36
TLC271 Stability Investigation Tim Green, MGTS Precision Linear Analog Applications February 25, 2015 1
TLC271 StabilityInvestigation
Tim Green, MGTS
Precision Linear Analog Applications
February 25, 2015
1
2
Loop Gain Analysis
Vcc
Vcc
J1
J1 -
+ +
U1 TLC271_5V_HB
Vcc 5
Voa
R1
82k
R2
120k
C1
100n
R3 100k R4 100k
C2 22p
C3 330n
L1 10u
C4
10p
R5
50k
C5 3.3u C6 100n
R6
220k
L2 1
T
C7 1T
+
VG1
VFB
L3 10u
C8
10p
R7 15k
C9
132pVin_ac Loop Gain = VFB
External Load
2.028666V
2.028666V
Mohan TLC271 Loop.TSC
3
Loop Gain Analysis
T
Ga
in (
dB
)
-40
-20
0
20
40
60
80
100
Frequency (Hz)
1 10 100 1k 10k 100k 1M 10M
Ph
ase
[de
g]
-45
0
45
90
135
180 fcl
Phase Margin = 45 degrees
Loop Gain Analysis
Gain : VFB A:(1.643883M; -10.685897f)
Phase : VFB A:(1.643883M; 49.351372)
a
4
Customer Schematic: See Speaker Notes for Comments
TLC271 Stability5V Supplies Only
Appendix
Tim Green, MGTS
Precision Linear Analog Applications
February 24, 2015
5
6
TLC271_5V_HB
TLC271: 5V Supply, High Bias Mode
Zo Revised for Proper Cload Phase Margin
7
TLC271 – Bias Modes of Operation
680uA 100uA 10uA
CL=20pFCL=20pF
HB
8
TLC271_5V_HB Cap Load Testing
25.8deg
39.4deg
45.7deg
Test 1
Test 2
Test 3
9
TLC271_5V_HB Web Cap Load Test 1
-
+ +
U1 TLC271_5V_HB
V1 5
V2 2.5
Vout
CL 100p
L1 1
TC1 1T
+
VG1
2.498894V
TLC271_5V_HB Web Cload.TSC
10
TLC271_5V_HB Web Cap Load Test 1
T
Ga
in (
dB
)
-28.42
29.45
87.31
Frequency (Hz)
1.00 3.16k 10.00M
Ph
ase
[de
g]
-194.28
-97.44
0.00fcl
Phase Margin IS: 45 degreesPhase Margin SHOULD BE: 25.8 degrees
TLC271_5V_HB Web MacroCL=100pF
Gain : Vout A:(1.663941M; 7.96585f)
Phase : Vout A:(1.663941M; -135.049732)
a
11
TLC271_5V_HB TG-Revised Cap Load Test 1
-
+ +
U1 TLC271_5V_HB
V1 5
V2 2.5
Vout
CL 100p
L1 1
TC1 1T
+
VG1
2.498894V
TLC271_5V_HB TG Cload 100pF.TSC
12
TLC271_5V_HB TG-Revised Cap Load Test 1
T
Ga
in (
dB
)
-37.91
24.70
87.31
Frequency (Hz)
1.00 3.16k 10.00M
Ph
ase
[de
g]
-241.37
-120.99
0.00
Close enough to datasheet!
fcl
TLC271_5V_HB TG-Revised MacroCap Load Test 1 (CL=100pF)
Phase Margin IS: 25.6 degreesPhase Margin SHOULD BE: 25.8 degrees
Gain : Vout A:(1.546424M; -11.636525f)
Phase : Vout A:(1.546424M; -154.416465)
a
13
TLC271_5V_HB TG-Revised Cap Load Test 2
T
Ga
in (
dB
)
-32.95
27.18
87.31
Frequency (Hz)
1.00 3.16k 10.00M
Ph
ase
[de
g]
-226.54
-113.57
0.00
TLC271_5V_HB TG-Revised MacroCap Load Test 2 (CL= 50pF)
Close enough to datasheet!
