LT1880 - SOT-23, Rail-to-Rail Output, Picoamp Input Current Precision Op Amp

LT1880
SOT-23, Rail-to-Rail Output,
Picoamp Input Current
Precision Op Amp
DESCRIPTION
FEATURES
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Offset Voltage: 150μV Max
Input Bias Current: 900pA Max
Offset Voltage Drift: 1.2μV/°C Max
Rail-to-Rail Output Swing
Operates with Single or Split Supplies
Open-Loop Voltage Gain: 1 Million Min
1.2mA Supply Current
Slew Rate: 0.4V/μs
Gain Bandwidth: 1.1MHz
Low Noise: 13nV/√Hz at 1kHz
Low Profile (1mm) ThinSOT™ Package
The LT®1880 op amp brings high accuracy input performance and rail-to-rail output swing to the SOT-23 package.
Input offset voltage is trimmed to less than 150μV and
the low drift maintains this accuracy over the operating
temperature range. Input bias current is an ultralow 900pA
maximum.
The amplifier works on any total power supply voltage
between 2.7V and 36V (fully specified from 5V to ±15V).
Output voltage swings to within 55mV of the negative
supply and 250mV of the positive supply, which makes
the amplifier a good choice for low voltage single supply
operation.
APPLICATIONS
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Slew rates of 0.4V/μs with a supply current of 1.2mA give
superior response and settling time performance in a low
power precision amplifier.
Thermocouple Amplifiers
Bridge Transducer Conditioners
Instrumentation Amplifiers
Battery-Powered Systems
Photocurrent Amplifiers
The LT1880 is available in a 5-lead SOT-23 package.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
TYPICAL APPLICATION
Precision Photodiode Amplifier
Distribution of Input Offset Voltage
C1
39pF
35
R1
100k, 1%
VS+
VL
–
LT1880
S1
+
OUT
VOUT = 0.1V/μA
PERCENT OF UNITS (%)
30
25
20
15
10
5
VS–
1880 TA01
320μV OUTPUT OFFSET, WORST CASE OVER 0°C TO 70°C
60kHz BANDWIDTH
5.8μs RISE TIME, 10% TO 90%, 100mV OUTPUT STEP
52μVRMS OUTPUT NOISE, MEASURED ON A 100kHz BW
VS = ±1.5V TO ±18V
S1: SIEMENS INFINEON BPW21 PHOTODIODE (~580pF)
0
–140 –100
100
60
–60 –20 20
INPUT OFFSET VOLTAGE (μV)
140
1880 TA01b
1880fa
1
LT1880
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
Supply Voltage (V + to V –) .........................................40V
Differential Input Voltage (Note 2) .......................... ±10V
Input Voltage......................................................V + to V –
Input Current (Note 2) .......................................... ±10mA
Output Short-Circuit Duration (Note 3) ............ Indefinite
Operating Temperature Range (Note 4) ...– 40°C to 85°C
Specified Temperature Range (Note 5) ....– 40°C to 85°C
Maximum Junction Temperature .......................... 150°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
TOP VIEW
5 V+
OUT 1
V– 2
+IN 3
4 –IN
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
TJMAX = 150°C, θJA = 250°C/W
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
SPECIFIED TEMPERATURE RANGE
LT1880CS5#PBF
LT1880CS5#TRPBF
LTUM
5-Lead Plastic TSOT-23
0°C to 70°C
LT1880IS5#PBF
LT1880IS5#TRPBF
LTVW
5-Lead Plastic TSOT-23
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VS = 5V, 0V; VCM = 2.5V unless otherwise noted. (Note 5)
