ISO255 [BB]

Precision, Powered, Three-Port Isolated INSTRUMENTATION AMPLIFIER; 精度，供电，三端口隔离仪表放大器


型号：	ISO255
厂家：	BURR-BROWN CORPORATION
描述：	Precision, Powered, Three-Port Isolated INSTRUMENTATION AMPLIFIER 精度，供电，三端口隔离仪表放大器仪表放大器
文件：	总9页 (文件大小：99K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

ISO255

Precision, Powered, Three-Port Isolated

INSTRUMENTATION AMPLIFIER

FEATURES

DESCRIPTION

● RATED

ISO255 is a precision three-port isolated instrumenta-

tion amplifier incorporating a novel duty cycle modu-

lation-demodulation technique and has excellent accu-

racy. Internal input protection can withstand up to

±40V input differential 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. 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

● GAINS OF 1 TO 10,000

● LOW NONLINEARITY: ±0.05% typ

● LOW INPUT BIAS CURRENT: ±10nA max

● LOW INPUT OFFSET VOLTAGE

● INPUTS PROTECTED TO ±40V

● BIPOLAR OPERATION V_O= ±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

ISO255

● INDUSTRIAL PROCESS CONTROL

Transducer Isolator, Thermocouple

Isolator, RTD Isolator, Pressure Bridge

Isolator, Flow Meter Isolator

+V_IN

+R_G

V_OUT

INA

–R_G

–V_IN

● POWER MONITORING

● MEDICAL INSTRUMENTATION

● ANALYTICAL MEASUREMENTS

● BIOMEDICAL MEASUREMENTS

● DATA ACQUISITION

Com1

+V_S1

–V_S1

Com2

+V_S2

–V_S2

GND1

GND2

● TEST EQUIPMENT

● GROUND LOOP ELIMINATION

GND3 SYNC +V_S3

International Airport Industrial Park

•

Mailing Address: PO Box 11400, Tucson, AZ 85734

FAXLine: (800) 548-6133 (US/Canada Only)

•

Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706

•

Tel: (520) 746-1111

•

Twx: 910-952-1111

Internet: http://www.burr-brown.com/

•

Cable: BBRCORP

•

Telex: 066-6491

•

FAX: (520) 889-1510

•

Immediate Product Info: (800) 548-6132

PDS-1312B

Printed in U.S.A. April, 1996

SPECIFICATIONS

At T_A= +25°C, V_S3= 15V, R_L= 2kΩ, and 220nF capacitors on all generated supplies, unless otherwise noted.

ISO255P

TYP

PARAMETER

CONDITIONS

MIN

MAX

UNITS

ISOLATION

Voltage Rated Continuous:

100% Test (AC 50Hz)

Rated One Min

Isolation-Mode Rejection

_MINto T_MAX

1500

2500

Vrms

1s; Partial Discharge ≤ 5pC

120

AC 50Hz

1500Vrms

Barrier Impedance

Leakage Current

10¹⁴|| 2

1.4

Ω || pF

µArms

VISO = 240Vrms, 50Hz

GAIN

Gain Equation

Gain Error

1 + 50kΩ/R_G

0.15

V/V

G = 1

G = 10

G = 100

G = 1000

G = 1

±0.35

±0.95

0.15

0.2

±50

±0.05

Gain vs Temperature

Nonlinearity

ppm/°C

G = 10

G = 100

G = 1000

G = 1

G = 10

G = 100

G = 1000

±0.102

±0.104

INPUT OFFSET VOLTAGE

Initial Offset

vs Temperature

CMRR

± (0.125 + 101/G)

µV/°C

± (1 + 520/G)

vs Supply

mV/V

INPUT

Voltage Range

Bias Current

vs Temperature

Offset Current

vs Temperature

±10

pA/°C

±10

±40

OUTPUT

Voltage Range

Current Drive

±10

±5

Capacitive Load Drive

Ripple Voltage

0.1

µF

mVp-p

FREQUENCY RESPONSE

Small Signal Bandwidth

G = 1

G = 10

G = 100

G = 1000

G = 10

G = 1

G = 10

G = 100

G = 1000

0.2

240

kHz

V/µs

µs

Slew Rate

Settling Time, 0.1%

POWER SUPPLIES

Rated Voltage

Voltage Range

Quiescent Current

Rated Output Voltage

14.5

13.2

No Load

50mA Load On Two Supplies

Load Regulation

Line Regulation

SYNC Frequency

Output Voltage Ripple

mV/mA

V/V

MHz

1.4

TEMPERATURE RANGE

Operating

Storage

–40

°C

ISO255

PIN CONFIGURATION

ABSOLUTE MAXIMUM RATINGS

Supply Voltage ................................................................................... +18V

