High-Speed, Single-Supply, Rail-to-Rail
OPERATIONAL AMPLIFIERS
Micro
Amplifier
TM
Series
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
Out D
In D
+In D
V
+In C
In C
Out C
NC
Out A
In A
+In A
+V
+In B
In B
Out B
NC
OPA4350
SSOP-16
A
D
B
C
1
2
3
4
5
6
7
14
13
12
11
10
9
8
Out D
In D
+In D
V
+In C
In C
Out C
Out A
In A
+In A
V+
+In B
In B
Out B
OPA4350
SO-14
A
D
B
C
APPLICATIONS
q
CELL PHONE PA CONTROL LOOPS
q
DRIVING A/D CONVERTERS
q
VIDEO PROCESSING
q
DATA ACQUISITION
q
PROCESS CONTROL
q
AUDIO PROCESSING
q
COMMUNICATIONS
q
ACTIVE FILTERS
q
TEST EQUIPMENT
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 opera-
tion (38MHz, 22V/
s) make them ideal for driving sampling
Analog-to-Digital (A/D) converters. They are also well suited
for cell phone PA control loops and video processing (75
drive capability) as well as audio and general purpose appli-
cations. Single, dual, and quad versions have identical speci-
fications 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 10k
load. Dual and quad designs feature completely inde-
pendent circuitry for lowest crosstalk and freedom from inter-
action.
The single (OPA350) and dual (OPA2350) come in the
miniature MSOP-8 surface mount, SO-8 surface mount,
and DIP-8 packages. The quad (OPA4350) packages are
the space-saving SSOP-16 surface mount and SO-14 sur-
face mount. All are specified from 40
C to +85
C and
operate from 55
C to +150
C.
OPA350
OPA2350
OPA4350
FEATURES
q
RAIL-TO-RAIL INPUT
q
RAIL-TO-RAIL OUTPUT (within 10mV)
q
WIDE BANDWIDTH: 38MHz
q
HIGH SLEW RATE: 22V/
s
q
LOW NOISE: 5nV/
Hz
q
LOW THD+NOISE: 0.0006%
q
UNITY-GAIN STABLE
q
Micro
SIZE PACKAGES
q
SINGLE, DUAL, AND QUAD
1
2
3
4
8
7
6
5
NC
V+
Output
NC
NC
In
+In
V
OPA350
DIP-8, SO-8, MSOP-8
1
2
3
4
8
7
6
5
V+
Out B
In B
+In B
Out A
In A
+In A
V
OPA2350
DIP-8, SO-8, MSOP-8
A
B
OPA350
OPA2
350
OPA4350
OPA4350
SPICE Model available at www.ti.com
SBOS099A JULY 2001
www.ti.com
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
Copyright 1999, Texas Instruments Incorporated
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
OPA350, 2350, 4350
2
SBOS099A
PACKAGE
SPECIFIED
DRAWING
PACKAGE
TEMPERATURE
PACKAGE
ORDERING
TRANSPORT
PRODUCT
PACKAGE
NUMBER
DESIGNATOR
RANGE
MARKING
NUMBER
(1)
MEDIA
Single
OPA350EA
MSOP-8
337
DGK
40
C to +85
C
C50
OPA350EA/250
Tape and Reel
"
"
"
"
"
"
OPA350EA/2K5
Tape and Reel
OPA350UA
SO-8
182
D
40
C to +85
C
OPA350UA
OPA350UA
Rails
"
"
"
"
"
"
OPA350UA/2K5
Tape and Reel
OPA350PA
DIP-8
006
P
40
C to +85
C
OPA350PA
OPA350PA
Rails
Dual
OPA2350EA
MSOP-8
337
DGK
40
C to +85
C
D50
OPA2350EA/250
Tape and Reel
"
"
"
"
"
"
OPA2350EA/2K5
Tape and Reel
OPA2350UA
SO-8
182
D
40
C to +85
C
OPA2350UA
OPA2350UA
Rails
"
"
"
"
"
"
OPA2350UA/2K5
Tape and Reel
OPA2350PA
DIP-8
006
P
40
C to +85
C
OPA2350PA
OPA2350PA
Rails
Quad
OPA4350EA
SSOP-16
322
DBQ
40
C to +85
C
OPA4350EA
OPA4350EA/250
Tape and Reel
"
"
"
"
"
"
OPA4350EA/2K5
Tape and Reel
OPA4350UA
SO-14
235
D
40
C to +85
C
OPA4350UA
OPA4350UA
Rails
"
"
"
"
"
"
OPA4350UA/2K5
Tape and Reel
NOTES: (1) 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.