Phase Margin IS: 35.6 degreesPhase Margin SHOULD BE: 39.4 degrees
Gain : Vout A:(1.630583M; -5.356826f)
Phase : Vout A:(1.630583M; -144.357717)
a
14
TLC271_5V_HB TG-Revised Aol Test
V1 5
V2 2.5
Vout
L1 1
TC1 1T
+
VG1
RL
10k
CL
20p
-
+ +
U1 TLC271_5V_HB
2.498888V
TLC271_5V_HB TG Aol.TSC
15
TLC271_5V_HB TG-Revised Aol TestT
Ga
in (
dB
)
-29.30
28.76
86.83
Frequency (Hz)
1 10 100 1k 10k 100k 1M 10M
Ph
ase
[de
g]
-199.92
-100.26
0.00
Aol_DC IS: 86.83dBAol_DC SHOULD BE: 87.23dB
Gain : Vout A:(1.605771M; 4.302114E-16)
Phase : Vout A:(1.605771M; -135.046138)
TLC271_5V_HB TG-Revised MacroAol Test (CL= 20pF, RL=10kohm)
Phase Margin IS: 45 degreesPhase Margin SHOULD BE: 46 degrees
UGBW IS: 1.6MHzUGBW SHOULD BE: 1.7MHz
Close enough to datasheet!
a
16
TLC271_5V_MB
TLC271: 5V Supply, Medium Bias Mode
Zo Revised for Proper Cload Phase Margin
17
TLC271 – Bias Modes of Operation
680uA 100uA 10uA
CL=20pFCL=20pF
MB
18
TLC271_5V_MB Cap Load Testing
25.8deg
39.4deg
40deg
Test 1
Test 2
Test 3
19
TLC271_5V_MB Web Cap Load Test 1
V1 5
V2 2.5
Vout
CL 100p
L1 1
TC1 1T
+
VG1
-
+ +
U1 TLC271_5V_MB
2.498898V
TLC271_5V_MB Web Cload.TSC
20
TLC271_5V_MB Web Cap Load Test 1
T
Ga
in (
dB
)
-48.94
27.73
104.40
Frequency (Hz)
1.00 3.16k 10.00M
Ph
ase
[de
g]
-202.56
-106.98
-11.40
Phase IS: 39.2 degreesPhase Margin SHOULD BE: 25.8 degrees
TLC271_5V_MB Web Cap Load Test 1CL=100pF
Gain : Vout A:(547.471207k; -8.631984f)
Phase : Vout A:(547.471207k; -140.785892)
a
21
TLC271_5V_MB TG-Revised Cap Load Test 1
V1 5
V2 2.5
Vout
CL 50p
L1 1
TC1 1T
+
VG1
-
+ +
U1 TLC271_5V_MB
2.498898V
TLC271_5V_MB TG Revised Cload.TSC
22
TLC271_5V_MB TG-Revised Cap Load Test 1
T
Ga
in (
dB
)
-59.19
22.61
104.40
Frequency (Hz)
1.00 3.16k 10.00M
Ph
ase
[de
g]
-251.18
-131.29
-11.40
Phase IS: 30.39 degreesPhase Margin SHOULD BE: 25.8 degrees Close enough to DatasheetPhase IS: 30.39 degreesPhase Margin SHOULD BE: 25.8 degrees
TLC271_5V_MB TG Revised Cap Load Test 1CL=100pF
Gain : Vout A:(541.625142k; -23.502034f)
Phase : Vout A:(541.625142k; -149.605338)
a
23
TLC271_5V_MB TG-Revised Cap Load Test 2
T
Ga
in (
dB
)
-54.07
25.17
104.40
Frequency (Hz)
1.00 3.16k 10.00M
Ph
ase
[de
g]
-237.26
-124.33
-11.40
Gain : Vout A:(546.046255k; 8.271162f)
Phase : Vout A:(546.046255k; -144.624159)
TLC271_5V_MB TG Revised Cap Load Test 2CL=50pF
Phase IS: 30.39 degreesPhase Margin SHOULD BE: 25.8 degreesPhase IS: 35.38 degreesPhase Margin SHOULD BE: 39.4 degrees Close enough to Datasheet
a
24
TLC271_5V_MB TG-Revised Aol Test
V1 5
V2 2.5
Vout
L1 1
TC1 1T
+
VG1
RL
100k
CL
20p
-
+ +
U1 TLC271_5V_MB
TLC271_5V_MB TG Revised Aol.TSC
25
TLC271_5V_MB TG-Revised Aol Test
T
Ga
in (
dB
)
-49.80
27.28
104.35
Frequency (Hz)
1.00 3.16k 10.00M
Ph
ase
[de
g]
-211.83
-111.61
-11.39
Aol_DC IS: 104.35dBAoll_DC SHOULD BE: 104.6dB
Close enough to Datasheet
UGBW IS: 545kHzUGBW SHOULD BE: 500kHz
Phase IS: 38.65 degreesPhase Margin SHOULD BE: 40 degrees