SYMBOL PARAMETER
VOS
Input Offset Voltage
Input Offset Voltage Drift
(Note 6)
IOS
IB
CONDITIONS
MIN
0°C < TA < 70°C
–40°C < TA < 85°C
l
l
0°C < TA < 70°C
–40°C < TA < 85°C
l
l
0°C < TA < 70°C
–40°C < TA < 85°C
l
l
0°C < TA < 70°C
–40°C < TA < 85°C
l
l
Input Offset Current
Input Bias Current
TYP
MAX
UNITS
40
150
200
250
μV
μV
μV
0.3
0.3
1.2
1.2
μV/°C
μV/°C
150
900
1200
1400
pA
pA
pA
150
900
1200
1500
pA
pA
pA
Input Noise Voltage
0.1Hz to 10Hz
0.5
μVp-p
en
Input Noise Voltage Density
f = 1kHz
13
nV/√Hz
in
Input Noise Current Density
f = 1kHz
0.07
pA/√Hz
RIN
Input Resistance
Differential
Common Mode, VCM = 1V to 3.8V
380
210
MΩ
GΩ
CIN
Input Capacitance
VCM
Input Voltage Range
3.7
l
(V– + 1.0)
pF
(V+ – 1.2)
V
1880fa
2
LT1880
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VS = 5V, 0V; VCM = 2.5V unless otherwise noted. (Note 5)
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
CMRR
Common Mode Rejection Ratio
1V < VCM < 3.8V
l
116
135
dB
Power Supply Rejection Ratio
V– = 0V, V
l
110
135
dB
500
400
400
300
300
250
1600
PSRR
CM
= 1.5V; 2.7V < V+ < 32V
l
Minimum Operating Supply Voltage
AVOL
Large Signal Voltage Gain
RL = 10k; 1V < VOUT < 4V
RL = 2k; 1V < VOUT < 4V
RL = 1k; 1V < VOUT < 4V
l
l
l
2.4
MAX
UNITS
2.7
V
V/mV
V/mV
V/mV
V/mV
V/mV
V/mV
800
400
VOL
Output Voltage Swing Low
No Load
ISINK = 100μA
ISINK = 1mA
l
l
l
20
35
130
55
65
200
mV
mV
mV
VOH
Output Voltage Swing High
(Referred to V+)
V+ = 5V; No Load
V+ = 5V; ISOURCE = 100μA
V+ = 5V; ISOURCE = 1mA
l
l
l
130
150
220
250
270
380
mV
mV
mV
IS
Supply Current per Amplifier
V+ = 3V
1.2
1.8
2.2
mA
mA
1.2
1.9
2.3
mA
mA
1.35
2
2.4
mA
mA
V+ = 5V
V+ = 12V
ISC
Short-Circuit Current
VOUT Short to GND
VOUT Short to V+
GBW
Gain-Bandwidth Product
f = 20kHz
tS
Settling Time
0.01%, VOUT = 1.5V to 3.5V
AV = –1, RL = 2k
FPBW
Full Power Bandwidth (Note 7)
VOUT = 4VP-P
THD
Total Harmonic Distortion and Noise
VO = 2VP-P, AV = –1, f = 1kHz, Rf = 1k, BW = 22kHz
VO = 2VP-P, AV = 1, f = 1kHz, RL = 10k, BW = 22kHz
SR+
Slew Rate Positive
AV = –1
SR –
Slew Rate Negative
AV = –1
l
l
l
l
l
10
10
18
20
mA
mA
0.8
1.1
MHz
10
μs
32
kHz
0.002
0.0008
%
%
l
0.25
0.2
0.4
V/μs
V/μs
l
0.25
0.25
0.55
V/μs
V/μs
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VS= ±15V, VCM = 0V unless otherwise noted. (Note 5)
SYMBOL PARAMETER
VOS
Input Offset Voltage
Input Offset Voltage Drift
(Note 6)
IOS
IB
CONDITIONS
0°C < TA < 70°C
–40°C < TA < 85°C
l
l
0°C < TA < 70°C
–40°C < TA < 85°C
l
l
0°C < TA < 70°C
–40°C < TA < 85°C
l
l
0°C < TA < 70°C
–40°C < TA < 85°C
l
l
Input Offset Current
Input Bias Current
Input Noise Voltage
MIN
0.1Hz to 10Hz
TYP
MAX
UNITS
40
150
200
250
μV
μV
μV
0.3
0.3
1.2
1.2
μV/°C
μV/°C
150
900
1200
1400
pA
pA
pA
150
900
1200
1500
pA
pA
pA
0.5
μV/p-p
1880fa
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LT1880
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VS = ± 15V; VCM = 0V unless otherwise noted. (Note 5)
SYMBOL PARAMETER
en
Input Noise Voltage Density
in
RIN
CIN
Input Capacitance
VCM
Input Voltage Range
CONDITIONS
MIN
TYP
MAX
UNITS
f = 1kHz
13
nV/√Hz
Input Noise Current Density
f = 1kHz
0.07
