LINER LT1792 Low noise, precision, jfet input op amp Datasheet

LT1792
Low Noise, Precision,
JFET Input Op Amp
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FEATURES
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DESCRIPTIO
The LT®1792 achieves a new standard of excellence in
noise performance for a JFET op amp. The 4.2nV/√Hz
voltage noise combined with low current noise and
picoampere bias currents make the LT1792 an ideal choice
for amplifying low level signals from high impedance
capacitive transducers.
100% Tested Low Voltage Noise: 6nV/√Hz Max
A Grade 100% Temperature Tested
Voltage Gain: 1.2 Million Min
Offset Voltage Over Temp: 800µV Max
Gain-Bandwidth Product: 5.6MHz Typ
Guaranteed Specifications with ±5V Supplies
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APPLICATIO S
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Photocurrent Amplifiers
Hydrophone Amplifiers
High Sensitivity Piezoelectric Accelerometers
Low Voltage and Current Noise Instrumentation
Amplifier Front Ends
Two and Three Op Amp Instrumentation Amplifiers
Active Filters
The LT1792 is unconditionally stable for gains of 1 or more,
even with load capacitances up to 1000pF. Other key
features are 600µV VOS and a voltage gain of over 4 million.
Each individual amplifier is 100% tested for voltage noise,
slew rate and gain bandwidth.
The design of the LT1792 has been optimized to achieve
true precision performance with an industry standard
pinout in the SO-8 package. Specifications are also provided for ±5V supplies.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
Low Noise Hydrophone Amplifier with DC Servo
R3
3.9k
5V TO 15V
2
–
40
7
LT1792
3
C1*
6
+
R2
200Ω
OUTPUT
C2
0.47µF
4
–5V TO –15V
R6
100k
6
2
3
R5
1M
LT1097
R7
1M
DC OUTPUT ≤ 2.5mV FOR TA < 70°C
OUTPUT VOLTAGE NOISE = 128nV/√Hz AT 1kHz (GAIN = 20)
C1 ≈ CT ≈ 100pF TO 5000pF; R4C2 > R8CT; *OPTIONAL
+
R8
100M
–
CT
HYDROPHONE
R4
1M
PERCENT OF UNITS (%)
R1*
100M
1kHz Input Noise Voltage Distribution
VS = ±15V
TA = 25°C
270 OP AMPS TESTED
30
20
10
0
3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6
INPUT VOLTAGE NOISE (nV/√Hz)
1792 TA02
1792 TA01
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LT1792
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ABSOLUTE
RATI GS
(Note 1)
Supply Voltage ..................................................... ±20V
Differential Input Voltage ...................................... ±40V
Input Voltage (Equal to Supply Voltage) ............... ±20V
Output Short-Circuit Duration ........................ Indefinite
Operating Temperature Range ............... – 40°C to 85°C
Specified Temperature Range
Commercial (Note 8) ......................... – 40°C to 85°C
Industrial ........................................... – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec) ................ 300°C
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PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
