Amplifier and Data Converter Selection Guide

48 Amplifiers
➔
Isolation Amplifiers
There are many applications where it is
desirable, even essential, that a sensor not
have a direct (galvanic) electrical connection
with the system to which it is supplying data
in order to avoid either dangerous voltages or
currents from one half of the system from
damaging the other half. Such a system is
said to be "isolated", and the area which
passes a signal without galvanic connections
is known as an "isolation barrier".
Isolation barrier protection works in both
directions, and may be needed in either half
of the system, sometimes both. Common
applications requiring isolation protection are
3.3V, High-Speed Digital Isolators
ISO721, ISO722
those where sensors may accidentally
encounter high voltages and the system it is
driving must be protected. Or a sensor may
need to be isolated from accidental high
voltages arising downstream in order to
protect its environment: examples include
prevention of explosive gas ignition caused
by sparks at sensor locations or protecting
patients from electric shock by ECG, EEG and
EMG test and monitoring equipment. The
ECG application may require isolation barriers
in both directions: the patient must be
protected from the very high voltages
(>7.5kV) applied by the defibrillator, and the
technician handling the device must be
protected from unexpected feedback.
Applications for Isolation Amplifiers
• Sensor is at a high potential relative to
other circuitry (or may become so under
fault conditions)
• Sensor may not carry dangerous voltages,
irrespective of faults in other circuitry (e.g.
patient monitoring and intrinsically safe
equipment for use with explosive gases)
• To break ground loops
Get samples, datasheets, EVMs and app reports at: www.ti.com/sc/device/ISO721
Key Features
• 4000V isolation
• Fail-safe output
• Signaling rate up to 100Mbps
• UL 1577, IEC 60747-5-2 (VDE 0884,
Rev. 2), IEC 61010-1 and CSA Approved
• 25kV/µs transient immunity
Applications
• Industrial fieldbus
• Servo monitoring and control
The ISO721 digital isolator is a logic input and output buffer separated by a silicon oxide (SiO 2 )
insulation barrier that provides galvanic isolation of up to 4000V. Used in conjunction with
isolated power supplies, the device prevents noise currents on a data bus or other circuits from
entering the local ground and interfering with or damaging sensitive circuitry.
A binary input signal is conditioned, translated to a balanced signal, then differentiated by the
capacitive isolation barrier. Across the isolation barrier, a differential comparator receives the
logic transition information, then sets or resets a flip-flop and the output circuit accordingly. A
periodic update pulse is sent across the barrier to ensure the proper dc level of the output. If
this dc-refresh pulse is not received for more than 4µs, the input is assumed to be unpowered
or not functional and the fail-safe circuit drives the output to a logic high state.
ISO721 functional
block diagram.
OSC
+
PWM
DC Channel
Isolation
Barrier
V REF
Filter
PWD
Carrier
Detect
POR
BIAS
POR
Isolation Amplifiers Selection Guide
IN
Input
+
Filter
AC Channel
V REF
(722 Only)
Data MUX
EN
AC Detect
3-State OUT
Output
Buffer
Isolation Isolation Isolation Input Small-
Voltage Cont Voltage Pulse/ Mode Gain Offset Voltage Signal
Peak (DC) Test Peak Rejection DC Nonlinearity Drift (±µV/°C) Bandwidth
Device Description (V) (V) (dB) (typ) (%) (max) (max) (kHz) (typ) Package(s) Price *
ISO122 1500V RMS Isolation, Buffer 2121 2400 140 0.02 200 50 DIP-16, SOIC-28 $9.40
ISO124 1500V RMS Isolation, Buffer 2121 2400 140 0.01 200 50 DIP-16, SOIC-28 $7.20
Digital Couplers
Isolation Isolation Peak Working Data Transient Propagation
Voltage Cont Voltage Pulse/ Transient Voltage Rate Immunity Delay PWD ICCQ
Peak (DC) Test Peak Overvoltage VIORM (max) (min) at 5V (max) at 5V (max) at 5V (max) Supply
Device Description (V) (V) VIOTM (V) (V) (Mbps) (KV/µs) (ns) (ns) (mA) Voltage Package(s) Price *
ISO150 Dual Channel Bi-directional 1500 2400 — — 80 1.6 40 6 10 5V DIP-12, SO-12 $8.10
Digital Isolator
ISO721 Single Channel, 3.3V/5V — — 4000 560 100 25 24 2 13 3.3V, 5V SO-8 $1.65
Digital Isolators
ISO721M Single Channel, 3.3V/5V — — 4000 560 150 25 16 1 13 3.3V, 5V SO-8 $1.65
Digital Isolators
* Suggested resale price in U.S. dollars in quantities of 1,000. New products are listed in bold red.
Amplifier and Data Converter Selection Guide Texas Instruments 3Q 2006