pA/√Hz
Input Resistance
Differential
Common Mode, VCM = –13.5V to 13.5V
380
190
MΩ
GΩ
3.7
pF
l
–13.5
13.5
V
CMRR
Common Mode Rejection Ratio
–13.5V < VCM < 13.5V
l
118
135
dB
+PSRR
Positive Power Supply Rejection
Ratio
V – = –15V, VCM = 0V; 1.5V < V+ < 18V
l
110
135
dB
–PSRR
Negative Power Supply Rejection
Ratio
V + = 15V, VCM = 0V; –1.5V < V – < –18V
l
110
135
dB
l
Minimum Operating Supply Voltage
AVOL
Large Signal Voltage Gain
RL = 10k; –13.5V < VOUT < 13.5V
RL = 2k; –13.5V < VOUT < 13.5V
l
l
±1.2
1000
700
500
300
±1.35
1600
V
V/mV
V/mV
V/mV
V/mV
1000
VOL
Output Voltage Swing Low
(Referred to VEE)
No Load
ISINK = 100μA
ISINK = 1mA
l
l
l
25
35
130
65
75
200
mV
mV
mV
VOH
Output Voltage Swing High
(Referred to VCC)
No Load
ISINK = 100μA
ISINK = 1mA
l
l
l
185
195
270
350
370
450
mV
mV
mV
IS
Supply Current per Amplifier
l
1.5
1.8
2.3
2.8
mA
mA
ISC
Short-Circuit Current
VOUT Short to V –
VOUT Short to V +
FPBW
Full Power Bandwidth (Note 7)
VOUT = 14VP-P
GBW
Gain Bandwidth Product
f = 20kHz
THD
Total Harmonic Distortion and Noise
VO = 25VP-P, AV = –1, f = 100kHz, Rf = 10k, BW = 22kHz
VO = 25VP-P, AV = 1, f = 100kHz, RL = 10k, BW = 22kHz
SR+
Slew Rate Positive
AV = –1
SR –
Slew Rate Negative
AV = –1
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The inputs are protected by back-to-back diodes. If the differential
input voltage exceeds 10V, see Application Information, the input current
should be limited to less than 10mA.
Note 3: A heat sink may be required to keep the junction temperature
below absolute maximum ratings.
l
10
10
25
25
mA
mA
l
10
10
20
20
mA
mA
9
kHz
0.8
1.1
MHz
0.00029
0.00029
%
%
l
0.25
0.2
0.4
V/μs
V/μs
l
0.25
0.2
0.55
V/μs
V/μs
Note 4: The LT1880C and LT1880I are guaranteed functional over the
operating temperature range of –40°C to 85°C.
Note 5: The LT1880C is guaranteed to meet specified performance from
0°C to 70°C and is designed, characterized and expected to meet specified
performance from –40°C to 85°C but is not tested or QA sampled at these
temperatures. The LT1880I is guaranteed to meet specified performance
from –40°C to 85°C.
Note 6: This parameter is not 100% tested.
Note 7: Full power bandwidth is calculated from the slew rate.
FPBW = SR/(2πVP)
1880fa
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LT1880
TYPICAL PERFORMANCE CHARACTERISTICS
Input Offset Voltage
vs Temperature
100
50
0
–50
–100
–150
1000
TA = 25°C
TA = –40°C
TA = 85°C
800
INPUT BIAS CURRENT (pA)
600
400
IB–
200
0
–200
IB+
–400
–600
5
25
45 65 85 105 125
TEMPERATURE (°C)
IB+
–500
–500
IB+
–1000
–14.6
TA = –40°C
TA = 25°C
TA = 85°C
–13.8
–14.2
–13.4
COMMON MODE VOLTAGE (V)
OUTPUT VOLTAGE
SWING (V+)
INPUT BIAS CURRENT (pA)
IB–
IB–
100
50
0
–50
–100
IB+
–150
–200
–250
–13.0
–300
–50
–25
25
50
0
TEMPERATURE (°C)
75
Warm Up Drift
6
CURRENT NOISE DENSITY (fA/√Hz)
VOLTAGE NOISE DENSITY (nV/√Hz)
5
VS = ±15V
3
2
VS = ±2.5V
1
1
2
3
4
TIME AFTER POWER ON (MIN)
5
1880 G05
TA = 25°C
–1.5
1.5
TA = 25°C
1.0
TA = 85°C
0.5
TA = –40°C
10
8
1880 G04
0.1 to 10Hz Noise
VS = ±15V
TA = 25°C
CURRENT NOISE
100
VOLTAGE NOISE
10
VS = ±15V
TA = 25°C
1
0
TA = 85°C
–1.0
–10 –8 –6 –4 –2 0 2
4 6
