OPA350 [BB]
High-Speed, Single-Supply, Rail-to-Rail OPERATIONAL AMPLIFIERS MicroAmplifier ⑩ Series; 高速，单电源，轨至轨运算放大器MicroAmplifier ⑩系列
| 型号： | OPA350 |
| 厂家： | 
BURR-BROWN CORPORATION |
| 描述： | High-Speed, Single-Supply, Rail-to-Rail OPERATIONAL AMPLIFIERS MicroAmplifier ⑩ Series |
| 文件： | 总11页 (文件大小：209K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
®
OPA350
OPA350
OPA2350
OPA4350
OPA2350
O
PA4350
O
PA
4350
For most current data sheet and other product
information, visit www.burr-brown.com
High-Speed, Single-Supply, Rail-to-Rail
OPERATIONAL AMPLIFIERS
™
MicroAmplifier Series
FEATURES
APPLICATIONS
● RAIL-TO-RAIL INPUT
● CELL PHONE PA CONTROL LOOPS
● DRIVING A/D CONVERTERS
● VIDEO PROCESSING
● DATA ACQUISITION
● PROCESS CONTROL
● AUDIO PROCESSING
● COMMUNICATIONS
● RAIL-TO-RAIL OUTPUT (within 10mV)
● WIDE BANDWIDTH: 38MHz
● HIGH SLEW RATE: 22V/µs
● LOW NOISE: 5nV/√Hz
● LOW THD+NOISE: 0.0006%
● UNITY-GAIN STABLE
● MicroSIZE PACKAGES
● ACTIVE FILTERS
● SINGLE, DUAL, AND QUAD
● TEST EQUIPMENT
DESCRIPTION
OPA350 series rail-to-rail CMOS operational amplifi-
ers are optimized for low voltage, single-supply opera-
tion. Rail-to-rail input/output, low noise (5nV/√Hz),
and high speed operation (38MHz, 22V/µs) make them
ideal for driving sampling analog-to-digital converters.
They are also well suited for cell phone PA control
loops and video processing (75Ω drive capability) as
well as audio and general purpose applications. Single,
dual, and quad versions have identical specifications
for maximum design flexibility.
extends 300mV below ground and 300mV above the
positive supply. Output voltage swing is to within 10mV
of the supply rails with a 10kΩ load. Dual and quad
designs feature completely independent circuitry for low-
est crosstalk and freedom from interaction.
The single (OPA350) and dual (OPA2350) come in
the miniature MSOP-8 surface mount, SO-8 surface
mount, and 8-pin DIP packages. The quad (OPA4350)
packages are the space-saving SSOP-16 surface mount
and SO-14 surface mount. All are specified from
–40°C to +85°C and operate from –55°C to +125°C.
The OPA350 series operates on a single supply as low as
2.5V with an input common-mode voltage range that
SPICE Model available at www.burr-brown.com
OPA350
OPA4350
NC
NC
–In
+In
V–
1
2
3
4
8
7
6
5
Out A
–In A
+In A
+V
1
2
3
4
5
6
7
8
16 Out D
15 –In D
14 +In D
13 –V
V+
OPA4350
A
B
D
C
Output
NC
Out A
–In A
+In A
V+
1
2
3
4
5
6
7
14 Out D
13 –In D
12 +In D
11 V–
OPA2350
+In B
–In B
Out B
NC
12 +In C
11 –In C
10 Out C
8-Pin DIP, SO-8, MSOP-8
Out A
A
B
D
C
1
2
3
4
8
7
6
5
V+
A
–In A
+In A
V–
Out B
–In B
+In B
+In B
–In B
Out B
10 +In C
9
NC
B
9
8
–In C
Out C
SSOP-16
8-Pin DIP, SO-8, MSOP-8
SO-14
International Airport Industrial Park
•
Mailing Address: PO Box 11400, Tucson, AZ 85734
•
Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706
• Tel: (520) 746-1111
Twx: 910-952-1111 Internet: http://www.burr-brown.com/
•
•
Cable: BBRCORP Telex: 066-6491
•
•
FAX: (520) 889-1510 Immediate Product Info: (800) 548-6132
•
© 1998 Burr-Brown Corporation
PDS-1470B
Printed in U.S.A. March, 1999
SPECIFICATIONS: VS = 2.7V to 5.5V
At TA = +25°C, RL = 1kΩ connected to VS/2 and VOUT = VS /2, unless otherwise noted.
