AD648BQ ,Dual Precision, Low Power BiFET Op AmpCHARACTERISTICSInput Offset Voltage 1.0 2.0 0.5 1.0 0.2 0.4 mVInput Offset Voltage T to T 3.0/3.0/3 ..
AD648CQ ,Dual Precision, Low Power BiFET Op Ampapplications.6. Crosstalk between amplifiers is less than –120 dB at 1 kHz.The AD648 is pinned out ..
AD648CQ ,Dual Precision, Low Power BiFET Op Ampapplications.0.30 mV and offset voltage drift to less than 3 μV/°C. This level2. The AD648 is pin c ..
AD648CQ ,Dual Precision, Low Power BiFET Op AmpCHARACTERISTICSVoltage @ R ≥ 10 kΩ,LT to T ±12/±12/±12 ±13 ±12 ±13 ±12 ±13 VMIN MAXVoltage @ R ≥ 5 ..
AD648JN ,Dual Precision, Low Power BiFET Op AmpSPECIFICATIONSSModel AD648J/A/S AD648K/B/T AD648CMin Typ Max Min Typ M ..
AD648JR ,Dual Precision, Low Power BiFET Op AmpCHARACTERISTICSVoltage @ R ≥ 10 kΩ,LT to T ±12/±12/±12 ±13 ±12 ±13 ±12 ±13 VMIN MAXVoltage @ R ≥ 5 ..
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AD648AH-AD648AQ-AD648BQ-AD648CQ-AD648JN-AD648JR-AD648KN-AD648KR
Dual Precision, Low Power BiFET Op Amp
REV.C
Dual Precision,
Low Power BiFET Op Amp
FEATURES
DC Performance
400 mA max Quiescent Current
10 pA max Bias Current, Warmed Up (AD648C)
300 mV max Offset Voltage (AD648C)
3 mV/8C max Drift (AD648C)
2 mV p-p Noise, 0.1 Hz to 10 Hz
AC Performance
1.8 V/ms Slew Rate
1 MHz Unity Gain Bandwidth
Available in Plastic Mini-DIP, Cerdip, Plastic SOIC
and Hermetic Metal Can Packages
MIL-STD-883B Parts Available
Surface Mount (SOIC) Package Available in Tape and
Reel in Accordance with EIA-481A Standard
Single Version: AD548
PRODUCT DESCRIPTIONThe AD648 is a matched pair of low power, precision mono-
lithic operational amplifiers. It offers both low bias current
(10 pA max, warmed up) and low quiescent current (400 μA
max) and is fabricated with ion-implanted FET and laser wafer
trimming technologies. Input bias current is guaranteed over the
AD648’s entire common-mode voltage range.
The economical J grade has a maximum guaranteed offset volt-
age of less than 2 mV and an offset voltage drift of less than
20 μV/°C. The C grade reduces offset voltage to less than
0.30 mV and offset voltage drift to less than 3 μV/°C. This level
of dc precision is achieved utilizing Analog’s laser wafer drift
trimming process. The combination of low quiescent current
and low offset voltage drift minimizes changes in input offset
voltage due to self-heating effects. Five additional grades are
offered over the commercial, industrial and military temperature
ranges.
The AD648 is recommended for any dual supply op amp appli-
cation requiring low power and excellent dc and ac perfor-
mance. In applications such as battery-powered, precision
instrument front ends and CMOS DAC buffers, the AD648’s
excellent combination of low input offset voltage and drift, low
bias current and low 1/f noise reduces output errors. High
common-mode rejection (86 dB, min on the “C” grade) and
high open-loop gain ensures better than 12-bit linearity in high
impedance, buffer applications.
The AD648 is pinned out in a standard dual op amp configura-
tion and is available in seven performance grades. The AD648J
and AD648K are rated over the commercial temperature range
of 0°C to +70°C. The AD648A, AD648B and AD648C are
rated over the industrial temperature range of –40°C to +85°C.
The AD648S and AD648T are rated over the military tempera-
ture range of –55°C to +125°C and are available processed to
MIL-STD-883B, Rev. C.
The AD648 is available in an 8-pin plastic mini-DIP, cerdip,
SOIC, TO-99 metal can, or in chip form.