PACKAGE/ORDERING INFORMATION
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 +150
C
Storage Temperature ..................................................... 55
C to +150
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.
ABSOLUTE MAXIMUM RATINGS
(1)
ELECTROSTATIC
DISCHARGE SENSITIVITY
This integrated circuit can be damaged by ESD. Texas Instru-
ments 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.
OPA350, 2350, 4350
3
SBOS099A
OPA350EA, UA, PA
OPA2350EA, UA, PA
OPA4350EA, UA
ELECTRICAL CHARACTERISTICS: V
S
= 2.7V to 5.5V
Boldface limits apply over the specified temperature range, T
A
= 40
C to +85
C. V
S
= 5V.
At T
A
= +25
C, R
L
= 1k
connected to V
S
/2 and V
OUT
= V
S
/2, unless otherwise noted.
PARAMETER
CONDITION
MIN
TYP
(1)
MAX
UNITS
OFFSET VOLTAGE
Input Offset Voltage
V
OS
V
S
= 5V
150
500
V
T
A
= 40
C to +85
C
1
mV
vs Temperature
T
A
= 40
C to +85
C
4
V/
C
vs Power-Supply Rejection Ratio
PSRR
V
S
= 2.7V to 5.5V, V
CM
= 0V
40
150
V/V
T
A
= 40
C to +85
C
V
S
= 2.7V to 5.5V, V
CM
= 0V
175
V/V
Channel Separation (dual, quad)
dc
0.15
V/V
INPUT BIAS CURRENT
Input Bias Current
I
B
0.5
10
pA
vs Temperature
See Typical Characteristics
Input Offset Current
I
OS
0.5
10
pA
NOISE
Input Voltage Noise, f = 100Hz to 400kHz
4
Vrms
Input Voltage Noise Density, f = 10kHz
e
n
7
nV/
Hz
f = 100kHz
5
nV/
Hz
Current Noise Density, f = 10kHz
i
n
4
fA/
Hz
INPUT VOLTAGE RANGE
Common-Mode Voltage Range
V
CM
T
A
= 40
C to +85
C
0.1
(V+)+0.1
V
Common-Mode Rejection Ratio
CMRR
V
S
= 2.7V, 0.1V < V
CM
< 2.8V
66
84
dB
V
S
= 5.5V, 0.1V < V
CM
< 5.6V
76
90
dB
T
A
= 40
C to +85
C
V
S
= 5.5V, 0.1V < V
CM
< 5.6V
74
dB
INPUT IMPEDANCE
Differential
10
13
|| 2.5
|| pF
Common-Mode
10
13
|| 6.5
|| pF
OPEN-LOOP GAIN
Open-Loop Voltage Gain
A
OL
R
L
= 10k
, 50mV < V
O
< (V+) 50mV
100
122
dB
T
A
= 40
C to +85
C
R
L
= 10k
, 50mV < V
O
< (V+) 50mV
100
dB
R
L
= 1k
, 200mV < V
O
< (V+) 200mV
100
120
dB
T
A
= 40
C to +85
C
R
L
= 1k
, 200mV < V
O
< (V+) 200mV
100
dB
FREQUENCY RESPONSE
C
L
= 100pF
Gain-Bandwidth Product
GBW
G = 1
38
MHz
Slew Rate
SR
G = 1
22
V/
s
Settling Time, 0.1%
G =
1, 2V Step
0.22
s
0.01%
G =
1, 2V Step
0.5
s
Overload Recovery Time
V
IN
G = V
S
0.1
s
Total Harmonic Distortion + Noise
THD+N
R
L
= 600
, V
O
= 2.5Vp-p
(2)
, G = 1, f = 1kHz
0.0006
%
Differential Gain Error
G = 2, R
L
= 600
, V
O
= 1.4V
(3)
0.17
%
Differential Phase Error
G = 2, R
L
= 600
, V
O
= 1.4V
