LTC1250
Very Low Noise
Zero-Drift Bridge Amplifier
FEATURES
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DESCRIPTIO
Very Low Noise: 0.75µV
P-P
Typ, 0.1Hz to 10Hz
DC to 1Hz Noise Lower Than OP-07
Full Output Swing into 1k Load
Offset Voltage: 10µV Max
Offset Voltage Drift: 50nV/°C Max
Common-Mode Rejection Ratio: 110dB Min
Power Supply Rejection Ratio: 115dB Min
No External Components Required
Pin-Compatible with Standard 8-Pin Op Amps
APPLICATI
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The LTC
®
1250 is a high performance, very low noise zero-
drift operational amplifier. The LTC1250’s combination of
low front-end noise and DC precision makes it ideal for use
with low impedance bridge transducers. The LTC1250
features typical input noise of 0.75µV
P-P
from 0.1Hz to
10Hz, and 0.2µV
P-P
from 0.1Hz to 1Hz. The LTC1250 has
DC to 1Hz noise of 0.35µV
P-P
, surpassing that of low noise
bipolar parts including the OP-07, OP-77, and LT1012.
The LTC1250 uses the industry-standard single op amp
pinout, and requires no external components or nulling
signals, allowing it to be a plug-in replacement for bipolar
op amps.
The LTC1250 incorporates an improved output stage
capable of driving 4.3V into a 1k load with a single 5V
supply; it will swing
±4.9V
into 5k with
±5V
supplies. The
input common mode range includes ground with single
power supply voltages above 12V. Supply current is 3mA
with a
±5V
supply, and overload recovery times from
positive and negative saturation are 0.5ms and 1.5ms,
respectively. The internal nulling clock is set at 5kHz for
optimum low frequency noise and offset drift; no external
connections are necessary.
The LTC1250 is available in standard 8-pin ceramic and
plastic DIPs, as well as an 8-pin SOIC package.
Electronic Scales
Strain Gauge Amplifiers
Thermocouple Amplifiers
High Resolution Data Acquisition
Low Noise Transducers
Instrumentation Amplifiers
and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATI
5V
50Ω
GAIN
TRIM
Differential Bridge Amplifier
5V
1000pF
Input Referred Noise 0.1Hz to 10Hz
2
V
S
= ±5V
A
V
= 10k
1
0.1µF
18.2k
µV
0
350Ω
STRAIN
GAUGE
2
–
+
7
6
A
V
= 100
LTC1250
3
4
–1
1000pF
–5V
18.2k
–5V
1250 TA01
–2
0
U
2
6
4
TIME (s)
8
10
LT1250 TA02
UO
UO
1
LTC1250
ABSOLUTE
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
NC 1
–IN 2
+IN 3
V
–
4
8
7
6
5
NC
V
+
OUT
NC
Total Supply Voltage (V
+
to V
–
) ............................. 18V
Input Voltage ........................ (V
+
+ 0.3V) to (V
–
– 0.3V)
Output Short Circuit Duration ......................... Indefinite
Operating Temperature Range
LTC1250M..................................... – 55°C to 125°C
LTC1250C .......................................... 0°C TO 70°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec.)................ 300°C
ORDER PART
NUMBER
LTC1250MJ8
LTC1250CJ8
LTC1250CN8
LTC1250CS8
S8 PART MARKING
1250
N8 PACKAGE
J8 PACKAGE
8-LEAD CERAMIC DIP 8-LEAD PLASTIC DIP
S8 PACKAGE
8-LEAD PLASTIC SOIC
T
JMAX
= 150°C,
θ
JA
= 100°CW (J8)
T
JMAX
= 110°C,
θ
JA
= 130°CW (N8)
T
JMAX
= 110°C,
θ
JA
= 200°CW (S8)
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
V
OS
Input Offset Voltage
∆V
OS
Average Input Offset Drift
Long Term Offset Drift
e
n
Input Noise Voltage (Note 2)
i
n
I
B
I
OS
CMRR
PSRR
A
VOL
Input Noise Current
Input Bias Current
Input Offset Current
Common-Mode Rejection Ratio
Power Supply Rejection Ratio
Large-Signal Voltage Gain
Maximum Output Voltage Swing
Slew Rate
Gain-Bandwidth Product
Supply Current
Internal Sampling Frequency
CONDITIONS
T
A
= 25°C (Note 1)
(Note 1)
V
IN
=
±5V,
T
A
= Operating Temperature Range, unless otherwise noted.
