ISO256 [BB]
Precision, Powered, Three-Port Isolated OPERATIONAL AMPLIFIER; 精度，供电，三端口隔离运算放大器
| 型号： | ISO256 |
| 厂家： | 
BURR-BROWN CORPORATION |
| 描述： | Precision, Powered, Three-Port Isolated OPERATIONAL AMPLIFIER |
| 文件： | 总9页 (文件大小：127K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
®
ISO256
ISO256
Precision, Powered, Three-Port Isolated
OPERATIONAL AMPLIFIER
FEATURES
DESCRIPTION
● RATED
ISO256 is a precision three-port isolation operational
amplifier incorporating an uncommitted operational
amplifier for input conditioning and a novel duty cycle
modulation-demodulation technique which has excel-
lent accuracy. Internal input protection can withstand
up to ±30V input differential without damage. The
signal is transmitted digitally across a differential
capacitive barrier. With digital modulation the barrier
characteristics do not affect signal integrity. This re-
sults in excellent reliability and good high frequency
transient immunity across the barrier. The DC/DC
converter, amplifier and barrier capacitors are housed
in a plastic DIP.
1500Vrms Continuous
2500Vrms for One Minute
● 100% TESTED FOR PARTIAL DISCHARGE
● LOW NONLINEARITY: ±0.05% typ
● LOW INPUT BIAS CURRENT: ±5nA max
● INPUTS PROTECTED TO ±30V
● BIPOLAR OPERATION VO = ±10V
● SYNCHRONIZATION CAPABILITY
● 28-PIN PLASTIC DIP: 0.6" Wide
A power supply range of 11V to 18V makes this
amplifier ideal for a wide range of applications.
APPLICATIONS
● INDUSTRIAL PROCESS CONTROL
Transducer Isolator, Thermocouple
Isolator, RTD Isolator, Pressure Bridge
Isolator, Flow Meter Isolator
2
1
FB MOD
ISO256
● POWER MONITORING
–VIN
3
4
● MEDICAL INSTRUMENTATION
● ANALYTICAL MEASUREMENTS
● BIOMEDICAL MEASUREMENTS
● DATA ACQUISITION
VOUT
OPA
14
+VIN
● TEST EQUIPMENT
Com1
+VS1
–VS1
Com2
+VS2
–VS2
● GROUND LOOP ELIMINATION
26
28
27
25
13
12
11
10
GND1
GND2
GND3 SYNC +VS3
17 16 15
©1996 Burr-Brown Corporation
PDS-1311B
Printed in U.S.A. April, 1996
SPECIFICATIONS
At TA = +25°C, VS3 = 15V, RL = 2kΩ, and 220nF capacitors on all generated supplies, unless otherwise noted.
ISO256P
TYP
PARAMETER
CONDITIONS
MIN
MAX
UNITS
ISOLATION
Voltage Rated Continuous:
AC
100% Test (AC 50Hz)
Rated One Minute
Isolation-Mode Rejection
DC
T
MIN to TMAX
1500
2500
2500
Vrms
Vrms
Vrms
1s; Partial Discharge ≤ 5pC
120
95
dB
dB
AC 50Hz
1500Vrms
Barrier Impedance
Leakage Current
1014 || 2
1.4
Ω || pF
µArms
VISO = 240Vrms, 50Hz
2
GAIN ISO AMP
Gain Error
Gain vs Temperature
Nonlinearity
G = 1
G = 1
G = 1
0.15
±50
0.046
±0.3
±0.1
%
ppm/°C
%
INPUT OFFSET VOLTAGE OP AMP
Initial Offset
vs Temperature
vs Supply
60
± 1.2
3
µV
µV/°C
µV/V
dB
CMRR
115
INPUT OP AMP
Voltage Range
Bias Current
vs Temperature
Offset Current
vs Temperature
±10
V
nA
pA/°C
nA
pA/°C
±5
±5
±60
±85
INPUT ISO AMP
Initial Offset
vs Supply
±50
1
200
±100
mV
mV/V
kΩ
Input Resistance
OUTPUT ISO AMP
Voltage Range
Current Drive
±10
±5
V
mA
Capacitive Load Drive
Ripple Voltage
0.1
10
µF
mVp-p
FREQUENCY RESPONSE
Small Signal Bandwidth
G = 1
G = 10
G = 100
G = 1000
20
20
4
kHz
kHz
kHz
kHz
V/µs
µs
µs
µs
µs
7
Slew Rate
Settling Time, 0.1%
0.2
100
400
600
950
G = 1
G = 10
G = 100
G = 1000
POWER SUPPLIES
Rated Voltage
Voltage Range
Quiescent Current
Rated Output Voltage
15
V
V
mA
V
11
25
13
12
18
55
40
14.5
13.2
28
No Load
50mA Load On Two Supplies
16
V
Load Regulation
Line Regulation
