
200KΩ
C52
47pF/25V
Css
0.22uF/25V
R71
R72
12KΩ
1KΩ
Rset
VREF
VFB
VCC
FEAO
PRIDRV
D_IN-
PRIDRVB
D_IN+
SRDRV
DEAO
SRDRVB
CSS
GND
Ilim
RT/CT
CM6900
C54
0.1uF/25V
12VS
16
15
14
13
12
11
PRIDRVH
PRIDRVL
SECDRVH
RT
47KΩ
SECDRVL
10
9
CT
C51
C56
620pF/25V NPO0.1uF/25V0.1uF/25V
IPLIMIT
Graph 4 CM6900G Circuit and component values used
2008/04/12
Champion Microelectronic Corporation
Page 5
CM6900 Application Note A-003A
Design parameter is as follows:
Subject: The Half-bridge power supply design
(series resonant converter )
Design specifications.
−3
3
k ≡ 10
−6
m ≡ 10
−9
μ ≡ 10
− 12
n ≡ 10
p ≡ 10
Input Specification
Vin_max:= 400
Vin_min := 330
Vin_nor := 395
Output Specification
Vout1 := 12
Iout1min := 0.01
Iout1max := 12.5
Vripple := 100⋅ m
Vout2 := 12
Iout2min := 0.01
Iout2max := 12.5
Vripple := 100⋅ m
Pout := ( Vout1⋅ Iout1max) + ( Vout2⋅ Iout2max)
Pout = 300
η := 0.96
Watt
Power stage Specification
Fresonant := 50⋅ k
Lm := 6m
Bdelta := 2000
Rds := 3⋅ m
Gauss
Vmosfet := ( Iout1max + Iout2max) ⋅ Rds
Q := 0.3
Control Specification use CM6900G
Vref := 7.5
Fmin := 50⋅ k
Fmax:= 200⋅ k
CM6900 parameter design
fosc = 1 / (tRAMP + t DEADTIME)
tRAMP = RT * CT * ln((VREF + ICHG*RT -1.25)/(VREF + ICHG*RT -3)) where ICHG = 4*(FEAO-VBE)/RSET
tDEADTIME = 2.125V/2.5mA * CT = 850 * CT
Ct :=
850
− 10
Ct = 5.882 × 10
2008/04/12
Ct := 620⋅ p
Ct is 620pF
Champion Microelectronic Corporation
uses NPO material
Page 6
CM6900 Application Note A-003A
2.Minimum Frequency
Foscmin := Fmin⋅ 2
1
Tramp_max :=
Rt :=
Foscmin
Tramp_max
Ct⋅ ln⎡⎢
−6
Tramp_max = 9.5 × 10
( Vref − 1.25) ⎤
⎥
⎣ ( Vref − 3) ⎦
4
Rt := 47k
Rt = 4.664 × 10
Rt is 47Kohm
3.Maxmum Frequency
Foscmax := Fmax⋅ 2
1
Tramp_min :=
Foscmax
−6
Tramp_min = 2 × 10
⎛ Tramp_min ⎞ ⎤
⎡
⎢ 20⋅ Rt − 20⋅ e⎜⎝ Rt ⋅Ct ⎟⎠ ⋅ Rt⎥
⎣
⎦
Rset :=
⎛⎜ Tramp_min ⎞⎟
Rt ⋅Ct
⎠ − 6.25
4.5⋅ e⎝
4
Rset := 47⋅ k
Rset = 4.669 × 10
Rset is 47Kohm
4.Soft-start capacitor
Tsoft := 0.05
⎛ 7.5⋅ μ ⋅ Tsoft ⎞
⎟
2.5
⎝
⎠
−7
Css := ⎜
Css = 1.5 × 10
Css is 0.22uF
Main transformer design
1.Select a core for power supply
PQ-32/30 Ae:1.61
ERL-35 Ae:1.07
Ae := 1.07
Trnum := 1
Topology := 2
Full Bridge=1
Half Bridge =2
2.Dertermine the turn ratio Np/Ns
