AD515A_15 Datasheet, PDF (1/6 Pages) Analog Devices – Monolithic Precision, Low Power FET-Input Electrometer Op Amp

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Monolithic Precision, Low Power
FET-Input Electrometer Op Amp
AD515A
FEATURES
PIN CONFIGURATION
Ultralow Bias Current: 75 fA max (AD515AL)
Ultralow Bias Current: 150 fA max (AD515AK)
Ultralow Bias Current: 300 fA max (AD515AJ)
Low Power: 1.5 mA max Quiescent Current
Low Power: (0.6 mA typ)
Low Offset Voltage: 1.0 mV max (AD515AK & L)
OBSOLETE Low Drift: 15 ␮V/؇C max (AD515AK)
Low Noise: 4 ␮V p-p, 0.1 Hz to 10 Hz
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
PRODUCT HIGHLIGHTS
1. The AD515A provides subpicoampere bias currents in an
integrated circuit amplifier.
• The ultralow input bias currents are specified as the maxi-
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.
• By using ± 5 V supplies, input bias current can typically be
applications. This amplifier is also an excellent choice for all forms
brought below 50 fA.
of biomedical instrumentation such as pH/pIon sensitive elec-
2. The input offset voltage on all grades is laser trimmed, typically
trodes, very low current oxygen sensors, and high impedance
less than 500 µV.
biological microprobes. In addition, the low cost and pin
• The offset voltage drift is 15 µV/°C maximum on the
compatibility of the AD515A with standard FET op amps will
K grade.
allow designers to upgrade the performance of present systems
• If additional pulling is desired, the amount required will
at little or no additional cost. The 10¹⁵ Ω common-mode input
have a minimal effect on offset drift (approximately 3 µV/°C
impedance ensures that the input bias current is essentially
per mV).
independent of common-mode voltage.
3. The low quiescent current drain of 0.6 mA typical and
As with previous electrometer amplifier designs from Analog
1.5 mA maximum, keeps self-heating effects to a minimum
Devices, the case is brought out to its own connection (Pin 8)
and renders the AD515A suitable for a wide range of remote
so it can be independently connected to a point at the same
probe applications.
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.
4. The combination of low input noise voltage and very low
input noise current is such that for source impedances from
1M Ω to 10¹¹ Ω, the Johnson noise of the source will easily
The AD515A is available in three versions of bias current and
dominate the noise characteristic.
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
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© Analog Devices, Inc., 1997