SYNC Frequency
Output Voltage Ripple
mV/mA
V/V
MHz
mV
1
1 to 1.4
50
TEMPERATURE RANGE
Operating
Storage
–40
–40
85
85
°C
°C
®
2
ISO256
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
Supply Voltage ................................................................................... +18V
VIN, Analog Input Voltage Range ....................................................... ±40V
Com1 to GND1 .................................................................................... ±1V
Com2 to GND2 .................................................................................... ±1V
Continuous Isolation Voltage: .................................................... 1500Vrms
..................................................................................... 2500Vrms one min
IMV, dv/dt ...................................................................................... 20kV/µs
Junction Temperature ...................................................................... 150°C
Storage Temperature ........................................................ –40°C to +85°C
Lead Temperature (soldering, 10s)................................................ +300°C
Output Short Duration .......................................... Continuous to Common
MOD
FB
1
2
3
4
28 +VS1
–VS1
27
26
25
–VIN
+VIN
Com1
GND1
GND2
–VS2
10
11
12
13
14
ELECTROSTATIC
+VS2
GND3
SYNC
+VS3
17
16
15
DISCHARGE SENSITIVITY
Com2
VOUT
Any integrated circuit can be damaged by ESD. Burr-Brown
recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling
and installation procedures can cause damage.
ESD damage can range from subtle performance degrada-
tion to complete device failure. Precision integrated circuits
may be more susceptible to damage because very small
parametric changes could cause the device not to meet
published specifications.
PACKAGE INFORMATION
PACKAGE DRAWING
NUMBER(1)
PRODUCT
PACKAGE
ISO256P
28-Pin Plastic DIP
335
NOTE: (1) For detailed drawing and dimension table, please see end of data
sheet, or Appendix C of Burr-Brown IC Data Book.
ORDERING INFORMATION
PRODUCT
PACKAGE
ISO256P
28-Pin Plastic DIP
TYPICAL PERFORMANCE CURVES
At TA = +25°C, +VS3 = 15V, RL = 2kΩ, and 220nF capacitors on all generated supplies, unless otherwise noted.
PSRR vs FREQUENCY
(G = 10)
PSRR vs FREQUENCY
(G = 1)
80
60
40
20
0
80
60
40
20
0
1
10
100
1k
10k
100k
1
10
100
1K
10K
100K
Frequency (Hz)
Frequency (Hz)
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
®
3
ISO256
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, +VS3 = 15V, RL = 2kΩ, and 220nF capacitors on all generated supplies, unless otherwise noted.
ISOLATION LEAKAGE CURRENT vs FREQUENCY
(V = 240Vrms)
IMR vs FREQUENCY
120
100
80
1k
100
10
60
40
1
1
10
100
1k
10k
1
10
100
1k
10k
100k
Frequency (Hz)
Frequency (Hz)
SINE RESPONSE
(f = 1kHz, G = 1)
SIGNAL RESPONSE vs CARRIER FREQUENCY
10
5
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
–5
5
0
–5
–10
0
100k 200k 300k 400k 500k 600k 700k 800k
Frequency (Hz)
0
500
1000
1500
2000
Time (µs)
SINE RESPONSE
(f = 10kHz, G = 1)
PULSE RESPONSE
(f = 1kHz, G = 1)
10
5
1
0
0
–1
–5
1
0
5
0
–1
–5
–10
0
50
100
150
200
0
500
1000
Time (µs)
Time (µs)
®
4
ISO256
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, +VS3 = 15V, RL = 2kΩ, and 220nF capacitors on all generated supplies, unless otherwise noted.
