Burr-Brown OPA350 High-speed, single-supply, rail-to-rail operational amplifiers microamplifier â ¢ sery Datasheet

®
OPA350
OPA2350
OPA4350
OPA
350
OPA
235
0
OPA
4
350
O PA
435
0
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
●
●
●
●
●
●
●
●
●
● CELL PHONE PA CONTROL LOOPS
● DRIVING A/D CONVERTERS
● VIDEO PROCESSING
● DATA ACQUISITION
● PROCESS CONTROL
● AUDIO PROCESSING
● COMMUNICATIONS
● ACTIVE FILTERS
● TEST EQUIPMENT
RAIL-TO-RAIL INPUT
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
SINGLE, DUAL, AND QUAD
DESCRIPTION
OPA350 series rail-to-rail CMOS operational amplifiers are optimized for low voltage, single-supply operation. 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.
The OPA350 series operates on a single supply as low as
2.5V with an input common-mode voltage range that
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 lowest 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.
SPICE Model available at www.burr-brown.com
OPA350
OPA4350
NC
1
8
NC
–In
2
7
V+
+In
3
6
Output
V–
4
5
NC
OPA4350
OPA2350
8-Pin DIP, SO-8, MSOP-8
Out A
–In A
+In A
V–
1
2
3
4
A
7
B
6
5
8-Pin DIP, SO-8, MSOP-8
1
16
Out D
–In A
2
15
–In D
+In A
3
14
+In D
A
D
Out A
1
14
Out D
+V
4
13
–V
–In A
2
13
–In D
+In B
5
12
+In C
+In A
3
12
+In D
–In B
6
11
–In C
V+
4
11
V–
Out B
7
10
Out C
+In B
5
10
+In C
NC
8
9
NC
–In B
6
9
–In C
Out B
7
8
Out C
A
8
Out A
D
V+
B
C
Out B
B
–In B
+In B
C
SSOP-16
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
TYP(1)
MAX
UNITS
VS = 5V
±150
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
±500
±1
µV
mV
µV/°C
µV/V
µV/V
µV/V
CONDITION
OFFSET VOLTAGE
Input Offset Voltage
TA = –40°C to +85°C
vs Temperature
vs Power Supply Rejection Ratio
TA = –40°C to +85°C
Channel Separation (dual, quad)
VOS
PSRR
INPUT BIAS CURRENT
Input Bias Current
vs Temperature
Input Offset Current
0.15
IOS
in
TA = –40°C to
VS = 2.7V, –0.1V <
VS = 5.5V, –0.1V <
VS = 5.5V, –0.1V <
VCM
CMRR
TA = –40°C to +85°C
+85°C
VCM < 2.8V
VCM < 5.6V
VCM < 5.6V
–0.1
66
76
74
AOL
TA = –40°C to +85°C
FREQUENCY RESPONSE
Gain-Bandwidth Product
Slew Rate
Settling Time, 0.1%
0.01%
Overload Recovery Time
Total Harmonic Distortion + Noise
Differential Gain Error
Differential Phase Error
OUTPUT
Voltage Output Swing from Rail(4)
TA = –40°C to +85°C
TA = –40°C to +85°C
Output Current
Short-Circuit Current
Capacitive Load Drive
POWER SUPPLY
Operating Voltage Range
Minimum Operating Voltage
Quiescent Current (per amplifier)
TA = –40°C to +85°C
TEMPERATURE RANGE
Specified Range
Operating Range
Storage Range
Thermal Resistance
MSOP-8 Surface Mount
SO-8 Surface Mount
8-Pin DIP
SO-14 Surface Mount
SSOP-16 Surface Mount
GBW
SR
THD+N
RL = 10kΩ, 50mV < VO < (V+) –50mV
RL = 10kΩ, 50mV < VO < (V+) –50mV
RL = 1kΩ, 200mV < VO < (V+) –200mV
R L = 1kΩ, 200mV < VO < (V+) –200mV
100
100
100
100
CL = 100pF
G=1
G=1
G = ±1, 2V Step
G = ±1, 2V Step
VIN • G = VS
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)
VOUT
IQ
TA = –40°C to +85°C
V
dB
dB
dB
1013 || 2.5
1013 || 6.5
Ω || pF
Ω || pF
122
dB
dB
dB
dB
120
25
MHz
V/µs
µs
µs
µs
%
%
deg
50
50
200
200
mV
mV
mV
mV
mA
mA
5.5
7.5
8.5
V
V
mA
mA
+85
+125
+125
°C
°C
°C
±40(5)
±80
See Typical Curve
CLOAD
VS
(V+)+0.1
10
I OUT
I SC
2.7
2.5
5.2
IO = 0
IO = 0
pA
84
90
38
22
0.22
