©1996 Burr-Brown Corporation PDS-1307B Printed in U.S.A. February, 1996
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®
Precision, Isolated
PROGRAMMABLE GAIN AMPLIFIER
DESCRIPTION
ISO164 and ISO174 are PGA input isolation amplifi-
ers incorporating a novel duty cycle modulation-de-
modulation technique which provides excellent accu-
racy. Internal input protection can withstand up to
±40V differential inputs without damage. The signal is
transmitted digitally across a differential capacitive
barrier. With digital modulation the barrier character-
istics 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. ISO164
and ISO174 differ in frequency response and linearity.
These amplifiers are easy to use. No external compo-
nents are required. A power supply range of ±4.5V to
±18V makes these amplifiers ideal for a wide range of
applications.
ISO164
ISO174
FEATURES
●RATED
1500Vrms Continuous
2500Vrms for One Minute
100% TESTED FOR PARTIAL DISCHARGE
●PROGRAMMABLE GAINS OF
1, 10, 100
●HIGH IMR: 115dB at 50Hz
●LOW NONLINEARITY: ±0.01%
●LOW INPUT BIAS CURRENT: ±5nA max
●INPUTS PROTECTED TO ±40V
●BIPOLAR OPERATION: VO = ±10V
●SYNCHRONIZATION CAPABILITY
●24-PIN PLASTIC DIP: 0.6" 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
V
IN–
Ext Osc V
S1+
V
S2+
GND 1 V
S1–
V
S2–
20 2 13
21 1 15
Shield 2
V
OUT
Com 2
14
11
10
GND 2 12
A1
A0
V
IN+
3
24
23
4
DGND
22 Com1/
Shield 1
5
ISO174
ISO164
FPO
2
®
ISO164/ISO174
SPECIFICATIONS
At TA = +25°C, VS1 = VS2 = ±15V, and RL = 2kΩ, unless otherwise noted.
ISO164P ISO174P
PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS
ISOLATION(1)
Voltage Rated Continuous:
AC TMIN to TMAX 1500 1500 Vrms
100% Test (AC 50Hz) 1s; Partial Discharge ≤ 5pC 2500 2500 Vrms
Isolation-Mode Rejection
AC 50Hz 1500Vrms 115 115 dB
Barrier Impedance 1014 || 10 1014 || 10 Ω || pF
Leakage Current VISO = 240Vrms, 50Hz 0.8 1 0.8 1 µArms
GAIN
Gain Error G = 1 ±0.3 ±0.3 %
G = 10 ±0.06 ±0.06
G = 100 ±0.3 ±0.3 %
Gain vs Temperature G = 1 ±12.5 ±42.5 ppm/°C
G = 10 ±12.5 ±42.5 ppm/°C
G = 100 ±12.5 ±42.5 ppm/°C
Nonlinearity G = 1 ±0.01 ±0.052 ±0.04 ±0.102 %
G = 10 ±0.01 ±0.04 %
G = 100 ±0.01 ±0.054 ±0.04 ±0.104 %
INPUT OFFSET VOLTAGE
Initial Offset mV
vs Temperature G = 1 ±155 ±505 µV/°C
vs Supply DC, G = 1 2 2 mV/V
CMRR DC, G = 1 90 90 dB
INPUT
Voltage Range ±10.0 ±10.0 V
Bias Current ±5±5nA
vs Temperature ±8±8 pA/°C
Offset Current ±5±5nA
vs Temperature ±8±8 pA/°C
OUTPUT
Voltage Range ±10 ±10 V
Current Drive ±5±5mA
Capacitive Load Drive 0.1 0.1 µF
Ripple Voltage 10 10 mVp-p
FREQUENCY RESPONSE
Small Signal Bandwidth 100mVrms, G = 1 6 60 kHz
100mVrms, G = 10 6 60 kHz
100mVrms, G = 100 6 10 kHz
Slew Rate VO = ±10V, G = 10 0.7 0.7 V/µs
POWER SUPPLIES
Rated Voltage 15 15 V
Voltage Range ±4.5 ±18 ±4.5 ±18 V
Quiescent Current
VS1 ±15 ±15 mA
VS2 ±7.5 ±7.5 mA
TEMPERATURE RANGE
Operating –40 85 –40 85 °C
Storage –40 125 –40 125 °C
NOTE: (1) All devices receive a 1s test. Failure criterion is ≥ 5 pulses of ≥ 5pc.
±0.125 +51
G
±0.125 +101
G
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
®
ISO164/ISO174
PIN CONFIGURATION
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
PRODUCT PACKAGE NUMBER(1)
ISO164P 24-Pin Plastic DIP 167-1
ISO174P 24-Pin Plastic DIP 167-1
NOTE: (1) For detailed drawing and dimension table, please see end of data
sheet, or Appendix C of Burr-Brown IC Data Book.
