Analog Devices AD515A Datasheet

Monolithic Precision, Low Power

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FEATURES
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)
Low Drift: 15 mV/8C max (AD515AK)
Low Noise: 4 mV 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 laser­trimmed 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 measure­ment, 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 elec­trodes, 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.

15

Ω common-mode input

FET-Input Electrometer Op Amp

AD515A

PIN CONFIGURATION

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

brought below 50 fA.

2. The input offset voltage on all grades is laser trimmed, typically
less than 500 µV.

• The offset voltage drift is 15 µV/°C maximum on the

K grade.

• If additional pulling is desired, the amount required will

have a minimal effect on offset drift (approximately 3 µV/°C
per mV).

3. The low quiescent current drain of 0.6 mA typical and

1.5 mA maximum, keeps self-heating effects to a minimum
and renders the AD515A suitable for a wide range of remote
probe applications.

4. The combination of low input noise voltage and very low
input noise current is such that for source impedances from
1M Ω to 10
dominate the noise characteristic.

11

Ω, the Johnson noise of the source will easily

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use, nor for any infringements of patents or other rights of third parties
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Fax: [phone] © Analog Devices, Inc., 1997

AD515A–SPECIFICATIONS

(typical @ +258C and VS = 615 V dc, unless otherwise noted)

Model AD515AJ AD515AK AD515AL

OPEN-LOOP GAIN

V

= ±10 V, RL ≥ 2 kΩ 20,000 V/V min 40,000 V/V min 25,000 V/V min

OUT

V

= ±10 V, RL ≥ 10 kΩ 40,000 V/V min 100,000 V/V min 50,000 V/V min

OUT

1

TA = min to max RL ≥ 2 kΩ 15,000 V/V min 40,000 V/V min 25,000 V/V min

OUTPUT CHARACTERISTICS

Voltage @ RL = 2 kΩ, TA = min to max 610 V min (612 V typ) **

Voltage @ RL = 10 kΩ, TA = min to max 612 V min (613 V typ) **

Load Capacitance

2

1000 pF

Short-Circuit Current 10 mA min (20 mA typ)

FREQUENCY RESPONSE

Unity Gain, Small Signal 1 MHz * *
Full Power Response 5 kHz min (50 kHz typ) * *
Slew Rate Inverting Unity Gain 0.3 V/µs min (3.0 V/µs typ) * *
Overload Recovery Inverting Unity Gain 100 µs max (2 µs typ) * *

INPUT OFFSET VOLTAGE

3

3.0 mV max (0.4 mV typ) 1.0 mV max (0.4 mV typ) 1.0 mV max (0.4 mV typ)
vs. Temperature, TA = min to max 50 mV/8C max 15 mV/8C max 25 mV/8C max
vs. Supply, TA = min to max 400 mV/V max (50 mV/V typ) 100 mV/V max 200 mV/V max

INPUT BIAS CURRENT

Either Input

INPUT IMPEDANCE

Differential V

4

= ±1 V 1.6 pFi10

DIFF

300 fA max 150 fA max 75 fA max

13

Ω **

Common Mode 0.8 pFi1015 Ω **

INPUT NOISE

Voltage, 0.1 Hz to 10 Hz 4.0 µV (p-p) * *

f = 10 Hz 75 nV/V/√
f = 100 Hz 55 nV/√

Hz **

Hz **

f = l kHz 50 nV/√Hz **

Current, 0.1 Hz to 10 Hz 0.007 pA (p-p) * *

10 Hz to 10 kHz 0.01 pA rms * *

INPUT VOLTAGE RANGE

Differential 620 V min **
Common Mode, T
Common-Mode Rejection, VIN = ±10 V 66 dB min (94 dB typ) 80 dB min 70 dB min
Maximum Safe Input Voltage

= min to max 610 V min (+ 12 V, –11 typ) **

A

5

±V

S

**

POWER SUPPLY

Rated Performance ±15 V * *
Operating 65 V min (618 V max) **
Quiescent Current 1.5 mA max (0.6 mA typ) *

TEMPERATURE

Operating, Rated Performance 0°C to + 70°C* *
Storage –65°C to +150°C

PACKAGE OPTION

TO-99 (H-08A) AD515AJH AD515AKH AD515ALH

NOTES
*Specifications same as AD515AJ.

1

Open Loop Gain is specified with or without pulling of VOS.

2

A conservative design would not exceed 750 pF of load capacitance.

3

Input Offset Voltage specifications are guaranteed after 5 minutes of
operation at TA = +25°C.

4

Bias Current specifications are guaranteed after 5 minutes of operation at
TA = +25°C. For higher temperatures, the current doubles every +10° C.

5

1f it is possible for the input voltage to exceed the supply voltage, a series
protection resistor should be added to limit input current to 0.1 mA.
The input devices can handle overload currents of 0.1 mA indefinitely without
damage. See next page.

Specifications shown in boldface are tested on all production units at final test.
Specifications subject to change without notice.

CAUTION

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.

–2–

WARNING!

ESD SENSITIVE DEVICE

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