VOS ADJ 1
8 NC
–IN A 2
+
+IN A 3
V
–
A
7 V
6 OUT
5 VOS ADJ
4
LT1792ACN8
LT1792CN8
LT1792AIN8
LT1792IN8
ORDER PART
NUMBER
TOP VIEW
VOS ADJ 1
8 NC
–IN A 2
7 V+
+IN A 3
V
–
A
LT1792ACS8
LT1792CS8
LT1792AIS8
LT1792IS8
6 OUT
5 VOS ADJ
4
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 140°C, θJA = 130°C/W
TJMAX = 160°C, θJA = 190°C/W
S8 PART MARKING
1792A
1792
1792AI
1792I
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
TA = 25°C, VS = ±15V, VCM = 0V, unless otherwise noted. (Note 9)
LT1792AC/LT1792AI
MIN
TYP
MAX
LT1792C/LT1792I
MIN
TYP
MAX
VS = ± 5V
0.2
0.4
0.6
1.0
0.2
0.4
0.8
1.3
mV
mV
Input Offset Current
Warmed Up (Note 3)
100
400
100
400
pA
IB
Input Bias Current
Warmed Up (Note 3)
300
800
300
800
pA
en
Input Noise Voltage
0.1Hz to 10Hz
2.4
2.4
µVP-P
Input Noise Voltage Density
fO = 10Hz
fO = 1000Hz
8.3
4.2
6.0
8.3
4.2
6.0
nV/√Hz
nV/√Hz
fO = 10Hz, fO = 1000Hz (Note 4)
10
10
1011
1011
1010
1011
1011
1010
Ω
Ω
Ω
14
27
14
27
pF
pF
SYMBOL
PARAMETER
VOS
Input Offset Voltage
IOS
in
Input Noise Current Density
RIN
Input Resistance
Differential Mode
Common Mode
CIN
Input Capacitance
VCM
Input Voltage Range (Note 5)
CMRR
Common Mode Rejection Ratio
PSRR
Power Supply Rejection Ratio
2
CONDITIONS (Note 2)
VCM = –10V to 8V
VCM = 8V to 11V
VS = ±5V
UNITS
fA/√Hz
13.0
–10.5
13.5
–11.0
13.0
–10.5
13.5
–11.0
V
V
VCM = –10V to 13V
85
105
82
100
dB
VS = ±4.5V to ±20V
88
105
83
98
dB
LT1792
ELECTRICAL CHARACTERISTICS
TA = 25°C, VS = ±15V, VCM = 0V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
LT1792AC/LT1792AI
MIN
TYP
MAX
LT1792C/LT1792I
MIN
TYP
MAX
AVOL
Large-Signal Voltage Gain
VO = ±12V, RL = 10k
VO = ±10V, RL = 1k
1200
600
4800
4000
1000
500
4500
3000
V/mV
V/mV
VOUT
Output Voltage Swing
RL = 10k
RL = 1k
±13.0
±12.0
±13.2
±12.3
±13.0
±12.0
±13.2
±12.3
V
V
SR
Slew Rate
RL ≥ 2k (Note 7)
2.3
3.4
2.3
3.4
V/µs
GBW
Gain-Bandwidth Product
fO = 100kHz
4.0
5.6
4.0
5.6
MHz
IS
Supply Current
Offset Voltage
Adjustment Range
VS = ±5V
4.2
4.2
RPOT (to VEE) = 10k
10
5.20
5.15
4.2
4.2
5.20
5.15
10
UNITS
mA
mA
mV
The ● denotes specifications which apply over the temperature range 0°C ≤ TA ≤ 70°C. VS = ±15V, VCM = 0V,
unless otherwise noted. (Note 9)
SYMBOL
PARAMETER
VOS
Input Offset Voltage
∆VOS
∆Temp
Average Input Offset
Voltage Drift
IOS
CONDITIONS (Note 2)
MIN
LT1792AC
TYP
MAX
MIN
LT1792C
TYP
MAX
UNITS
VS = ± 5V
●
●
0.4
0.6
0.8
1.2
0.8
1.2
2.7
3.2
mV
mV
(Note 6)
●
4
10
7
40
µV/°C
Input Offset Current
●
180
500
180
500
pA
IB
Input Bias Current
●
500
1800
500
1800
pA
VCM
Input Voltage Range
●
●
12.9
–10.0
13.4
–10.8
CMRR
Common Mode Rejection Ratio
VCM = –10V to 12.9V
●
81
104
79
99
dB
PSRR
Power Supply Rejection Ratio
VS = ±4.5V to ±20V
●
85
99
81
97
dB
AVOL
Large-Signal Voltage Gain
VO = ±12V, RL = 10k
VO = ±10V, RL = 1k
●
●
900
500
3600
2600
800
400
3400
2400
VOUT
Output Voltage Swing
RL = 10k
RL = 1k
●
●
SR
Slew Rate
