FODM217A - DC Sensing Input Phototransistor Optocoupler | onsemi
MPN: FODM217A ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.85 | $0.85 |
| 10 | $0.74 | $7.40 |
| 100 | $0.58 | $58.00 |
| 500 | $0.46 | $230.00 |
| 1,000 | $0.39 | $390.00 |
| 3,000 | $0.31 | $930.00 |
FODM217A Overview
Phototransistor optocouplers are isolation components that transfer electrical signals between two galvanically isolated domains using an optical link. The category sits within optoisolators -> optocouplers -> discrete semiconductor interface devices, and is widely used in industrial communication buses, PLC I/O, SMPS feedback loops, and microcontroller GPIO isolation. Compared with AC-input variants, DC-sensing-input optocouplers are tuned with a forward-only infrared LED polarity and use a polarised input stage, which lowers turn-on threshold variation across the temperature range and simplifies single-rail logic interfaces.
Key features of the FODM217A include a wide operating temperature range from -40 C to +110 C, current transfer ratio (CTR) typically characterised at low collector currents for low-power logic interfaces, and 3,750 VACrms isolation voltage that satisfies reinforced insulation requirements in many industrial and consumer isolation standards. The half-pitch mini-flat 4-pin package enables compact PCB layouts and provides a typical creepage distance suitable for basic and reinforced insulation.
The GaAs infrared emitter and phototransistor detector use mature onsemi process technology. The device exhibits a typical rise/fall time suitable for digital signal rates commonly encountered in GPIO isolation, comparator feedback, and low-speed serial data links. The 4-pin SOP configuration separates anode, cathode, emitter, and collector, allowing direct replacement of legacy 4-pin optocoupler footprints.
Typical applications for the FODM217A include isolated digital signal transfer between microcontrollers and power inverters, PLC input/output modules, switched-mode power supply feedback paths, isolated gate-driver interfaces, and AC-line crossing detection circuits where DC-only input sensing is acceptable.
When designing with this part, place a current-limiting resistor in series with the LED anode to set the forward current within the recommended operating range, and verify that the collector load resistance and supply voltage keep the phototransistor within its active region.
This page synthesises distributor pricing, drop-in same-package alternatives, and practical design considerations that supplement the manufacturer datasheet to accelerate BOM selection and second-source qualification.
Drop-in alternatives for FODM217A — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with FODM217A (same form factor and footprint) — differing in Isolation Voltage (VISO), Package.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
FODM217
✅ Drop-In📋 Reference alternative (not in catalog)
FODM217B
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
FODM217C
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
FODM217D
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
VOM617A
✅ Drop-In📋 Reference alternative (not in catalog)
VOM618A
✅ Drop-In📋 Reference alternative (not in catalog)
FODM217A Maximum Ratings & Electrical Characteristics
| Channel Count | 1 |
| Input Type | DC Sensing |
| Output Type | Phototransistor |
| Isolation Voltage (VISO) | 3,750 VACrms |
| Package | 4-SOP (Half-Pitch Mini-Flat) |
| Number of Pins | 4 |
| Emitter Material | Gallium Arsenide (GaAs) Infrared LED |
| Detector Type | Silicon Phototransistor |
| Operating Temperature Range | -40 C to +110 C |
| Forward Voltage (VF) Typical | 1.2 V at IF = 10 mA |
| Reverse Voltage (VR) Maximum | 6 V |
| Collector-Emitter Voltage (VCEO) Maximum | 80 V |
| Emitter-Base Voltage (VEBO) Maximum | 7 V |
| Collector Current (IC) Maximum | 50 mA |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant |
FODM217A Pin Configuration
| Pin 1 | Anode — LED anode (positive forward-current input) |
| Pin 2 | Cathode — LED cathode (LED return) |
| Pin 3 | Emitter — Phototransistor emitter |
| Pin 4 | Collector — Phototransistor collector (switched output) |
Typical Applications
FODM217A is suitable for 6 applications: Isolated Digital Signal Transfer (Microcontroller to Power Inverter), PLC Digital Input Module Isolation, Switched-Mode Power Supply (SMPS) Feedback Loop, Isolated Gate-Driver Interface for Solid-State Relays, Isolated Serial Communication Interface, Battery Management System (BMS) Cell Monitoring Isolation.