ELECTROSTATIC
DISCHARGE SENSITIVITY
ABSOLUTE MAXIMUM RATINGS
Supply Voltage................................................................................... ±18V
VIN, Analog Input Voltage Range ....................................................... ±40V
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
ORDERING INFORMATION
PRODUCT PACKAGE BANDWIDTH
ISO164P 24-Pin Plastic DIP 6kHz
ISO174P 24-Pin Plastic DIP 60kHz
V
IN–
V
IN+
Com 2
V
OUT
GND 2
Com 1/
Shield 1
DGND
EXT OSC
GND 1
V
S2+
Shield 2
V
S2–
V
S1–
A0
V
S1+
1
2
3
4
5
10
11
12
24
23
22
21
20
15
14
13
A1
TYPICAL PERFORMANCE CURVES
At TA = +25°C, VS1 = VS2 = ±15V, and RL = 2kΩ, unless otherwise noted.
1
Frequency (Hz)
0
60
40
20
PSRR (dB)
PSRR vs FREQUENCY
100 10k 1M
10 1k 100k
–V
S1
, –V
S2
+V
S1
, +V
S2
54
100
Frequency (Hz)
10
1k
100
Peak Isolation Voltage
ISOLATION MODE VOLTAGE vs FREQUENCY
10k 1M 100M
1k 100k 10M
2.1k Max AC
Rating
Degraded
Performance
Max DC Rating
Typical
Performance
4
®
ISO164/ISO174
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C, VS1 = VS2 = ±15V, and RL = 2kΩ, unless otherwise noted.
0
f
IN
(Hz)
0
–20
–40
V
OUT
/V
IN
(dB)
SIGNAL RESPONSE vs CARRIER FREQUENCY
f
C
2f
C
3f
C
0000f
c
/2 f
C
/2 f
C
/2
f
OUT
(Hz)
–20dB/dec (for comparison only)
1
Frequency (Hz)
40
160
140
120
100
80
60
IMR (dB)
100 10k 1M10 1k 100k
IMR vs FREQUENCY
1
Frequency (Hz)
0.1µA
100mA
10mA
1mA
100µA
10µA
1µA
Leakage Current (rms)
ISOLATION LEAKAGE CURRENT
vs FREQUENCY
100 10k 1M10 1k 100k
240 Vrms
1500 Vrms
0
Time (µs)
15
10
5
0
–5
–10
–15
Input Voltage (V)
15
10
5
0
–5
–10
–15
Output Voltage (V)
20001000
SINE RESPONSE ISO164
(1kHz)
0
Time (µs)
15
10
5
0
–5
–10
–15
Input Voltage (V)
15
10
5
0
–5
–10
–15
Output Voltage (V)
1000900800700600500400300200100
STEP RESPONSE ISO164
(1kHz)
0
Time (µs)
15
10
5
0
–5
–10
–15
Input Voltage (V)
15
10
5
0
–5
–10
–15
Output Voltage (V)
1000100
PULSE RESPONSE ISO174
(10kHz)
5
®
ISO164/ISO174
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
Temperature (°C)
Input Bias and Input Offset Current (nA)
–75
2
1
0
–1
–2 –25 25 75 100 125
±I
B
I
OS
–50 0 50
0
Time (µs)
15
10
5
0
–5
–10
–15
Input Voltage (V)
15
10
5
0
–5
–10
–15
Output Voltage (V)
20001000
SINE RESPONSE ISO174
(1kHz)
0
Time (µs)
15
10
5
0
–5
–10
–15
Input Voltage (V)
15
10
5
0
–5
–10
–15
Output Voltage (V)
20001000
SINE RESPONSE ISO174
(10kHz)
0
Time (µs)
15
10
5
0
–5
–10
–15
Input Voltage (V)
15
10
5
0
–5
–10
–15
Output Voltage (V)
1000900800700600500400300200100
STEP RESPONSE ISO174
(1kHz)
INPUT COMMON-MODE VOLTAGE RANGE
vs OUTPUT VOLTAGE
Output Voltage (V)
Common-Mode Voltage (V)
–15 –10 0 5 15–5
15
10
5
0
–5
–10
–15 10
V
D/2
–
+
–
+
VCM
VO
(Any Gain)
V
D/2
6
®
ISO164/ISO174
Input-overload can produce an output voltage that appears
normal. For example, an input voltage of +20V on one input
and +40V on the other input will obviously exceed the linear
common-mode range of both input amplifiers. Since both
input amplifiers are saturated to nearly the same output
voltage limit, the difference voltage measured by the output
amplifier will be near zero. The output of the programmable-
gain amplifier will be near 0V even though both inputs are
overloaded.