RL ≥ 2k (Note 7)
●
2.1
3.1
2.1
3.1
V/µs
GBW
Gain-Bandwidth Product
fO = 100kHz
●
3.2
4.5
3.2
4.5
MHz
IS
Supply Current
VS = ±5V
●
●
12.9
–10.0
±12.9 ±13.2
±11.9 ±12.15
4.2
4.2
13.4
–10.8
V
V
V/mV
V/mV
±12.9 ±13.2
±11.9 ±12.15
5.30
5.25
4.2
4.2
V
V
5.30
5.25
mA
mA
3
LT1792
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the temperature range
– 40°C ≤ TA ≤ 85°C. VS = ±15V, VCM = 0V, unless otherwise noted. (Notes 8, 9)
LT1792AC/LT1792AI
MIN
TYP
MAX
LT1792C/LT1792I
MIN
TYP
MAX
VS = ±5V
●
●
0.5
0.8
1.0
1.4
1.2
1.5
3.7
4.2
mV
mV
(Note 6)
●
4
10
7
40
µV/°C
Input Offset Current
●
300
800
300
800
pA
IB
Input Bias Current
●
1200
4000
1200
4000
pA
VCM
Input Voltage Range
●
●
12.6
–10.0
13.0
–10.5
12.6
–10.0
13.0
–10.5
V
V
CMRR
Common Mode Rejection Ratio
VCM = –10V to 12.6V
●
80
103
78
98
dB
PSRR
Power Supply Rejection Ratio
VS = ±4.5V to ± 20V
●
83
98
79
96
AVOL
Large-Signal Voltage Gain
VO = ±12V, RL = 10k
VO = ±10V, RL = 1k
●
●
850
400
3300
2200
750
300
3000
2000
V/mV
V/mV
VOUT
Output Voltage Swing
RL = 10k
RL = 1k
●
●
±12.8
±11.8
±13.1
±12.1
±12.8
±11.8
±13.1
±12.1
V
V
SR
Slew Rate
RL ≥ 2k
●
2.0
3.0
2.0
3.0
V/µs
GBW
Gain-Bandwidth Product
fO = 100kHz
●
2.9
4.3
2.9
4.3
MHz
IS
Supply Current
VS = ±5V
●
●
SYMBOL
PARAMETER
VOS
Input Offset Voltage
∆VOS
∆Temp
Average Input Offset
Voltage Drift
IOS
CONDITIONS (Note 2)
Note 1: Absolute Maximum Ratings are those values beyond which the
life of a device may be impaired.
Note 2: Typical parameters are defined as the 60% yield of parameter
distributions of individual amplifiers.
Note 3: Warmed-up IB and IOS readings are extrapolated to a chip
temperature of 32°C from 25°C measurements and 32°C characterization
data.
Note 4: Current noise is calculated from the formula:
in = (2qIB)1/2
where q = 1.6 • 10 –19 coulomb. The noise of source resistors up to 200M
swamps the contribution of current noise.
Note 5: Input voltage range functionality is assured by testing offset
voltage at the input voltage range limits to a maximum of 2.3mV
(A grade), to 2.8mV (C grade).
4
4.2
4.2
5.40
5.35
4.2
4.2
UNITS
dB
5.40
5.35
mA
mA
Note 6: This parameter is not 100% tested.
Note 7: Slew rate is measured in AV = – 1; input signal is ±7.5V, output
measured at ±2.5V.
Note 8: The LT1792AC and LT1792C are guaranteed to meet specified
performance from 0°C to 70°C and are designed, characterized and
expected to meet these extended temperature limits, but are not tested at
– 40°C and 85°C. The LT1792I is guaranteed to meet the extended
temperature limits. The LT1792AC and LT1792AI grade are 100%
temperature tested for the specified temperature range.
Note 9: The LT1792 is measured in an automated tester in less than one
second after application of power. Depending on the package used,
power dissipation, heat sinking, and air flow conditions, the fully
warmed-up chip temperature can be 10°C to 50°C higher than the
ambient temperature.
