BB ISO176

®
ISO176
ISO
176
Precision, Isolated
OPERATIONAL AMPLIFIER
FEATURES
DESCRIPTION
● RATED
1500Vrms Continuous
2500Vrms for One Minute
100% TESTED FOR PARTIAL DISCHARGE
ISO176 is a precision isolation amplifier incorporating
an uncommitted operational amplifier for input conditioning, a novel duty cycle modulation-demodulation
technique and excellent accuracy. Internal input protection can withstand up to ±30V 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 results in excellent reliability and good high
frequency transient immunity across the barrier. Both
the amplifier and barrier capacitors are housed in a
plastic DIP.
● HIGH IMR: 115dB at 50Hz
● LOW NONLINEARITY: ±0.05%
● LOW INPUT BIAS CURRENT: ±5nA max
● LOW INPUT OFFSET VOLTAGE: ±20µV
● OP AMP INPUTS PROTECTED TO ±30V
● MOD INPUT PROTECTED TO ±100V
● BIPOLAR OPERATION: VO = ±10V
● SYNCHRONIZATION CAPABILITY
ISO176 is easy to use. No external components are
required. A power supply range of ±4.5V to ±18V
makes this amplifier ideal for a wide range of applications.
● 24-PIN PLASTIC DIP: 0.3" Wide
APPLICATIONS
● INDUSTRIAL PROCESS CONTROL
Transducer Isolator, Thermocouple
Isolator, RTD Isolator, Pressure Bridge
Isolator, Flow Meter Isolator
● POWER MONITORING
● MEDICAL INSTRUMENTATION
● ANALYTICAL MEASUREMENTS
● BIOMEDICAL MEASUREMENTS
● DATA ACQUISITION
● TEST EQUIPMENT
● POWER MONITORING
● GROUND LOOP ELIMINATION
5
Shield 1
21
MOD
2
VOUT
22
Ext Osc
4
+VS1
15
+VS2
Shield 2
OUT
24
VIN–
1
VIN+
Com2
GND1
–VS1
20
3
Com1
23
–VS2
13
14
11
10
GND2
12
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111
Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
©
1996 Burr-Brown Corporation
PDS-1294A
A
Printed in U.S.A. May, 1996
SPECIFICATIONS
At TA = +25°C, VS1 = VS2 = ±15V, and RL = 2kΩ unless otherwise noted.
ISO176P
PARAMETER
ISOLATION(1)
Voltage Rated Continuous:
AC
DC
100% Test (AC, 50Hz)
Isolation-Mode Rejection
AC 50Hz
DC
Barrier Impedance
Leakage Current
ISO AMP - GAIN
Gain Error(2)
Gain vs Temperature
Nonlinearity
CONDITIONS
MIN
TMIN to TMAX
TMIN to TMAX
1s; Partial Discharge ≤ 5pC
1500
2121
2500
1500Vrms
TYP
±0.05
±10
G=1
G=1
G=1
UNITS
Vrms
VDC
Vrms
115
160
1014 || 6
0.8
VISO = 240Vrms, 50Hz
MAX
1
dB
dB
Ω || pF
µArms
±0.102
%FSR
ppm/°C
%
ISO AMP - OFFSET VOLTAGE
Offset
vs Temperature
vs Supply
±500
±2
mV
µV/°C
µV/V
ISO AMP - INPUT
Input Resistance
200
kΩ
0.1
10
V
mA
µF
mVp-p
100
ISO AMP - OUTPUT
Voltage Range
Current Drive
Capacitive Load Drive
Ripple Voltage
±10
±5
OP AMP - INPUT
Voltage Range
Bias Current
vs Temperature
Offset Voltage
Offset Current
vs Temperature
±13
±15
±20
±1.5
FREQUENCY RESPONSE
Small Signal Bandwidth
Slew Rate
100mV, G = 1
100mV, G = 10
100mV, G = 100
V O = ±10V, G = 10
±5
±5
60
60
60
0.3
POWER SUPPLIES
Rated Voltage
Voltage Range
Quiescent Current
VCC1
VCC2
kHz
kHz
kHz
V/µs
15
±4.5
±18
9
7.5
TEMPERATURE RANGE
Operating
Storage
–40
–40
V
nA
pA/°C
µV
nA
pA/°C
V
V
mA
mA
85
125
°C
°C
NOTE: (1) All devices receive a 1s test. Failure criterion is ≥ 5 pulses of ≥ 5pX. (2) Tested as a OPA and ISO, max ±0.35% FSR.
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.