OUTPUT CURRENT (mA)
en, in vs Frequency
1000
TA = 25°C
4
100
TA = –40°C
–0.5
1880 G03
1880 G02B
14.6
Output Voltage Swing
vs Load Current
VS = ±15V
150
500
13.8
14.2
13.4
COMMON MODE VOLTAGE (V)
1880 G02A
OUTPUT VOLTAGE
SWING (V–)
VS = ±15V
0
–1000
13.0
Input Bias Current vs Temperature
200
1000
15
1880 G02
Input Bias Current
vs Common Mode Near VEE
INPUT BIAS CURRENT (pA)
0
TA = –45°C
TA = 25°C
TA = 85°C
VS = ±15V
–1000
–10
0
5
10
–15
–5
COMMON MODE VOLTAGE (V)
1880 G01
OFFSET VOLTAGE CHANGE (μV)
500
–800
–200
–55 –35 –15
0
VS = ±15V
IB–
NOISE VOLTAGE (0.2μV/DIV)
INPUT OFFSET VOLTAGE (μV)
1000
TEMPCO: –55°C TO 125°C
10 REPRESENTATIVE UNITS
150
Input Bias Current
vs Common Mode Near VCC
INPUT BIAS CURRENT (pA)
200
Input Bias Current
vs Common Mode Voltage
1
10
100
FREQUENCY (Hz)
1k
1880 G08
0
2
6
4
TIME (SEC)
8
10
1880 G09a
1880fa
5
LT1880
TYPICAL PERFORMANCE CHARACTERISTICS
0.01 to 1Hz Noise
PSRR vs Frequency
Gain vs Frequency
140
160
POWER SUPPLY REJECTION RATIO (dB)
VS = ±15V
NOISE VOLTAGE (0.2μV/DIV)
120
100
GAIN (dB)
80
60
40
20
0
VS = ±15V
TA = 25°C
60
40
TIME (SEC)
80
10
1
0.1
VOLTAGE GAIN (dB)
100
80
60
40
20
0
100k
40
PHASE SHIFT
–20
GAIN
0
–40
–10
–60
–20
–80
20
15
10
25
SETTLING TIME (μs)
30
35
1880 G15
0.1%
0.01%
2
0
–2
–4
0.01%
0.1%
–8
–10
0
5
10
35
15 20 25 30
SETTLING TIME (μs)
1880 G14
VS = ±15V
SLEW RATE
0.4
68
0.3
1.10
–50
&M
60
GBW
–25
25
50
0
TEMPERATURE (°C)
40
Slew Rate, Gain-Bandwidth
Product and Phase Margin
vs Power Supply
75
100
1880 G16
SLEW RATE (V/μs)
SLEW RATE (V/μs)
0.5
GAIN BANDWIDTH
PRODUCT (MHz)
OUTPUT STEP (V)
–10
VS = ±15V
AV = –1
1880 G13
1.12
–8
100k 1M
0.5
TA = 25°C
0.4
SLEW RATE
64
0.3
&M
60
1.12
56
1.11
PHASE MARGIN (DEG)
0.01%
10 100 1k 10k
FREQUENCY (Hz)
–6
–100
10M
100k
1M
FREQUENCY (Hz)
1.14
5
4
PHASE MARGIN (DEG)
0.01%
–2
0
6
40
0
64
0.1%
60
10
0
–6
8
Slew Rate, Gain-Bandwidth
Product and Phase Margin
vs Temperature
2
–4
80
20
Settling Time vs Output Step
0.1%
10
20
1880 G12
4
100
30
–30
10k
1M
VS = ±15V
AV = 1
1
1880 G11
OUTPUT STEP (V)
50
6
20
Settling Time vs Output Step
VS = ±15V
60
120
8
40
0
0.1
PHASE SHIFT (DEG)
POWER SUPPLY REJECTION RATIO (dB)
VS = ±15V
100
1k
10k
FREQUENCY (Hz)
+PSRR
60
Gain and Phase vs Frequency
70
140
10
–PSRR
80
1880 G10
CMRR vs Frequency
160
10
100
100 1k 10k 100k 1M 10M
FREQUENCY (Hz)
1880 G09b
1
120
–40
100
GAIN BANDWIDTH
PRODUCT (MHz)
20
0
–20
VS = ±15V
140
GBW
1.10
0
2.5
7.5
10
5
POWER SUPPLY (±V)
12.5
15
1880 G17
1880fa
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LT1880
TYPICAL PERFORMANCE CHARACTERISTICS
Gain vs Frequency
with CLOAD, AV = –1
Gain vs Frequency
with CLOAD, AV = 1
0
0
1000pF
–10
0pF
500pF
500pF
GAIN (dB)
GAIN (dB)
1000pF
–20
–30
–40
Output Impedance vs Frequency
100
10
–10
0pF
–20
OUTPUT IMPEDANCE (Ω)
10
VS = ±15V
10
AV = 100
AV = 10
1.0
AV = 1
0.1
–30
10k
1k
100k
1M
FREQUENCY (Hz)
10M
–40
100M
1k
10k
100k
1M
FREQUENCY (Hz)
1880 G18
10M
100M
0.01
0.01
0.1
1.0
10
FREQUENCY (MHz)
1880 G17A
1880 G19
Total Harmonic Distortion + Noise
vs Frequency
100
Small Signal Response
Small Signal Response
THD + NOISE (%)
10
VS = 5V, 0V
VCM = 2.5V
R = R = 1k
1.0 V f =G 2V
OUT
P-P
