Shenzhen Mingjiada Electronics Co., Ltd. supplies the TI ISO7731 high-speed, electromagnetic interference (EMC)-hardened three-channel digital isolator.
I. ISO7731 Product Description
The ISO7731 high-speed, electromagnetic interference (EMI)-resistant, enhanced three-channel digital isolator belongs to the ISO773x series. It is available in two package types: a 16-pin wide-body SOIC (DW) and QSOP/SSOP (DBQ). The channel configuration comprises two forward channels and one reverse channel. The device does not incorporate an integrated isolated power supply and must be used in conjunction with an isolated DC/DC power supply. The ISO7731 employs a dual-capacitor silicon dioxide (SiO₂) isolation gate structure to isolate CMOS/LVCMOS single-ended digital I/O on both sides. It supports the transmission of single-ended signals—such as GPIO, PWM and UART—across ground potentials, and is typically used in conjunction with isolated RS-485, RS-232 and CAN serial bus transceivers. It serves as a core interface isolation device in industrial control, motor drives, energy metering, automotive electronics and medical equipment, isolating ground-loop noise and ensuring personal and system safety.
II. Key Features of the ISO7731
1. Isolation Architecture: Dual-capacitor SiO₂ gate, with enhanced and basic dual insulation ratings
Each isolation channel of the ISO7731 consists of an input logic buffer and an output logic buffer separated by a dual-capacitor SiO₂ insulated gate. This capacitive digital isolation solution, compared to traditional optocouplers, eliminates issues such as LED ageing and CTR drift, whilst offering better timing consistency and a longer service life. The series is divided into two insulation classes: models without the letter ‘B’ suffix feature reinforced insulation, meeting the reinforced insulation certification requirements of VDE, CSA, TÜV, CQC and others; the ISO7731B, with the ‘B’ suffix, features basic insulation and is intended for applications requiring only basic insulation ratings.
2. Channel Direction and Supported Signal Types
The ISO7731 is fixed in a 2-forward / 1-reverse configuration. One reverse channel is naturally suited to carrying the UART RX signal; when combined with two forward TX / GPIO / PWM channels, it can form a typical isolated serial communication link. The device supports GPIO, PWM and UART single-ended signals; It should be noted that this device utilises a single-ended CMOS isolation architecture and does not directly define differential interface standards. Differential transceivers for the physical layer of buses such as RS-485, CAN and RS-232 must be selected separately; the ISO7731 is responsible for isolating and forwarding single-ended logic signals from the master side to the bus transceiver side.
3. High-Speed Performance and Timing Parameters
The ISO7731 has a maximum data rate of 100 Mbps, which is sufficient to meet the isolation requirements for industrial UART, PWM, GPIO and medium-to-low-speed SPI-type parallel control signals. In terms of timing, the propagation delay under a 5 V supply is typically 11 ns and maximally 17 ns; the maximum output offset between devices is 4.5 ns, whilst the maximum output offset between channels is 4 ns. These low and symmetrical delay characteristics facilitate the synchronised transmission of PWM drive signals and multi-channel timing alignment, making the device suitable for applications such as servo systems and variable-frequency drives where channel-to-channel offset is critical.
4. Wide Supply Voltage Range and Bidirectional Level Conversion
The supply voltages on both sides, VCCI and VCCO, are independently powered, with a voltage range of 2.25 V to 5.5 V each, enabling cross-side level conversion between different logic levels of 2.25 V, 3.3 V and 5 V. This feature enables the device to interface directly with low-voltage MCUs and 5 V industrial logic, eliminating the need for additional level-shifting chips and simplifying the BOM for the isolated interface. Decoupling capacitors for both power supplies should be placed close to the corresponding power supply pins and ground, in accordance with the data sheet requirements.
5. Isolation Voltage Rating, Surge Immunity and Insulation Life
The isolation capabilities of the ISO7731 vary by package type: the wide-body SOIC (DW) package complies with the 5000 VRMS isolation rating specified in UL 1577, with a transient isolation voltage (VIOTM) of 8000 VPK; the QSOP/SSOP (DBQ) package has a rating of 3000 VRMS, with a transient rating of 4242 VPK; Surge isolation voltage (VIOSM) covers 7.8 kVPK, 10 kVPK and 12.8 kVPK grades, with a maximum of 12.8 kV.
6. Common-Mode Transient Immunity
The CMTI (minimum 85 kV/µs, typical ±100 kV/µs) specified in ISO 7731 characterises the ability of the isolation gate to withstand rapid ground potential transients on both sides without malfunctioning. A high CMTI is particularly critical in high-interference environments: when ground potential rebounds caused by the operation of inverters, servo drives, relays and contactors, or when common-mode noise propagates along the bus, the device is less prone to output inversion or latching, thereby significantly enhancing the stability of the entire system in industrial environments.