Isolated Digital Signal Transfer (Microcontroller to Power Inverter)
The FODM217A provides galvanic isolation between a low-voltage microcontroller GPIO and a higher-voltage IGBT or MOSFET gate-driver stage in motor-drive and inverter systems. Its 3,750 VACrms isolation voltage withstands the high dV/dt transients typical of 400 V to 600 V DC bus switching, while the DC-sensing input stage accepts a clean 3.3 V or 5 V logic-level drive directly. The 80 V VCEO and 50 mA collector-current rating allow direct interfacing to logic-level gate-driver enable pins or fault-feedback inputs without an additional buffer stage. Designers should place an external current-limiting resistor on the LED anode sized for a 5 mA to 10 mA forward current.
Recommended
PLC Digital Input Module Isolation
In PLC digital input modules, the FODM217A isolates the field-side 24 V logic from the backplane-side 3.3 V or 5 V controller logic. Its half-pitch mini-flat 4-SOP package enables high-density input-card layouts where dozens of channels share a single backplane connector, and its -40 C to +110 C operating range supports the wider thermal envelope of unenclosed industrial cabinets. The 50 mA collector-current rating allows direct pull-up to the backplane logic rail via an external resistor, simplifying the BOM versus higher-current optocoupler alternatives. This part is widely used in 24 V DC sinking-input modules per IEC 61131-2 type 1/3 characteristics.
Recommended
Switched-Mode Power Supply (SMPS) Feedback Loop
The FODM217A is commonly used in primary-to-secondary feedback isolation for low-to-medium power AC-DC and DC-DC switched-mode power supplies. Its phototransistor output delivers an analog current proportional to primary-side error-amplifier drive, enabling the classic optocoupler-based TL431 feedback loop with 3,750 VACrms isolation across the safety barrier. The DC-sensing input stage ensures predictable loop bandwidth independent of switching ripple polarity. Designers must bias the LED near its nominal forward current (typically 5 mA to 10 mA) for stable CTR across temperature.
Recommended
Isolated Gate-Driver Interface for Solid-State Relays
The FODM217A serves as the low-voltage-side input stage for optically-isolated gate drivers in solid-state relay (SSR) and isolated IGBT driver assemblies. Its 50 mA collector rating and 80 V VCEO let it drive the gate of small logic-level MOSFETs or interface directly to secondary-side controller logic. The 3,750 VACrms isolation voltage supports reinforced-insulation SSR designs per IEC 61800-5-1. Compact 4-SOP half-pitch packaging permits dense driver arrays in modular inverter and rectifier designs.
Recommended
Isolated Serial Communication Interface
The FODM217A provides an isolated link for low-speed UART, I2C, or SPI-style serial communication between two ground domains in industrial, medical, or process-control equipment. With typical rise/fall times in the microsecond range, the part supports data rates up to tens of kilobaud when properly biased, well above the bandwidth required for many command/status interfaces. The DC-sensing input stage simplifies transmitter design compared to AC-input variants, and the half-pitch 4-SOP package keeps channel density high on multi-isolator boards.
Recommended
Battery Management System (BMS) Cell Monitoring Isolation
In multi-cell battery management systems, the FODM217A provides channel-by-channel isolation between high-voltage battery stacks and the low-voltage monitoring MCU. The 3,750 VACrms isolation rating supports the 600 V-plus stack voltages typical of e-mobility and energy-storage applications, while the half-pitch 4-SOP package enables per-cell or per-module isolation cards. The DC-sensing input stage cleanly handles the polarised logic-level drive from cell-balancing controllers, simplifying signal integrity versus AC-input alternatives.
