AD515 Analog Devices, AD515 Datasheet

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AD515

Manufacturer Part Number
AD515
Description
Monolithic Precision/ Low Power FET-Input Electrometer Op Amp
Manufacturer
Analog Devices
Datasheet

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a
PRODUCT DESCRIPTION
The AD515A is a monolithic FET-input operational amplifier
with a guaranteed maximum input bias current of 75 fA
(AD515AL). The AD515A is a monolithic successor to the
industry standard AD515 electrometer, and will replace the
AD515 in most applications. The AD515A also delivers laser-
trimmed offset voltage, low drift, low noise and low power, a
combination of features not previously available in ultralow bias
current circuits. All devices are internally compensated, protected
against latch-up and are short circuit protected.
The AD515A’s combination of low input bias current, low
offset voltage and low drift optimizes it for a wide variety of
electrometer and very high impedance buffer applications
including photocurrent detection, vacuum ion-gage measure-
ment, long-term precision integration and low drift sample/hold
applications. This amplifier is also an excellent choice for all forms
of biomedical instrumentation such as pH/pIon sensitive elec-
trodes, very low current oxygen sensors, and high impedance
biological microprobes. In addition, the low cost and pin
compatibility of the AD515A with standard FET op amps will
allow designers to upgrade the performance of present systems
at little or no additional cost. The 10
impedance ensures that the input bias current is essentially
independent of common-mode voltage.
As with previous electrometer amplifier designs from Analog
Devices, the case is brought out to its own connection (Pin 8)
so it can be independently connected to a point at the same
potential as the input, thus minimizing stray leakage to the case.
This feature will also shield the input circuitry from external
noise and supply transients.
The AD515A is available in three versions of bias current and
offset voltage, the “J”, “K” and “L”; all are specified for rated
performance from 0 C to +70 C and supplied in a hermetically
sealed TO-99 package.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
FEATURES
Ultralow Bias Current: 75 fA max (AD515AL)
Ultralow Bias Current:
Ultralow Bias Current:
Low Power: 1.5 mA max Quiescent Current
Low Power:
Low Offset Voltage: 1.0 mV max (AD515AK & L)
Low Drift: 15 V/ C max (AD515AK)
Low Noise: 4 V p-p, 0.1 Hz to 10 Hz
(0.6 mA typ)
150 fA max (AD515AK)
300 fA max (AD515AJ)
15
common-mode input
Monolithic Precision, Low Power
PRODUCT HIGHLIGHTS
1. The AD515A provides subpicoampere bias currents in an
2. The input offset voltage on all grades is laser trimmed, typically
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
3. The low quiescent current drain of 0.6 mA typical and
4. The combination of low input noise voltage and very low
FET-Input Electrometer Op Amp
integrated circuit amplifier.
• The ultralow input bias currents are specified as the maxi-
• By using 5 V supplies, input bias current can typically be
less than 500 V.
• The offset voltage drift is 15 V/ C maximum on the
• If additional pulling is desired, the amount required will
1.5 mA maximum, keeps self-heating effects to a minimum
and renders the AD515A suitable for a wide range of remote
probe applications.
input noise current is such that for source impedances from
1M
dominate the noise characteristic.
mum measured at either input with the device fully warmed
up on 15 V supplies at +25 C ambient with no heat sink.
This parameter is 100% tested.
brought below 50 fA.
K grade.
have a minimal effect on offset drift (approximately 3 V/ C
per mV).
to 10
11
, the Johnson noise of the source will easily
PIN CONFIGURATION
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 1997
AD515A

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AD515 Summary of contents

Page 1

... This feature will also shield the input circuitry from external noise and supply transients. The AD515A is available in three versions of bias current and offset voltage, the “J”, “K” and “L”; all are specified for rated performance from +70 C and supplied in a hermetically sealed TO-99 package ...

Page 2

... ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD515A features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality ...

Page 3

... AD515A can deliver. The best performance will be realized by using a teflon IC socket for the AD515A minimum a teflon standoff should be used for the high impedance lead. If this is not feasible, the input guarding scheme shown in Figure 1 will minimize leakage as much as possible ...

Page 4

... AD515A COAXIAL CABLE AND CAPACITANCE EFFECTS not possible to attach the AD515A virtually on top of the signal source, considerable care should be exercised in designing the connecting lines carrying the high impedance signal. Shielded coaxial cable must be used for noise reduction, but use of coaxial cables for high impedance work can add problems from cable leakage, noise and capacitance ...

Page 5

... V to 1.5 V above the other terminal. Input current limits under these conditions. AD515A CIRCUIT APPLICATION NOTES The AD515A is quite simple to apply to a wide variety of applications because of the pretrimmed offset voltage and internal compensation, which minimize required external components and eliminate the need for adjustments to the device itself ...

Page 6

... AD515A the total noise by about 40%. Noise currents driving the resistors also add, but in the AD515A are significant only above 10 Figure 11. Very High Impedance Instrumentation Amplifier Figure 12. Low Drift Integrator and Low Leakage Guarded Reset LOW LEVEL CURRENT-TO-VOLTAGE CONVERTERS Figure 2 shows a standard low level current-to-voltage converter. ...

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