Boldface limits apply over the specified temperature range, TA = –40°C to +85°C. VS = 5V.
OPA350EA, UA, PA
OPA2350EA, UA, PA
OPA4350EA, UA
PARAMETER
CONDITION
MIN
TYP(1)
MAX
UNITS
OFFSET VOLTAGE
Input Offset Voltage
TA = –40°C to +85°C
VOS
VS = 5V
±150
±500
±1
µV
mV
vs Temperature
vs Power Supply Rejection Ratio
TA = –40°C to +85°C
Channel Separation (dual, quad)
TA = –40°C to +85°C
VS = 2.7V to 5.5V, VCM = 0V
VS = 2.7V to 5.5V, VCM = 0V
dc
±4
40
µV/°C
µV/V
µV/V
µV/V
PSRR
150
175
0.15
INPUT BIAS CURRENT
Input Bias Current
vs Temperature
IB
±0.5
±10
pA
pA
See Typical Performance Curve
Input Offset Current
IOS
±0.5
±10
NOISE
Input Voltage Noise, f = 100Hz to 400kHz
Input Voltage Noise Density, f = 10kHz
f = 100kHz
4
7
5
4
µVrms
nV/√Hz
nV/√Hz
fA/√Hz
en
in
Current Noise Density, f = 10kHz
INPUT VOLTAGE RANGE
Common-Mode Voltage Range
Common-Mode Rejection Ratio
VCM
CMRR
TA = –40°C to +85°C
–0.1
66
76
(V+)+0.1
V
VS = 2.7V, –0.1V < VCM < 2.8V
VS = 5.5V, –0.1V < VCM < 5.6V
VS = 5.5V, –0.1V < VCM < 5.6V
84
90
dB
dB
dB
TA = –40°C to +85°C
74
INPUT IMPEDANCE
Differential
Common-Mode
1013 || 2.5
1013 || 6.5
Ω || pF
Ω || pF
OPEN-LOOP GAIN
Open-Loop Voltage Gain
TA = –40°C to +85°C
AOL
RL = 10kΩ, 50mV < VO < (V+) –50mV
RL = 10kΩ, 50mV < VO < (V+) –50mV
RL = 1kΩ, 200mV < VO < (V+) –200mV
RL = 1kΩ, 200mV < VO < (V+) –200mV
100
100
100
100
122
120
dB
dB
dB
dB
TA = –40°C to +85°C
FREQUENCY RESPONSE
Gain-Bandwidth Product
Slew Rate
Settling Time, 0.1%
0.01%
CL = 100pF
G = 1
G = 1
G = ±1, 2V Step
G = ±1, 2V Step
GBW
SR
38
22
0.22
0.5
MHz
V/µs
µs
µs
Overload Recovery Time
Total Harmonic Distortion + Noise
Differential Gain Error
Differential Phase Error
VIN • G = VS
0.1
µs
%
%
deg
THD+N
VOUT
RL = 600Ω, VO = 2.5Vp-p(2), G = 1, f = 1kHz
G = 2, RL = 600Ω, VO = 1.4V(3)
G = 2, RL = 600Ω, VO = 1.4V(3)
0.0006
0.17
0.17
OUTPUT
Voltage Output Swing from Rail(4)
TA = –40°C to +85°C
RL = 10kΩ, AOL ≥ 100dB
RL = 10kΩ, AOL ≥ 100dB
RL = 1kΩ, AOL ≥ 100dB
RL = 1kΩ, AOL ≥ 100dB
10
25
50
50
200
200
mV
mV
mV
mV
mA
mA
TA = –40°C to +85°C
Output Current
Short-Circuit Current
Capacitive Load Drive
IOUT
ISC
CLOAD
±40(5)
±80
See Typical Curve
POWER SUPPLY
Operating Voltage Range
Minimum Operating Voltage
Quiescent Current (per amplifier)
TA = –40°C to +85°C
VS
IQ
TA = –40°C to +85°C
2.7
5.5
V
V
mA
mA
2.5
5.2
IO = 0
IO = 0
7.5
8.5
TEMPERATURE RANGE
Specified Range
Operating Range
–40
–55
–55
+85
+125
+125
°C
°C
°C
Storage Range
Thermal Resistance
MSOP-8 Surface Mount
SO-8 Surface Mount
8-Pin DIP
SO-14 Surface Mount
SSOP-16 Surface Mount
θJA
150
150
100
100
100
°C/W
°C/W
°C/W
°C/W
°C/W
NOTES: (1) VS = +5V. (2) VOUT = 0.25V to 2.75V. (3) NTSC signal generator used. See Figure 6 for test circuit. (4) Output voltage swings are measured between
the output and power supply rails. (5) See typical performance curve, “Output Voltage Swing vs Output Current.”
®
OPA350, 2350, 4350
2
ABSOLUTE MAXIMUM RATINGS(1)
ELECTROSTATIC
DISCHARGE SENSITIVITY
Supply Voltage ................................................................................... 5.5V
