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FODM121G Optoisolator Equivalent & Substitute Parts
Part Overview
The FODM121G is a 3750Vrms optoisolator with transistor output manufactured by onsemi in a 4-SMD gull wing package. This component is classified as obsolete, making equivalent substitutes necessary for new designs and ongoing production requirements. The part provides single-channel isolation suitable for DC input applications with 80V maximum output voltage and 80mA output current capability.
Substiute Parts
Key Parameters
| Parameter | Value |
|---|---|
| Isolation Voltage | 3750Vrms |
| Number of Channels | 1 |
| Output Type | Transistor |
| Input Type | DC |
| Voltage - Output (Max) | 80V |
| Current - Output / Channel | 80mA |
| Current Transfer Ratio (Min) | 50% @ 5mA |
| Current Transfer Ratio (Max) | 600% @ 5mA |
| Vce Saturation (Max) | 400mV |
| Operating Temperature Range | -40°C ~ 110°C |
| Mounting Type | Surface Mount |
| Package / Case | 4-SMD, Gull Wing |
Substitute Part Grouping Explanation
Substitution for the FODM121G is determined by the following critical parameters:
- Isolation voltage of 3750Vrms (mandatory match)
- Single-channel configuration
- Transistor output topology
- DC input type
- Maximum output voltage of 80V
- Surface mount technology with compatible package footprint
- Current transfer ratio range compatibility
- Operating temperature range coverage
Substitute parts are grouped into three categories based on packaging and electrical performance:
Category 1: onsemi FODM121 Series (Same Manufacturer) Direct parametric equivalents with identical electrical specifications but different packaging configurations.
Category 2: Broadcom HCPL-181 Series (4-Mini-Flat Package) Functionally equivalent with 3750Vrms isolation and transistor output, featuring different current transfer ratio grades and 4-Mini-Flat packaging.
Category 3: Cross-Manufacturer Alternatives Everlight EL357ND(TA)-G offering equivalent isolation and output characteristics with 4-SOP package option.
Parameter Comparison
| Part Number | Manufacturer | Isolation Voltage | CTR Min @ 5mA | CTR Max @ 5mA | Vce Sat (Max) | Output Current | Package | Product Status |
|---|---|---|---|---|---|---|---|---|
| FODM121G | onsemi | 3750Vrms | 50% | 600% | 400mV | 80mA | 4-SMD, Gull Wing | Obsolete |
| FODM121R2 | onsemi | 3750Vrms | 50% | 600% | 400mV | 80mA | 4-SMD, Gull Wing | Active |
| FODM121V | onsemi | 3750Vrms | 50% | 600% | 400mV | 80mA | 4-SMD, Gull Wing | Active |
| EL357ND(TA)-G | Everlight Electronics | 3750Vrms | 300% | 600% | 200mV | 50mA | 4-SOP (2.54mm) | Active |
| HCPL-181-000E | Broadcom Limited | 3750Vrms | 50% | 600% | 200mV | 50mA | 4-SOIC (0.209", 5.30mm) | Active |
| HCPL-181-00AE | Broadcom Limited | 3750Vrms | 80% | 160% | 200mV | 50mA | 4-Mini-Flat | Active |
| HCPL-181-00BE | Broadcom Limited | 3750Vrms | 130% | 260% | 200mV | 50mA | 4-Mini-Flat | Active |
| HCPL-181-00CE | Broadcom Limited | 3750Vrms | 200% | 400% | 200mV | 50mA | 4-Mini-Flat | Active |
| HCPL-181-00DE | Broadcom Limited | 3750Vrms | 300% | 600% | 200mV | 50mA | 4-Mini-Flat | Active |
| HCPL-181-06BE | Broadcom Limited | 3750Vrms | 130% | 260% | 200mV | 50mA | 4-Mini-Flat | Active |
| HCPL-181-06DE | Broadcom Limited | 3750Vrms | 300% | 600% | 200mV | 50mA | 4-Mini-Flat | Active |
Engineering Selection Recommendations
Primary Recommendation: FODM121R2 or FODM121V
Both parts are manufactured by onsemi and provide identical electrical specifications to the FODM121G with active product status. FODM121R2 is supplied in Tape & Reel packaging with ROHS3 compliance. FODM121V is supplied in Box packaging with ROHS3 compliance. Both maintain the original 4-SMD gull wing package footprint, eliminating PCB redesign requirements. Current inventory levels support production deployment.