RL = 10k
VOUT
(20mV/DIV)
VOUT
(20mV/DIV)
0.1
0.01
AV = –1
0.001
AV = –1
NO LOAD
AV = 1
0.0001
10
100
1k
10k
FREQUENCY (Hz)
TIME (2μs/DIV)
1880 G20
AV = 1
NO LOAD
TIME (2μs/DIV)
1880 G21
100k
1880 G17B
Small Signal Response
Large Signal Response
VOUT
(20mV/DIV)
Large Signal Response
VOUT
(5V/DIV)
VOUT
(5V/DIV)
AV = 1
CL = 500pF
TIME (2μs/DIV)
1880 G22
AV = –1
TIME (50μs/DIV)
1880 G23
AV = 1
TIME (50μs/DIV)
1880 G24
1880fa
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LT1880
APPLICATIONS INFORMATION
Preserving Input Precision
Preserving the input voltage accuracy of the LT1880
requires that the applications circuit and PC board layout
do not introduce errors comparable to or greater than the
40μV offset. Temperature differentials across the input
connections can generate thermocouple voltages of 10’s
of microvolts. PC board layouts should keep connections
to the amplifier’s input pins close together and away from
heat dissipating components. Air currents across the board
can also generate temperature differentials.
The extremely low input bias currents, 150pA, allow high
accuracy to be maintained with high impedance sources and
feedback networks. The LT1880’s low input bias currents
are obtained by using a cancellation circuit on-chip. This
causes the resulting IBIAS+ and IBIAS– to be uncorrelated, as
implied by the lOS specification being comparable to IBIAS.
The user should not try to balance the input resistances in
each input lead, as is commonly recommended with most
amplifiers. The impedance at either input should be kept
as small as possible to minimize total circuit error.
PC board layout is important to insure that leakage currents
do not corrupt the low IBIAS of the amplifier. In high
precision, high impedance circuits, the input pins should
be surrounded by a guard ring of PC board interconnect,
with the guard driven to the same common mode voltage
as the amplifier inputs.
Input Common Mode Range
The LT1880 output is able to swing nearly to each power
supply rail, but the input stage is limited to operating
between V – + 1V and V+ – 1.2V. Exceeding this common
mode range will cause the gain to drop to zero, however
no gain reversal will occur.
Input Protection
The inverting and noninverting input pins of the LT1880
have limited on-chip protection. ESD protection is provided
to prevent damage during handling. The input transistors
have voltage clamping and limiting resistors to protect
against input differentials up to 10V. Short transients
above this level will also be tolerated. If the input pins can
see a sustained differential voltage above 10V, external
limiting resistors should be used to prevent damage to
the amplifier. A 1k resistor in each input lead will provide
protection against a 30V differential voltage.
Capacitive Loads
The LT1880 can drive capacitive loads up to 600pF in unity
gain. The capacitive load driving capability increases as
the amplifier is used in higher gain configurations, see the
graph labled Capacitive Load Response. Capacitive load
driving may be increased by decoupling the capacitance
from the output with a small resistance.