Signal Input Terminals, Voltage(2) .................. (V–) – 0.3V to (V+) + 0.3V
Current(2) .................................................... 10mA
This integrated circuit can be damaged by ESD. Burr-Brown
recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling
and installation procedures can cause damage.
Output Short Circuit(3) .............................................................. Continuous
Operating Temperature ..................................................–55°C to +125°C
Storage Temperature .....................................................–55°C to +125°C
Junction Temperature ...................................................................... 150°C
Lead Temperature (soldering, 10s)................................................. 300°C
NOTES: (1) Stresses above these ratings may cause permanent damage.
Exposure to absolute maximum conditions for extended periods may de-
grade device reliability. (2) Input terminals are diode-clamped to the power
supply rails. Input signals that can swing more than 0.3V beyond the supply
rails should be current-limited to 10mA or less. (3) Short circuit to ground,
one amplifier per package.
ESD damage can range from subtle performance degrada-
tion to complete device failure. Precision integrated circuits
may be more susceptible to damage because very small
parametric changes could cause the device not to meet its
published specifications.
PACKAGE/ORDERING INFORMATION
PACKAGE
DRAWING
NUMBER(1)
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
MARKING
ORDERING
NUMBER(2)
TRANSPORT
MEDIA
PRODUCT
PACKAGE
Single
OPA350EA
MSOP-8 Surface Mount
337
"
–40°C to +85°C
C50
"
OPA350EA/250
OPA350EA/2K5
OPA350UA
OPA350UA/2K5
OPA350PA
Tape and Reel
Tape and Reel
Rails
Tape and Reel
Rails
"
OPA350UA
"
"
"
SO-8 Surface-Mount
182
"
–40°C to +85°C
"
OPA350UA
"
"
OPA350PA
8-Pin DIP
006
–40°C to +85°C
OPA350PA
Dual
OPA2350EA
MSOP-8 Surface-Mount
337
"
–40°C to +85°C
D50
"
OPA2350EA/250
OPA2350EA/2K5
OPA2350UA
OPA2350UA/2K5
OPA2350PA
Tape and Reel
Tape and Reel
Rails
Tape and Reel
Rails
"
"
"
OPA2350UA
"
SO-8 Surface-Mount
182
"
–40°C to +85°C
"
OPA2350UA
"
"
OPA2350PA
8-Pin DIP
006
–40°C to +85°C
OPA2350PA
Quad
OPA4350EA
SSOP-16 Surface-Mount
322
"
235
"
–40°C to +85°C
OPA4350EA
OPA4350EA/250
OPA4350EA/2K5
OPA4350UA
Tape and Reel
Tape and Reel
Rails
"
"
"
"
OPA4350UA
SO-14 Surface Mount
–40°C to +85°C
OPA4350UA
"
"
"
"
OPA4350UA/2K5
Tape and Reel
NOTES: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. (2) Models with a slash (/) are
available only in Tape and Reel in the quantities indicated (e.g., /2K5 indicates 2500 devices per reel). Ordering 2500 pieces of “OPA2350EA/2K5” will get a single
2500-piece Tape and Reel. For detailed Tape and Reel mechanical information, refer to Appendix B of Burr-Brown IC Data Book.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility
for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or
licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support
devices and/or systems.
