FODM121FV Optoisolator Equivalent & Substitute Parts

Part Overview

The FODM121FV is a 3750Vrms optoisolator with transistor output manufactured by onsemi in a 4-SMD package. This component provides galvanic isolation for single-channel DC input applications with 80mA output current capability. The part is currently obsolete, making equivalent substitutes necessary for new designs and production continuity. Active alternatives from onsemi and other manufacturers maintain the same electrical isolation rating and output characteristics while offering improved availability and compliance status.

Key Parameters

Parameter	Value
Voltage - Isolation	3750Vrms
Number of Channels	1
Output Type	Transistor
Voltage - Output (Max)	80V
Current - Output / Channel	80mA
Current Transfer Ratio (Min)	50% @ 5mA
Current Transfer Ratio (Max)	600% @ 5mA
Rise / Fall Time (Typ)	3µs, 3µs
Vce Saturation (Max)	400mV
Operating Temperature	-40°C ~ 110°C
Mounting Type	Surface Mount
Input Type	DC

Substitute Part Grouping Explanation

Substitution for the FODM121FV is determined by strict equivalence across the following critical parameters:

Isolation Voltage: 3750Vrms (mandatory match)
Number of Channels: 1 (mandatory match)
Output Type: Transistor (mandatory match)
Input Type: DC (mandatory match)
Maximum Output Voltage: 80V (mandatory match)
Output Current Capability: 50mA minimum (FODM121FV rated 80mA; substitutes rated 50mA are acceptable as they meet minimum requirements)
Current Transfer Ratio Range: 50% to 600% @ 5mA (substitutes must fall within or overlap this range)
Mounting Type: Surface Mount (mandatory match)
Moisture Sensitivity Level: 1 (Unlimited) (mandatory match)

Substitutes are grouped into two categories:

Direct onsemi Equivalents (FODM121R2, FODM121V): Identical electrical specifications with different packaging formats (Tape & Reel, Box). These are pin-compatible replacements with active product status.

Cross-Manufacturer Alternatives (Broadcom HCPL-181 series, Everlight EL357ND): Meet all critical electrical parameters with different package styles (4-SOIC, 4-Mini-Flat, 4-SOP). These require PCB layout adaptation but provide equivalent functional performance.

Parameter Comparison

Parameter	FODM121FV	FODM121R2	FODM121V	EL357ND(TA)-G	HCPL-181-000E	HCPL-181-00BE	HCPL-181-00CE	HCPL-181-00DE
Voltage - Isolation	3750Vrms	3750Vrms	3750Vrms	3750Vrms	3750Vrms	3750Vrms	3750Vrms	3750Vrms
Number of Channels	1	1	1	1	1	1	1	1
Output Type	Transistor	Transistor	Transistor	Transistor	Transistor	Transistor	Transistor	Transistor
Voltage - Output (Max)	80V	80V	80V	80V	80V	80V	80V	80V
Current - Output / Channel	80mA	80mA	80mA	50mA	50mA	50mA	50mA	50mA
Current Transfer Ratio (Min)	50% @ 5mA	50% @ 5mA	50% @ 5mA	300% @ 5mA	50% @ 5mA	130% @ 5mA	200% @ 5mA	300% @ 5mA
Current Transfer Ratio (Max)	600% @ 5mA	600% @ 5mA	600% @ 5mA	600% @ 5mA	600% @ 5mA	260% @ 5mA	400% @ 5mA	600% @ 5mA
Rise / Fall Time (Typ)	3µs, 3µs	3µs, 3µs	3µs, 3µs	3µs, 4µs	4µs, 3µs	4µs, 3µs	4µs, 3µs	4µs, 3µs
Vce Saturation (Max)	400mV	400mV	400mV	200mV	200mV	200mV	200mV	200mV
Operating Temperature	-40°C ~ 110°C	-40°C ~ 110°C	-40°C ~ 110°C	-55°C ~ 110°C	-55°C ~ 100°C	-55°C ~ 100°C	-55°C ~ 100°C	-55°C ~ 100°C
Package / Case	4-SMD, Gull Wing	4-SMD, Gull Wing	4-SMD, Gull Wing	4-SOP (2.54mm)	4-SOIC (0.209", 5.30mm Width)	4-Mini-Flat	4-Mini-Flat	4-Mini-Flat
Product Status	Obsolete	Active	Active	Active	Active	Active	Active	Active
RoHS Status	Not specified	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

For Direct Replacement (No PCB Modification Required):

FODM121R2 and FODM121V are the primary substitutes. Both maintain identical pinout, package footprint, and electrical specifications to the FODM121FV. FODM121R2 is supplied in Tape & Reel format for production environments, while FODM121V is supplied in Box format for lower-volume applications. Both are ROHS3 compliant and carry active product status, ensuring long-term availability.