®
ISO176
2
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
Supply Voltage ................................................................................... ±18V
Op Amp Analog Input Voltage Range ................................................. ±VS1
External Oscillator Input ..................................................................... ±25V
Signal Common 1 to Ground 1 ............................................................ ±1V
Signal Common 2 to Ground 2 ............................................................ ±1V
Continuous Isolation Voltage: .................................................... 1500Vrms
IMV, dv/dt ...................................................................................... 20kV/µs
Junction Temperature ...................................................................... 150°C
Storage Temperature ...................................................... –40°C to +125°C
Lead Temperature (soldering, 10s) ................................................ +300°C
Output Short Duration .......................................... Continuous to Common
MOD Input Voltage Range ............................................................... ±100V
ELECTROSTATIC
DISCHARGE SENSITIVITY
VIN+
1
24 VIN–
VOUT
2
23 Com 1
–VS1
3
22 Ext OSC
+VS1
4
21 MOD
Shield 1
5
20 GND 1
Com 2 10
OUT 11
GND 2 12
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 degradation 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.
15 +VS2
14 Shield 2
13 –VS2
PACKAGE/ORDERING INFORMATION
PRODUCT
ISO176P
PACKAGE
PACKAGE
DRAWING
NUMBER(1)
BANDWIDTH
24-Pin Plastic DIP
243-2
60kHz
NOTE: (1) For detailed drawing and dimension table, please see end of data
sheet, or Appendix C of Burr-Brown IC Data Book.
®
3
ISO176
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, VS1 = VS2 = ±15V, and RL = 2kΩ, unless otherwise noted.
ISOLATION MODE VOLTAGE vs FREQUENCY
PSRR vs FREQUENCY
60
54
Max AC
Rating
1k
40
PSRR (dB)
Degraded
Performance
100
+VS1, +VS2
–VS1, –VS2
20
Typical
Performance
10
0
100
10k
1k
100k
1M
10M
100M
1
10
100
Frequency (Hz)
10k
100k
1M
100k
1M
IMR vs FREQUENCY
100mA
160
10mA
140
120
IMR (dB)
1mA
1500 Vrms
100µA
10µA
100
80
240 Vrms
60
1µA
40
0.1µA
10
1
100
1k
10k
100k
1
1M
10
100
1k
10k
Frequency (Hz)
Frequency (Hz)
SIGNAL RESPONSE
vs CARRIER FREQUENCY
SINE RESPONSE
(10kHz)
Input Voltage (V)
Leakage Current (rms)
ISOLATION LEAKAGE CURRENT
vs FREQUENCY
0
VOUT/VIN (dB)
1k
Frequency (Hz)
–20dB/dec (for comparison only)
15
10
5
0
–5
–10
–20
10
5
0
–5
–40
–10
–15
fIN (Hz)
0
fC
2fC
0
3fC
20
40
60
80
100 120 140
Time (µs)
fOUT (Hz) 0
fc /2
0
fC /2
0
fC /2
0
®
ISO176
4
160 180 200
Input Voltage (V)
Peak Isolation Voltage
Max DC Rating
2.1k
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, VS1 = VS2 = ±15V, and RL = 2kΩ, unless otherwise noted.
INPUT BIAS AND INPUT OFFSET CURRENT
vs TEMPERATURE
10
5
0
–5
10
5
0
–5
–10
100 200 300
400 500 600 700
2
1
IB
I OS
0
–1
–2
–40
–15
800 900 1000
–15
10
35
60
85
Temperature (°C)
Time (µs)
STEP RESPONSE
(2kHz)
15
10
5
0
–5
–10
10
5
0
–5
–10
Input Voltage (V)
0
Input Voltage (V)
–10
Input Bias and Input Offset Current (nA)
15
Input Voltage (V)
Input Voltage (V)
SINE RESPONSE
(2kHz)
–15
0
50
100 150
200 250 300 350
400 450 500
Time (µs)
®
5
ISO176
BASIC OPERATION
INPUT BIAS CURRENT CANCELLATION
The input stage base current of the uncommitted op amp is
internally compensated with an equal and opposite cancellation current. The resulting input bias current is the difference
between the input stage base current and the cancellation
current. This residual input bias current can be positive or
negative.
ISO176 isolation amplifier comprises a precision uncommitted operational amplifier followed by an isolation amplifier.
The input and output isolation sections are galvanically
isolated by matched and EMI shielded capacitors.
Signal and Power Connections
Figure 1 shows power and signal connections. Each power
supply pin should be bypassed with a 1µF tantalum capacitor located as close to the amplifier as possible. All ground
connections should be run independently to a common
point. Signal Common on both input and output sections
provide a high-impedance point for sensing signal ground in
noisy applications. Com 1 and Com 2 must have a path to
ground for bias current return and should be maintained
within ±1V of GND1 and GND2, respectively.
When the bias current is cancelled in this manner, the input
bias current and input offset current are approximately the
same magnitude. As a result, it is not necessary to balance
the DC resistance seen at the two input terminals. A resistor
added to balance the input resistances may actually
increase offset and noise.
SYNCHRONIZED OPERATION
ISO176 can be synchronized to an external signal source.
This capability is useful in eliminating troublesome beat
frequencies in multichannel systems and in rejecting AC
signals and their harmonics. To use this feature, an external
signal must be applied to the Ext Osc pin. ISO176 can be
synchronized over the 400kHz to 700kHz range.