®
3
OPA350, 2350, 4350
TYPICAL PERFORMANCE CURVES
At TA = +25°C, VS = +5V, and RL = 1kΩ connected to VS/2, unless otherwise noted.
POWER SUPPLY AND COMMON-MODE
REJECTION RATIO vs FREQUENCY
OPEN-LOOP GAIN/PHASE vs FREQUENCY
160
140
120
100
80
0
100
90
80
70
60
50
40
30
20
10
0
PSRR
–45
–90
–135
–180
CMRR
(VS = +5V
CM = –0.1V to 5.1V)
φ
V
60
G
40
20
0
0.1
1
10
100
1k
10k 100k
1M
10M 100M
10
100
1k
10k
100k
1M
10M
Frequency (Hz)
Frequency (Hz)
INPUT VOLTAGE AND CURRENT NOISE
SPECTRAL DENSITY vs FREQUENCY
CHANNEL SEPARATION vs FREQUENCY
10k
1k
100k
10k
1k
140
130
120
110
100
90
Current Noise
100
10
Voltage Noise
100
10
80
1
70
Dual and quad devices.
0.1
1
60
10
100
1k
10k
100k
1M
10M
10
100
1k
10k
100k
1M
10M
Frequency (Hz)
Frequency (Hz)
TOTAL HARMONIC DISTORTION + NOISE
vs FREQUENCY
HARMONIC DISTORTION + NOISE vs FREQUENCY
1
1
0.1
G = 1
VO = 2.5Vp-p
RL = 600Ω
(–40dBc)
RL = 600Ω
0.1
(–60dBc)
G = 100, 3Vp-p (VO = 1V to 4V)
G = 10, 3Vp-p (VO = 1V to 4V)
0.01
(–80dBc)
0.01
G = 1, 3Vp-p (VO = 1V to 4V)
Input goes through transition region
0.001
(–100dBc)
0.001
0.0001
3rd Harmonic
2nd Harmonic
G = 1, 2.5Vp-p (VO = 0.25V to 2.75V)
Input does NOT go through transition region
0.0001
(–120dBc)
1k
10k
100k
Frequency (Hz)
1M
10
100
1k
10k
100k
Frequency (Hz)
®
OPA350, 2350, 4350
4
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, VS = +5V, and RL = 1kΩ connected to VS/2, unless otherwise noted.
OPEN-LOOP GAIN vs TEMPERATURE
DIFFERENTIAL GAIN/PHASE vs RESISTIVE LOAD
130
125
120
115
110
0.5
0.4
0.3
0.2
0.1
0
G = 2
V
O = 1.4V
Phase
NTSC Signal Generator
See Figure 6 for test circuit.