Set normal output voltage is 110% to 120% of transformer secondary output in SRC application
2008/04/12
Champion Microelectronic Corporation
Page 7
CM6900 Application Note A-003A
Vin_nor
Npmin :=
Topology ⋅ Trnum
8
⋅ 10
4⋅ Fmin⋅ Bdelta⋅ Ae
Npmin = 46.145
Npmin := 43
Primary side coil
Vin_nor
Topology ⋅Trnum
Nratio1 :=
Ns1 :=
( Vout1 + Vmosfet) ⋅ 1.15
Nratio1 = 14.223
Npmin
Nratio1
Ns1 = 3.023
Secondary side coil
Ns2 = 3.023
Secondary side coil
Vin_nor
Topology ⋅Trnum
Nratio2 :=
Ns2 :=
( Vout2 + Vmosfet) ⋅ 1.15
Nratio2 = 14.223
Npmin
Nratio2
Vin_max
8⎞
⎛
⎜ Topology ⋅ Trnum ⋅ 10 ⎟
Bmax:= ⎜
⎟
⎝ 4⋅ Fmin⋅ Npmin⋅ Ae ⎠
3
Bmax = 2.173 × 10
Main transformer magnetic flux density
3.Dertermine resonant components
Set Q value does not over 1 @ full load at resonant point
2
Ro1 :=
Vout1⋅ Nratio1
Iout1max
Ro1 = 194.194
Output reflex to primary side load
Ro2 = 194.194
Output reflex to primary side load
2
Ro2 :=
Vout2⋅ Nratio2
Iout2max
Rot := Ro1⋅
Ro2
( Ro1 + Ro2)
Zo := Q⋅ Rot
2008/04/12
Rot = 97.097
Output reflex to primary side total load
Zo = 29.129
Calculate Lr, Cr distinct resistance
Champion Microelectronic Corporation
Page 8
CM6900 Application Note A-003A
Calculation Cr
Lr=Zo*Cr
2
⎡ ⎛
1
⎞ ⎤⎥
⎢ ⎜
⎟
⎢ ⎝ 2⋅ πFresonant ⎠ ⎥
Cr :=
⎢
⎥
2
Zo
⎣
⎦
−7
Cr := 86⋅ n
−5
Lr := 120⋅ μ
Cr = 1.093 × 10
Resonant Capacitor
Calculation Lr
2
Lr := Zo ⋅ Cr
Fresonant :=
Lr = 7.297 × 10
1
4
Fresonant = 4.954 × 10
2⋅ π⋅ Lr⋅ Cr
Resonant Inductor
Resonant Frequency
Lr
Q :=
Cr
Q = 0.385
Rot
Q value
Calculation Lr voltage stress
VLr:= Q⋅
Vin_max
VLr = 76.942
Topology
Resonant inductor voltage
PQ-20/16
Ae:0.64
Blr_max:= 2500
Aelr := 0.64
Nlr :=
VLr
Aelr⋅ Blr_max⋅ 4.44⋅ Fmin
8
⋅ 10
Nlr = 21.662
Resonant inductor coil
Calculation Cr voltage stress
VCr_ac := VLr
Vin_max
VCr :=
+ VCr_ac
2
VCr = 276.942
Resonant Inductor Voltage
Resonant inductor voltage value is double or more
Suggest to use 800V high current durance MPP inductor
2008/04/12
Champion Microelectronic Corporation
Page 9
CM6900 Application Note A-003A
20
15
Vp in Transformer
Vs1 ( Fsw )
Vs2 ( Fsw )
Vs3 ( Fsw )
Vs4 ( Fsw )
10
Vs5 ( Fsw )
Vs6 ( Fsw )
5
2 .10
4
4 .10
6 .10
4
Graph 5
2008/04/12
4
8 .10
4
5
5
1 .10
1.2 .10
Fsw
Switch Frequency
5
1.4 .10
5
1.6 .10
5
1.8 .10
2 .10
SRC high voltage input load curve
