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LMV751
Low Noise, Low Vos, Single Op Amp
General Description
The LMV751 is a high performance CMOS operational amplifier intended for applications requiring low noise and low
input offset voltage.It offers modestbandwidth of 4.5MHz for
very low supply current and is unity gain stable.
The output stage is able to drive high capacitance, up to
1000pF and source or sink 8mA output current.
It is supplied in the space saving SOT23-5 Tiny package.
The LMV751 is designed to meet the demands of small size,
low power, and high performance required by cellular
phones and similar battery operated portable electronics.
Features
n Low Noise 6.5nV Rt-Hz typ.
n Low Vos (0.05mV typ.)
n Wideband 4.5MHz GBP typ.
n Low Supply Current 500uA typ.
n Low Suppy Voltage 2.7V to 5.0V
n Ground-referenced Inputs
n Unity gain stable
n Small Package
Applications
n Cellular Phones
n Portable Equipment
n Radio Systems
Connection Diagrams
Ordering Information
Package Ordering Info NSC Drawing Pkg Marking Supplied As
5-Pin SOT23-5 LMV751M5 MA05B A32A 1k Units Tape and Reel
LMV751M5X MA05B A32A 3k units Tape and Reel
SOT23-5
DS101081-1
Top View
August 1999
LMV751 Low Noise, Low Vos, Single Op Amp
© 1999 National Semiconductor Corporation DS101081 www.national.com
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National SemiconductorSales Office/
Distributors for availability and specifications.
ESD tolerance (Note 3)
Human Body Model 2000V
Machine Model 200V
Differential Input Voltage
±
Supply Voltage
Supply Voltage (V
+-V−
) 5.5V
Lead Temperature (Soldering, 10 sec) 260˚C
Storage Temperature Range −65˚C to 150˚C
Junction Temperature (T
J
) (Note 4) 150˚C
Recommended Operating
Conditions
Supply Voltage 2.7V to 5.0V
Temperature Range −40˚C ≤ T
J
≤ 85˚C
Thermal resisance (θ
JA
) (Note 6)
M5 Package, SOT23-5 274˚C/W
2.7V Electrical Characteristics
V+= 2.7V, V−= 0V, VCM= 1.35V, TA= 25˚C unless otherwise stated. Boldface limits apply over theTemperature Range.
Symbol Parameter Condition
Typ
(Note 5)
Limit
(Note 2)
Units
V
OS
Input Offset Voltage 0.05 1.0
1.5
mV
max
CMRR Common Mode Rejection Ratio 0V
<
V
CM
<
1.3V 100 85
70
dB
min
PSRR Power Supply Rejection Ratio V
+
=
2.7V to 5.0V 107 85
70
dB
min
I
S
Supply Current 0.5 0.7
0.75
mA
max
I
IN
Input Current 1.5 100 pA
max
I
OS
Input Offset Current 0.2 pA
A
VOL
Voltage Gain R
L
=
10k Connect to V
+
/2
V
O
=
0.2V to 2.2V
120 110
95
dB
min
R
L
=
2k Connect to V
+
/2
V
O
=
0.2V to 2.2V
120 100
85
V
O
Positive Voltage Swing R
L
=
10k Connect to V
+
/2 2.62 2.54
2.52
V
min
R
L
=
2k Connect to V
+
/2 2.62 2.54
2.52
V
O
NegativeVoltage Swing R
L
=
10k Connect to V
+
/2 78 140
160
mV
max
R
L
=
2k Connect to V
+
/2 78 140
160
I
O
Output Current Sourcing, V
O
=
0V
V
IN
(diff)
=
±
0.5V
12 6.0
1.5
mA
min
Sinking,V
O
=
2.7V
V
IN
(diff)
=
±
0.5V
11 6.0
1.5
e
n
(10Hz)
Input Referred Voltage Noise 15.5 nV/
e
n
(1kHz)
Input Referred Voltage Noise 7 nV/
e
n
(30kHz)
Input Referred Voltage Noise 7 10 nV/
max
I
N
(1kHz) Input Referred Current Noise 0.01 pA/
GBW Gain-Bandwidth Product 4.5 2 MHZ
min
SR Slew Rate 2 V/µs
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5.0V Electrical Characteristics
V
+
=
5.0V, V
−
=
0V, V
CM
= 2.5V, TA= 25˚C unless otherwise stated.Boldface limits apply over theTemperature Range.
