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PDF LT1991 Data sheet ( Hoja de datos )
| Número de pieza | LT1991 | |
| Descripción | Precision / 100uA Gain Selectable Amplifier | |
| Fabricantes | Linear Technology | |
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LT1991www.DataSheet4U.com
Precision, 100µA
Gain Selectable Amplifier
FEATURES
n Pin Configurable as a Difference Amplifier,
Inverting and Noninverting Amplifier
n Difference Amplifier
Gain Range 1 to 13
CMRR >75dB
n Noninverting Amplifier
Gain Range 0.07 to 14
n Inverting Amplifier
Gain Range –0.08 to –13
n Gain Error <0.04%
n Gain Drift < 3ppm/°C
n Wide Supply Range: Single 2.7V to Split ±18V
n Micropower: 100μA Supply Current
n Precision: 50μV Maximum Input Offset Voltage
n 560kHz Gain Bandwidth Product
n Rail-to-Rail Output
n Space Saving 10-Lead MSOP and DFN Packages
APPLICATIONS
n Handheld Instrumentation
n Medical Instrumentation
n Strain Gauge Amplifiers
n Differential to Single-Ended Conversion
DESCRIPTION
The LT®1991 combines a precision operational amplifier
with eight precision resistors to form a one-chip solution
for accurately amplifying voltages. Gains from –13 to 14
with a gain accuracy of 0.04% can be achieved using no
external components. The device is particularly well suited
for use as a difference amplifier, where the excellent resis-
tor matching results in a common mode rejection ratio of
greater than 75dB.
The amplifier features a 50μV maximum input offset volt-
age and a gain bandwidth product of 560kHz. The device
operates from any supply voltage from 2.7V to 36V and
draws only 100μA supply current on a 5V supply. The
output swings to within 40mV of either supply rail.
The resistors have excellent matching, 0.04% over tem-
perature for the 450k resistors. The matching temperature
coefficent is guaranteed less than 3ppm/°C. The resistors
are extremely linear with voltage, resulting in a gain non-
linearity of less than 10ppm.
The LT1991 is fully specified at 5V and ±15V supplies and
from –40°C to 125°C. The device is available in space
saving 10-lead MSOP and low profile (0.8mm) 3mm ×
3mm DFN packages.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
VM(IN) –
ΔVIN +
VP(IN)
INPUT RANGE
–0.5V TO 5.1V
RIN = 900kΩ
Rail-to-Rail Gain = 1 Difference Amplifier
5V
50k
150k
450k
450k
150k
50k
450k
– 4pF
+ LT1991
450k
4pF
VOUT = VREF + ΔVIN
SWING 40mV TO
EITHER RAIL
ROUT <0.1Ω
VREF = 2.5V
1991 TA01
Distribution of Resistor Matching
40
450k RESISTORS
35 LT1991A
30
25
20
15
10
5
0
–0.04
–0.02
0
0.02
RESISTOR MATCHING (%)
0.04
1991 TA01b
1991fg
1
1 page  
LT1991www.DataSheet4U.com
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the operating
temperature range of –40°C to 125°C for H-grade parts, otherwise specifications are at TA = 25°C. Difference amplifier configuration,
VS = 5V, 0V or ±15V; VCM = VREF = half supply, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
ΔG Gain Error
VS = ±15V, VOUT = ±10V; RL = 10k
G=1
G = 3 or 9
l
l
±0.08
±0.12
%
%
GNL Gain Nonlinearity
VS = ±15V; VOUT = ±10V; RL = 10k
l
1 10 ppm
ΔG/ΔT
Gain Drift vs Temperature (Note 6)
VS = ±15V; VOUT = ±10V; RL = 10k
l
0.3 3 ppm/°C
CMRR
Common Mode Rejection Ratio,
Referred to Inputs (RTI)
VS = ±15V; VCM = ±15.2V
G=9
G=3
G=1
l 77
l 70
l 70
100
93
90
dB
dB
dB
VCM
Input Voltage Range (Note 7)
P1/M1 Inputs
VS = ±15V; VREF = 0V
VS = 5V, 0V; VREF = 2.5V
VS = 3V, 0V; VREF = 1.25V
l –28
l –0.5
l 0.75
27.6 V
5.1 V
2.35 V
P1/M1 Inputs, P9/M9 Connected to REF
VS = ±15V; VREF = 0V
VS = 5V, 0V; VREF = 2.5V
VS = 3V, 0V; VREF = 1.25V
l –60
l –14
l –1.5
60 V
16.8 V
7.3 V
P3/M3 Inputs
VS = ±15V; VREF = 0V
VS = 5V, 0V; VREF = 2.5V
VS = 3V, 0V; VREF = 1.25V
l –15.2
l 0.5
l 0.95
15.2 V
4.2 V
1.95 V
P9/M9 Inputs
VS = ±15V; VREF = 0V
VS = 5V, 0V; VREF = 2.5V
VS = 3V, 0V; VREF = 1.25V
l –15.2
l 0.85
l 1.0
15.2 V
3.9 V
1.9 V
VOS
Op Amp Offset Voltage (Note 8)
LT1991MS
25 100
μV
l 285 μV
LT1991DD
25 150
μV
l 295 μV
ΔVOS/ΔT
Op Amp Offset Voltage Drift (Note 6)
l 0.3 1 μV/°C
IB Op Amp Input Bias Current (Note 11)
2.5 5
nA
l 25 nA
IOS Op Amp Input Offset Current (Note 11)
50 1000
pA