Champion Microelectronic Corporation
Page 10
5
CM6900 Application Note A-003A
20
15
Vp in Transformer
Vs1 ( Fsw )
Vs2 ( Fsw )
Vs3 ( Fsw )
Vs4 ( Fsw )
10
Vs5 ( Fsw )
Vs6 ( Fsw )
5
2 .10
4
4 .10
Graph 6
2008/04/12
4
6 .10
4
8 .10
4
1 .10
Fsw
Switch Frequency
5
5
1.2 .10
5
1.4 .10
5
1.6 .10
5
1.8 .10
2 .10
SRC regular input voltage load curve
Champion Microelectronic Corporation
Page 11
5
CM6900 Application Note A-003A
20
15
Vp in Transformer
Vs1( Fsw)
Vs2( Fsw)
Vs3( Fsw)
Vs4( Fsw)
10
Vs5( Fsw)
Vs6( Fsw)
5
2 .10
4
4 .10
4
6 .10
4
8 .10
4
1 .10
1.2 .10
Fsw
Switch Frequency
5
5
1.4 .10
5
1.6 .10
5
1.8 .10
5
2 .10
5
Graph 7 SRC low input voltage load curve
Calculation Ripple current of Cout
Iripple := 0.448⋅ ( Iout1max + Iout2max)
Iripple = 11.2
Output inductor ripple current
Suggest inductor ripple current endurance need to be 30% more than needed
2008/04/12
Champion Microelectronic Corporation
Page 12
CM6900 Application Note A-003A
4.Feedback loop compensation design
CM6900 GM Modeling
−6
6
Ro := 1⋅ 10
−6
Gm := 135⋅ 10
Iodrv_max := 13⋅ 10
CM6900 GM compensation network
A. Voltage Loop FM Compensation
R1 := 150⋅ k
1
Z1 :=
2⋅ π⋅ R1⋅ C1
1
P1 :=
2⋅ π⋅ Ro⋅ C1
1
P2 :=
2⋅ π⋅ R1⋅ C2
2008/04/12
C1 := 1⋅ n
C2 := 0.47⋅ n
3
Z1 = 1.061 × 10
P1 = 159.155
3
P2 = 2.258 × 10
Champion Microelectronic Corporation
Page 13
CM6900 Application Note A-003A
A ( Fsw) := Gm⋅ Ro⋅
(1 + R1⋅ C1⋅ 2⋅ π⋅ Fsw)
(1 + R1⋅ C2⋅ 2⋅ π⋅ Fsw)⋅ ( 1 + Ro⋅ C1⋅ 2⋅ π⋅ Fsw)
Bode Plot
1 .10
3
Loop Gain of Compensator
100
10
A( Fsw)
1
0.1
0.01
1
10
1 .10
3
100
1 .10
1 .10
4
5
Fsw
Frequency
B. Voltage Loop Duty Compensation
High Loop Gain for Duty Compensation
Middle Loop Gain for Duty Compensation
2008/04/12
Champion Microelectronic Corporation
Page 14
CM6900 Application Note A-003A
6
R1 := 100⋅ k
Ro := 1⋅ 10
−6
P1 :=
P2 :=
C2 := 0.001⋅ p
R2 := 240⋅ k
Gm := 135⋅ 10
Z1 :=
C1 := 1⋅ n
1
3
Z1 = 1.592 × 10
2⋅ π⋅ R1⋅ C1
1
P1 = 159.155
2⋅ π⋅ Ro⋅ C1
1
9
P2 = 1.592 × 10
2⋅ π⋅ R1⋅ C2
A ( Fsw) := Gm⋅ Ro⋅
R2
Ro + R2
⋅
( 1 + R1⋅ C1⋅ 2⋅ π⋅ Fsw)
( 1 + R1⋅ C2⋅ 2⋅ π⋅ Fsw) ⋅ (1 + Ro⋅ C1⋅ 2⋅ π⋅ Fsw)
Bode Plot
Loop Gain of Compensator
100
10
A( Fsw)
1
0.1
1
10
1 .10
3
100
1 .10
1 .10
4
5
Fsw
Frequency
2008/04/12
Champion Microelectronic Corporation