Symbol Parameter
Typ
(Note 5)
Limit
(Note 2)
Units
V
OS
Input Offset Voltage 0.05 1.0
1.5
mV
max
CMRR Common Mode Rejection Ratio 0V
<
V
CM
<
3.6V 103 85
70
dB
min
PSRR Power Supply Rejection Ratio V
+
=
2.7V to 5.0V 107 85
70
dB
min
I
S
Supply Current 0.6 0.8
0.85
mA
max
I
IN
Input Current 1.5 100 pA
max
I
OS
Input offset Current 0.2 pA
A
VOL
Voltage Gain R
L
=
10k Connect to V
+
/2
V
O
=
0.2V to 4.5V
120 110
95
db
min
R
L
=
2k Connect to V
+
/2
V
O
=
0.2V to 4.5V
120 100
85
V
O
Positive Voltage Swing R
L
=
10k Connect to V
+
/2 4.89 4.82
4.80
V
min
R
L
=
2k Connect to V
+
/2 4.89 4.82
4.80
V
O
Negative Voltage Swing R
L
=
10k Connect to V
+
/2 86 160
180
mV
max
R
L
=
2k Connect to V
+
/2 86 160
180
I
O
Output Current Sourcing, V
O
=
0V
V
IN
(diff)
=
±
0.5V
15 8.0
2.5
mA
min
Sinking, V
O
=
5V
V
IN
(diff)
=
±
0.5V
20 8.0
2.5
e
n
(10Hz)
Input Referred Voltage Noise 15 nV/
e
n
(1kHz)
Input Referred Voltage Noise 6.5 nV/
e
n
(30kHz)
Input Referred Voltage Noise 6.5 10 nV/
max
I
N
(1kHz) Input Referred Current Noise 0.01 pA/
GBW Gain-Bandwidth Product 5 2 MHz
min
SR Slew Rate 2.3 V/µs
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.Electrical specifications do not apply when operating the device
beyond its rated operating conditions.
Note 2: All limits are guaranteed by testing or statistical analysis
Note 3: Human body model, 1.5kΩ in series with 100pF. Machine model, 200Ω in series with 1000pF.
Note 4: The maximum power dissipation is a function of T
J
(max), θJA, and TA. The maximum allowable power dissipation at any ambient temperature is
P
D
=
(T
J
(max) - TA)/θJA. All numbers apply for packages soldered directly into a PC board.
Note 5: Typical values represent the most likely parametric norm.
Note 6: All numbers are typical, and apply to packages soldered directly onto PC board in still air.
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Typical Performance Characteristics
Supply Curent vs. Voltage
DS101081-35
VOSvs. V
CM
V
+
=
2.7V
DS101081-38
VOSvs V
CM
V
+
=
5.0V
DS101081-37
Source Current vs Out
V
+
=
2.7V
DS101081-28
Source Current vs V
OUT
V
+
=
5.0V
DS101081-29
Gain/Phase
DS101081-3
Sinking Current vs V
OUT
V
+
=
2.7V
DS101081-30
Sinking Current vs V
OUT
V
+
=
5.0V
DS101081-31
VOSvs V
+
DS101081-36
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Typical Performance Characteristics (Continued)
V
IN
vs V
OUT
V
+
=
2.7V, R
L
=
2k
DS101081-32
VINvs V
OUT
V
+
=
5.0V, R
L
=
2k
DS101081-33
Input Bias vs V
CM
T
A
=
25˚C
DS101081-16
Input Bias vs V
CM
T
A
=
85˚C
DS101081-5
PSRR +
DS101081-26
PSRR −
DS101081-25
Voltage Noise
DS101081-2
CMRR
DS101081-39
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Application Hints
1.0 Noise
There are many sources of noise in a system: thermal noise,
shot noise, 1/f, popcorn noise, resistor noise, just to name a
few. In addition to starting with a low noise op amp, such as
the LMV751, careful attention to detail will result in the lowest overall noise for the system.
1.1 To invert or not invert?
Both inverting and non-inverting amplifiers employ feedback
to stabilize the closed loop gain of the block being designed.
The loop gain (in decibels) equals the algebraic difference
between the open loop and closed loop gains. Feedback improves the Total Harmonic Distortion (THD) and the output
impedance. The various noise sources, when input referred,
are amplified, not by the closed loop gain, but by the noise
gain. For a non-inverting amplifier, the noise gain is equal to
the closed loop gain, but for an inverting amplifier, the noise
gain is equal to the closed loop gain plus one. For large
gains, e.g., 100, the difference is negligible, but for small
gains, such as one, the noise gain for the inverting amplifier
would be two. This implies that non-inverting blocks are preferred at low gains.
1.2 Source impedance
Because noise sources are uncorrelated, the system noise
is calculated by taking the RMS sum of the various noise
sources, that is, the square root of the sum ofthe squares. At
very low source impedances, the voltage noise will dominate; at very high source impedances, the input noise current times the equivalent external resistance will dominate.
For a detailed example calculation, refer to Note 1.
1.3 Bias current compensation resistor
In CMOS input op amps,the input bias currents arevery low,
so there is no need to use R
COMP
(Figure 1 and 2) for bias
current compensation that would normallybe used with early
generation bipolar op amps. In fact, inclusion of the resistor
would act as another thermal noise source in the system, increasing the overall noise.