7. Enhanced EMC Design: ESD, EFT, Surge Immunity and Low Emissions
The ISO7731 series is positioned as ‘Robust EMC’, optimising system-level electromagnetic compatibility through chip architecture and layout design: The cross-isolator provides ±8 kV IEC 61000-4-2 contact discharge protection, whilst also offering system-level immunity to ESD, electrostatic fast transient (EFT) and surges. The device itself has low radiated emissions, which helps the entire system pass EMC certification smoothly and reduces the need for additional protective components at the PCB level.
8. Low Power Consumption, Wide Temperature Range and Enable Function
In terms of power consumption, the typical operating current per channel is 1.5 mA at a signal rate of 1 Mbps, and 0.97 mA per channel in DC mode, making it suitable for battery-powered industrial nodes requiring prolonged operation. The operating temperature range is –55 °C to +125 °C, covering industrial-grade and the vast majority of automotive environments. Each side is equipped with an enable (EN) pin, which can place the corresponding channel’s output into a high-impedance state. This supports redundant drive scenarios where multiple controllers share a bus and reduces power consumption when channels are idle; the enable pins of unused channels must be reliably pulled up or down to the levels specified in the data sheet to prevent false triggering caused by floating states.
9. Default output level: The ‘F’ suffix determines the power-up and power-down states
Models without the ‘F’ suffix output a high level by default when the input power or signal is lost; models with the ‘F’ suffix output a low level by default.
III. Typical Application Scenarios for the ISO7731
- For industrial automation equipment / PLC input/output modules: Isolation of digital I/O, status acquisition and bus interfaces; prevention of ground loop currents and surge crosstalk between workshop earthing systems.
- Suitable for servo drives and variable-frequency motor control: Isolation of PWM gate drive signals, overcurrent protection and fault feedback channels; ensuring stable drive timing through low inter-channel offset and high CMTI.
- Signal isolation for automotive electronics (ADAS peripherals, electric drive control, on-board BMS): Safety isolation between high-voltage battery-side sampling/status signals and the low-voltage vehicle body domain; automotive projects must use the ISO7731-Q1 automotive-grade version.
- Designed specifically for new energy storage and battery management systems (BMS): Isolated communication between high-voltage cell-side balancing control units and temperature sensing and management units, capable of withstanding high common-mode transient interference within the battery system.
- Suitable for smart meters and energy metering equipment: Signal isolation between high-voltage primary circuits and the main metering controller, meeting requirements for long-term maintenance-free insulation life and safety certification for metering equipment.
- Isolated serial bus interfaces: When used in conjunction with isolated RS-485, CAN and RS-232 transceivers, these form isolated fieldbus nodes, preventing bus noise currents from entering the local ground plane and damaging sensitive circuits.
- Interface isolation for medical electrical equipment: Based on IEC 60601-1 certification, providing an insulation barrier between patient-contact parts and control circuits.
- Side-control signal isolation for AI computing servers / high-density power modules: Ground potential isolation between power modules and motherboard control signals, reducing system-level noise coupling.
IV. ISO7731 Procurement, Selection and Buyer’s Guide
1. Breakdown of Model Naming Conventions
Taking ISO7731DWR as an example, the meaning of each segment of the part number is as follows: the prefix “ISO77” denotes the TI 77 Series family of three-channel digital isolators; “31” indicates a channel configuration of 2 forward / 1 reverse; the letter ‘B’ in the middle of the part number indicates basic insulation; the default is reinforced insulation; the suffix ‘F’ indicates a default low-level output; the default is a high-level output; the package code “DW” denotes a 16-pin wide-body SOIC, whilst “DBQ” denotes a 16-pin QSOP/SSOP; the final “R” indicates tape-and-reel packaging; “G4” is the TI tape-and-reel version identifier; the suffix “-Q1” indicates an automotive-grade certified version.
2. Commonly Available Models and Selection Guidelines
- ISO7731DWR: DW-16 wide-body SOIC, reinforced insulation, default high-level output, tape-and-reel packaging, 5000 VRMS isolation rating, 8 mm creepage/clearance; suitable for high-voltage side isolation requiring high insulation distances, as well as medical and measurement equipment certification applications.
- ISO7731DBQR: DBQ-16 QSOP/SSOP, reinforced insulation, default high-level output, tape-and-reel packaging, 3,000 VRMS, creepage/clearance 3.7 mm; suitable for industrial nodes and bus interfaces where space is limited and isolation distances are moderate.
- ISO7731DBQRG4: DBQ-16, reinforced insulation, default high-level output, G4 tape-and-reel version; the package and electrical parameters are identical to those of the DBQR; please verify the version against the PCB silkscreen and surface-mount component codes when purchasing.
- ISO7731FDWR: DW-16, reinforced insulation, default low output level, suitable for driver and relay control links where downstream components must remain switched off or in a safe low state during power-up and power-down phases.
- ISO7731FDBQR: DBQ-16, reinforced insulation, default low output level, also providing a default low safe state in a compact package.
- ISO7731BDWR: DW-16, basic insulation, default high-level output; intended for isolation scenarios where the equipment specification requires only basic insulation and cost is a consideration; must not be used in medical or safety-critical circuits where enhanced insulation is mandatory.
