riso with dual feedback plus rfx op amp stability opa192 definition-by-example collin wells tim...
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Riso with Dual FeedbackPlus RFx
Op Amp StabilityOPA192 Definition-by-Example
Collin Wells
Tim Green
Precision Linear Analog Applications
December 2, 20131
Riso with Dual FB plus FX Topology
2
RF 1kOhm
Vout
CL 10uF
+
-
V+
U1 OPA192
Vcc 5V
R1 37.4Ohm
Vref 2.5V
VOA
RFx 10kOhm CF 39nF+
VG1
VFB
FB#1
FB#2
2.5V
2.5V
2.5V
Overview.TSC
Zo Test
3
V1 2.5V
V2 2.5V
VOUT
L1 1GH
C1 1GF
IG1 0
+
-
V+
U1 OPA192
AC Current Generator
AC = 1
Zo(dB) = VOUT
Zo(ohms) = VOUT on Logarithmic scale
OPA192 Zo Test.TSC
Zo Test
4
T
3.32kohms
374ohms
Frequency (Hz)
1m 10m 100m 1 10 100 1k 10k 100k 1M 10M 100M
Ga
in (
dB
)
10
100
1k
10k
374ohms
3.32kohms
Zload on Aol
5
T
OPA192 Zo
ZM1Riso=37.4ohms, CL=10uF
Frequency (Hz)
1m 10m 100m 1 10 100 1k 10k 100k 1M 10M 100M
Ga
in (
dB
)
10.63
13.01k
15.92M
ZM1Riso=37.4ohms, CL=10uF
OPA192 Zo
Modified Aol
6
J1
J1
RF 1k
Vout
CL 10u
+
-
V+
U1 OPA192
Vcc 5
R1 37.4
LT 1T
Ccm- 6p
Vref 2.5
Cdiff 10p
+
VG1
CT 1T
VOA
VFB
VOA=Modif ied Aol
VOA/VFB = FB#1_1/
2.5V
2.5V
2.5V
OPA192 Riso Buffer Mod Aol.TSC
Modified Aol
7
T
Modified Aol
Riso=37.4ohms, CL=10uF
VOA
-40
-20
0
20
40
60
80
100
120
140
Frequency (Hz)
1 10 100 1k 10k 100k 1M 10M 100M
VOA
-90
-45
0
45
90
135
180
Modified Aol
Riso=37.4ohms, CL=10uF
FB#1 with CL=10uF, Riso=37.4ohms
8
J1
J1
RF 1k
Vout
CL 10u
+
-
V+
U1 OPA192
Vcc 5
R1 37.4
LT 1T
Ccm- 6p
Vref 2.5
Cdiff 10p
+
VG1
CT 1T
VOA
VFB
VOA=Modif ied Aol
VOA/VFB = FB#1_1/
2.5V
2.5V
2.5V
OPA192 Riso Buffer Mod Aol.TSC
FB#1 with CL=10uF, Riso=37.4ohms
9
T
Modified AolRiso=37.4ohms, CL=10uF
FB#1_1/
Frequency (Hz)
1 10 100 1k 10k 100k 1M 10M 100M
Vo
ltag
e (
V)
-40
-20
0
20
40
60
80
100
120
140
160
FB#1_1/
Modified AolRiso=37.4ohms, CL=10uF
FB#1 with CL=10uF, Riso=37.4ohmsAdd FB#2 for Stability
10
T
Modified AolRiso=37.4ohms, CL=10uF
FB#1_1/
Frequency (Hz)
1 10 100 1k 10k 100k 1M 10M 100M
Vo
ltag
e (
V)
-40
-20
0
20
40
60
80
100
120
140
160
fz1FB#2_1/
Net 1/
fcl
FB#1_1/
Modified AolRiso=37.4ohms, CL=10uF
FB#2 with CL=10uF, Riso=37.4ohms, RF=1k, RFx=10k
11
RFRFx FB#2_1/β fHi
CF)RFRFx(21
1fz
J1
J1
RF 1k
Vout
CL 10u
+
-
V+
U1 OPA192
Vcc 5
R1 37.4
LT 1T
Ccm- 6p
Vref 2.5
Cdiff 10p
+
VG1
CT 1T
VOA
VFB
RFx 10k CF 39n
L1 1T
C1
1T
VOA/VFB = FB#2_1/ 2.5V
2.5V
2.5V
FB2.TSC
FB#2 with CL=10uF, Riso=37.4ohms, RF=1k, RFx=10k
12
T
FB#2_1/
Frequency (Hz)
1m 10m 100m 1 10 100 1k 10k 100k 1M 10M 100M
b2
0
20
40
60
80
100
120
140
FB#2_1/
Loop Gain for CL=10uF, Riso=37.4ohms, RF=1k, RFx=10k
13
J1
J1
RF 1k
Vout
CL 10u
+
-
V+
U1 OPA192
Vcc 5
R1 37.4
LT 1T
Ccm- 6p
Vref 2.5
Cdiff 10p
+
VG1
CT 1T
VOA
VFB
RFx 10k CF 39n
VFB= Loop Gain 2.5V
2.5V
2.5V
FB1_FB2 Loop.TSC
T
Loop Gain Final
9.39 deg
VFB
-80
-60
-40
-20
0
20
40
60
80
100
120
140
Frequency (Hz)
1 10 100 1k 10k 100k 1M 10M 100M
VFB
-180
-135
-90
-45
0
45
90
135
180
VFB: VFB A:(87.588883k; -2.664535f)
VFB: VFB A:(87.588883k; 89.448147)
Loop Gain Final
9.39 deg
fcl
a
Loop Gain for CL=10uF, Riso=37.4ohms, RF=1k, RFx=10k
14
Phase Margin = 89.45 deg
Transient for CL=10uF, Riso=37.4ohms, RF=1k, RFx=10k
15
RF 1k
Vout
CL 10u
+
-
V+
U1 OPA192
Vcc 5
R1 37.4
Vref 2.5
VOA
RFx 10k CF 39n
+
VG1
2.5V
2.5V
Transient Final.TSC
Transient for CL=10uF, Riso=37.4ohms, RF=1k, RFx=10k
16
T
Time (s)
0.00 1.50m 3.00m
VG1
-10.00m
10.00m
VOA
2.31
2.70
Vout
2.49
2.51