Recommended
Recommended Products Summary
Engineering reference data for FODM217A — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | FODM217 | FODM217B | FODM217C | VOM617A |
|---|---|---|---|---|---|
| Package | 4-SOP (Half-Pitch Mini-Flat) | 4-SOP (Half-Pitch Mini-Flat) - same | 4-SOP (Half-Pitch Mini-Flat) - same | 4-SOP (Half-Pitch Mini-Flat) - same | 4-SOP (Half-Pitch Mini-Flat) - same |
| Brand | onsemi | onsemi | onsemi | onsemi | Vishay Intertechnology |
| Channel Count | 1 | 1 | 1 | 1 | 1 |
| Input Type | DC Sensing | AC/DC Sensing | DC Sensing | DC Sensing | DC Sensing |
| Output Type | Phototransistor | Phototransistor | Phototransistor | Phototransistor | Phototransistor |
| Isolation Voltage (VACrms) | 3,750 | 3,750 | 3,750 | 3,750 | 3,750 |
| VCEO Max (V) | 80 | 80 | 80 | 80 | 80 |
| Collector Current Max (mA) | 50 | 50 | 50 | 50 | 50 |
| Operating Temperature Range | -40 C to +110 C | -40 C to +110 C | -40 C to +110 C | -40 C to +110 C | -55 C to +110 C |
Key Differentiators
- Half-pitch mini-flat package enables 50 percent smaller PCB footprint than DIP-4 optocouplers (vs PC817 (DIP-4 footprint))
- DC-sensing input stage delivers tighter turn-on threshold across temperature (vs FODM217 (AC/DC sensing))
- 80 V VCEO supports direct interface to 24 V industrial logic rails (vs Lower-VCEO optocouplers (e.g., 30 V class))
Design Notes
Size the LED current-limiting resistor for a forward current (IF) of 5 mA to 10 mA under nominal logic-high drive to keep CTR stable across temperature. For 5 V logic, a 470 ohm to 680 ohm resistor is typical; for 3.3 V logic, a 220 ohm to 330 ohm resistor. Below 1 mA IF, CTR drops sharply and rise/fall time degrades; above 20 mA IF, accelerated LED ageing reduces long-term reliability. Always include a reverse-voltage protection path if the input may see transients above 6 V reverse.
The half-pitch mini-flat 4-SOP package has limited power dissipation capability; the LED forward current and the phototransistor collector current must both be kept within the absolute maximum ratings (50 mA IC, 60 mA IF) to avoid exceeding junction temperature. In enclosed industrial enclosures with ambient temperatures approaching +85 C, derate IF by 0.5 mA per degree above +70 C, or upgrade to a wider-pitch DIP-4 optocoupler that has higher thermal headroom.
Maintain the published creepage and clearance distances on the PCB around the FODM217A to preserve the 3,750 VACrms isolation rating. Avoid routing any copper traces between Pin 1-Pin 2 and Pin 3-Pin 4 on inner or outer layers; use a slot or keep-out region to maximise the isolation barrier length. Place the LED current-limiting resistor close to the anode pin to minimise parasitic inductance that could otherwise cause ringing on fast digital edges.
Do not assume CTR is constant across the operating temperature range - phototransistor optocouplers typically exhibit a 30 percent to 50 percent CTR variation from +25 C to +85 C. Validate that the minimum CTR over temperature still meets the design's logic-low VCE(sat) and logic-high collector-current requirements. Also avoid using the FODM217A in AC-input applications where the LED drive reverses polarity each cycle; the DC-sensing input stage is optimised for unidirectional current flow.
Compliance Information
RoHS and lead-free compliant per onsemi product page. Halogen-free status not explicitly stated in the verified data; set to unknown. AEC-Q100 not applicable for non-automotive-grade optocoupler.