0.5
0.1
0.0006
0.17
0.17
RL = 10kΩ, AOL ≥ 100dB
RL = 10kΩ, A OL ≥ 100dB
RL = 1kΩ, AOL ≥ 100dB
RL = 1kΩ, AOL ≥ 100dB
pA
µVrms
nV/√Hz
nV/√Hz
fA/√Hz
4
7
5
4
en
INPUT IMPEDANCE
Differential
Common-Mode
OPEN-LOOP GAIN
Open-Loop Voltage Gain
TA = –40°C to +85°C
150
175
±0.5
±10
See Typical Performance Curve
±0.5
±10
IB
NOISE
Input Voltage Noise, f = 100Hz to 400kHz
Input Voltage Noise Density, f = 10kHz
f = 100kHz
Current Noise Density, f = 10kHz
INPUT VOLTAGE RANGE
Common-Mode Voltage Range
Common-Mode Rejection Ratio
MIN
–40
–55
–55
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
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
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.
ESD damage can range from subtle performance degradation 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.
NOTES: (1) Stresses above these ratings may cause permanent damage.
Exposure to absolute maximum conditions for extended periods may degrade 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.
PACKAGE/ORDERING INFORMATION
PRODUCT
PACKAGE
PACKAGE
DRAWING
NUMBER(1)
Single
OPA350EA
MSOP-8 Surface Mount
337
–40°C to +85°C
C50
"
"
"
"
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
"
"
"
"
"
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
–40°C to +85°C
OPA4350EA
"
"
"
"
"
OPA4350UA
SO-14 Surface Mount
235
–40°C to +85°C
OPA4350UA
"
"
"
"
"
"
OPA350UA
"
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
MARKING
ORDERING
NUMBER(2)
TRANSPORT
MEDIA
OPA350EA/250
OPA350EA/2K5
OPA350UA
OPA350UA/2K5
OPA350PA
Tape and Reel
Tape and Reel
Rails
Tape and Reel
Rails
OPA2350EA/250
OPA2350EA/2K5
OPA2350UA
OPA2350UA/2K5
OPA2350PA
Tape and Reel
Tape and Reel
Rails
Tape and Reel
Rails
OPA4350EA/250
OPA4350EA/2K5
OPA4350UA
OPA4350UA/2K5
Tape and Reel
Tape and Reel
Rails
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
0
100
90
140
φ
80
–90
60
G
40
–135
PSRR, CMRR (dB)
100
PSRR
80
–45
Phase (°)
Voltage Gain (dB)
120
70
CMRR
(VS = +5V
VCM = –0.1V to 5.1V)
60
50
40
30
20
20
10
0
–180
0.1
1
10
100
1k
10k
100k
1M
10M
0
100M
10
100
1k
Frequency (Hz)
10k
100k
1M
10M
Frequency (Hz)
INPUT VOLTAGE AND CURRENT NOISE
SPECTRAL DENSITY vs FREQUENCY
CHANNEL SEPARATION vs FREQUENCY
10k
100k
140
130
100
1k
Voltage Noise
100
10
1
10
Channel Separation (dB)
1k
Current Noise
Current Noise (fA√Hz)
Voltage Noise (nV√Hz)
10k
120
110
100
90
80
70
1
10
100
1k
10k
100k
1M
0.1
10M
Dual and quad devices.
60
10
100
1k
Frequency (Hz)
TOTAL HARMONIC DISTORTION + NOISE
vs FREQUENCY
0.01
G = 10, 3Vp-p (VO = 1V to 4V)
Harmonic Distortion (%)
THD+N (%)
RL = 600Ω
G = 100, 3Vp-p (VO = 1V to 4V)
G = 1, 3Vp-p (VO = 1V to 4V)
Input goes through transition region
0.001
0.1
(–60dBc)
0.001
(–100dBc)
1k
10k
100k
G=1
VO = 2.5Vp-p
RL = 600Ω
3rd Harmonic
10k
100k
Frequency (Hz)
Frequency (Hz)
®
OPA350, 2350, 4350
10M
2nd Harmonic
0.0001
(–120dBc) 1k
0.0001
100
1M
0.01
(–80dBc)
G = 1, 2.5Vp-p (VO = 0.25V to 2.75V)
Input does NOT go through transition region
10
100k
HARMONIC DISTORTION + NOISE vs FREQUENCY
1
(–40dBc)
1
0.1
10k
Frequency (Hz)
4
1M
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
0.5
Open-Loop Gain (dB)
0.4
Differential Gain (%)
Differential Phase (°)
G=2
VO = 1.4V
NTSC Signal Generator
See Figure 6 for test circuit.