RL = 1kΩ
RL = 10kΩ
Gain
RL = 600Ω
–75
–50 –25
0
25
50
75
100 125
0
100 200 300 400 500 600 700 800 900 1000
Temperature (°C)
Resistive Load (Ω)
COMMON-MODE AND POWER SUPPLY REJECTION RATIO
vs TEMPERATURE
SLEW RATE vs TEMPERATURE
100
90
80
70
60
110
100
90
40
35
30
25
20
15
10
5
CMRR, VS = 5.5V
(VCM = –0.1V to +5.6V)
Negative Slew Rate
Positive Slew Rate
CMRR, VS = 2.7V
(VCM = –0.1V to +2.8V)
PSRR
80
70
0
–75
–50
–25
0
25
50
75
100
125
–75
–50
–25
0
25
50
75
100
125
Temperature (°C)
Temperature (°C)
QUIESCENT CURRENT AND
SHORT-CIRCUIT CURRENT vs TEMPERATURE
QUIESCENT CURRENT vs SUPPLY VOLTAGE
Per Amplifier
6.0
5.5
5.0
4.5
4.0
3.5
3.0
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
100
90
80
70
60
50
40
30
+ISC
–ISC
IQ
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
–75
–50
–25
0
25
50
75
100
125
Supply Voltage (V)
Temperature (°C)
®
5
OPA350, 2350, 4350
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, VS = +5V, and RL = 1kΩ connected to VS/2, unless otherwise noted.
INPUT BIAS CURRENT
vs INPUT COMMON-MODE VOLTAGE
INPUT BIAS CURRENT vs TEMPERATURE
1k
100
10
1.5
1.0
0.5
1
0.0
0.1
–0.5
–75
–50
–25
0
25
50
75
100
125
–0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
Temperature (°C)
Common-Mode Voltage (V)
CLOSED-LOOP OUTPUT IMPEDANCE vs FREQUENCY
MAXIMUM OUTPUT VOLTAGE vs FREQUENCY
100
10
6
VS = 5.5V
Maximum output
voltage without
slew rate-induced
distortion.
5
4
3
2
1
0
1
G = 100
VS = 2.7V
0.1
G = 10
G = 1
0.01
0.001
0.0001
1
10
100
1k
10k 100k
1M
10M 100M
100k
1M
10M
100M
Frequency (Hz)
Frequency (Hz)
OUTPUT VOLTAGE SWING vs OUTPUT CURRENT
OPEN-LOOP GAIN vs OUTPUT VOLTAGE SWING
IOUT = 250µA
IOUT = 2.5mA
V+
(V+)–1
(V+)–2
(V–)+2
(V–)+1
(V–)
140
130
120
110
100
90
+25°C
–55°C
+125°C
Depending on circuit configuration
(including closed-loop gain) performance
may be degraded in shaded region.
IOUT = 4.2mA
+25°C
–55°C
80
+125°C
70
60
0
±10
±20
Output Current (mA)
±30
±40
0
20
40
60
80 100 120 140 160 180 200
Output Voltage Swing from Rails (mV)
®
OPA350, 2350, 4350
6
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, VS = +5V, and RL = 1kΩ connected to VS/2, unless otherwise noted.
OFFSET VOLTAGE DRIFT
PRODUCTION DISTRIBUTION
OFFSET VOLTAGE
PRODUCTION DISTRIBUTION
20
18
16
14
12
10
8
18
16
14
12
10
8
Typical production
distribution of
packaged units.
Typical distribution of
packaged units.
6
6
4
4
2
2
0
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15
Offset Voltage Drift (µV/°C)
Offset Voltage (µV)
SMALL-SIGNAL OVERSHOOT vs LOAD CAPACITANCE
SETTLING TIME vs CLOSED-LOOP GAIN
80
70
60
50
40
30
20
10
0
10
G = 1
0.01%
G = –1
1
G = ±10
0.1%
0.1
10
100
1k
10k
100k
1M
–1
–10
–100
Load Capacitance (pF)
Closed-Loop Gain (V/V)
LARGE-SIGNAL STEP RESPONSE
CL = 100pF
SMALL-SIGNAL STEP RESPONSE
CL = 100pF
200ns/div
100ns/div
®
7
OPA350, 2350, 4350
the OPA350 in unity-gain configuration. Operation is
from a single +5V supply with a 1kΩ load connected to
VS /2. The input is a 5Vp-p sinusoid. Output voltage swing
is approximately 4.95Vp-p.