(3)
0.17
deg
OUTPUT
Voltage Output Swing from Rail
(4)
V
OUT
R
L
= 10k
, A
OL
100dB
10
50
mV
T
A
= 40
C to +85
C
R
L
= 10k
,
A
OL
100dB
50
mV
R
L
= 1k
,
A
OL
100dB
25
200
mV
T
A
= 40
C to +85
C
R
L
= 1k
, A
OL
100dB
200
mV
Output Current
I
OUT
40
(5)
mA
Short-Circuit Current
I
SC
80
mA
Capacitive Load Drive
C
LOAD
See Typical Characteristics
POWER SUPPLY
Operating Voltage Range
V
S
T
A
= 40
C to +85
C
2.7
5.5
V
Minimum Operating Voltage
2.5
V
Quiescent Current (per amplifier)
I
Q
I
O
= 0
5.2
7.5
mA
T
A
= 40
C to +85
C
I
O
= 0
8.5
mA
TEMPERATURE RANGE
Specified Range
40
+85
C
Operating Range
55
+150
C
Storage Range
55
+150
C
Thermal Resistance
JA
MSOP-8 Surface Mount
150
C/W
SO-8 Surface Mount
150
C/W
DIP-8
100
C/W
SO-14 Surface Mount
100
C/W
SSOP-16 Surface Mount
100
C/W
NOTES: (1) V
S
= +5V. (2) V
OUT
= 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 characteristic, "Output Voltage Swing vs Output Current."
OPA350, 2350, 4350
4
SBOS099A
TYPICAL CHARACTERISTICS
At T
A
= +25
C, V
S
= +5V, and R
L
= 1k
connected to V
S
/2, unless otherwise noted.
POWER SUPPLY AND COMMON-MODE
REJECTION RATIO vs FREQUENCY
100
90
80
70
60
50
40
30
20
10
0
PSRR, CMRR (dB)
Frequency (Hz)
10
100
1k
10k
100k
1M
10M
PSRR
CMRR
(V
S
= +5V
V
CM
= 0.1V to 5.1V)
INPUT VOLTAGE AND CURRENT NOISE
SPECTRAL DENSITY vs FREQUENCY
100k
10k
1k
100
10
1
10k
1k
100
10
1
0.1
Voltage Noise (nV
Hz)
Frequency (Hz)
10
100
1k
10k
100k
1M
10M
Current Noise (fA
Hz)
Voltage Noise
Current Noise
CHANNEL SEPARATION vs FREQUENCY
Frequency (Hz)
Channel Separation (dB)
140
130
120
110
100
90
80
70
60
100
10
1k
1M
100k
10k
10M
Dual and quad devices.
HARMONIC DISTORTION + NOISE vs FREQUENCY
1
(40dBc)
0.1
(60dBc)
0.01
(80dBc)
0.001
(100dBc)
0.0001
(120dBc)
Harmonic Distortion (%)
Frequency (Hz)
1k
10k
100k
1M
G = 1
V
O
= 2.5Vp-p
R
L
= 600
3rd Harmonic
2nd Harmonic
OPEN-LOOP GAIN/PHASE vs FREQUENCY
0.1
1
160
140
120
100
80
60
40
20
0
Voltage Gain (dB)
0
45
90
135
180
Phase (
)
Frequency (Hz)
10
100
1k
10k
100k
1M
10M
100M
G
TOTAL HARMONIC DISTORTION + NOISE
vs FREQUENCY
1
0.1
0.01
0.001
0.0001
THD+N (%)
Frequency (Hz)
10
100
1k
10k
100k
R
L
= 600
G = 100, 3Vp-p (V
O
= 1V to 4V)
G = 10, 3Vp-p (V
O
= 1V to 4V)
G = 1, 3Vp-p (V
O
= 1V to 4V)
Input goes through transition region
G = 1, 2.5Vp-p (V
O
= 0.25V to 2.75V)
Input does NOT go through transition region
OPA350, 2350, 4350
5
SBOS099A
TYPICAL CHARACTERISTICS
(Cont.)