INPUT PROTECTION
The amplifier inputs of ISO176 are protected with 500Ω
series input 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 behavior of unity-gain follower applications, but it will not damage the op amp. The MOD input is a 200kΩ resistor and can
withstand ±100V without damage.
The ideal external clock signal for ISO176 is a ±4V sine
wave or ±4V, 50% duty-cycle triangle wave. The Ext Osc
pin of the ISO176 can be driven directly with a ±3V to ±5V
sine or 25% to 75% duty-cycle triangle wave and the ISO
amp’s internal modulator/demodulator circuitry will synchronize to the signal.
–
0.1µF
–
1µF
+
+
1µF
0.1µF
+VS1
+VS2
5
Shield 1
22
Ext Osc
4
+VS1
15
+VS2
21 MOD
Shield 2
14
2 VOUT
OUT 11
24 VIN–
Com2
1 VIN+
VIN+
–VS1
0.1µF
GND 1
–VS1
20
3
Com 1
23
–
+
1µF
®
6
RLOAD
GND 2
13
FIGURE 1. Basic Connections.
ISO176
–VS2
10
12
–
+
1µF
–VS2
0.1µF
When periodic noise from external sources such as system
clocks and DC/DC converters are a problem, ISO176 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.
ISO176 can also be synchronized to a 400kHz to 700kHz
Square-Wave External Clock since an internal clamp and
filter provide signal conditioning. A square-wave signal of
25% to 75% duty cycle, and ±3V to ±20V level can be used
to directly drive the ISO176.
With the addition of the signal conditioning circuit shown in
Figure 2, any 10% to 90% duty-cycle square-wave signal
can be used to drive the ISO176 Ext Osc pin. With the values
shown, the circuit can be driven by a 4Vp-p TTL signal. For
a higher or lower voltage input, increase or decrease the 1kΩ
resistor, RX, proportionally, e.g. for a ±4V square-wave
(8Vp-p) RX should be increased to 2kΩ. The value of CX
used in the Figure 2 circuit depends on the frequency of the
external clock signal. CX should be 30pF for ISO176.
ISOLATION MODE VOLTAGE
Isolation Mode Voltage (IMV) is the voltage appearing
between isolated grounds GND1 and GND2. The IMV can
induce error at the output as indicated by the plots of IMV
versus Frequency. It should be noted that if the IMV frequency exceeds fC/2, the output will display spurious outputs in a 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 inputreferred 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 convenience, this is plotted in the typical performance curves for
the 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
voltages below ±15V may decrease the dV/dT to 500V/µs
for typical performance, but the maximum dV/dT of 20kV/
µs remains unchanged.
10kΩ
1µF
Square-Wave In
RX
1kΩ
CX
OPA602
Triangle Out
to ISO166/176
Ext Osc
FIGURE 2. Square-Wave to Triangle Wave Signal Conditioner for Driving ISO176 Ext Osc Pin.
CARRIER FREQUENCY CONSIDERATIONS
ISO176 amplifier transmits 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 frequencies above fC/2, the behavior becomes more complex. The
Signal Response versus Carrier Frequency performance curve
describes this behavior graphically. The upper curve illustrates the response for input signals varying from DC to fC/
2. At input frequencies at or above fC/2, the device generates
an output signal component that varies in both amplitude
and frequency, as shown by the lower curve. The lower
horizontal scale shows the periodic variation in the frequency of the output component. Note that at the carrier
frequency and its harmonics, both the frequency and amplitude of the response go to zero. These characteristics can be
exploited in certain applications.
Leakage current is determined solely by the impedance of
the barrier capacitance and is plotted in the “Isolation Leakage Current vs Frequency” curve.
ISOLATION VOLTAGE RATINGS
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 continuous derated maximum specification is an important one.
Historically, Burr-Brown has chosen a deliberately conservative 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 ISO176.
It should be noted that for the ISO176, the carrier frequency
is nominally 500kHz and the –3dB point of the amplifier is
60kHz. Spurious signals at the output are not significant
under these circumstances unless the input signal contains
significant components above 250kHz.
®
7
ISO176
PARTIAL DISCHARGE
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 ionization 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 redistributes electrical charge within the dielectric and is known as partial
discharge. If, as is the case with AC, the applied 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 begins, 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 measurement 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 (transient) that
can be applied across the test device before destructive
partial discharge can begin. Measuring the bulk extinction
voltage provides a lower, more conservative voltage from
which to derive a safe continuous rating.
PARTIAL DISCHARGE TESTING
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 manufacturers, 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.
To accommodate poorly-defined transients, the part under
test is exposed to voltage that is 1.6 times the continuousrated voltage and must display less than or equal to 5pC
partial discharge level in a 100% production test.
APPLICATIONS
ISO176 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 measurements.
®
ISO176
8