Page 15
CM6900 Application Note A-003A
Typical application Circuit
+VDC
D10 SS16
Q12
R43
47Ω
CMT08N50
C30
100pF/1KV
DRVH
R44
47KΩ
C31
PQ-20/16
2
6
5
DRVHGND
T5
47nF/630V
C32
47nF/630V
10
CMT08N50
C37
100pF/1KV
DRVL
CMT60N06
R45 47KΩ
L5
13
0.8uH/10A
14
15
24VSYNDRVH
ERL-35
C35
0.1uF/63V
CMT60N06
16
Q15
+ C33
+ C34
C36
1000uF/35V
1000uF/35V
0.1uF/63V 0.1uF/63V
R47 47KΩ
9
R49
47KΩ
L6
12VI+
10
11
Q16
12
+12V
24VSYNDRVL
2uH/3A
C40
R48
+24V
Q13
1
Q14
T4
11
D11 SS16
R46
47Ω
24VSYNDRVL
Lp(1.5mH)
0.1uF/63V
Q17
+ C38
+ C39
1000uF/16V
1000uF/16V
C41
0.1uF/63V
D12
IPLIMIT
1KΩ
C42
470nF/25V
R50
1KΩ
BAV99
24VSYNDRVH
D13
BAV99
2008/04/12
Champion Microelectronic Corporation
Page 16
C47
CM6900 Application Note A-003A
12VS
Q18
BC817
C44
+ C43
T6
100uF/25V
5
Q20
2.2uF/63V
DRVH
BC807
6
3
DRVHGND
12VS
+12V
+24V
+12V
12VS
2
R53
6.8KΩ
7
Q24
BC817
D14
R54
15K
DRVL
8
SCD12
R55
390Ω
U6
1
2
3
VREF
R58
430KΩ
4
R58
5
C50
R64
100KΩ
2MΩ
6
1nF/25V
7
SD
R57
910Ω
EE19
Q25
R56
620Ω
C49
R70
1KΩ
C51
8
R59
Rset
VREF
VFB
VCC
FEAO
PRIDRV
D_IN-
PRIDRVB
D_IN+
SRDRV
DEAO
SRDRVB
CSS
GND
Ilim
RT/CT
1nF/25V
R63
0.1uF/16V
150K
R65
100KΩ
R66
47KΩ
390KΩ
C52
47pF/25V
C53
0.1uF/25V
R58
100KΩ
D5
R71
C29
12KΩ
0.1uF/25V
BAV99
CM6900
R72
1KΩ
BC807
12VS
C54
16
VREF
15
12VS
14
Q19
BC817
13
12
R51
11
4.7Ω 1/4W
24VSYNDRVH
10
12VS
R73 47KΩ
9
Q22
VREF
BC807
C55
620pF/25VN
0.1uF/25V
C56
0.1uF/25V
12VS
Q21
BC817
R52
IPLIMIT
4.7Ω 1/4W
24VSYNDRVL
Q23
BC807
3. Conclusion
It is very easy to design serial resonant converter, above designs can all be achieved by using
This file provides a fast and easy design procedure and
provides to design the calculation formula most appropriate for its serial resonant converter.
Champion will update the matchcad file as needed to assist the users of CM6900 series for
enhanced design parameter functions.
Sales & Marketing
5F, No. 11, Park Avenue II,
Science-Based Industrial Park,
HsinChu City, Taiwan
T E L : +886-3-5679979
F A X : +886-3-5679909
7F-6, No.32, Sec. 1, Chenggong Rd.,
Nangang District, Taipei City 115,
Taiwan, R.O.C.
2008/04/12
T E L : +886-2-2788 0558
F A X : +886-2-2788 2985
Champion Microelectronic Corporation
Page 17
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