At T
A
= +25
C, V
S
= +5V, and R
L
= 1k
connected to V
S
/2, unless otherwise noted.
OPEN-LOOP GAIN vs TEMPERATURE
130
125
120
115
110
Open-Loop Gain (dB)
Temperature (
C)
75
50
25
0
25
50
75
100
125
R
L
= 600
R
L
= 1k
R
L
= 10k
SLEW RATE vs TEMPERATURE
Temperature (
C)
Slew Rate (V/
s)
40
35
30
25
20
15
10
5
0
75
50
25
0
25
50
75
100
125
Negative Slew Rate
Positive Slew Rate
DIFFERENTIAL GAIN/PHASE vs RESISTIVE LOAD
0.5
0.4
0.3
0.2
0.1
0
Differential Gain (%)
Differential Phase (
)
Resistive Load (
)
0
100
200
300
500
400
600
800
700
900 1000
G = 2
V
O
= 1.4V
NTSC Signal Generator
See Figure 6 for test circuit.
Phase
Gain
QUIESCENT CURRENT AND
SHORT-CIRCUIT CURRENT vs TEMPERATURE
Temperature (
C)
Quiescent Current (mA)
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
100
90
80
70
60
50
40
30
Short-Circuit Current (mA)
75
50
25
0
25
50
75
100
125
I
Q
+I
SC
I
SC
QUIESCENT CURRENT vs SUPPLY VOLTAGE
Supply Voltage (V)
Quiescent Current (mA)
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Per Amplifier
COMMON-MODE AND POWER-SUPPLY REJECTION RATIO
vs TEMPERATURE
100
90
80
70
60
CMRR (dB)
110
100
90
80
70
PSRR (dB)
Temperature (
C)
75
50
25
0
25
50
75
100
125
CMRR, V
S
= 5.5V
(V
CM
= 0.1V to +5.6V)
CMRR, V
S
= 2.7V
(V
CM
= 0.1V to +2.8V)
PSRR
OPA350, 2350, 4350
6
SBOS099A
TYPICAL CHARACTERISTICS
(Cont.)
At T
A
= +25
C, V
S
= +5V, and R
L
= 1k
connected to V
S
/2, unless otherwise noted.
INPUT BIAS CURRENT vs TEMPERATURE
Input Bias Current (pA)
Temperature (
C)
75
50
25
0
25
50
75
100
125
1k
100
10
1
0.1
INPUT BIAS CURRENT
vs INPUT COMMON-MODE VOLTAGE
Common-Mode Voltage (V)
Input Bias Current (pA)
1.5
1.0
0.5
0.0
0.5
0.5 0.0 0.5 1.0
2.0
1.5
2.5 3.0 3.5 4.0
5.0
4.5
5.5
MAXIMUM OUTPUT VOLTAGE vs FREQUENCY
100M
1M
10M
Frequency (Hz)
100k
6
5
4
3
2
1
0
Output Voltage (Vp-p)
Maximum output
voltage without
slew rate-induced
distortion.
V
S
= 2.7V
V
S
= 5.5V
OUTPUT VOLTAGE SWING vs OUTPUT CURRENT
Output Current (mA)
Output Voltage (V)
V+
(V+)1
(V+)2
(V)+2
(V)+1
(V)
0
10
20
30
40
+25
C
+125
C
55
C
55
C
+125
C
+25
C
Depending on circuit configuration
(including closed-loop gain) performance
may be degraded in shaded region.
OPEN-LOOP GAIN vs OUTPUT VOLTAGE SWING
140
130
120
110
100
90
80
70
60
Open-Loop Gain (dB)
Output Voltage Swing from Rails (mV)
0
20
40
60
100
80
120
160
140
180
200
I
OUT
= 4.2mA
I
OUT
= 250
A
I
OUT
= 2.5mA
OPA350, 2350, 4350
7
SBOS099A
TYPICAL CHARACTERISTICS
(Cont.)