LTC1250M
MIN TYP
MAX
±5
±10
±0.01 ±0.05
50
0.75
1.0
0.2
4.0
±50
±150
±950
±100 ±300
±500
110
130
115
130
125
170
±4.0
4.3/–4.7
±4.92
10
1.5
3.0
4.0
7.0
4.75
MIN
LTC1250C
TYP
MAX
±5
±10
±0.01 ±0.05
50
0.75
1.0
0.2
4.0
±50
±200
±450
±100 ±400
±500
130
130
170
4.3 /–4.7
±4.95
10
1.5
3.0
4.0
5.0
4.75
UNITS
µV
µV/°C
nV/√Mo
µV
P-P
µV
P-P
fA/√Hz
pA
pA
pA
pA
dB
dB
dB
V
V
V/µs
MHz
mA
mA
kHz
q
T
A
= 25°C, 0.1Hz to 10Hz
T
A
= 25°C, 0.1Hz to 1Hz
f = 10Hz
T
A
= 25°C (Note 3)
q
T
A
= 25°C (Note 3)
q
SR
GBW
I
S
f
S
V
CM
= – 4V to 3V
V
S
=
±2.375V
to
±8V
R
L
= 10k, V
OUT
=
±4V
R
L
= 1k
R
L
= 100k
R
L
= 10k, C
L
= 50pF
No Load, T
A
= 25°C
q
q
q
q
110
115
125
±4.0
q
T
A
= 25°C
V
IN
= 5V, T
A
= Operating Temperature Range, unless otherwise noted.
SYMBOL
V
OS
∆V
OS
e
n
I
B
I
OS
PARAMETER
Input Offset Voltage
Average Input Offset Drift
Input Noise Voltage (Note 2)
Input Bias Current
Input Offset Current
CONDITIONS
T
A
= 25°C (Note 1)
(Note 1)
T
A
= 25°C, 0.1Hz to 10Hz
T
A
= 25°C, 0.1Hz to 1Hz
T
A
= 25°C (Note 3)
T
A
= 25°C (Note 3)
LTC1250M
MIN TYP
MAX
±2
±5
±0.01 ±0.05
1.0
0.3
±20
±100
±40
±200
LTC1250C
MIN
TYP
MAX
±2
±5
±0.01 ±0.05
1.0
0.3
±20
±100
±40
±200
UNITS
µV
µV/°C
µV
P-P
µV
P-P
pA
pA
q
2
U
W
U
U
W W
W
LTC1250
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
Maximum Output Voltage Swing
I
S
f
S
Supply Current
Sampling Frequency
CONDITIONS
R
L
= 1k
R
L
= 100k
T
A
= 25°C
T
A
= 25°C
V
IN
= 5V, T
A
= Operating Temperature Range, unless otherwise noted.
LTC1250M
MIN TYP
MAX
4.0
4.3
4.95
1.8
2.5
3
LTC1250C
MIN
TYP
MAX
4.0
4.3
4.95
1.8
2.5
3
UNITS
V
V
mA
kHz
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
These parametes are guaranteed by design. Thermocouple effects
preclude measurement of these voltage levels during automated testing.
Note 2:
0.1Hz to 10Hz noise is specified DC coupled in a 10s window;
0.1Hz to 1Hz noise is specified in a 100s window with an RC high-pass
filter at 0.1Hz. The LTC1250 is sample tested for noise; for 100% tested
parts contact LTC Marketing Dept.
Note 3:
At T
≤
0°C these parameters are guaranteed by design and not
tested.
TYPICAL PERFOR A CE CHARACTERISTICS
Input Noise vs Supply Voltage
1.6
T
A
= 25°C
1.4
SAMPLING FREQUENCY (kHz)
SUPPLY CURRENT (mA)
INPUT NOISE (µV
P-P
)
1.2
1.0
0.8
0.6
0.4
0.1Hz TO 1Hz
0.2
0
4
10
6
8
12
14
TOTAL SUPPLY VOLTAGE, V
+
TO V
–
(V)
16
0.1Hz TO 10Hz
Input Noise vs Temperature
1.2
V
S
= ±5V
1.0
0.8
0.1Hz TO 10Hz
0.6
0.4
0.1Hz TO 1Hz
0.2
0
–50 –25
SUPPLY CURRENT (mA)
SAMPLING FREQUENCY (kHz)
INPUT NOISE (µV
P-P
)
50
25
75
0
TEMPERATURE (°C)
U W
LTC1250 G01
Supply Current vs Supply Voltage
4.0
T
A
= 25°C
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
4
2
5
6
Sampling Frequency vs Supply
Voltage
T
A
= 25°C
4
3
10
6
8
12
14
TOTAL SUPPLY VOLTAGE, V
+
TO V
–
(V)
16
4
10
6
8
12
14
TOTAL SUPPLY VOLTAGE, V
+
TO V
–
(V)
16
LTC1250 G02
LTC1250 G03
Supply Current vs Temperature
4.5
V
S
= ±5V
7
8
Sampling Frequency vs
Temperature
V
S
= ±5V
6
5
4
3
2
1
4.0
3.5
3.0
2.5
100
125
2.0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
0
–50 –25
0
75
50
25
TEMPERATURE (°C)
100
150
LTC1250 G04
LTC1250 G05
LTC1250 G06
3
LTC1250
TYPICAL PERFOR A CE CHARACTERISTICS