LT1792
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TYPICAL PERFOR A CE CHARACTERISTICS
Voltage Noise
vs Chip Temperature
Voltage Noise vs Frequency
VOLTAGE NOISE (1µV/DIV)
RMS VOLTAGE NOISE DENSITY (nV/√Hz)
100
10
VS = ±15V
TA = 25°C
9
VOLTAGE NOISE (AT 1kHz) (nV/√Hz)
0.1Hz to 10Hz Voltage Noise
10
1/f CORNER
30Hz
8
7
6
5
4
3
2
1
1
2
0
6
4
TIME (SEC)
8
1
10
10
100
1k
FREQUENCY (Hz)
300
200
BIAS CURRENT
100
OFFSET CURRENT
V+
VS = ±15V
30
10
3
1
IB
0.3
IOS
0.1
0.03
100 125
1792 G22
60
40
20
0
100k
1M
FREQUENCY (Hz)
4.0
3.5
3.0
10M
1792 G06
V – = – 5V TO – 20V
–20
60
100
20
TEMPERATURE (°C)
140
1792 G05
Voltage Gain vs Frequency
180
TA = 25°C
160
100
140
VOLTAGE GAIN (dB)
80
10k
–1.5
V –+ 2.0
– 60
120
POWER SUPPLY REJECTION RATIO (dB)
COMMON MODE REJECTION RATIO (dB)
TA = 25°C
VS = ± 15V
V + = 5V TO 20V
– 2.0
Power Supply Rejection Ratio
vs Frequency
120
1k
–1.0
1792 G04
Common Mode Rejection Ratio
vs Frequency
100
0
– 0.5
2.5
0.01
– 75 – 50 – 25 0
25 50 75
TEMPERATURE (°C)
15
Common Mode Limit
vs Temperature
COMMON MODE LIMIT
REFERRED TO POWER SUPPLY (V)
INPUT BIAS AND OFFSET CURRENT (nA)
INPUT BIAS AND OFFSET CURRENTS (pA)
100
10
–10
–5
0
5
COMMON-MODE RANGE (V)
1792 G03
Input Bias and Offset Current
vs Chip Temperature
TA = 25°C
VS = ±15V
NOT WARMED UP
100 125
1792 G02
Input Bias and Offset Current
Over the Common Mode Range
0
–15
0
–75 –50 –25 0 25 50 75
TEMPERATURE (°C)
10k
1792 G01
400
VS = ±15V
80
+PSRR
60
–PSRR
40
120
100
80
60
40
20
20
0
0
10
100
1k
10k 100k
FREQUENCY (Hz)
1M
10M
1792 G07
– 20
0.01
1
10k
100
FREQUENCY (Hz)
1M
100M
1792 G08
5
LT1792
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TYPICAL PERFOR A CE CHARACTERISTICS
Gain and Phase Shift
vs Frequency
TA = 25°C
VS = ±15V
CL = 10pF
100
120
30
140
20
GAIN
10
160
0
180
1
10
FREQUENCY (MHz)
0.1
AV = 1
CL = 10pF
VS = ±15V, ±5V
200
100
–10
5V/DIV
PHASE
PHASE SHIFT (DEG)
VOLTAGE GAIN (dB)
40
Large-Signal Transient Response
Small-Signal Transient Response
80
20mV/DIV
50
1µs/DIV
1792 G10
AV = 1
CL = 10pF
RL = 2k
VS = ±15V
1792 G11
5µs/DIV
1792 G09
Output Voltage Swing
vs Load Current
40
–55°C
– 1.4
–1.6
OVERSHOOT (%)
VS = ±5V TO ±20V
2.0
1.8
125°C
1.6
30
20
10
–55°C
1.2
SR
6
3
GBWP
2
4
0
0.1
1
100
1000
10
CAPACITIVE LOAD (pF)
TOTAL HARMONIC DISTROTION + NOISE (%)
SO-8 PACKAGE
60
45
N8 PACKAGE
30
15
0
0
25 50 75
– 75 – 50 – 25 0
TEMPERATURE (°C)
5
2
3
4
1
TIME AFTER POWER ON (MINUTES)
6
1792 G15
0
100 125
1792 G14
THD and Noise vs Frequency for
Noninverting Gain
VS = ±15V
TA = 25°C
75
10000
1792 G13
Warm-Up Drift
90
2
AV = 10
1792 G12
CHANGE IN OFFSET VOLTAGE (µV)
8
4
1
25°C
V – +1.0
–10 –8 –6 –4 –2 0 2 4 6 8 10
ISINK
ISOURCE
OUTPUT CURRENT (mA)
6
10
AV = 1
1.4
0
12
VS = ± 15V
5
1
ZL = 2k  15pF
VO = 20VP-P
AV = 1, 10, 100
MEASUREMENT BANDWIDTH