At T
A
= +25
C, V
S
= +5V, and R
L
= 1k
connected to V
S
/2, unless otherwise noted.
SMALL-SIGNAL STEP RESPONSE
C
L
= 100pF
100ns/div
50mV/div
SETTLING TIME vs CLOSED-LOOP GAIN
10
1
0.1
Settling Time (
s)
Closed-Loop Gain (V/V)
1
10
100
0.1%
0.01%
LARGE-SIGNAL STEP RESPONSE
C
L
= 100pF
200ns/div
1V/div
SMALL-SIGNAL OVERSHOOT vs LOAD CAPACITANCE
1M
100
1k
10k
100k
Load Capacitance (pF)
10
80
70
60
50
40
30
20
10
0
Overshoot (%)
G = 1
G = 1
G =
10
Offset Voltage (
V)
OFFSET VOLTAGE
PRODUCTION DISTRIBUTION
18
16
14
12
10
8
6
4
2
0
Percent of Amplifiers (%)
500
450
400
350
300
250
200
150
100
50
0
50
100
150
200
250
300
350
400
450
500
Typical distribution of
packaged units.
Offset Voltage Drift (
V/
C)
OFFSET VOLTAGE DRIFT
PRODUCTION DISTRIBUTION
20
18
16
14
12
10
8
6
4
2
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15
Percent of Amplifiers (%)
Typical production
distribution of
packaged units.
OPA350, 2350, 4350
8
SBOS099A
0
5V
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 suit-
able 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 (75
drive capability).
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 600
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
FIGURE 2. Simplified Schematic.
V
S
= +5, G = +1, R
L
= 1k
V
IN
1.25V/div
FIGURE 1. Rail-to-Rail Input and Output.
V
BIAS1
V
BIAS2
V
IN
+
V
IN
Class AB
Control
Circuitry
V
O
V
(Ground)
V+
Reference
Current
5V
0
V
OUT
the OPA350 in unity-gain configuration. Operation is
from a single +5V supply with a 1k
load connected to
V
S
/2. The input is a 5Vp-p sinusoid. Output voltage swing
is approximately 4.95Vp-p.
Power supply pins should be bypassed with 0.01
F 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 tested 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 that vary significantly
with operating voltage or temperature are shown in the
typical characteristics.
RAIL-TO-RAIL INPUT
The tested 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, as shown on 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.
OPA350, 2350, 4350
9
SBOS099A
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.
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.
characteristic "Small-Signal Overshoot vs Capacitive Load"
shows performance with a 1k
resistive load. Increasing
load resistance improves capacitive load drive capability.
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, R
F
, 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.
FIGURE 3. Input Current Protection for Voltages Exceeding
the Supply Voltage.
RAIL-TO-RAIL OUTPUT
A class AB output stage with common-source transistors is
used to achieve rail-to-rail output. For light resistive loads
(>10k
), the output voltage swing is typically ten millivolts
from the supply rails. With heavier resistive loads (600
to
10k
), the output can swing to within a few tens of milli-
volts from the supply rails and maintain high open-loop
gain. See the typical characteristics "Output Voltage Swing
vs Output Current" and "Open-Loop Gain vs Output Volt-
age."
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 that degrades the phase margin.
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
FIGURE 4. Feedback Capacitor Improves Dynamic Perfor-
mance.
5k
OPAx350
10mA max
V+
V
IN
V
OUT
I
OVERLOAD
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:
R
IN
C
IN
= R
F
C
F
where C
IN
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.
OPA350
V+
V
OUT
V
IN
R
IN
R
IN
C
IN
= R
F
C
F
R
F
C
L
C
IN
C
IN
C
F
Where C
IN
is equal to the OPA350's input
capacitance (approximately 9pF) plus any
parastic layout capacitance.
OPA350, 2350, 4350
10
SBOS099A
FIGURE 5. OPA4350 Driving Sampling A/D Converter.