V_IN, 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

+R_G

–R_G

–V_IN

+V_IN

28 +V_S1

–V_S1

Com1

GND1

GND2

–V_S2

ELECTROSTATIC

+V_S2

GND3

SYNC

+V_S3

DISCHARGE SENSITIVITY

Com2

V_OUT

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

ISO255P

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

ISO255P

28-Pin Plastic DIP

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.

ISO255

TYPICAL PERFORMANCE CURVES (CONT)

At T_A= +25°C, +V_S3= 15V, R_L= 2kΩ, and 220nF capacitors on all generated supplies, unless otherwise noted.

ISOLATION LEAKAGE CURRENT vs FREQUENCY

(V = 240Vrms)

IMR vs FREQUENCY

100

120

100

10k

100k

100

10k

Frequency (Hz)

SINE RESPONSE

(f = 1kHz, G = 1)

SIGNAL RESPONSE vs CARRIER FREQUENCY

–10

–20

–30

–40

–50

–60

–70

–80

–90

–5

–10

100k 200k 300k 400k 500k 600k 700k 800k

Frequency (Hz)

500

1000

1500

2000

Time (µs)

SINE RESPONSE

(f = 10kHz, G = 1)

PULSE RESPONSE

(f = 1kHz, G = 1)

–5

–10

100

150

200

500

1000

Time (µs)

ISO255

TYPICAL PERFORMANCE CURVES (CONT)

At T_A= +25°C, +V_S3= 15V, R_L= 2kΩ, and 220nF capacitors on all generated supplies, unless otherwise noted.

PULSE RESPONSE

(f = 10kHz, G = 1)

GAIN vs FREQUENCY

G = 1000

G = 100

G = 10

–1

–20

–40

G = 1

–1

100

10k

100k

Time (µs)

100

Frequency (Hz)

INPUT COMMON-MODE RANGE

vs OUTPUT VOLTAGE

COMMON-MODE REJECTION vs FREQUENCY

140

120

100

G ≥ 10

G=1000

G = 1

G=100

G=10

G = 1

–

V_D/2

V_CM

V_O

–

G=1

–5

–10

–15

All Gains

–10

All Gains

100

10k

100k

–15

–5

Frequency (Hz)

Output Voltage (V)

INPUT BIAS AND OFFSET CURRENT

vs TEMPERATURE

ISOLATION MODE VOLTAGE

vs FREQUENCY

Max DC Rating

I_OS

2.1k

Max AC

Rating

1.0k

±I_b

Degraded

Performance

–1

–2

–3

–4

–5

100

Typical

Performance

–75

–50

–25

100

125

100

10k

100k

10M

100M

Temperature (°C)

Frequency (Hz)

ISO255

internal feedback resistors of the input amplifiers. These on

chip metal film resistors are laser trimmed to accurate

absolute values. The accuracy and temperature coefficient of

these resistors are included in the gain accuracy and drift

specifications of the ISO255.

BASIC OPERATION

ISO255 is a precision, powered, three-port isolated instru-

mentation amplifier. The input and output sections are gal-

vanically isolated by matched and EMI shielded capacitors

built into the plastic package. The DC/DC converter input is

also galvanically isolated from both the input and output

supplies.

INPUT COMMON-MODE RANGE

The linear common-mode range of the input circuitry of the

ISO255 is approximately ±14V (or 1V from the power

supplies). As the output voltage increases.

SIGNAL AND POWER CONNECTIONS

Figure 1 shows proper power and signal connections. The

power supply input pin +V_S3should be bypassed with a

2.2µF tantalum capacitor and the outputs V_S1and V_S2with

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 the input

section provides a low-impedance point for sensing signal

ground in noisy applications. Com1 and Com2 must have a

path to ground for signal current return and should be

maintained within ±1V of GND1 and GND2 respectively.

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 input gain.

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 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 ampli-

fier will be near zero. The output of the instrumentation

amplifier will be near 0V even though both inputs are

overloaded.

