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FODM121AR1 Optoisolator Transistor Output 3750Vrms Equivalent & Substitute Parts
Part Overview
The FODM121AR1 is a 3750Vrms optoisolator with transistor output manufactured by onsemi in a 4-SMD surface mount package. This part is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement. The FODM121AR1 provides single-channel isolation with 80V maximum output voltage and 80mA output current capability, designed for DC input applications requiring high-voltage isolation in compact form factors.
Substiute Parts
Key Parameters
| Parameter | Value |
|---|---|
| Manufacturer Part Number | FODM121AR1 |
| Manufacturer | onsemi |
| Category | Optoisolators |
| Product Status | Obsolete |
| Number of Channels | 1 |
| Voltage - Isolation | 3750Vrms |
| Current Transfer Ratio (Min) | 100% @ 5mA |
| Current Transfer Ratio (Max) | 300% @ 5mA |
| Output Type | Transistor |
| Voltage - Output (Max) | 80V |
| Current - Output / Channel | 80mA |
| Vce Saturation (Max) | 400mV |
| Operating Temperature | -40°C ~ 110°C |
| Mounting Type | Surface Mount |
| Package / Case | 4-SMD, Gull Wing |
| Moisture Sensitivity Level (MSL) | 1 (Unlimited) |
Substitute Part Grouping Explanation
Substitution for the FODM121AR1 is determined by the following critical parameters:
Isolation Voltage: All substitute parts maintain 3750Vrms isolation voltage, the primary functional requirement for high-voltage isolation applications.
Output Configuration: All substitutes provide single-channel transistor output with maximum output voltage of 80V and input type DC, matching the original part's switching characteristics.
Current Transfer Ratio Range: The FODM121AR1 specifies 100–300% CTR @ 5mA. Substitute parts are grouped into two categories:
- Parametric Equivalents (FODM121AR2, FODM121AR2V): Identical 100–300% CTR range
- Similar Parts (FODM121R2, EL357ND(TA)-G, HCPL-181 series): Broader CTR ranges (50–600% or 130–600%) suitable for applications with flexible gain requirements
Package Compatibility: The original 4-SMD Gull Wing package is maintained in most onsemi and Broadcom substitutes. The EL357ND(TA)-G uses 4-SOP (2.54mm) package, requiring PCB layout modification.
Output Current: The FODM121AR1 supports 80mA output current. Most substitutes (HCPL-181, EL357ND(TA)-G) provide 50mA, suitable for lower-current applications. The FODM121R2 and FODM121AR2 variants maintain 80mA capability.
Temperature Range: The FODM121AR1 operates -40°C to 110°C. Broadcom HCPL-181 parts operate -55°C to 100°C, providing extended low-temperature performance but reduced high-temperature operation.
Parameter Comparison
| Part Number | Manufacturer | Status | Isolation (Vrms) | CTR Min @ 5mA | CTR Max @ 5mA | Output Current (mA) | Vce Sat (Max) | Temp Range (°C) | Package |
|---|---|---|---|---|---|---|---|---|---|
| FODM121AR1 | onsemi | Obsolete | 3750 | 100% | 300% | 80 | 400mV | -40 to 110 | 4-SMD, Gull Wing |
| FODM121AR2 | onsemi | Active | 3750 | 100% | 300% | 80 | 400mV | -40 to 110 | 4-SMD, Gull Wing |
| FODM121AR2V | onsemi | Active | 3750 | 100% | 300% | 80 | 400mV | -40 to 110 | 4-SMD, Gull Wing |
| FODM121R2 | onsemi | Active | 3750 | 50% | 600% | 80 | 400mV | -40 to 110 | 4-SMD, Gull Wing |
| EL357ND(TA)-G | Everlight Electronics | Active | 3750 | 300% | 600% | 50 | 200mV | -55 to 110 | 4-SOP (2.54mm) |
| HCPL-181-000E | Broadcom Limited | Active | 3750 | 50% | 600% | 50 | 200mV | -55 to 100 | 4-SOIC (0.209", 5.30mm) |
| HCPL-181-00AE | Broadcom Limited | Active | 3750 | 80% | 160% | 50 | 200mV | -55 to 100 | 4-Mini-Flat |
| HCPL-181-00BE | Broadcom Limited | Active | 3750 | 130% | 260% | 50 | 200mV | -55 to 100 | 4-Mini-Flat |
| HCPL-181-00CE | Broadcom Limited | Active | 3750 | 200% | 400% | 50 | 200mV | -55 to 100 | 4-Mini-Flat |
| HCPL-181-00DE | Broadcom Limited | Active | 3750 | 300% | 600% | 50 | 200mV | -55 to 100 | 4-Mini-Flat |
| HCPL-181-06BE | Broadcom Limited | Active | 3750 | 130% | 260% | 50 | 200mV | -55 to 100 | 4-Mini-Flat |
Engineering Selection Recommendations
Direct Parametric Equivalents (Recommended for Pin-Compatible Replacement):
FODM121AR2 and FODM121AR2V are active-status direct replacements for the obsolete FODM121AR1. Both parts maintain identical electrical specifications: 100–300% CTR @ 5mA, 80mA output current, 400mV Vce saturation, and -40°C to 110°C operating range. FODM121AR2 is supplied in Tape & Reel packaging; FODM121AR2V is supplied in Cut Tape & Digi-Reel format. Both are RoHS3 compliant and REACH unaffected. These parts require no PCB layout modification and provide the highest compatibility assurance.