APPLICATIONS INFORMATION
OPA350 series op amps are fabricated on a state-of-the-art
0.6 micron CMOS process. They are unity-gain stable and
suitable for a wide range of general purpose applications.
Rail-to-rail input/output make them ideal for driving sam-
pling A/D converters. They are also well suited for control-
ling the output power in cell phones. These applications
often require high speed and low noise. In addition, the
OPA350 series offers a low cost solution for general purpose
and consumer video applications (75Ω drive capability).
Power supply pins should be bypassed with 0.01µF ceramic
capacitors.
OPERATING VOLTAGE
OPA350 series op amps are fully specified from +2.7V to
+5.5V. However, supply voltage may range from +2.5V to
+5.5V. Parameters are guaranteed over the specified supply
range—a unique feature of the OPA350 series. In addition,
many specifications apply from –40°C to +85°C. Most
behavior remains virtually unchanged throughout the full
operating voltage range. Parameters which vary signifi-
cantly with operating voltage or temperature are shown in
the typical performance curves.
Excellent ac performance makes the OPA350 series well
suited for audio applications. Their bandwidth, slew rate,
low noise (5nV/√Hz), low THD (0.0006%), and small pack-
age options are ideal for these applications. The class AB
output stage is capable of driving 600Ω loads connected to
any point between V+ and ground.
Rail-to-rail input and output swing significantly increases
dynamic range, especially in low voltage supply applica-
tions. Figure 1 shows the input and output waveforms for
RAIL-TO-RAIL INPUT
The guaranteed input common-mode voltage range of the
OPA350 series extends 100mV beyond the supply rails. This
is achieved with a complementary input stage—an
N-channel input differential pair in parallel with a P-channel
differential pair (see Figure 2). The N-channel pair is active
for input voltages close to the positive rail, typically
(V+) – 1.8V to 100mV above the positive supply, while the
P-channel pair is on for inputs from 100mV below the
negative supply to approximately (V+) – 1.8V. There is a
small transition region, typically (V+) – 2V to (V+) – 1.6V, in
which both pairs are on. This 400mV transition region can
vary ±400mV with process variation. Thus, the transition
region (both input stages on) can range from (V+) – 2.4V to
(V+) – 2.0V on the low end, up to (V+) – 1.6V to (V+) – 1.2V
on the high end.
VS = +5, G = +1, RL = 1kΩ
5V
VIN
0
5V
VOUT
0
FIGURE 1. Rail-to-Rail Input and Output.
V+
Reference
Current
VIN+
VIN–
VBIAS1
Class AB
Control
VO
Circuitry
VBIAS2
V–
(Ground)
FIGURE 2. Simplified Schematic.
®
OPA350, 2350, 4350
8
OPA350 series op amps are laser-trimmed to reduce offset
voltage difference between the N-channel and
P-channel input stages, resulting in improved common-
mode rejection and a smooth transition between the
N-channel pair and the P-channel pair. However, within the
400mV transition region PSRR, CMRR, offset voltage,
offset drift, and THD may be degraded compared to opera-
tion outside this region.
performance curve “Small-Signal Overshoot vs Capacitive
Load” shows performance with a 1kΩ resistive load. In-
creasing load resistance improves capacitive load drive ca-
pability.
FEEDBACK CAPACITOR IMPROVES RESPONSE
For optimum settling time and stability with high-imped-
ance feedback networks, it may be necessary to add a
feedback capacitor across the feedback resistor, RF, as
shown in Figure 4. This capacitor compensates for the zero
created by the feedback network impedance and the
OPA350’s input capacitance (and any parasitic layout
capacitance). The effect becomes more significant with
higher impedance networks.
A double-folded cascode adds the signal from the two input
pairs and presents a differential signal to the class AB output
stage. Normally, input bias current is approximately 500fA.
