FODM121F Optoisolator Equivalent & Substitute Parts

Part Overview

The FODM121F 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 FODM121F is classified as obsolete, necessitating identification of active equivalent and substitute parts for new designs and ongoing production requirements. Substitute parts must maintain electrical compatibility across isolation voltage, output current, and switching characteristics while accommodating different packaging formats and Current Transfer Ratio (CTR) specifications.

Key Parameters

Parameter	FODM121F Value	Unit
Isolation Voltage	3750	Vrms
Number of Channels	1	—
Output Type	Transistor	—
Current Transfer Ratio (Min)	50	% @ 5mA
Current Transfer Ratio (Max)	600	% @ 5mA
Output Current / Channel	80	mA
Maximum Output Voltage	80	V
Rise / Fall Time	3 / 3	µs
Operating Temperature Range	-40 to 110	°C
Input Type	DC	—
Mounting Type	Surface Mount	—
Product Status	Obsolete	—

Substitute Part Grouping Explanation

Substitution of the FODM121F is determined by the following critical parameters:

Mandatory Compatibility Parameters:

Isolation voltage: 3750Vrms (all substitutes match)
Output type: Transistor (all substitutes match)
Input type: DC (all substitutes match)
Number of channels: 1 (all substitutes match)
Maximum output voltage: 80V (all substitutes match)

Flexible Parameters (Allow Variation):

Current Transfer Ratio (CTR): Range 50–600% @ 5mA; substitutes may have narrower or different CTR bands
Output current per channel: FODM121F supports 80mA; some substitutes support 50mA (reduced capability)
Rise/Fall time: FODM121F specifies 3µs/3µs; substitutes range 3–4µs (acceptable variation)
Operating temperature: FODM121F range -40 to 110°C; some substitutes extend to -55°C (enhanced capability)
Package format: 4-SMD, 4-SOP, 4-SOIC, 4-Mini-Flat (mechanical substitution with pin compatibility)

Substitute Categories:

Direct onsemi Variants (FODM121 Series): FODM121A, FODM121R2, FODM121V — same base product with different packaging and CTR grades; all active status
Broadcom HCPL-181 Series: HCPL-181-000E, HCPL-181-00AE, HCPL-181-00BE, HCPL-181-00CE, HCPL-181-00DE, HCPL-181-06BE — different package formats (4-SOIC, 4-Mini-Flat) with CTR variants; all active status
Everlight EL357ND(TA)-G: Alternative manufacturer with 4-SOP package; active status; reduced output current (50mA vs. 80mA)

Parameter Comparison

Part Number	Manufacturer	Isolation (Vrms)	CTR Min / Max (% @ 5mA)	Output Current (mA)	Rise / Fall Time (µs)	Temp Range (°C)	Package	Status
FODM121F	onsemi	3750	50 / 600	80	3 / 3	-40 to 110	4-SMD	Obsolete
FODM121A	onsemi	3750	100 / 300	80	3 / 3	-40 to 110	4-SMD	Active
FODM121R2	onsemi	3750	50 / 600	80	3 / 3	-40 to 110	4-SMD	Active
FODM121V	onsemi	3750	50 / 600	80	3 / 3	-40 to 110	4-SMD	Active
EL357ND(TA)-G	Everlight	3750	300 / 600	50	3 / 4	-55 to 110	4-SOP	Active
HCPL-181-000E	Broadcom	3750	50 / 600	50	4 / 3	-55 to 100	4-SOIC	Active
HCPL-181-00AE	Broadcom	3750	80 / 160	50	4 / 3	-55 to 100	4-Mini-Flat	Active
HCPL-181-00BE	Broadcom	3750	130 / 260	50	4 / 3	-55 to 100	4-Mini-Flat	Active
HCPL-181-00CE	Broadcom	3750	200 / 400	50	4 / 3	-55 to 100	4-Mini-Flat	Active
HCPL-181-00DE	Broadcom	3750	300 / 600	50	4 / 3	-55 to 100	4-Mini-Flat	Active
HCPL-181-06BE	Broadcom	3750	130 / 260	50	4 / 3	-55 to 100	4-Mini-Flat	Active

Engineering Selection Recommendations

Tier 1 — Direct Replacement (Recommended for Pin-Compatible Designs):

FODM121R2 and FODM121V are the primary substitutes. Both maintain identical electrical specifications to FODM121F (3750Vrms isolation, 80mA output current, 50–600% CTR range, 3µs rise/fall time, -40 to 110°C operation) and use the same 4-SMD package. Both are active products with ROHS3 compliance and unlimited moisture sensitivity rating. FODM121R2 is supplied in Tape & Reel format with 7600 units in stock; FODM121V is supplied in Box format with 3768 units in stock. FODM121A is also active but specifies a narrower CTR range (100–300%) and may not satisfy applications requiring the full 50–600% CTR envelope of FODM121F.