- ISO7731FBDWR: DW-16, basic insulation, default low-level output.
3. Key Considerations for Selection
Firstly, confirm the channel direction. For bidirectional UART communication requiring a 2/1 configuration, select the ISO7731; for three unidirectional signals, select the ISO7730; if additional reverse channels are required, opt for the four- or five-channel isolator series; do not attempt to force a fit by multiplexing adjacent channels.
Secondly, confirm the insulation class. If the complete unit requires reinforced insulation certification, select a model without the ‘B’ suffix; for basic insulation applications only, the ‘B’ suffix may be selected to reduce costs. The certification criteria shall be determined by the safety engineer responsible for the complete unit.
Thirdly, confirm the package type and creepage distance. For high-voltage sides, high operating voltages or environments with high pollution levels, prioritise the DW wide-body package (8 mm creepage distance); for low-voltage control boards or modules with space constraints, the DBQ package (3.7 mm) may be selected. The final creepage distance must be calculated in accordance with the relevant safety standards based on the operating voltage, pollution level and overvoltage category; the device package size is merely one of the conditions that must be met.
Fourthly, confirm the default output level: if the downstream circuit must be in the high state at power-up, select a non-‘F’ model; if it must be in the low or off state, select an ‘F’ model. Safety-related pins, such as those for braking, enable signals and relays, must undergo simulation or actual testing to verify their behaviour in the de-energised state.
Fifth, verify that temperature specifications meet automotive grade requirements. For general industrial projects, use catalogue-grade components rated from -55°C to +125°C; for automotive products, the ISO 7731-Q1 automotive grade version must be used, and functional safety documentation must be requested; consumer-grade wide-temperature boards must not be used as direct derated substitutes for automotive-grade components.
4. Procurement and Goods Inspection
- Part number verification: Upon receipt, check each item against the complete part number (insulation class letter, ‘F’ suffix, package code, R/G4 tape marking, Q1 marking) to ensure consistency with the BOM, PCB silkscreen and the procurement contract.
- Traceability to Original Manufacturer: Suppliers must provide a statement of origin from the original manufacturer or an authorised distributor, along with the batch number and traceable lot number; particular attention must be paid to preventing the use of dismantled and refurbished components, sanded-down and re-labelled components, and the mixing of loose components.
- Appearance and Silkscreen: Verify the TI logo, complete model abbreviation, batch number and country of origin on the component surface; ensure pin plating is smooth and free from deformation, oxidation, solder marks or re-marking.
- Packaging and Moisture Protection: Confirm the reel and tape specifications, original factory taping direction and labelling.
V. Mingjiada Electronics: ISO7731 Series Supply Quality and Delivery Assurance
1. Supply Operations
Focused supply scope: Mingjiada Electronics supplies the full range of TI ISO7731 three-channel digital isolators, along with配套 interfaces and power devices, to customers in the industrial control, telecommunications, automotive electronics, new energy and medical sectors. This covers part numbers such as ISO7731DWR, ISO7731DBQR, ISO7731DBQRG4, ISO7731FDWR, ISO7731FDBQR, ISO7731BDWR and ISO7731FBDWR, amongst others. We can also assist with selecting alternatives from the same series, including ISO7730, automotive-grade ISO7731-Q1, upgraded ISO6431 and cost-optimised ISO6731 components.
Quality Assurance System: We adhere to the principle of supplying genuine, original products with traceable supply chain origins; for each batch of materials, we verify the original manufacturer’s model number, batch number and packaging markings. Incoming materials undergo inspections for visual appearance, silkscreen markings, pin configuration and batch consistency; sensitive components are handled and packaged under full ESD protection throughout the process. Samples are inspected prior to delivery and batches are re-verified; lead times and quantities are confirmed via formal quotations, and we do not make any parameter commitments that deviate from the original manufacturer’s specifications.
Delivery and Service: We combine stock on hand with established supply chain resources, prioritising the rapid dispatch of stock orders; we support sample requests, small-batch trial production and bulk supply, and coordinate between tape-and-reel original packaging and loose components according to surface-mount requirements; we provide pre-sales technical support including part number substitution recommendations, parameter verification and BOM gap analysis; post-sales records of batch numbers and dispatch details are retained to facilitate quality traceability and the coordination of returns and exchanges.
2. Recycling Services
Recyclable Categories: In addition to supply and sales, Mingjiada Electronics also operates an electronic component recycling service for manufacturers, solution providers and warehouse clearance operators; these two business lines operate independently and are quoted separately. The categories accepted for recycling primarily consist of idle, obsolete, discontinued and surplus engineering stock.
Recycling Collaboration Process: The customer provides an inventory list (brand, part number, quantity, batch number, package type, and whether in original packaging); Mingjiada verifies this and provides a recycling quotation; upon confirmation, handover and settlement take place in accordance with the agreed method; components from dismantled equipment, refurbished items and non-original materials are separately marked during the recycling assessment and are not circulated as genuine supply materials, ensuring clear quality boundaries within the supply chain.
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