= 10Hz TO 80kHz
0.1
AV = 100
0.01
AV = 10
0.001
AV = 1
NOISE FLOOR
THD and Noise vs Frequency for
Inverting Gain
TOTAL HARMONIC DISTROTION + NOISE (%)
OUTPUT VOLTAGE SWING (V)
–1.2
6
VS = ±15V
TA = 25°C
RL ≥ 10k
VO = 100mVP-P
AV = 10
RF = 10k
CF = 20pF
SLEW RATE (V/µs)
50
125°C
25°C
GAIN-BANDWIDTH PRODUCT (fO = 100kHz) (MHz)
V + – 0.8
–1.0
Slew Rate and Gain-Bandwidth
Product vs Temperature
Capacitive Load Handling
1
ZL = 2k  15pF
VO = 20VP-P
AV = – 1, – 10, – 100
MEASUREMENT BANDWIDTH
= 10Hz TO 80kHz
0.1
0.01
AV = – 100
AV = – 10
0.001
AV = – 1
NOISE FLOOR
0.0001
0.0001
20
100
1k
FREQUENCY (Hz)
10k 20k
1792 G16
20
100
1k
FREQUENCY (Hz)
10k 20k
1792 G17
LT1792
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TYPICAL PERFOR A CE CHARACTERISTICS
THD and Noise vs Output
Amplitude for Inverting Gain
1
TOTAL HARMONIC DISTORTION + NOISE (%)
TOTAL HARMONIC DISTORTION + NOISE (%)
THD and Noise vs Output
Amplitude for Noninverting Gain
ZL = 2k  15pF, fO = 1kHz
AV = 1, 10, 100
MEASUREMENT BANDWIDTH
= 10Hz TO 22kHz
0.1
AV = 100
0.01
AV = 10
0.001
AV = 1
0.0001
0.3
1
10
OUTPUT SWING (VP-P)
1
ZL = 2k  15pF, fO = 1kHz
AV = – 1, – 10, – 100
MEASUREMENT BANDWIDTH
= 10Hz TO 22kHz
0.1
AV = –100
0.01
AV = –10
0.001
AV = –1
0.0001
30
0.3
1
10
OUTPUT SWING (VP-P)
30
1792 G18
1792 G19
Short-Circuit Output Current
vs Temperature
40
Supply Current vs Temperature
5
VS = ±15V
SUPPLY CURRENT (mA)
OUTPUT CURRENT (mA)
35
30
SINK
SOURCE
25
20
VS = ±15V
4
VS = ± 5V
15
10
– 75 – 50 – 25 0
25 50 75
TEMPERATURE (°C)
3
– 75 – 50 – 25 0
25 50 75
TEMPERATURE (°C)
100 125
100 125
1792 G20
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APPLICATI
1792 G21
S I FOR ATIO
The LT1792 may be inserted directly into OPA124, AD743,
AD745, AD645, AD544 and AD820 sockets with improved
noise performance. Offset nulling will be compatible with
these devices with the wiper of the potentiometer tied to
the negative supply (Figure 1a). No appreciable change in
offset voltage drift with temperature will occur when the
device is nulled with a potentiometer ranging from 10k to
200k. Finer adjustments can be made with resistors in
series with the potentiometer (Figure 1b).
Being a low voltage noise JFET op amp, the LT1792 can
replace many bipolar op amps that are used in amplifying
low level signals from high impedance transducers. The
15V
15V
2
–
2
7
–
7
6
6
3
+
3
4
5
∆VOS = ±10mV
1
4
5
1792 F01a
∆VOS = ±1mV
1
10k
50k
– 15V
+
10k
50k
– 15V
(a)
1792 F01b
(b)
Figure 1
7
LT1792
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S I FOR ATIO
APPLICATI
1k
best bipolar op amps, with higher current noise, will
eventually lose out to the LT1792 when transducer impedance increases. The low voltage noise of the LT1792
allows it to surpass most single JFET op amps available.