TLC271_5V_MB TG Revised Aol(CL=20pF, RL=100k)
Gain : Vout A:(545.437139k; 10.713652f)
Phase : Vout A:(545.437139k; -141.349611)
a
26
TLC271_5V_LB
TLC271: 5V Supply, Low Bias Mode
Zo Revised for Proper Cload Phase Margin
27
TLC271 – Bias Modes of Operation
680uA 100uA 10uA
CL=20pFCL=20pF
LB
28
TLC271_5V_LB Cap Load Testing
26.3deg
30.9deg
33.7deg
Test 1
Test 2
Test 3
29
TLC271_5V_LB Web Cap Load Test 1
V1 5
V2 2.5
Vout
CL 100p
L1 1
TC1 1T
+
VG1
-
+ +
U1 TLC271_5V_LB
2.498899V
TLC271_5V_LB Web Cload.TSC
30
TLC271_5V_LB Web Cap Load Test 1
T
Ga
in (
dB
)
-82.22
10.53
103.28
Frequency (Hz)
1.00 3.16k 10.00M
Ph
ase
[de
g]
-205.01
-139.34
-73.67
Phase IS: 33.5 degreesPhase Margin SHOULD BE: 26.3 degrees
TLC271_5V_LB Web Cap Load Test 1CL=100pF
Gain : Vout A:(84.373115k; -32.751579f)
Phase : Vout A:(84.373115k; -146.502114)
a
31
TLC271_5V_LB TG-Revised Cap Load Test 1
V1 5
V2 2.5
Vout
CL 100p
L1 1
TC1 1T
+
VG1
-
+ +
U1 TLC271_5V_LB
2.498899V
TLC271_5V_LB TG Revised Cload.TSC
32
TLC271_5V_LB TG-Revised Cap Load Test 1
T
Ga
in (
dB
)
-105.29
-1.01
103.28
Frequency (Hz)
1.00 3.16k 10.00M
Ph
ase
[de
g]
-266.14
-169.90
-73.67
Close enough to Datasheet
Phase Margin IS: 26.4 degreesPhase Margin SHOULD BE: 26.3 degrees
TLC271_5V_LB TG Revised Cap Load Test 1CL=100pF
Gain : Vout A:(83.944272k; 19.51217f)
Phase : Vout A:(83.944272k; -153.651152)
a
33
TLC271_5V_LB TG-Revised Cap Load Test 2
T
Ga
in (
dB
)
-99.32
1.98
103.28
Frequency (Hz)
1.00 3.16k 10.00M
Ph
ase
[de
g]
-262.52
-168.10
-73.67
Phase Margin IS: 30.0 degreesPhase Margin SHOULD BE: 30.9 degrees
Close enough to Datasheet
TLC271_5V_LB TG Revised Cap Load Test 2CL=50pF
Gain : Vout A:(84.264475k; 10.408341f)
Phase : Vout A:(84.264475k; -150.026648)
a
34
TLC271_5V_LB TG-Revised Aol Test
V1 5
V2 2.5
Vout
L1 1
TC1 1T
+
VG1
RL
1M CL
20p
-
+ +
U1 TLC271_5V_LB
2.498899V
TLC271_5V_LB TG Revised Aol.TSC
35
TLC271_5V_LB TG-Revised Aol Test
T
Ga
in (
dB
)
-91.72
11.28
114.27
Frequency (Hz)
10.00m 316.23 10.00M
Ph
ase
[de
g]
-252.08
-127.02
-1.95
Close enough to Datasheet
Aol_DC IS: 114.3dBAoll_DC SHOULD BE: 113.6dB
UGBW IS: 84.23kHzUGBW SHOULD BE: 90kHz
Phase IS: 32.26 degreesPhase Margin SHOULD BE: 34 degrees
Gain : Vout A:(84.231082k; 12.601031f)
Phase : Vout A:(84.231082k; -147.741524)
TLC271_5V_LB TG Revised Aol(CL=20pF, RL=1M)
a
Op Amp Stability Reference
For detailed, definition-by-example of 10 different ways to stabilize op amps driving capacitive loads, and additional technical information on solving op amp stability problems, visit the Texas Instruments E2E Forum at:
http://e2e.ti.com/support/amplifiers/precision_amplifiers/w/design_notes/2645.solving-op-amp-stability-issues.aspx
Download Part 1, Part 2, Part 3, and Part 4.
36
All Embedded Schematics in this presentation can be run in the Free TINA_TI SPICE simulator available at:
http://www.ti.com/tool/tina-ti