Voltage Noise vs Frequency
80
70
VOLTAGE NOISE (nV/√Hz)
100
V
S
= ±5V
R
S
= 10Ω
40
30
20
10
0
1
10
100
1k
FREQUENCY (Hz)
10k
LTC1250 G11
GAIN (dB)
50
60
GAIN
40
20
0
–20
1k
10k
V
S
= ±5V OR
SINGLE 5V
T
A
= 25°C
C
L
= 100pF
PHASE:
R
L
= 100k
60
40
BIAS CURRENT (
|
pA
|
)
60
Overload Recovery
8
INPUT (V)
INPUT COMMON MODE RANGE (V)
0.2
0
0
OUTPUT (V)
CMRR (dB)
–5
500µs/DIV
A
V
= 100, R
L
= 100k, C
L
= 50pF, V
S
=
±5V
Transient Response
10
9
8
OUTPUT SWING (±V)
2V/DIV
OUTPUT SWING (V)
1µs/DIV
A
V
= 1, R
L
= 100k, C
L
= 50pF, V
S
=
±5V
4
U W
Gain/Phase vs Frequency
100
80
Bias Current (Magnitude) vs
Temperature
1000
V
S
= ±5V
80
PHASE MARGIN (DEG)
100
PHASE:
R
L
= 1k
20
0
100k
1M
FREQUENCY (Hz)
–20
10M
LTC1250 G10
10
–50
–25
50
75
0
25
TEMPERATURE (°C)
100
125
LTC1250 G14
Common-Mode Input Range
vs Supply Voltage
140
T
A
= 25°C
6
4
2
0
–2
–4
–6
–8
2
3
5
4
6
SUPPLY VOLTAGE (±V)
7
8
Common-Mode Rejection Ratio
vs Frequency
120
100
80
60
40
20
0
1
10
100
1k
FREQUENCY (Hz)
10k
100k
V
S
= ±5V
V
CM
= 1V
RMS
LTC1250 G07
LTC1250 G12
Output Swing vs Load
Resistance, Dual Supplies
18
Output Voltage Swing vs Load
Resistance, Single Supply
16
14
12
V
S
= 10V
10
8
6
4
V
S
= 5V
V
–
= GND
R
L
TO GND
0
1
2
3 4 5 6 7 8
LOAD RESISTANCE (kΩ)
9
10
V
S
= 16V
R
L
TO GND
V
S
= ±8V
7
6
5
4
3
2
1
0
0
1
2
NEGATIVE SWING
POSITIVE SWING
3 4 5 6 7 8
LOAD RESISTANCE (kΩ)
9
10
V
S
= ±2.5V
V
S
= ±5V
2
0
LTC1250 G08
LTC1250 G09
LTC1250
TYPICAL PERFOR A CE CHARACTERISTICS
Output Swing vs Output Current,
±5V
Supply
5
4
3
OUTPUT VOLTAGE (V)
V
S
= ±5V
5
SHORT-CIRCUIT CURRENT (mA)
2
1
0
–1
–2
–3
–4
–5
0.01
0.1
1
OUTPUT CURRENT (mA)
10
LTC1250 G16
OUTPUT VOLTAGE (V)
TEST CIRCUITS
Offset Test Circuit
100pF
100pF
100k
5V
2
10Ω
3
–
+
7
6
OUTPUT
LTC1250
4
–5V
1250 TC01
APPLICATI
Input Noise
S I FOR ATIO
The LTC1250, like all CMOS amplifiers, exhibits two types
of low frequency noise: thermal noise and 1/f noise. The
LTC1250 uses several design modifications to minimize
these noise sources. Thermal noise is minimized by rais-
ing the g
M
of the front-end transistors by running them at
high bias levels and using large transistor geometries. 1/f
noise is combated by optimizing the zero-drift nulling loop
to run at twice the 1/f corner frequency, allowing it to
reduce the inherently high CMOS 1/f noise to near thermal
levels at low frequencies. The resultant noise spectrum is
quite low at frequencies below the internal 5kHz clock
VOLTAGE NOISE (nV/√Hz)
U
W
U W
Output Swing vs Output Current,
Single 5V Supply
6
V
S
= SINGLE 5V
40
30
20
10
0
–10
–20
–30
Short-Circuit Current
vs Temperature
V
S
= ±15V
V
OUT
= V
–
4
3
2
1
0
0.01
V
OUT
= V
+
0.1
1
OUTPUT CURRENT (mA)
10
LTC1250 G17
–40
–50 –25
0
50
25
75
TEMPERATURE (°C)
100
125
LTC1250 G18
DC to 10Hz Noise Test Circuit
(for DC to 1Hz Multiply All Capacitor Values by 10)
100k
5V
2
10Ω
3
5V
2
6
800k
3
–
+
7
–
8
1
800k
0.04µF
800k
6
–
1/2
LT1057
7
OUTPUT
LTC1250
4
–5V
1/2
LT1057
+
4
–5V
5
+
0.02µF
0.01µF
1250 TC02
U
UO
80
70
OP-27
60
50
40
30
20
10
0
0.01
0.1
FREQUENCY (Hz)
1
LTC1250 F01
OP-07
V
S
= ±5V
R
S
= 10Ω
LTC1250
Figure 1. Voltage Noise vs Frequency
5
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