SETTING THE GAIN

Gain of the ISO255 is set by a single external resistor, R_G,

connected between pins 1 and 2:

50kΩ

(1)

G = 1+

R_G

The 50kΩ term in Equation 1 comes from the sum of the two

ISO255

+V_IN

+R_G

V_OUT14

V_IN

INA

V_OUT

R_G

–R_G

–V_IN

26 Com1

+V_S1

Com2 13

27 –V_S1

GND1

+V_S212

–V_S211

+15V_OUT

–15V_OUT

+15V_OUT

–15V_OUT

GND2 10

GND3 SYNC +V_S3

17 16 15

V_CM

220nF

2.2µF

220nF

SYNC +15V

FIGURE 1. Basic Connections.

ISO255

INPUT PROTECTION

When connecting up to eight ISO255’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.

The inputs of the amplifier are individually protected for

voltages up to ±40V. Internal circuitry on each input pro-

vides low series impedance under normal signal conditions.

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.

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.

DC/DC CONVERTER

ISO255 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 ISO255’s are used,

each channel can be synchronized via the SYNC pin.

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 ISO255 package. The control circuitry

consists of current limiting, soft start and synchronization

features. In instances where several ISO255’s are used in a

system, beat frequencies developed between the ISO255’s

are a potential source of low frequency noise in the supply

and ground paths. This noise may couple into the signal path

and can be avoided by synchronizing the individual ISO255’s

together by tying the SYNC pins together or using the circuit

in Figure 2 to drive the SYNC pins from an external source.

OUTPUT CURRENT RATINGS

The total current which can be drawn from each output

supply on the ISO255 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:

+15V

MC1472

or Equivalent

Peripheral

Driver

+5V

330Ω

I₁₊

+ I_1–+ I₂₊+ I_2–≤ 50mΑ

2N3904

TTL

+V_S3, GND3

SYNC

ISO255

620Ω

The waveform of the ground return current is an 800kHz

sawtooth. A capacitor between +V_S3and GND3 provides a

bypass for the AC portion of this current. The power should

never be instantaneously interrupted to the ISO255 (i.e., a

break in the line to +V_S3either by accidental or switch

means.) Normal power down of the +V_S3supply 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 ISO255.

2N3904

100Ω

To Other

ISO255’s

SYNCHRONIZED OPERATION

ISO255 can be synchronized to an external signal source.

This capability is useful in eliminating troublesome beat

FIGURE 2. External SYNC drive.

ISO255

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.

ISO255 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).

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.

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.

CARRIER FREQUENCY CONSIDERATIONS

ISO255 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, f_C. For signal frequen-

cies above f_C/2, the behavior becomes more complex. The

“Signal Response vs Carrier Frequency” performance curve

describes this behavior graphically.

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 ISO255.

It should be noted that for the ISO255, the carrier frequency

is nominally 400kHz 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 200kHz.

When periodic noise from external sources such as system

clocks and DC/DC converters are a problem, ISO255 can be

used to reject this noise. The amplifier can be synchronized

to an external frequency source, f_EXT, placing the amplifier

response curve at one of the frequency and amplitude nulls

indicated in the “Signal Response vs Carrier Frequency”

performance curve.

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

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 f_C/2, the output will display spurious outputs, 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 ISO255 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.

ISO255

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.

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 continuous-

rated voltage and must display less than or equal to 5pC

partial discharge level in a 100% production test.

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

APPLICATIONS

The ISO255 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

+15V

–15V

1µF Tantalum

200kΩ

Offset

+V_S1

1MΩ

REF102

45kΩ

OPA27

0.1µF

+R_G

+V_IN

–R_G

–V_S1

100kΩ

V_OUT

10kΩ

22kΩ

–V_IN

ISO255

+V_S1

–V_S1

Com2

+V_S2

–V_S2

220nF

OPA27

220nF

0.1µF

10kΩ

Com1

GND1

GND2

+V_S3

220nF

GND3

–V_S1

2.2µF

+15V

FIGURE 3. Conditioning a Bridge Circuit.

ISO255

ISO255 [BB]

相关型号：

ISO255P

ISO256

ISO256P

ISO2H823V2.5

ISO2H823V25

ISO3

ISO3080

ISO3080DW

ISO3080DWG4

ISO3080DWR

ISO3080DWRG4

ISO3080_09