However, large inputs (greater than 300mV beyond the
supply rails) can turn on the OPA350’s input protection
diodes, causing excessive current to flow in or out of the
input pins. Momentary voltages greater than 300mV beyond
the power supply can be tolerated if the current on the input
pins is limited to 10mA. This is easily accomplished with an
input resistor as shown in Figure 3. Many input signals are
inherently current-limited to less than 10mA, therefore, a
limiting resistor is not required.
CF
RIN
RF
V+
VIN
CIN
V+
RIN • CIN = RF • CF
VOUT
OPA350
IOVERLOAD
CL
10mA max
CIN
VOUT
OPAx350
VIN
5kΩ
Where CIN is equal to the OPA350’s input
capacitance (approximately 9pF) plus any
parastic layout capacitance.
FIGURE 3. Input Current Protection for Voltages Exceeding
the Supply Voltage.
FIGURE 4. Feedback Capacitor Improves Dynamic Perfor-
mance.
RAIL-TO-RAIL OUTPUT
It is suggested that a variable capacitor be used for the
feedback capacitor since input capacitance may vary be-
tween op amps and layout capacitance is difficult to
determine. For the circuit shown in Figure 4, the value of
the variable feedback capacitor should be chosen so that
the input resistance times the input capacitance of the
OPA350 (typically 9pF) plus the estimated parasitic layout
capacitance equals the feedback capacitor times the feed-
back resistor:
A class AB output stage with common-source transistors is
used to achieve rail-to-rail output. For light resistive loads
(>10kΩ), the output voltage swing is typically a ten milli-
volts from the supply rails. With heavier resistive loads
(600Ω to 10kΩ), the output can swing to within a few tens
of millivolts from the supply rails and maintain high open-
loop gain. See the typical performance curves “Output
Voltage Swing vs Output Current” and “Open-Loop Gain vs
Output Voltage.”
RIN • CIN = RF • CF
CAPACITIVE LOAD AND STABILITY
OPA350 series op amps can drive a wide range of capacitive
loads. However, all op amps under certain conditions may
become unstable. Op amp configuration, gain, and load
value are just a few of the factors to consider when determin-
ing stability. An op amp in unity gain configuration is the
most susceptible to the effects of capacitive load. The
capacitive load reacts with the op amp’s output impedance,
along with any additional load resistance, to create a pole in
the small-signal response which degrades the phase margin.
where CIN is equal to the OPA350’s input capacitance
(sum of differential and common-mode) plus the layout
capacitance. The capacitor can be varied until optimum
performance is obtained.
DRIVING A/D CONVERTERS
OPA350 series op amps are optimized for driving medium
speed (up to 500kHz) sampling A/D converters. However,
they also offer excellent performance for higher speed
converters. The OPA350 series provides an effective means
of buffering the A/D’s input capacitance and resulting
charge injection while providing signal gain.
In unity gain, OPA350 series op amps perform well with
very large capacitive loads. Increasing gain enhances the
amplifier’s ability to drive more capacitance. The typical
®
9
OPA350, 2350, 4350
Figure 5 shows the OPA350 driving an ADS7861. The
ADS7861 is a dual, 500kHz 12-bit sampling converter in
the tiny SSOP-24 package. When used with the miniature
package options of the OPA350 series, the combination is
ideal for space-limited applications. For further informa-
tion, consult the ADS7861 data sheet.
from becoming too high, which can cause stability prob-
lems when driving capacitive loads. As mentioned previ-
ously, the OPA350 has excellent capacitive load drive
capability for an op amp with its bandwidth.
VIDEO LINE DRIVER
Figure 6 shows a circuit for a single supply, G = 2 com-
posite video line driver. The synchronized outputs of a
composite video line driver extend below ground. As
shown, the input to the op amp should be ac-coupled and
shifted positively to provide adequate signal swing to
account for these negative signals in a single-supply con-
figuration.