Tier 2 — Package-Variant Substitutes (For Layout Flexibility):

Broadcom HCPL-181 series parts provide 3750Vrms isolation with transistor output in alternative package formats (4-SOIC, 4-Mini-Flat). All HCPL-181 variants are active with ROHS3 compliance. The trade-off is reduced output current (50mA vs. 80mA for FODM121F). HCPL-181-00DE matches the full 50–600% CTR range and is available in high quantity (44,400 units). HCPL-181-00CE (200–400% CTR, 1174 units) and HCPL-181-00BE (130–260% CTR, 103,100 units) provide narrower CTR bands for applications with defined gain requirements. Operating temperature range is -55 to 100°C (lower maximum than FODM121F).

Tier 3 — Alternative Manufacturer (For Multi-Source Strategy):

Everlight EL357ND(TA)-G provides 3750Vrms isolation in 4-SOP package with 300–600% CTR. Output current is limited to 50mA. Operating temperature extends to -55°C. This part is suitable for applications where the 50mA output current is sufficient and alternative sourcing is required.

Compliance and Certification:

All recommended substitutes carry ROHS3 compliance and REACH Unaffected status. Moisture sensitivity level is 1 (Unlimited) across all parts. ECCN classification is EAR99 for all parts.

Frequently Asked Questions (FAQ)

Q: Can FODM121A replace FODM121F directly?

A: FODM121A is electrically compatible for isolation voltage, output type, and package format. However, FODM121A specifies a narrower Current Transfer Ratio range (100–300% @ 5mA) compared to FODM121F (50–600% @ 5mA). If the application circuit design depends on CTR values below 100% or above 300%, FODM121A is not suitable. For applications operating within the 100–300% CTR window, FODM121A is a direct substitute.

Q: What is the impact of reduced output current in Broadcom HCPL-181 parts?

A: FODM121F supports 80mA output current per channel; Broadcom HCPL-181 series supports 50mA. If the load circuit requires more than 50mA, HCPL-181 parts cannot be used. If the application load draws 50mA or less, HCPL-181 parts are electrically compatible. Verify load current requirements before selection.

Q: Are package changes between 4-SMD, 4-SOIC, and 4-Mini-Flat interchangeable?

A: No. These are different physical packages with different footprints and pin spacing. 4-SMD (Gull Wing) uses one footprint; 4-SOIC (0.209" width, 5.30mm) uses a different footprint; 4-Mini-Flat uses a third footprint. PCB layout and assembly equipment must be compatible with the selected package. Pin function and electrical behavior are equivalent across these packages for the same part family.

Q: Does the extended temperature range of HCPL-181 (-55 to 100°C) affect compatibility?

A: The HCPL-181 maximum operating temperature is 100°C, while FODM121F is rated to 110°C. If the application operates above 100°C, HCPL-181 parts are not suitable. If the application operates within -55 to 100°C, the extended lower temperature limit of HCPL-181 provides additional margin. The lower maximum temperature is the limiting factor for high-temperature applications.

Q: What is the difference between FODM121R2 and FODM121V?

A: Both parts are electrically identical to FODM121F (3750Vrms, 80mA, 50–600% CTR, 3µs rise/fall time, -40 to 110°C). The difference is packaging format: FODM121R2 is supplied in Tape & Reel (TR) format; FODM121V is supplied in Box format. Selection depends on assembly process requirements and inventory management. FODM121R2 has higher stock availability (7600 units vs. 3768 units).

Q: Can EL357ND(TA)-G be used in applications requiring 80mA output current?

A: No. EL357ND(TA)-G is rated for 50mA maximum output current. Applications requiring 80mA output current must use FODM121 series parts (FODM121A, FODM121R2, FODM121V) or accept the 50mA limitation of Broadcom HCPL-181 series. Exceeding rated output current causes device damage.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. All recommended substitutes (FODM121A, FODM121R2, FODM121V, EL357ND(TA)-G, and all HCPL-181 variants) carry ROHS3 compliance certification. FODM121F does not specify RoHS status. For applications requiring RoHS compliance, all listed substitutes are qualified.

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