For the best performance versus area available anywhere,
the LT1792 is offered in the SO-8 surface mount package
with no degradation in performance.
H
z)
INPUT NOISE VOLTAGE (nV/√
The low voltage and current noise offered by the LT1792
makes it useful in a wide range of applications, especially
where high impedance, capacitive transducers are used
such as hydrophones, precision accelerometers and photo
diodes. The total output noise in such a system is the gain
times the RMS sum of the op amp input referred voltage
noise, the thermal noise of the transducer, and the op amp
bias current noise times the transducer impedance.
Figure 2 shows total input voltage noise versus source
resistance. In a low source resistance (<5k) application
the op amp voltage noise will dominate the total noise.
This means the LT1792 will beat out any JFET op amp, only
the lowest noise bipolar op amps have the edge
at low source resistances. As the source resistance increases from 5k to 50k, the LT1792 will match the best
bipolar op amps for noise performance, since the thermal
noise of the transducer (4kTR) begins to dominate the
total noise. A further increase in source resistance, above
50k, is where the op amp’s current noise component (2qIB
RTRANS) will eventually dominate the total noise. At these
high source resistances, the LT1792 will out perform
the lowest noise bipolar op amp due to the inherently low
LT1007*
–
100
+
CS
LT1792†
10
LT1792
LT1007
RESISTOR NOISE ONLY
1
100
1k
10k 100k
1M
10M
SOURCE RESISTANCE (Ω)
1792 F02
Vn = AV √Vn2(OP AMP) + 4kTR + 2qIB • R2
Figure 2. Comparison of LT1792 and LT1007 Total Output
1kHz Voltage Noise Versus Source Resistance
current noise of FET input op amps. Clearly, the LT1792
will extend the range of high impedance transducers
that can be used for high signal-to-noise ratios. This
makes the LT1792 the best choice for high impedance,
capacitive transducers.
The high input impedance JFET front end makes the
LT1792 suitable in applications where very high charge
sensitivity is required. Figure 3 illustrates the LT1792 in its
inverting and noninverting modes of operation. A charge
amplifier is shown in the inverting mode example; here the
gain depends on the principal of charge conservation at
RF
CF
RB
–
–
R1
OUTPUT
+
RS
TRANSDUCER
CB ≅ CS
RB = RS
RS > R1 OR R2
100M
SOURCE RESISTANCE = 2RS = R
* PLUS RESISTOR
†
PLUS RESISTOR  1000pF CAPACITOR
CB
CS
RS
+
TRANSDUCER
CB
RB
1792 F03
Figure 3. Noninverting and Inverting Gain Configurations
8
LT1007†
VO
RS
R2
CS
LT1792*
CS
RS
OUTPUT
CB = CF CS
RB = RF RS
dQ
dV
Q = CV; = I = C
dt
dt
LT1792
W
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APPLICATI
S I FOR ATIO
the input of the LT1792. The charge across the transducer
capacitance, CS, is transferred to the feedback capacitor
CF, resulting in a change in voltage, dV, equal to dQ/CF.
The gain therefore is CF/CS. For unity gain, the CF should
equal the transducer capacitance plus the input capacitance of the LT1792 and RF should equal RS. In the
noninverting mode example, the transducer current is
converted to a change in voltage by the transducer capacitance; this voltage is then buffered by the LT1792 with a
gain of 1 + R1/R2. A DC path is provided by RS, which is
either the transducer impedance or an external resistor.
Since RS is usually several orders of magnitude greater
than the parallel combination of R1 and R2, RB is added to
balance the DC offset caused by the noninverting input
bias current and RS. The input bias currents, although
small at room temperature, can create significant errors at
higher temperature, especially with transducer resistances
of up to 100M or more. The optimum value for RS is
determined by equating the thermal noise (4kTRS) to the
current noise times RS, [(2qIB) • RS], resulting in
RB = 2VT/IB (VT = 26mV at 25°C). A parallel capacitor, CB,
is used to cancel the phase shift caused by the op amp
input capacitance and RB.