PRODUCT HIGHLIGHTSA combination of low supply current, excellent dc and ac
performance and low drift makes the AD648 the ideal op
amp for high performance, low power applications.The AD648 is pin compatible with industry standard dual op
amps such as the LF442, TL062, and AD642, enabling
designers to improve performance while achieving a reduc-
tion in power dissipation of up to 85%.Guaranteed low input offset voltage (2 mV max) and drift
(20 μV/°C max) for the AD648J are achieved utilizing Analog
Devices’ laser drift trimming technology.Analog Devices specifies each device in the warmed-up con-
dition, insuring that the device will meet its published specifi-
cations in actual use.Matching characteristics are excellent for all grades. The
input offset voltage matching between amplifiers in the
AD648J is within 2 mV, for the C grade matching is within
0.4 mV.Crosstalk between amplifiers is less than –120 dB at 1 kHz.The AD648 is available in chip form.
CONNECTION DIAGRAMS
AD648–SPECIFICATIONS(@ + 258C and VS = 615 V dc, unless otherwise noted)
AD648—Typical Characteristics
AD648
APPLICATION NOTESThe AD648 is a pair of JFET-input op amps with a guaranteed
maximum IB of less than 10 pA, and offset and drift laser-
trimmed to 0.3 mV and 3 μV/°C, respectively (AD648C). AC
specs include 1 MHz bandwidth, 1.8 V/μs typical slew rate and
8 μs settling time for a 20 V step to ±0.01%—all at a supply
current less than 400 μA. To capitalize on the device’s perfor-
mance, a number of error sources should be considered.
The minimal power drain and low offset drift of the AD648 re-
duce self-heating or “warm-up” effects on input offset voltage,
making the AD648 ideal for on/off battery powered applica-
tions. The power dissipation due to the AD648’s 400 μA supply
current has a negligible effect on input current, but heavy out-
put loading will raise the chip temperature. Since a JFET’s
input current doubles for every 10°C rise in chip temperature,
this can be a noticeable effect.
The amplifier is designed to be functional with power supply
voltages as low as ±4.5 V. It will exhibit a higher input offset
voltage than at the rated supply voltage of ±15 V, due to power
supply rejection effects. Common-mode range extends from 3 V
more positive than the negative supply to 1 V more negative
than the positive supply. Designed to cleanly drive up to 10 kΩ
and 100 pF loads, the AD648 will drive a 2 kΩ load with re-
duced open-loop gain.
Figure 21 shows the recommended crosstalk test circuit. A typi-
cal value for crosstalk is –120 dB at 1 kHz.
Figure 21.Crosstalk Test Circuit
LAYOUTTo take full advantage of the AD648’s 10 pA max input current,
parasitic leakages must be kept below an acceptable level. The
practical limit of the resistance of epoxy or phenolic circuit
board material is between 1 × 1012 Ω and 3 × 1012 Ω. This can
result in an additional leakage of 5 pA between an input of 0 V
and a –15 V supply line. Teflon or a similar low leakage material
(with a resistance exceeding 1017 Ω) should be used to isolate
high impedance input lines from adjacent lines carrying high
voltages. The insulator should be kept clean, since contaminants
will degrade the surface resistance.
A metal guard completely surrounding the high impedance
nodes and driven by a voltage near the common-mode input
potential can also be used to reduce some parasitic leakages.
The guarding pattern in Figure 22 will reduce parasitic leakage
due to finite board surface resistance; but it will not compensate
for a low volume resistivity board.
Figure 22.Board Layout for Guarding Inputs
INPUT PROTECTIONThe AD648 is guaranteed to withstand input voltages equal to
the power supply potential. Exceeding the negative supply volt-
age on either input will forward bias the substrate junction of
the chip. The induced current may destroy the amplifier due to
excess heat.
Input protection is required in applications such as a flame de-
tector in a gas chromatograph, where a very high potential may
be applied to the input terminals during a sensor fault condi-
tion. Figures 23a and 23b show simple current limiting schemes
that can be used. RPROTECT should be chosen such that the
maximum overload current is 1.0 mA (for example 100 kΩ for a
100 V overload).
Figure 23a.Input Protection of l-to-V Converter
Figure 23b.Voltage Follower Input Protection Method
Figure 23b shows the recommended method for protecting a
voltage follower from excessive currents due to high voltage
breakdown. The protection resistor, RP, limits the input current.
A nominal value of 100 kΩ will limit the input current to less
than 1 mA with a 100 volt input voltage applied.
The stray capacitance between the summing junction and
ground will produce a high frequency roll-off with a corner
frequency equal to:
fcorner=1πRPCstray