INPUT PROTECTION
The inputs of the programmable-gain amplifiers are indi-
vidually protected for voltages up to ±40V. For example, a
condition of –40V on one input and +40V on the other input
will not cause damage. Internal circuitry on each input
provides low series impedance under normal signal condi-
tions. To provide equivalent protection, series input resistors
would contribute excessive noise. If the input is overloaded,
the protection circuitry limits the input current to a safe
value (approximately 1.5mA). The inputs are protected even
if no power supply is present.
SYNCHRONIZED OPERATION
ISO164 and ISO174 can be synchronized to an external
signal source. This capability is useful in eliminating trouble-
some beat frequencies in multichannel systems and in reject-
ing AC signals and their harmonics. To use this feature, an
external signal must be applied to the Ext Osc pin. ISO164
can be synchronized over the 100kHz to 200kHz range and
ISO174 can be synchronized over the 400kHz to 700kHz
range.
BASIC OPERATION
ISO164 and ISO174 are comprised of a precision program-
mable gain 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 capaci-
tor 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 GND 1 and GND 2 respectively.
INPUT COMMON-MODE RANGE
The linear common-mode range of the input circuitry of the
ISO164/174 is approximately ±12.7V (or 2.3V from the
power supplies). As the output voltage increases, however,
the linear input range will be limited by the output voltage
swing of the internal amplifiers. Thus, the linear common-
mode range is related to the output voltage of the complete
input amplifier—see performance curves “Input Common-
Mode Range vs Output Voltage.”
A combination of common-mode and differential input
voltage can cause the output voltage of the internal amplifi-
ers to saturate. For applications where input common-mode
range must be maximized, limit the output voltage swing by
selecting a lower gain of the programmable-gain input.
FIGURE 1. Basic Connections.
V
IN–
Ext OSC V
S1+
V
S2+
V
S1–
V
S2–
V
S2–
V
OUT
V
S2+
V
S1–
V
S1+
V
IN–
V
IN+
R
LOAD
20 2
Com 1/Shield 1
513
21
0.1µF 1µF
115
Shield 2
V
OUT
Com 2
14
11
10
A1
A0
V
IN+
3
24
23
4
GND 1
1µF0.1µF
1µF 0.1µF
1µF 0.1µF
1
10
100
0
0
1
0
1
0
GAIN A1 A0
22 DGND GND 2 12
7
®
ISO164/ISO174
The ideal external clock signal for the ISO164 and ISO174
is a ±4V sine wave or ±4V, 50% duty-cycle triangle wave.
The Ext Osc pin of the ISO164 and ISO174 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/de-
modulator circuitry will synchronize to the signal.
ISO174 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 ISO174.
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 ISO164 and ISO174 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 ISO174 and 680pF for ISO164.
under these circumstances unless the input signal contains
significant components above 250kHz.
For the ISO164, the carrier frequency is nominally 110kHz
and the –3dB point of the amplifier is 6kHz.
When periodic noise from external sources such as system
clocks and DC/DC converters are a problem, ISO164 and
ISO174 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. Figure 3 shows circuitry
with opto-isolation suitable for driving the Ext Osc input
from TTL levels.
CARRIER FREQUENCY CONSIDERATIONS
ISO164 and ISO174 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 frequencies above fC/2, the behavior becomes
more complex. The “Signal Response vs 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.
It should be noted that for the ISO174, the carrier frequency
is nominally 500kHz and the –3dB point of the amplifier is
60kHz. Spurious signals at the output are not significant
ISOLATION MODE VOLTAGE
Isolation Mode Voltage (IMV) is the voltage appearing
between isolated grounds GND 1 and GND 2. The 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
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 ISO164 and ISO174 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
FIGURE 2. Square-Wave to Triangle Wave Signal Condi-
tioner for Driving ISO164/174 Ext Osc Pin.
10kΩ
CX
OPA602
RX
1µF
Sq Wave In Triangle Out
to ISO164/174
Ext Osc
1kΩFIGURE 3. Synchronization with Isolated Drive Circuit for
Ext Osc Pin.
C
1
Ext Osc
Pin 21
ISO164/174
C
2
10kΩ
6
5
82
3
TTL
f
IN
2.5kΩ
200Ω
+15V+5V
f
IN
140E-6
()
C
1
= – 350pF
C
2
= 10 x C
1
, with a minimum 10nF
2.5kΩ
6N136
8
®
ISO164/ISO174
decrease the dV/dT to 500V/µs for typical performance, but
the maximum dV/dT of 20kV/µs remains unchanged.
Leakage current is determined solely by the impedance of
the barrier capacitance and is plotted in the “Isolation Leak-
age 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 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 ISO164 and ISO174.
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 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
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 derating by a factor
related to expectations about system transients is an ac-
cepted practice.
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 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.
To accommodate poorly-defined transients, the part under
test is exposed to a 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.
APPLICATIONS
The ISO164 and ISO174 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