Reduced Power Supply Operation
expense of reduced dynamic range. To illustrate this
benefit, let’s take the following example:
An LT1792CS8 operates at an ambient temperature of
25°C with ±15V supplies, dissipating 159mW of power
(typical supply current = 5.3mA). The SO-8 package has a
θJA of 190°C/W, which results in a die temperature increase of 30.2°C or a room temperature die operating
temperature of 55.2°C. At ±5V supplies, the die temperature increases by only one third of the previous amount or
10.1°C resulting in a typical die operating temperature of
only 35.1°C. A 20 degree reduction of die temperature is
achieved at the expense of a 20V reduction in dynamic
range.
To take full advantage of a wide input common mode
range, the LT1792 was designed to eliminate phase reversal. Referring to the photographs shown in Figure 4, the
LT1792 is shown operating in the follower mode (AV = 1)
at ±5V supplies with the input swinging ±5.2V. The output
of the LT1792 clips cleanly and recovers with no phase
reversal. This has the benefit of preventing lock-up in
servo systems and minimizing distortion components.
High Speed Operation
The LT1792 can be operated from ±5V supplies for lower
power dissipation resulting in lower IB and noise at the
The low noise performance of the LT1792 was achieved
by making the input JFET differential pair large to maximize the first stage gain. Increasing the JFET geometry
INPUT: ±5.2V Sine Wave
LT1792 Output
1792 F04a
1792 F03b
Figure 4. Voltage Follower with Input Exceeding the Common Mode Range ( VS = ±5V)
9
LT1792
W
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APPLICATI
S I FOR ATIO
CF
also increases the parasitic gate capacitance, which if left
unchecked, can result in increased overshoot and ringing. When the feedback around the op amp is resistive
(RF), a pole will be created with RF, the source resistance
and capacitance (RS, CS), and the amplifier input capacitance (CIN = 27pF). In low gain configurations and with
RS and RF in the kilohm range (Figure 5), this pole can
create excess phase shift and even oscillation. A small
capacitor (CF) in parallel with RF eliminates this problem.
With RS(CS + CIN) = RFCF, the effect of the feedback pole
is completely removed.
RF
–
RS
CIN
+
CS
OUTPUT
1792 F05
Figure 5
UO
TYPICAL APPLICATI
S
Accelerometer Amplifier with DC Servo
C1
1250pF
R1
100M
C2
2µF
R3
2k
R2
18k
–
6
+
2
–
3
R5
20M
R4C2 = R5C3 > R1 (1 + R2/R3) C1
OUTPUT = 0.8mV/pC* = 8.0mV/g**
DC OUTPUT ≤ 2.7mV
OUTPUT NOISE = 6nV/√
Hz AT 1kHz
*PICOCOULOMBS
**g = EARTH’S GRAVITATIONAL CONSTANT
C3
2µF
7
6
LT1792
3
R4
20M
LT1792
5V TO 15V
ACCELEROMETER
B & K MODEL 4381
OR EQUIVALENT
2
OUTPUT
+
1792 TA03
4
– 5V TO –15V
10Hz Fourth Order Chebyshev Lowpass Filter (0.01dB Ripple)
C1
33nF
R2
237k
R1
237k
R3
249k
VIN
C2
100nF
C3
10nF
R5
154k
15V
2
–
7
LT1792
3
6
R4
154k
R6
249k
2
–
C4
330nF
3
+
+
4
LT1792
6
VOUT
–15V
TYPICAL OFFSET ≈ 0.8mV
1% TOLERANCES
FOR VIN = 10VP-P, VOUT = –121dB AT f > 330Hz
= – 6dB AT f = 16.3Hz