PULSE RESPONSE
(f = 10kHz, G = 1)
GAIN vs FREQUENCY
G = 1000
60
1
40
G = 100
G = 10
20
0
–1
1
G = 1
–20
–40
–1
1
10
100
1k
Frequency (Hz)
10k
100k
1M
0
20
40
Time (µs)
60
80
100
INPUT COMMON-MODE RANGE
vs OUTPUT VOLTAGE
CMRR vs FREQUENCY
15
10
5
150
140
130
120
110
100
90
G ≥ 10
G ≥ 10
G = 1
G = 1
–
VD/2
VD/2
VCM
VO
0
+
–
+
–5
–10
–15
80
–15
–10
–5
0
5
10
15
1
10
100
1k
10k
100k
Frequency (Hz)
Output Voltage (V)
INPUT BIAS AND INPUT OFFSET CURRENT
vs TEMPERATURE
ISOLATION MODE VOLTAGE
vs FREQUENCY
2
1
Max DC Rating
2.1k
1.0k
Max AC
Rating
IB
Degraded
Performance
IOS
0
100
10
–1
Typical
Performance
–2
–40
–15
10
35
60
85
100
1k
10k
100k
1M
10M
100M
Temperature (°C)
Frequency (Hz)
®
5
ISO256
resistors and diode clamps. The inputs can withstand ±30V
differential inputs without damage. The protection diodes
will of course conduct current when the inputs are over-
driven. This may disturb the slewing rate in unity gain
follower applications, but will not damage the op-amp.
BASIC OPERATION
ISO256 is a precision, powered, three-port isolated ampli-
fier. The input and output sections are galvanically isolated
by matched and EMI shielded capacitors built into the
plastic package. The DC/DC converter input is also galvani-
cally isolated from both the input and output supplies.
DC/DC CONVERTER
ISO256 provides a reliable solution to the need for integral
power. The high isolation rating being achieved by careful
design and attention to the physical construction of the
transformer. In addition to the high dielectric strength a low
leakage coating increases the isolation voltage range. The
soft start oscillator/driver design eliminates high inrush
currents during turn-on. Input current sensing protects both
the converter and the load from possible thermal damage
during a fault condition. The DC/DC converter is synchro-
nized to the amplifier and when multiple ISO256’s are used,
each channel can be synchronized via the SYNC pin.
SIGNAL AND POWER CONNECTIONS
Figure 1 shows proper power and signal connections. The
power supply input pin +VS3 should be bypassed with a
2.2µF tantalum capacitor and the outputs VS1 and VS2 with
220nF ceramic capacitors located as close to the amplifier as
possible. All ground connections should be run indepen-
dently to a common point. Signal Common on both input
and output sections provide a high-impedance point for
sensing signal ground in noisy applications. Com1 and
Com2 must have a path to ground for bias current return and
should be maintained within ±1V of GND1 and GND2
respectively.
The DC/DC converter consists of a free-running oscillator,
control and switch driver circuitry, MOSFET switches, a
transformer, rectifier diodes and filter capacitors all con-
tained within the ISO256 package. The control circuitry
consists of current limiting, soft start and synchronization
features. In instances where several ISO256’s are used in a
system, beat frequencies developed between the ISO256’s
are a potential source of low frequency noise in the supply
and ground paths. This noise may couple into the signal path
INPUT COMMON-MODE RANGE
The linear common-mode range of the input circuitry of the
ISO256 is approximately ±11V.
INPUT PROTECTION
The inputs of the ISO256 are protected with 500Ω series
RIN
RFB
2
1
RFB
FB MOD
ISO256
G = 1 +
RIN
3
4
–VIN
VOUT 14
OPA
VOUT
+VIN
26 Com1
+VS1
Com2 13
28
27 –VS1
GND1
+VS2 12
+15VOUT
–VS2 11
–15VOUT
+15VOUT
–15VOUT
GND2 10
25
VIN
GND3 SYNC +VS3
17 16 15
220nF
220nF
2.2µF
220nF
220nF
SYNC +15V
FIGURE 1. Basic Connections.
®
6
ISO256
and can be avoided by synchronizing the individual ISO256’s
together by tying the SYNC pins together or using the circuit
in Figure 2 to drive the SYNC pins from an external source.
supply on the ISO256 is a function of the total power drawn
from all outputs. For example if three outputs are not used
then maximum current can be drawn from one output. In all
cases, the total maximum current that can be drawn from any
combination of outputs is:
When connecting up to eight ISO256’s without a driver the
unit with the highest natural frequency will determine the
synchronized running frequency. The SYNC pin is sensitive
to capacitive loading: 150pf or less is recommended. If
unused, the SYNC pin should be left open. Avoid shorting
the SYNC pin directly to ground or supply potentials;
otherwise damage may result.
I1+
+ I1– + I2+ + I2– ≤ 50mΑ
+VS3, GND3
The waveform of the ground return current is an 800kHz
sawtooth. A capacitor between +VS3 and GND3 provides a
bypass for the AC portion of this current. The power should
never be instantaneously interrupted to the ISO256 (i.e., a
break in the line to +VS3 either by accidental or switch
means.) Normal power down of the +VS3 supply is not
considered instantaneous. Should a rapid break, in input
power occur the internal transformers voltage will rapidly
rise to maintain current flow and may cause internal damage
to the ISO256.