Secondary Recommendation: HCPL-181-00DE or HCPL-181-06DE
Broadcom HCPL-181-00DE and HCPL-181-06DE provide matching current transfer ratio specifications (300% to 600% @ 5mA) with improved Vce saturation performance (200mV vs. 400mV). These parts require package footprint evaluation due to 4-Mini-Flat configuration. Both carry ROHS3 compliance and active product status with substantial inventory availability.
Alternative for Current-Limited Applications: HCPL-181-00AE or HCPL-181-06BE
Applications requiring reduced current transfer ratio (80-160% or 130-260% @ 5mA) may utilize HCPL-181-00AE or HCPL-181-06BE respectively. These options provide lower output current capability (50mA vs. 80mA) and narrower CTR ranges, suitable for specific circuit requirements.
Cross-Manufacturer Option: EL357ND(TA)-G
Everlight EL357ND(TA)-G offers equivalent isolation voltage with 4-SOP package. This part features higher minimum current transfer ratio (300% @ 5mA) and lower Vce saturation (200mV). Output current is limited to 50mA. Operating temperature range extends to -55°C. Package conversion from 4-SMD to 4-SOP requires PCB layout modification.
All recommended substitutes maintain 3750Vrms isolation voltage, single-channel configuration, DC input type, and 80V maximum output voltage specifications.
Frequently Asked Questions (FAQ)
Q: Can FODM121R2 or FODM121V directly replace FODM121G without PCB modification?
A: Yes. Both parts maintain identical 4-SMD gull wing package footprint and electrical specifications. Only packaging format differs (Tape & Reel vs. original). No PCB layout changes are required.
Q: What is the primary difference between HCPL-181 variants (00AE, 00BE, 00CE, 00DE)?
A: The variants differ in current transfer ratio (CTR) specifications. HCPL-181-00AE provides 80-160% CTR, HCPL-181-00BE provides 130-260% CTR, HCPL-181-00CE provides 200-400% CTR, and HCPL-181-00DE provides 300-600% CTR. All maintain 3750Vrms isolation and 50mA output current. Selection depends on circuit gain requirements.
Q: Does EL357ND(TA)-G require circuit redesign if substituted for FODM121G?
A: Yes. EL357ND(TA)-G uses 4-SOP (2.54mm) package instead of 4-SMD gull wing, requiring PCB footprint modification. Output current is reduced to 50mA. Minimum CTR is higher at 300% @ 5mA. Operating temperature range extends to -55°C minimum.
Q: Are all recommended substitutes RoHS3 compliant?
A: FODM121R2, FODM121V, and all Broadcom HCPL-181 variants listed carry RoHS3 compliance certification. EL357ND(TA)-G carries RoHS3 compliance. Original FODM121G does not specify RoHS status.
Q: What is the significance of Vce saturation differences between FODM121G (400mV) and HCPL-181 series (200mV)?
A: Lower Vce saturation reduces output voltage drop across the transistor, improving output voltage swing capability and reducing power dissipation. HCPL-181 series provides superior saturation performance. This difference is significant in low-voltage output applications.
Q: Can HCPL-181-00AE be used in applications designed for FODM121G?
A: HCPL-181-00AE provides narrower current transfer ratio range (80-160% vs. 50-600%) and reduced output current (50mA vs. 80mA). Substitution is valid only if circuit design accommodates these reduced specifications. Isolation voltage and package compatibility require evaluation.
Q: What inventory considerations apply to these substitutes?
A: FODM121R2 provides highest inventory (7600 pcs), followed by HCPL-181-00BE (103100 pcs) and HCPL-181-00DE (44400 pcs). FODM121V maintains 3768 pcs. All recommended parts show active production status with adequate supply for deployment.
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