Capacitance Load Response
30
VS = ±15V
TA = 25°C
25
OVERSHOOT (%)
The LT1880 single op amp features exceptional input
precision with rail-to-rail output swing. Slew rate and small
signal bandwidth are superior to other amplifiers with
comparable input precision. These characteristics make
the LT1880 a convenient choice for precision low voltage
systems and for improved AC performance in higher voltage
precision systems. Obtaining beneficial advantage of the
precision inherent in the amplifier depends upon proper
applications circuit design and board layout.
20
15
AV = 1
10
5
0
AV = 10
10
100
1000
CAPACITIVE LOAD (pF)
10000
1880 G25
Getting Rail-to-Rail Operation without Rail-to-Rail
Inputs
The LT1880 does not have rail-to-rail inputs, but for most
inverting applications and noninverting gain applications,
this is largely inconsequential. Figure 1 shows the basic
op amp configurations, what happens to the op amp
inputs, and whether or not the op amp must have railto-rail inputs.
1880fa
8
LT1880
APPLICATIONS INFORMATION
+
VREF
RG
+
VIN
–
VIN
+
VIN
–
–
RF
RF
RG
VREF
INVERTING: AV = –RF /RG
OP AMP INPUTS DO NOT MOVE,
BUT ARE FIXED AT DC BIAS
POINT VREF
NONINVERTING: AV = 1 +RF /RG
INPUTS MOVE BY AS MUCH AS
VIN, BUT THE OUTPUT MOVES
MORE
INPUT DOES NOT HAVE TO BE
RAIL-TO-RAIL
INPUT MAY NOT HAVE TO BE
RAIL-TO-RAIL
NONINVERTING: AV = +1
INPUTS MOVE AS MUCH AS
OUTPUT
INPUT MUST BE
RAIL-TO-RAIL FOR OVERALL
CIRCUIT RAIL-TO-RAIL
PERFORMANCE
1880 F01
Figure 1. Some Op Amp Configurations Do Not Require
Rail-to Rail Inputs to Achieve Rail-to-Rail Outputs
The circuit of Figure 2 shows an extreme example of the
inverting case. The input voltage at the 1M resistor can
swing ±13.5V and the LT1880 will output an inverted,
divided-by-ten version of the input voltage. The input
accuracy is limited by the resistors to 0.2%. Output
referred, this error becomes 2.7mV. The 40μV input offset
voltage contribution, plus the additional error due to input
bias current times the ~100k effective source impedance,
contribute only negligibly to error.
1.5V
±13.5V SWINGS
WELL OUTSIDE
SUPPLY RAILS
±1.35V
OUTPUT
SWING
+
LT1880
VIN
–
Precision Photodiode Amplifier
Photodiode amplifiers usually employ JFET op amps because of their low bias current; however, when precision
is required, JFET op amps are generally inadequate due to
their relatively high input offset voltage and drift. The
LT1880 provides a high degree of precision with very low
bias current (IB = 150pA typical) and is therefore applicable to this demanding task. Figure 3 shows an LT1880
configured as a transimpedance photodiode amplifier.
CF
WORST-CASE
OUTPUT OFFSET
≤196μV AT 25°C
≤262μV 0°C TO 70°C
≤323μV –40°C TO 85°C
RF 51.1k
5V
1M, 0.1%
100k, 0.1%
–1.5V
–
PHOTODIODE
(SEE TEXT)
CD
LT1880
+
OUT
1880 F02
Figure 2. Extreme Inverting Case: Circuit Operates Properly with
Input Voltage Swing Well Outside Op Amp Supply Rails.
–5V
1880 F02
Figure 3. Precision Photodiode Amplifier
1880fa
9
LT1880
APPLICATIONS INFORMATION
The transimpedance gain is set to 51.1kΩ by RF. The
feedback capacitor, CF, may be as large as desired where
response time is not an issue, or it may be selected for
maximally flat response and highest possible bandwidth
given a photodiode capacitance CD. Figure 4 shows a
chart of CF and rise time versus CD for maximally flat
response. Total output offset is below 262μV, worst-case,
over temperature (0°C to 70°C). With a 5V output swing,
this guarantees a minimum 86dB dynamic range over
temperature (0°C to 70°C), and a full-scale photodiode
current of 98μA.