Phase
0.3
0.2
Gain
125
RL = 1kΩ
RL = 10kΩ
120
RL = 600Ω
115
0.1
110
0
0
100 200 300 400
500 600
–75
700 800 900 1000
–50
–25
COMMON-MODE AND POWER SUPPLY REJECTION RATIO
vs TEMPERATURE
100
50
75
100
125
40
CMRR, VS = 5.5V
(VCM = –0.1V to +5.6V)
35
90
100
PSRR
70
Slew Rate (V/µs)
90
CMRR, VS = 2.7V
(VCM = –0.1V to +2.8V)
30
PSRR (dB)
CMRR (dB)
25
SLEW RATE vs TEMPERATURE
110
80
0
Temperature (°C)
Resistive Load (Ω)
80
Negative Slew Rate
25
Positive Slew Rate
20
15
10
5
60
–75
0
70
–50
–25
0
25
50
75
100
125
–75
–50
–25
QUIESCENT CURRENT AND
SHORT-CIRCUIT CURRENT vs TEMPERATURE
100
6.0
90
5.5
+ISC
IQ
60
4.5
50
4.0
40
–25
0
25
50
75
100
125
75
100
5.0
4.5
4.0
3.5
3.0
30
–50
Quiescent Current (mA)
70
Short-Circuit Current (mA)
Quiescent Current (mA)
80
–ISC
5.5
3.5
–75
50
Per Amplifier
6.5
5.0
25
QUIESCENT CURRENT vs SUPPLY VOLTAGE
7.0
6.0
0
Temperature (°C)
Temperature (°C)
2.0
125
2.5
3.0
3.5
4.0
4.5
5.0
5.5
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
1k
1.5
100
1.0
Input Bias Current (pA)
Input Bias Current (pA)
INPUT BIAS CURRENT vs TEMPERATURE
10
1
0.5
0.0
0.1
–75
–50
–25
0
25
50
Temperature (°C)
75
100
–0.5
–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
125
Common-Mode Voltage (V)
MAXIMUM OUTPUT VOLTAGE vs FREQUENCY
6
10
5
Output Voltage (Vp-p)
Output Impedance (Ω)
CLOSED-LOOP OUTPUT IMPEDANCE vs FREQUENCY
100
1
0.1
G = 100
0.01
G = 10
0.001
G=1
10
Maximum output
voltage without
slew rate-induced
distortion.
4
VS = 2.7V
3
2
1
0
100k
0.0001
1
VS = 5.5V
100
1k
10k
100k
1M
10M
100M
1M
Frequency (Hz)
OUTPUT VOLTAGE SWING vs OUTPUT CURRENT
100M
OPEN-LOOP GAIN vs OUTPUT VOLTAGE SWING
140
V+
(V+)–1
Open-Loop Gain (dB)
(V+)–2
+25°C
–55°C
+125°C
Depending on circuit configuration
(including closed-loop gain) performance
may be degraded in shaded region.
(V–)+2
+25°C
+125°C
–55°C
IOUT = 2.5mA
IOUT = 250µA
130
Output Voltage (V)
10M
Frequency (Hz)
120
110
IOUT = 4.2mA
100
90
80
(V–)+1
70
60
(V–)
±10
0
±20
±30
±40
0
Output Current (mA)
40
60
80
100 120
140 160 180 200
Output Voltage Swing from Rails (mV)
®
OPA350, 2350, 4350
20
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
Typical distribution of
packaged units.
Typical production
distribution of
packaged units.