LOWER RESISTOR VALUES WILL RESULT IN LOWER THERMAL NOISE AND LARGER CAPACITORS
10
1792 TA06
LT1792
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TYPICAL APPLICATI
S
Low Noise Light Sensor with DC Servo
C1
2pF
R1
1M
2
–
3
+
6
LT1792
OUTPUT
C2
0.022µF
D2
1N914
V+
R3
1k
2N3904
R5
1k
HAMAMATSU
S1336-5BK
7
6
2
+
D1
1N914
–
CD
3
R2
100k
LT1792
4
R4
1k
V–
R2C2 > C1R1
CD = PARASITIC PHOTODIODE CAPACITANCE
VO = 100mV/µWATT FOR 200nm WAVE LENGTH
330mV/µWATT FOR 633nm WAVE LENGTH
V–
1792 TA05
Paralleling Amplifiers to Reduce Voltage Noise
3
2
+
6
An
LT1792
1k
–
51Ω
1k
10k
3
2
15V
+
6
A2
LT1792
1k
2
–
3
+
–
7
LT1792
1k
51Ω
6
OUTPUT
4
15V
–15V
3
2
+
7
6
A1
LT1792
–
4
–15V
51Ω
1k
1k
1. ASSUME VOLTAGE NOISE OF LT1792 AND 51Ω SOURCE RESISTOR = 4.3nV/√
H
z
2. GAIN WITH n LT1792s IN PARALLEL = n × 200
3. OUTPUT NOISE = √
n × 200 × 4.3nV/√
 H z
OUTPUT NOISE 4.3
4. INPUT REFERRED NOISE =
=
nV/√
Hz
n × 200
√n
5. NOISE CURRENT AT INPUT INCREASES √
1792 TA04
 n TIMES
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
LT1792
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TYPICAL APPLICATI
S
Light Balance Detection Circuit
I1
Unity-Gain Buffer with Extended
Load Capacitance Drive Capability
R1
1M
R2
1k
C1
2pF TO 8pF
C1
–
PD1
–
I2
VOUT
LT1792
+
+
VIN
VOUT
LT1792
PD2
R1
33Ω
CL
1792 TA08
C1 = CL ≤ 0.1µF
OUTPUT SHORT-CIRCUIT CURRENT
(∼ 30mA) WILL LIMIT THE RATE AT WHICH THE
VOLTAGE CAN CHANGE ACROSS LARGE CAPACITORS
1792 TA07
VOUT = 1M × (I1 – I2)
PD1,PD2 = HAMAMATSU S1336-5BK
WHEN EQUAL LIGHT ENTERS PHOTODIODES, VOUT < 3mV.
I=C
U
PACKAGE DESCRIPTIO
( )
dV
dt
Dimensions in inches (millimeters) unless otherwise noted.
N8 Package
8-Lead PDIP (Narrow 0.300)
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1510)
(LTC DWG # 05-08-1610)
0.400*
(10.160)
MAX
8
7
6
8
(
+0.035
0.325 –0.015
+0.889
8.255
–0.381
)
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
0.009 – 0.015
(0.229 – 0.381)
5
5
0.255 ± 0.015*
(6.477 ± 0.381)
0.300 – 0.325
(7.620 – 8.255)
0.189 – 0.197*
(4.801 – 5.004)
7
6
2
3
4
0.130 ± 0.005
(3.302 ± 0.127)
0.045 – 0.065
(1.143 – 1.651)
0.008 – 0.010
(0.203 – 0.254)
0.065
(1.651)
TYP
0.100 ± 0.010
(2.540 ± 0.254)
1
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.125
(3.175) 0.020
MIN (0.508)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
N8 1197
2
3
4
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
*DIMENSION DOES NOT INCLUDE MOLD FLASH.
MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH.
INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.050
(1.270)
TYP SO8 0996
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
RELATED PARTS
PART NUMBER
DESCRIPTION
LT1113
Low Noise Dual JFET Op Amp
Dual Version of LT1792, VNOISE = 4.5nV/√Hz
LT1169
Low Noise Dual JFET Op Amp
Dual Version of LT1793, IB = 10pA, VNOISE = 6nV/√Hz
LT1793
Low Noise Single Op Amp
Lower IB Version of LT1792, IB = 10pA, VNOISE = 6nV/√Hz
12
Linear Technology Corporation
COMMENTS
1792f LTTP 0599 4K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 1999