+15V
MC1472
or Equivalent
Peripheral
Driver
+5V
330Ω
2N3904
TTL
SYNC
ISO256
ISO256
620Ω
16
17
15
15
2N3904
SYNCHRONIZED OPERATION
100Ω
ISO256 can be synchronized to an external signal source.
This capability is useful in eliminating troublesome beat
frequencies in multi-channel systems and in rejecting AC
signals and their harmonics. To use this feature, tie all sync
pins together or apply an external signal to the SYNC pin.
ISO256 can be synchronized to an external oscillator over
the range 1-1.4MHz (this corresponds to a modulation fre-
quency of 500kHz to 700kHz as SYNC is internally divided
by 2).
16
17
To Other
ISO256’s
FIGURE 2. External SYNC drive.
Soft start circuitry protects the MOSFET switches during
startup. This is accomplished by holding the gate-to-source
voltage of both MOSFET switches low until the free-run-
ning oscillator is fully operational. In addition, soft start
circuitry and input current sensing also protects the switches.
This current limiting keeps the MOSFET switches operating
in their safe operating area under fault conditions or exces-
sive loads. When either of these conditions occur, the peak
input current exceeds a safe limit. The result is an approxi-
mate 5% duty cycle, 300µs drive period to the MOSFET
switches. This protects the internal MOSFET switches as
well as the external load from any thermal damage. When
the fault or excessive load is removed, the converter resumes
normal operation. A delay period of approximately 50µs
incorporated in the current sensing circuitry allows the
output filter capacitors to fully charge after a fault is re-
moved. This delay period corresponds to a filter capacitance
of no more than 1µf at either of the output pins. This
provides full protection of the MOSFET switches and also
sufficiently filters the output ripple voltage. The current
sensing circuitry is designed to provide thermal protection
for the MOSFET switches over the operating temperature
range as well. When these conditions are exceeded, the unit
will go into its shutdown mode.
CARRIER FREQUENCY CONSIDERATIONS
ISO256 amplifiers transmit the signal across the ISO-barrier
by a duty-cycle modulation technique. This system works
like any linear amplifier for input signals having frequencies
below one half the carrier frequency, fC. For signal frequen-
cies above fC/2, the behavior becomes more complex.
It should be noted that for the ISO256, the carrier frequency
is nominally 400kHz and the –3dB point of the amplifier is
50kHz. Spurious signals at the output are not significant
under these circumstances unless the input signal contains
significant components above 200kHz.
When periodic noise from external sources such as system
clocks and DC/DC converters are a problem, ISO256 can be
used to reject this noise. The amplifier can be synchronized
to an external frequency source, fEXT, placing the amplifier
response curve at one of the frequency and amplitude nulls
indicated in the “Signal Response vs Carrier Frequency”
performance curve.
ISOLATION MODE VOLTAGE
Isolation Mode Voltage (IMV) is the voltage appearing
between isolated grounds GND1 and GND2. IMV can
induce errors at the output as indicated by the plots of IMV
vs Frequency. It should be noted that if the IMV frequency
exceeds fC/2, the output will display spurious outputs in a
OUTPUT CURRENT RATINGS
The total current which can be drawn from each output
®
7
ISO256
manner similar to that described above, and the amplifier
response will be identical to that shown in the “Signal
Response vs Carrier Frequency” performance curve. This
occurs because IMV-induced errors behave like input-
referred error signals. To predict the total IMR, divide the
isolation voltage by the IMR shown in “IMR vs Frequency”
performance curve and compute the amplifier response to
this input-referred error signal from the data given in the
“Signal Response vs Carrier Frequency” performance curve.
Due to effects of very high-frequency signals, typical IMV
performance can be achieved only when dV/dT of the
isolation mode voltage falls below 1000V/µs. For conve-
nience, this is plotted in the typical performance curves
for the ISO256 as a function of voltage and frequency for
sinusoidal voltages. When dV/dT exceeds 1000V/µs but
falls below 20kV/µs, performance may be degraded. At rates
of change above 20kV/µs, the amplifier may be damaged,
but the barrier retains its full integrity. Lowering the power
supply voltage below 15V may decrease the dV/dT to
500V/µs for typical performance, but the maximum dV/dT
of 20kV/µs remains unchanged.
voltage gradient across the device continues to rise, another
partial discharge cycle begins. The importance of this
phenomenon is that, if the discharge does not occur, the
insulation system retains its integrity. If the discharge be-
gins, and is allowed to continue, the action of the ions and
electrons within the defect will eventually degrade any
organic insulation system in which they occur. The measure-
ment of partial discharge is still useful in rating the devices
and providing quality control of the manufacturing process.