1.4 Resistor types
Thermal noise is generated by any passive resistive element. This noise is ″white″; meaning it has a constant spectral density. Thermal noise can be represented by a meansquare voltage generator e
R
2
in series with a noiseless
resistor, where e
R
2
is given by: Where:
e
R
2
= 4K TRB (volts)
2
Where T = temperature in ˚K
R = resistor value in ohms
B = noise bandwidth in Hz
K = Boltzmann’s constant (1.38 x 10-23 W-sec/˚K)
Actual resistor noise measurements may have more noise
than the calculatedvalue. This additionalnoise component is
known as excess noise. Excess noise has a 1/f spectral response, and isproportional to the voltage dropacross the resistor. It is convenient to define a noise index when referring
to excess noise in resistors. The noise index is the RMS
value in uV of noise in the resistor per volt of DC drop across
the resistor in a decade of frequency.Noise index expressed
in dB is:
NI = 20 log ((E
EX/VDC
)x106)db
Where: E
EX
= resistor excess noise in uV per frequency de-
cade.
V
DC
= DC voltage drop across the resistor.
Excess noise incarbon composition resistors corresponds to
a large noiseindex of +10 dB to-20 dB. Carbon film resistors
have a noise index of -10 dB to -25 dB. Metal film and wire
wound resistors show the least amount of excess noise, with
a noise index figure of -15 dB to -40 dB.
1.5 Other noise sources:
As the op amp and resistor noise sources are decreased,
other noise contributors will nowbe noticeable. Small air currents across thermocouples will result in low frequency
variations.Any two dissimilar metals, such as thelead on the
IC and the solder and copper foil of the pc board, will form a
thermocouple. The source itself mayalso generate noise.An
example would be a resistive bridge. All resistive sources
generate thermal noise based on the same equation listed
above under ″resistor types″.(2)
DS101081-23
Figure 1
DS101081-24
Figure 2
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Application Hints (Continued)
1.6 Putting it all together
To a first approximation, the total input referred noise of an
op amp is:
E
t
2
=e
n
2
+e
req
2
+(in*Req)
2
where Req is the equivalent source resistance at the inputs.
At low impedances, voltage noise dominates.At high impedances, current noise dominates. With a typical noise current
on most CMOS input op amps of 0.01 pA/rt-Hz, the current
noise contribution will be smaller than the voltage noise for
Req less than one megohm.
2.0 Other Considerations
2.1 Comparator operation
Occasionally operational amplifiers are used as comparators. This is not optimum for the LMV751 for several reasons. First, the LMV751 is compensated for unity gain stability, so the speed will be less than could be obtained on the
same process with a circuit specifically designed for comparator operation. Second, op amp output stages are designed to be linear, and will not necessarily meet the logic
levels required under all conditions. Lastly, the LMV751 has
the newer PNP-NPN common emitter output stage, characteristic of many rail-to-rail output op amps. This means that
when used in open loop applications, such as comparators,
with very light loads, the output PNP will saturate, with the
output current being diverted into the previous stage. As a
result, the supply current will increase to the 20-30 mA.
range. When used as acomparator,a resistive load between
2kΩ and 10kΩshould be usedwith a small amount ofhysteresis to alleviate this problem. When used as an op amp, the
closed loop gain will drive the inverting input to within a few
millivolts of the non-inverting input. This will automatically reduce the output drive as the output settles to the correct
value; thus it is onlywhen used as a comparator that the current will increase to the tens of milliampere range.
2.2 Rail-to-Rail
Because of the output stage discussed above, the LMV751
will swing “rail-to-rail” on the output. This normally means
within a few hundred millivolts of each rail with a reasonable
load. Referring to the Electrical Characteristics table for 2.7V
to 5.0V, it can be seen that this is true for resistive loads of
2kΩ and 10kΩ. The input stage consists of cascoded
P-channel MOSFETS, so the input common mode range includes ground, but typically requires 1.2V to 1.3V headroom
from the positive rail. This is better than the industry standard LM324 and LM358 that have PNPinput stages, and the
LMV751 has the advantage of much lower input bias currents.
2.3 Loading
The LMV751 is a low noise, high speed op amp with excellent phase margin and stablility. Capacitive loads up to 1000
pF can behandled, but larger capacitive loadsshould be isolated from the output. The most straightforward way to do
this is to put a resistor in series with the output. This resistor
will also preventexcess power dissapationif the output is accidentally shorted.
2.4 General Circuits
With the low noise and low input bias current, the LMV751
would be useful in active filters, integrators, current to voltage converters, low frequency sine wave generators, and instrumentation amplifiers. (3)
Note: 1. Sherwin, Jim“Noise Specs Confusing?” AN-104, National Semicon-
ductor.
2. Christensen, John, “Noise-figure curve ease the selection of
low-noise op amps”, EDN, pp 81-84,Aug. 4, 1994
3. “Op Amp Circuit Collection”, AN-31, National Semiconductor.
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Page 8
Physical Dimensions inches (millimeters) unless otherwise noted
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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
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1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
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whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
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www.national.com
SOT23-5
Order Number LMV751M5
NS Package Number MA05B
LMV751 Low Noise, Low Vos, Single Op Amp
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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