OUTPUT IMPEDANCE
The low frequency open-loop output impedance of the
OPA350’s common-source output stage is approximately
1kΩ. When the op amp is connected with feedback, this
value is reduced significantly by the loop gain of the op
amp. For example, with 122dB of open-loop gain, the
output impedance is reduced in unity-gain to less than
0.001Ω. For each decade rise in the closed-loop gain, the
loop gain is reduced by the same amount which results in
a ten-fold increase in effective output impedance (see the
typical performance curve, “Output Impedance vs Fre-
quency”).
The input is terminated with a 75Ω resistor and ac-coupled
with a 47µF capacitor to a voltage divider that provides the
dc bias point to the input. In Figure 6, this point is
approximately (V–) + 1.7V. Setting the optimal bias point
requires some understanding of the nature of composite
video signals. For best performance, one should be careful
to avoid the distortion caused by the transition region of
the OPA350’s complementary input stage. Refer to the
discussion of rail-to-rail input.
At higher frequencies, the output impedance will rise as
the open-loop gain of the op amp drops. However, at these
frequencies the output also becomes capacitive due to
parasitic capacitance. This prevents the output impedance
CB1
+5V
2kΩ
2kΩ
2
3
4
1/4
1
7
8
OPA4350
VIN B1
0.1µF
0.1µF
CB0
24
+VD
13
+VA
2kΩ
2kΩ
2
3
23
22
21
20
19
18
17
16
15
14
CH B1+
CH B1–
CH B0+
CH B0–
CH A1+
CH A1–
CH A0+
CH A0–
REFIN
SERIAL DATA A
SERIAL DATA B
BUSY
6
1/4
4
OPA4350
5
5
VIN B0
CLOCK
6
CA1
CS
Serial
Interface
7
ADS7861
RD
CONVST
A0
2kΩ
2kΩ
8
9
9
10
11
1/4
M0
OPA4350
10
VIN A1
REFOUT
M1
CA0
DGND
1
AGND
12
2kΩ
2kΩ
12
13
14
1/4
OPA4350
VIN A0
11
VIN = 0V to 2.45V for 0V to 4.9V output.
Choose CB1, CB0, CA1, CA0 to filter high frequency noise.
FIGURE 5. OPA4350 Driving Sampling A/D Converter.
®
OPA350, 2350, 4350
10
RG
RF
1kΩ
1kΩ
+5V
C1
C4
220µF
0.1µF
+
0.1µF
10µF
2
3
7
C5
1000µF
ROUT
Cable
6
VOUT
OPA350
C2
47µF
RL
Video
In
4
R1
75Ω
R2
5kΩ
+5V (pin 7)
R3
5kΩ
R4
5kΩ
C3
10µF
FIGURE 6. Single-Supply Video Line Driver.
+5V
50kΩ
(2.5V)
8
RG
REF1004-2.5
4
R1
R2
100kΩ
25kΩ
+5V
R3
R4
25kΩ
100kΩ
1/2
OPA2350
1/2
OPA2350
VO
RL
10kΩ
200kΩ
G = 5 +
RG
FIGURE 7. Two Op-Amp Instrumentation Amplifier With Improved High Frequency Common-Mode Rejection.
C1
R1
4.7nF
10.5kΩ
+2.5V
+2.5V
C1
1830pF
C2
270pF
R1
2.74kΩ
R2
19.6kΩ
VOUT
VOUT
OPA350
OPA350
RL
20kΩ
RL
20kΩ
VIN
VIN
C2
R2
1nF
49.9kΩ
–2.5V
–2.5V
FIGURE 8. 10kHz Low-Pass Filter.
FIGURE 9. 10kHz High-Pass Filter.
®
11
OPA350, 2350, 4350
相关型号：
OPA350OPA2350OPA4350
OPA350 OPA2350 OPA4350 - High-Speed. Single-Supply. Rail-to-Rail OPERATIONAL AMPLIFIERS MicroAmplifier Series
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