The inception voltage for these voids tends to be constant, so
that the measurement of total charge being redistributed
within the dielectric is a very good indicator of the size of the
voids and their likelihood of becoming an incipient failure.
The bulk inception voltage, on the other hand, varies with
the insulation system, and the number of ionization defects
and directly establishes the absolute maximum voltage (tran-
sient) that can be applied across the test device before
destructive partial discharge can begin. Measuring the bulk
extinction voltage provides a lower, more conservative volt-
age from which to derive a safe continuous rating. In
production, measuring at a level somewhat below the ex-
pected inception voltage and then de-rating by a factor
related to expectations about system transients is an ac-
cepted practice.
Leakage current is determined solely by the impedance of
the barrier and transformer capacitance and is plotted in the
“Isolation Leakage Current vs Frequency” curve.
Partial Discharge Testing
ISOLATION VOLTAGE RATINGS
Not only does this test method provide far more qualitative
information about stress-withstand levels than did previous
stress tests, but it provides quantitative measurements from
which quality assurance and control measures can be based.
Tests similar to this test have been used by some manufac-
turers, such as those of high-voltage power distribution
equipment, for some time, but they employed a simple
measurement of RF noise to detect ionization. This method
was not quantitative with regard to energy of the discharge,
and was not sensitive enough for small components such as
isolation amplifiers. Now, however, manufacturers of HV
test equipment have developed means to quantify partial
discharge. VDE in Germany, an acknowledged leader in
high-voltage test standards, has developed a standard test
method to apply this powerful technique. Use of partial
discharge testing is an improved method for measuring the
integrity of an isolation barrier.
Because a long-term test is impractical in a manufacturing
situation, the generally accepted practice is to perform a
production test at a higher voltage for some shorter time.
The relationship between actual test voltage and the continu-
ous derated maximum specification is an important one.
Historically, Burr-Brown has chosen a deliberately conser-
vative one: VTEST = (2 x ACrms continuous rating) +
1000V for 10 seconds, followed by a test at rated ACrms
voltage for one minute. This choice was appropriate for
conditions where system transients are not well defined.
Recent improvements in high-voltage stress testing have
produced a more meaningful test for determining maximum
permissible voltage ratings, and Burr-Brown has chosen to
apply this new technology in the manufacture and testing of
the ISO256.
Partial Discharge
To accommodate poorly-defined transients, the part under
test is exposed to voltage that is 1.6 times the continuous-
rated voltage and must display less than or equal to 5pC
partial discharge level in a 100% production test.
When an insulation defect such as a void occurs within an
insulation system, the defect will display localized corona or
ionization during exposure to high-voltage stress. This ion-
ization requires a higher applied voltage to start the
discharge and lower voltage to maintain it or extinguish it
once started. The higher start voltage is known as the
inception voltage, while the extinction voltage is that level
of voltage stress at which the discharge ceases. Just as the
total insulation system has an inception voltage, so do the
individual voids. A voltage will build up across a void until
its inception voltage is reached, at which point the void will
ionize, effectively shorting itself out. This action redistrib-
utes electrical charge within the dielectric and is known as
partial discharge. If, as is the case with AC, the applied
APPLICATIONS
The ISO256 isolation amplifiers are used in three categories
of applications:
• Accurate isolation of signals from high voltage ground
potentials
• Accurate isolation of signals from severe ground noise and
• Fault protection from high voltages in analog measure-
ments
®
8
ISO256
+VS1 (+15V)
0.02µF
REF200
100µA
1nF
75kΩ
+VS2 (+15V)
0.1µF
2
1
3.3kΩ
FB
Mod
3
4
–VIN
16kΩ
16kΩ
14
VOUT
OPA27
4-20mA
25Ω
1nF
+VIN
0.1µF
ISO256
26
28
27
13
12
11
COM1
+VS1
COM2
+VS2
–VS2 (–15)
20kΩ
–VS1
–VS2
220nF
220nF
220nF
220nF
20kΩ
25
GND1
GND3
+VS3
15
2.2µF
17
+15V
FIGURE 3. Isolated 4-20mA Current Receiver with O/P Filter.
®
9
ISO256
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