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 (SBAS110A).
OUTPUT IMPEDANCE
The low frequency open-loop output impedance of the
OPA350's common-source output stage is approximately
1k
. 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
0.001
. 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 characteristic, "Output Impedance vs Frequency").
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
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.
The input is terminated with a 75
resistor and ac-coupled
with a 47
F 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.
1/4
OPA4350
V
IN
B1
2
3
4
2k
2k
C
B1
CH B1+
CH B1
CH B0+
CH B0
CH A1+
CH A1
CH A0+
CH A0
REF
IN
REF
OUT
SERIAL DATA A
SERIAL DATA B
BUSY
CLOCK
CS
RD
CONVST
A0
M0
M1
2
3
4
5
6
7
8
9
10
11
23
22
21
20
19
18
17
16
15
14
1/4
OPA4350
V
IN
B0
+5V
6
5
2k
2k
C
B0
1/4
OPA4350
V
IN
A1
9
10
12
13
8
7
1
2k
2k
C
A1
1/4
OPA4350
V
IN
A0
14
11
1
12
2k
2k
C
A0
0.1
F
0.1
F
+V
A
+V
D
24
13
Serial
Interface
DGND
AGND
ADS7861
V
IN
= 0V to 2.45V for 0V to 4.9V output.
Choose C
B1
, C
B0
, C
A1
, C
A0
to filter high frequency noise.
OPA350, 2350, 4350
11
SBOS099A
FIGURE 6. Single-Supply Video Line Driver.
FIGURE 8. 10kHz Low-Pass Filter.
FIGURE 9. 10kHz High-Pass Filter.
+2.5V
V
IN
R
2
19.6k
R
1
2.74k
2.5V
C
2
1nF
R
L
20k
OPA350
V
OUT
C
1
4.7nF
+2.5V
V
IN
C
2
270pF
C
1
1830pF
2.5V
R
2
49.9k
R
L
20k
OPA350
V
OUT
R
1
10.5k
FIGURE 7. Two Op-Amp Instrumentation Amplifier With Improved High Frequency Common-Mode Rejection.
OPA350
+5V
V
OUT
+5V (pin 7)
Video
In
R
OUT
R
L
Cable
R
F
1k
R
G
1k
R
4
5k
R
3
5k
C
3
10
F
0.1
F
10
F
+
6
7
4
3
2
C
4
0.1
F
C
5
1000
F
C
2
47
F
R
2
5k
R
1
75
C
1
220
F
1/2
OPA2350
1/2
OPA2350
R
3
25k
R
2
25k
R
G
R
1
100k
R
4
100k
R
L
10k
V
O
50k
G = 5 +
200k
R
G
+5V
+5V
REF1004-2.5
4
8
(2.5V)
PACKAGING INFORMATION
ORDERABLE DEVICE
STATUS(1)
PACKAGE TYPE
PACKAGE DRAWING
PINS
PACKAGE QTY
OPA2350EA/250
ACTIVE
VSSOP
DGK
8
250
OPA2350EA/2K5
ACTIVE
VSSOP
DGK
8
2500
OPA2350PA
ACTIVE
PDIP
P
8
50
OPA2350UA
ACTIVE
SOIC
D
8
100
OPA2350UA/2K5
ACTIVE
SOIC
D
8
2500
OPA350EA/250
ACTIVE
VSSOP
DGK
8
250
OPA350EA/2K5
ACTIVE
VSSOP
DGK
8
2500
OPA350PA
ACTIVE
PDIP
P
8
50
OPA350UA
ACTIVE
SOIC
D
8
100
OPA350UA/2K5
ACTIVE
SOIC
D
8
2500
OPA4350EA/250
ACTIVE
SSOP
DBQ
16
250
OPA4350EA/2K5
ACTIVE
SSOP
DBQ
16
2500
OPA4350UA
ACTIVE
SOIC
D
14
58
OPA4350UA/2K5
ACTIVE
SOIC
D
14
2500
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in
a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
PACKAGE OPTION ADDENDUM
www.ti.com
3-Oct-2003
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