Percent of Amplifiers (%)
18
14
12
10
8
6
4
16
14
12
10
8
6
4
2
2
0
0
0
–500
–450
–400
–350
–300
–250
–200
–150
–100
–50
0
50
100
150
200
250
300
350
400
450
500
Percent of Amplifiers (%)
16
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
10
70
G=1
Settling Time (µs)
50
G = –1
40
30
G = ±10
20
0.01%
1
10
0.1%
0
0.1
10
100
1k
10k
100k
1M
–1
–10
Load Capacitance (pF)
Closed-Loop Gain (V/V)
SMALL-SIGNAL STEP RESPONSE
CL = 100pF
LARGE-SIGNAL STEP RESPONSE
CL = 100pF
–100
1V/div
50mV/div
Overshoot (%)
60
200ns/div
100ns/div
®
7
OPA350, 2350, 4350
APPLICATIONS INFORMATION
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.
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 sampling A/D converters. They are also well suited for controlling 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 significantly 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 package 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 applications. 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
1.25V/div
VIN
0
5V
VOUT
0
FIGURE 1. Rail-to-Rail Input and Output.
V+
Reference
Current
VIN+
VIN–
VBIAS1
VBIAS2
V–
(Ground)
FIGURE 2. Simplified Schematic.
®
OPA350, 2350, 4350
8
Class AB
Control
Circuitry
VO
OPA350 series op amps are laser-trimmed to reduce offset
voltage difference between the N-channel and
P-channel input stages, resulting in improved commonmode 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 operation outside this region.
performance curve “Small-Signal Overshoot vs Capacitive
Load” shows performance with a 1kΩ resistive load. Increasing load resistance improves capacitive load drive capability.
FEEDBACK CAPACITOR IMPROVES RESPONSE
For optimum settling time and stability with high-impedance 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
VIN
V+
CIN
V+
IOVERLOAD
10mA max
RIN • CIN = RF • CF
OPA350
VOUT
CL
OPAx350
CIN
VOUT
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 Performance.
RAIL-TO-RAIL OUTPUT
It is suggested that a variable capacitor be used for the
feedback capacitor since input capacitance may vary between 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 feedback 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 millivolts 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 openloop 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 determining 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
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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 information, consult the ADS7861 data sheet.
from becoming too high, which can cause stability problems when driving capacitive loads. As mentioned previously, 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 composite 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 configuration.
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 Frequency”).
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
4
1/4
3 OPA4350
VIN B1
1
0.1µF
0.1µF
CB0
24
2kΩ
2kΩ
2
3
6
1/4
5 OPA4350
VIN B0
7
4
5
6
CA1
7
2kΩ
2kΩ
8
9
9
1/4
10 OPA4350
VIN A1
10
8
11
SERIAL DATA A
CH B1–
SERIAL DATA B
CH B0+
BUSY
CH B0–
CLOCK
CH A1+
CS
CH A1–
12
VIN A0
13
1/4
OPA4350
14
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
ADS7861
RD
CH A0+
CONVST
CH A0–
A0
REFIN
M0
REFOUT
M1
1
2kΩ
+VA
CH B1+
DGND
CA0
2kΩ
13
+VD
AGND
12
23
22
21
20
19
18
17
16
15
14
Serial
Interface
RF
1kΩ
RG
1kΩ
+5V
C1
220µF
C4
0.1µF
+
0.1µF
2
10µF
7
6
OPA350
C2
47µF
C5
1000µF
ROUT
Cable
VOUT
RL
3
Video
In
R1
75Ω
4
R2
5kΩ
R3
5kΩ
+5V (pin 7)
R4
5kΩ
C3
10µF
FIGURE 6. Single-Supply Video Line Driver.
+5V
50kΩ
(2.5V)
8
RG
REF1004-2.5
4
R1
100kΩ
R2
25kΩ
+5V
R3
25kΩ
1/2
OPA2350
R4
100kΩ
1/2
OPA2350
G=5+
VO
RL
10kΩ
200kΩ
RG
FIGURE 7. Two Op-Amp Instrumentation Amplifier With Improved High Frequency Common-Mode Rejection.
C1
4.7nF
R1
10.5kΩ
+2.5V
R1
2.74kΩ
R2
19.6kΩ
+2.5V
C1
1830pF
VOUT
OPA350
RL
20kΩ
VIN
C2
1nF
C2
270pF
RL
20kΩ
R2
49.9kΩ
–2.5V
FIGURE 8. 10kHz Low-Pass Filter.
VOUT
OPA350
VIN
–2.5V
FIGURE 9. 10kHz High-Pass Filter.
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OPA350, 2350, 4350