For Cross-Manufacturer Substitution (PCB Layout Adaptation Required):

The Broadcom HCPL-181 series (HCPL-181-000E, HCPL-181-00BE, HCPL-181-00CE, HCPL-181-00DE) and Everlight EL357ND(TA)-G provide functional equivalence with different package geometries. These require PCB redesign to accommodate alternative pinouts and package dimensions. Selection among HCPL-181 variants depends on required Current Transfer Ratio: HCPL-181-000E and HCPL-181-00DE match the full 50%-600% range; HCPL-181-00BE and HCPL-181-06BE provide 130%-260% range. All Broadcom variants are ROHS3 compliant with active status and higher inventory availability.

The Everlight EL357ND(TA)-G offers superior Vce saturation performance (200mV vs. 400mV) and extended lower temperature rating (-55°C vs. -40°C), beneficial for demanding thermal environments. It requires 4-SOP package accommodation.

Compliance Considerations:

All active substitutes carry ROHS3 compliance and REACH Unaffected status, matching the original part's regulatory requirements. The obsolete status of FODM121FV necessitates transition to an active equivalent for new production and long-term supply chain stability.

Frequently Asked Questions (FAQ)

Q: Can FODM121R2 or FODM121V be used as direct drop-in replacements for FODM121FV?

A: Yes. FODM121R2 and FODM121V are electrically and mechanically identical to FODM121FV. They share the same 4-SMD Gull Wing package, pinout, and all critical electrical parameters. The only differences are packaging format (Tape & Reel vs. Box) and product status (Active vs. Obsolete). No PCB modifications are required.

Q: What is the difference between HCPL-181-00BE, HCPL-181-00CE, and HCPL-181-00DE?

A: These three Broadcom variants differ only in Current Transfer Ratio specification: HCPL-181-00BE provides 130%-260%, HCPL-181-00CE provides 200%-400%, and HCPL-181-00DE provides 300%-600%. All other electrical parameters, package type (4-Mini-Flat), and compliance certifications are identical. Selection depends on the required CTR range for your application.

Q: Why does EL357ND(TA)-G have lower output current (50mA vs. 80mA) than FODM121FV?

A: The EL357ND(TA)-G is rated for 50mA maximum output current, while FODM121FV is rated for 80mA. This difference reflects the design specifications of each manufacturer. If your application requires the full 80mA output capability, FODM121R2 or FODM121V are preferred. If your circuit draws less than 50mA, EL357ND(TA)-G is functionally equivalent.

Q: Can I use HCPL-181 series parts without modifying my PCB?

A: No. HCPL-181 series parts use different package types (4-SOIC or 4-Mini-Flat) compared to FODM121FV (4-SMD Gull Wing). PCB layout and footprint modifications are required. If PCB redesign is not feasible, use FODM121R2 or FODM121V instead.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. All active substitute parts listed (FODM121R2, FODM121V, EL357ND(TA)-G, and all HCPL-181 variants) are ROHS3 compliant. The original FODM121FV does not specify RoHS status due to its obsolete classification.

Q: What is the temperature operating range difference between FODM121FV and its substitutes?

A: FODM121FV operates from -40°C to 110°C. FODM121R2 and FODM121V maintain this range. Broadcom HCPL-181 series parts operate from -55°C to 100°C (lower maximum temperature). Everlight EL357ND(TA)-G operates from -55°C to 110°C (extended lower temperature). For applications requiring operation above 100°C, use FODM121R2, FODM121V, or EL357ND(TA)-G.

Q: What does Vce Saturation (Max) represent and why does it differ?

A: Vce Saturation is the collector-emitter voltage when the transistor output is fully saturated (conducting). FODM121FV specifies 400mV maximum, while most substitutes specify 200mV. Lower saturation voltage indicates better output transistor performance and lower power dissipation. This difference does not prevent substitution but may improve circuit efficiency with alternative parts.

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