Amplifier and Data Converter Selection Guide (Rev. B

AmplifiersIsolation Amplifiers49➔There are many applications where it isdesirable, even essential, that a sensor nothave a direct (galvanic) electrical connectionwith the system to which it is supplying datain order to avoid either dangerous voltages orcurrents from one half of the system fromdamaging the other half. Such a system issaid to be "isolated", and the area whichpasses a signal without galvanic connectionsis known as an "isolation barrier".Isolation barrier protection works in bothdirections, and may be needed in either halfof the system, sometimes both. Commonapplications requiring isolation protection are3.3V, High-Speed Digital IsolatorsISO721, ISO722those where sensors may accidentallyencounter high voltages and the system it isdriving must be protected. Or a sensor mayneed to be isolated from accidental highvoltages arising downstream in order toprotect its environment: examples includeprevention of explosive gas ignition causedby sparks at sensor locations or protectingpatients from electric shock by ECG, EEG andEMG test and monitoring equipment. TheECG application may require isolation barriersin both directions: the patient must beprotected from the very high voltages(>7.5kV) applied by the defibrillator, and thetechnician handling the device must beprotected from unexpected feedback.Applications for Isolation Amplifiers• Sensor is at a high potential relative toother circuitry (or may become so underfault conditions)• Sensor may not carry dangerous voltages,irrespective of faults in other circuitry (e.g.patient monitoring and intrinsically safeequipment for use with explosive gases)• To break ground loopsGet samples, datasheets, evaluation modules and app reports at: www.ti.com/ISO721 and www.ti.com/sc/device/ISO722Key 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 immunityApplications• Industrial fieldbus• Servo monitoring and controlThe 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 withisolated power supplies, the device prevents noise currents on a data bus or other circuits fromentering the local ground and interfering with or damaging sensitive circuitry.A binary input signal is conditioned, translated to a balanced signal, then differentiated by thecapacitive isolation barrier. Across the isolation barrier, a differential comparator receives thelogic transition information, then sets or resets a flip-flop and the output circuit accordingly. Aperiodic update pulse is sent across the barrier to ensure the proper dc level of the output. Ifthis dc-refresh pulse is not received for more than 4µs, the input is assumed to be unpoweredor not functional and the fail-safe circuit drives the output to a logic high state.ISO721 functionalblock diagram.OSC+PWMDC ChannelIsolationBarrierV REFFilterPWDCarrierDetectPORBIASPORIsolation Amplifiers Selection GuideINInput+FilterAC ChannelV REF(722 Only)Data MUXENAC Detect3-State OUTOutputBufferIsolation Isolation Isolation Input Small-Voltage Cont Voltage Pulse/ Mode Gain Offset Voltage SignalPeak (DC) Test Peak Rejection DC Nonlinearity Drift (±µV/°C) BandwidthDevice Description (V) (V) (dB) (typ) (%) (max) (max) (kHz) (typ) Package(s) Price *ISO122 1500V RMS Isolation, Buffer 1500 2400 140 0.05 200 50 DIP-16, SOIC-28 $9.40ISO124 1500V RMS Isolation, Buffer 1500 2400 140 0.01 200 50 DIP-16, SOIC-28 $7.20Digital CouplersIsolation Isolation Peak Working Data Transient PropagationVoltage Cont Voltage Pulse/ Transient Voltage Rate Immunity Delay PWD I CCQPeak (DC) Test Peak Overvoltage V IORM (max) (min) at 5V (max) at 5V (max) at 5V (max) SupplyDevice 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 3V to 5.5V SO-28 $8.10Digital IsolatorISO721 Single Channel, 3.3V/5V — — 4000 560 100 25 24 2 13 3.3V, 5V SO-8 $1.65Digital IsolatorsISO721M Single Channel, 3.3V/5V — — 4000 560 150 25 16 1 13 3.3V, 5V SO-8 $1.65Digital Isolators* Suggested resale price in U.S. dollars in quantities of 1,000. New products are listed in bold red.Texas Instruments 3Q 2007Amplifier and Data Converter Selection Guide