Single-Supply Current Source for Platinum RTD
The precision, low bias current input stage of the LT1880
makes it ideal for precision integrators and current
sources. Figure 5 shows the LT1880 providing a simple
precision current source for a remote 1kΩ RTD on a 4-wire
connection. The LT1634 reference places 1.25V at the
noninverting input of the LT1880, which then maintains
its inverting input at the same voltage by driving 1mA
of current through the RTD and the total 1.25kΩ of
resistance set by R1 and R2. Imprecise components R4
and C1 ensure circuit stability, which would otherwise be
excessively dependant on the cable characteristics. R5 is
also noncritical and is included to improve ESD immunity
and decouple any cable capacitance from the LT1880’s
output. The 4-wire cable allows Kelvin sensing of the RTD
voltage while excluding the cable IR drops from the voltage
reading. With 1mA excitation, a 1kΩ RTD will have 1V
across it at 0°C, and +3.85mV/°C temperature response.
This voltage can be easily read in myriad ways, with the
best method depending on the temperature region to be
emphasized and the particular ADC that will be reading
the voltage.
R5
180Ω, 5%
RISE TIME (μs), CF (pF)
100
+
CF
10
VOUT = 1.00V AT 0°C + 3.85mV/°C
– –50°C TO 600°C
1kΩ
AT 0°C
RTD*
RISE TIME
1
R4
1k, 5%
100mV OUTPUT STEP
0.1
0.1
1
10
CD (pF)
100
1000
1880 F04
Figure 4. Feedback CF and Rise Time vs Photodiode CD
R1
1.24K
0.1%
R2
10Ω
1%
C1
0.1μF
5V
–
+
LT1880
R3
150k, 1%
LT1634ACS8
5V
-1.25
*OMEGA F3141 1kΩ, 0.1% PLATINUM RTD
(800) 826-6342
1880 F05
Figure 5. Single Supply Current Source for Platinum RTD
1880fa
10
LT1880
SIMPLIFIED SCHEMATIC
V+
5
R3
R4
100μA
CX1
R27
R5
Q41
Q23
Q6
Q38
RCM1
Q5
CM1
Q4
Q3
Q58
Q47
B
A
Q59
1 OUT
35μA
Q48
Q12
RCM2
CM2
Q16
V–
R1
500Ω
CM3
Q46
C
B
A
–IN 4
+IN 3
Q14
7μA
R2
500Ω
Q24
Q1
Q2
10μA
Q20
R22
500Ω
Q45
Q7
Q44
Q8
R38
21μA
V– 2
1880 SD
PACKAGE DESCRIPTION
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
0.62
MAX
0.95
REF
2.90 BSC
(NOTE 4)
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
0.09 – 0.20
(NOTE 3)
1.90 BSC
S5 TSOT-23 0302 REV B
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
1880fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LT1880
TYPICAL APPLICATION
All SOT-23 JFET Input Transimpedance Photodiode Amplifier
C4
1.2pF
V+
R5
100k, 1%
1k
TIME DOMAIN
RESPONSE TRIM
C5
1.2pF
J1
R2
220k, 5%
C1
0.01μF
+
R7
47Ω
5%
U1
LT1880
R1
220k, 5%
–
S1
R3
10k
5%
C2
0.1μF
N1
R6
47Ω
5%
C3
0.01μF
V–
–
U2
LT1806
VOUT
+
J1: ON SEMI MMBF4416 JFET
N1:ON SEMI MMBT3904 NPN
S1: SIEMENS/INFINEON SFH213FA PHOTODIODE (~3pF)
VSUPPLY = ±5V
BANDWIDTH = 7MHz
NOISE FIGURE = 2dB AT 100kHz, 25°C
AZ = 100kΩ
1880 TA02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1782
Rugged, General Purpose SOT-23 Op Amp
Rail-to-Rail I/O
LT1792
Low Noise JFET Op Amp
4.2nV/√Hz
LT1881/LT1882
Dual/Quad Precision Op Amps
50μV VOS(MAX), 200pA IB(MAX) Rail-to-Rail Output
LTC2050
Zero Drift Op Amp in SOT-23
3μV VOS(MAX), Rail-to-Rail Output
LT6010
135μA Rail-to-Rail Output Precision Op Amp
Lower Power Version of LT1880
1880fa
12 Linear Technology Corporation
LT 0909 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2009