onsemi Family Alternatives (Broader CTR Tolerance):
FODM121R2 maintains the same package footprint and 80mA output current but specifies a broader CTR range of 50–600% @ 5mA. This part is suitable for applications where the original 100–300% CTR specification is not a critical design constraint. FODM121R2 is active status and RoHS3 compliant.
Cross-Manufacturer Substitutes (Package Modification Required):
Broadcom HCPL-181 series parts provide 3750Vrms isolation in 4-Mini-Flat or 4-SOIC packages. These parts require PCB layout redesign due to different package geometry. HCPL-181-00BE and HCPL-181-06BE offer CTR ranges (130–260%) closest to the original specification. HCPL-181-00CE provides 200–400% CTR, overlapping the upper range of the FODM121AR1. All HCPL-181 variants reduce output current to 50mA and lower maximum operating temperature to 100°C. All are RoHS3 compliant and REACH unaffected.
Everlight EL357ND(TA)-G provides 3750Vrms isolation in 4-SOP package with 300–600% CTR range and 50mA output current. This part offers extended low-temperature operation (-55°C) and lower Vce saturation (200mV) but requires package-level PCB modification.
Compliance and Availability:
All substitute parts listed are active-status products with RoHS3 compliance and REACH unaffected status. Inventory availability ranges from 1,174 to 103,100 units across the substitute portfolio, ensuring procurement feasibility for production volumes.
Frequently Asked Questions (FAQ)
Q: Can FODM121AR2 or FODM121AR2V be used as direct drop-in replacements for FODM121AR1?
A: Yes. FODM121AR2 and FODM121AR2V are parametric equivalents with identical electrical specifications and the same 4-SMD Gull Wing package footprint. No PCB layout modification is required. The primary difference is product status: FODM121AR1 is obsolete, while FODM121AR2 and FODM121AR2V are active products.
Q: What is the difference between FODM121AR2 and FODM121AR2V?
A: Both parts have identical electrical specifications. The difference is packaging format: FODM121AR2 is supplied in Tape & Reel (TR) format for automated assembly; FODM121AR2V is supplied in Cut Tape (CT) & Digi-Reel format for mixed-volume applications.
Q: Can I use HCPL-181 series parts as substitutes?
A: HCPL-181 series parts provide equivalent isolation voltage and single-channel transistor output but require PCB layout modification due to different package geometry (4-Mini-Flat or 4-SOIC vs. 4-SMD Gull Wing). Output current is reduced to 50mA, and maximum operating temperature is limited to 100°C. These parts are suitable only if PCB redesign is acceptable.
Q: What is the significance of Current Transfer Ratio (CTR) in optoisolator selection?
A: CTR determines the gain of the optoisolator—the ratio of output current to input current. The FODM121AR1 specifies 100–300% CTR @ 5mA, meaning output current ranges from 5mA to 15mA for a 5mA input. Substitute parts with broader CTR ranges (e.g., 50–600%) provide greater design flexibility but may require circuit compensation if the original design depends on the narrower CTR specification.
Q: Why do some substitutes have lower output current (50mA vs. 80mA)?
A: Output current capability is determined by the internal transistor design. HCPL-181 and EL357ND(TA)-G parts are rated for 50mA maximum output current, suitable for lower-power switching applications. If your design requires 80mA output current, use FODM121AR2, FODM121AR2V, or FODM121R2, which maintain the original 80mA specification.
Q: Are all substitute parts RoHS3 compliant?
A: Yes. All substitute parts listed are RoHS3 compliant and REACH unaffected, meeting current environmental and regulatory requirements for electronic components.
Q: What is the temperature operating range difference between onsemi and Broadcom parts?
A: onsemi FODM121 series parts operate -40°C to 110°C. Broadcom HCPL-181 series parts operate -55°C to 100°C, providing extended low-temperature performance but reduced high-temperature capability. Select based on your application's thermal requirements.
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