l 4500 pA
Op Amp Input Noise Voltage
0.01Hz to 1Hz
0.01Hz to 1Hz
0.1Hz to 10Hz
0.1Hz to 10Hz
en
Input Noise Voltage Density
G = 1; f = 1kHz
G = 9; f = 1kHz
0.35 μVP-P
0.07 μVRMS
0.25 μVP-P
0.05 μVRMS
180 nV/√Hz
46 nV/√Hz
RIN
Input Impedance (Note 10)
P1 (M1 = Ground)
P3 (M3 = Ground)
P9 (M9 = Ground)
l 630
l 420
l 350
900 1170
600 780
500 650
kΩ
kΩ
kΩ
M1 (P1 = Ground)
M3 (P3 = Ground)
M9 (P9 = Ground)
l 315 450 585
l 105 150 195
l 35 50 65
kΩ
kΩ
kΩ
ΔR
Resistor Matching (Note 9)
450k Resistors
Other Resistors
l
0.02 0.08
%
l
0.04 0.12
%
ΔR/ΔT
Resistor Temperature Coefficient (Note 6) Resistor Matching
Absolute Value
l 0.3 3 ppm/°C
l –30 ppm/°C
1991fg
5
5 Page 
LT1991www.DataSheet4U.com
APPLICATIONS INFORMATION
The maximum voltage allowed on the P3, M3, P9, and
M9 inputs includes the positive and negative supply plus
a diode drop. These pins should not be driven more than
0.2V outside of the supply rails. This is because they are
connected through diodes to internal manufacturing post-
package trim circuitry, and through a substrate diode to
VEE. If more than 10mA is allowed to flow through these
pins, there is a risk that the LT1991 will be detrimmed or
damaged. The P1 and M1 inputs do not have clamp diodes
or substrate diodes or trim circuitry and can be taken well
outside the supply rails. The maximum allowed voltage on
the P1 and M1 pins is ±60V.
The input voltage range of the internal op amp extends
to within 1.2V of VCC and 1V of VEE. The voltage at which
the op amp inputs common mode is determined by the
voltage at the op amp’s +input, and this is determined by
the voltages on pins P1, P3, P9 and REF (see “Calculating
Input Voltage Range” section). This is true provided that
the op amp is functioning and feedback is maintaining the
inputs at the same voltage, which brings us to the third
requirement.
For valid circuit function, the op amp output must not be
clipped. The output will clip if the input signals are attempt-
ing to force it to within 40mV of its supply voltages. This
usually happens due to too large a signal level, but it can
also occur with zero input differential and must therefore
be included as an example of a common mode problem.
Consider Figure 1. This shows the LT1991 configured
5V
7
8 50k
9 150k
450k
4pF
10
–
VDM
0V+ 1
VCM
2.5V 2
450k
450k
150k
–
+
4pF
6
VOUT = 13 • VDM
3 50k
450k
4
REF 5
LT1991
1991 F01
Figure 1. Difference Amplifier Cannot Produce
0V on a Single Supply. Provide a Negative
Supply, or Raise Pin 5, or Provide 4mV of VDM
as a gain of 13 difference amplifier on a single supply
with the output REF connected to ground. This is a great
circuit, but it does not support VDM = 0V at any common
mode because the output clips into ground while trying
to produce 0VOUT. It can be fixed simply by declaring the
valid input differential range not to extend below +4mV,
or by elevating the REF pin above 40mV, or by providing
a negative supply.
Calculating Input Voltage Range
Figure 2 shows the LT1991 in the generalized case of
a difference amplifier, with the inputs shorted for the
common mode calculation. The values of RF and RG are
dictated by how the P inputs and REF pin are connected.
By superposition we can write:
VINT = VEXT • (RF/(RF + RG)) + VREF • (RG/(RF + RG))
Or, solving for VEXT:
VEXT = VINT • (1 + RG/RF) – VREF • RG/RF
But valid VINT voltages are limited to VCC – 1.2V and VEE
+ 1V, so:
MAX VEXT = (VCC – 1.2) • (1 + RG/RF) – VREF • RG/RF
and:
MIN VEXT = (VEE + 1) • (1 + RG/RF) – VREF • RG/RF
RF
VEXT
VCC
RG
–
VINT
RG
+
VEE
RF
VREF
1991 F02
Figure 2. Calculating CM Input Voltage Range
These two voltages represent the high and low extremes
of the common mode input range, if the other limits have
not already been exceeded (1 and 3, above). In most
cases, the inverting inputs M1 through M9 can be taken
further than these two extremes because doing this does
not move the op amp input common mode. To calculate
the limit on this additional range, see Figure 3. Note that,
1991fg
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LT1991.PDF ] | |
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