6N138SD Optoisolator Equivalent & Substitute Parts

Part Overview

The 6N138SD is an optoisolator with Darlington output and base connection, manufactured by onsemi. It provides 2500Vrms isolation in an 8-SMD surface mount package. The product is currently obsolete, making equivalent and substitute parts necessary for ongoing design support and production continuity. Substitute parts must maintain functional compatibility across isolation voltage, output configuration, channel count, and thermal operating range while accommodating packaging and compliance variations.

Key Parameters

Parameter	6N138SD
Manufacturer	onsemi
Product Status	Obsolete
Number of Channels	1
Voltage - Isolation	2500Vrms
Output Type	Darlington with Base
Current Transfer Ratio (Min)	300% @ 1.6mA
Voltage - Output (Max)	7V
Current - Output / Channel	60mA
Operating Temperature	-40°C ~ 85°C
Mounting Type	Surface Mount
Package / Case	8-SMD, Gull Wing
Moisture Sensitivity Level (MSL)	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution for the 6N138SD is determined by the following critical parameters:

Mandatory Compatibility Criteria:

Single channel configuration
Darlington output with base connection
Isolation voltage ≥ 2500Vrms
Output current capability ≥ 60mA
Surface mount package (8-SMD or equivalent pin-compatible)
MSL rating 1 (Unlimited)

Acceptable Variations:

Isolation voltage may exceed 2500Vrms (higher isolation provides design margin)
Operating temperature range may differ if application requirements are met
Current transfer ratio variations are acceptable if minimum specification is met
Packaging format may vary (8-SMD, 8-DIP Gull Wing) if pin configuration is compatible
RoHS and REACH compliance status may differ

The 6N138SDM (onsemi) provides direct substitution with enhanced 5000Vrms isolation. The HCPL-4701 series (Broadcom Limited) offers functional equivalence with higher current transfer ratios and output voltage capability, though with different packaging and compliance profiles.

Parameter Comparison

Parameter	6N138SD	6N138SDM	HCPL-4701#300	HCPL-4701-300E	HCPL-4701-320E	HCPL-4701-360E	HCPL-4701-500E	HCPL-4701-520E	HCPL-4701-560E
Manufacturer	onsemi	onsemi	Broadcom Limited	Broadcom Limited	Broadcom Limited	Broadcom Limited	Broadcom Limited	Broadcom Limited	Broadcom Limited
Product Status	Obsolete	Active	Active	Active	Active	Active	Active	Active	Active
Number of Channels	1	1	1	1	1	1	1	1	1
Voltage - Isolation	2500Vrms	5000Vrms	3750Vrms	3750Vrms	5000Vrms	3750Vrms	3750Vrms	5000Vrms	3750Vrms
Current Transfer Ratio (Min)	300% @ 1.6mA	300% @ 1.6mA	600% @ 500µA	600% @ 500µA	600% @ 500µA	600% @ 500µA	600% @ 500µA	600% @ 500µA	600% @ 500µA
Output Type	Darlington with Base	Darlington with Base	Darlington with Base	Darlington with Base	Darlington with Base	Darlington with Base	Darlington with Base	Darlington with Base	Darlington with Base
Voltage - Output (Max)	7V	7V	18V	18V	18V	18V	18V	18V	18V
Current - Output / Channel	60mA	60mA	60mA	60mA	60mA	60mA	60mA	60mA	60mA
Operating Temperature	-40°C ~ 85°C	-40°C ~ 100°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Package / Case	8-SMD, Gull Wing	8-SMD, Gull Wing	8-SMD, Gull Wing	8-SMD, Gull Wing	8-SMD, Gull Wing	8-SMD, Gull Wing	8-SMD, Gull Wing	8-SMD, Gull Wing	8-SMD, Gull Wing
Supplier Device Package	8-SMD	8-SMD	8-DIP Gull Wing	8-DIP Gull Wing	8-DIP Gull Wing	8-DIP Gull Wing	8-DIP Gull Wing	8-DIP Gull Wing	8-DIP Gull Wing
Moisture Sensitivity Level (MSL)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)
RoHS Status	Not specified	ROHS3 Compliant	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
REACH Status	REACH Unaffected	REACH Unaffected	REACH Unaffected	REACH Unaffected	REACH Unaffected	REACH Unaffected	REACH Unaffected	REACH Unaffected	REACH Unaffected

Engineering Selection Recommendations

Primary Substitute: 6N138SDM (onsemi)

The 6N138SDM is the direct onsemi equivalent with enhanced specifications. It maintains the same manufacturer lineage, 8-SMD package format, and Darlington output configuration. The 5000Vrms isolation exceeds the 6N138SD requirement, providing additional design margin. Operating temperature extends to 100°C, supporting wider thermal applications. ROHS3 compliance status is confirmed. This part is recommended for designs requiring manufacturer continuity and proven pin-compatible replacement.

Alternative Substitutes: HCPL-4701 Series (Broadcom Limited)

The HCPL-4701 series provides functional equivalence across multiple isolation voltage ratings (3750Vrms and 5000Vrms). All variants maintain single-channel Darlington output with base connection, 60mA output current, and MSL 1 rating. Higher current transfer ratios (600% minimum) and increased output voltage capability (18V maximum) offer enhanced performance margins. ROHS3-compliant variants (HCPL-4701-300E, HCPL-4701-320E, HCPL-4701-360E, HCPL-4701-500E, HCPL-4701-520E, HCPL-4701-560E) are available in both Tube and Tape & Reel packaging.

Packaging Consideration:

The HCPL-4701 series uses 8-DIP Gull Wing supplier packaging while maintaining 8-SMD case designation. Pin configuration compatibility must be verified against PCB layout before implementation. The 6N138SDM maintains identical 8-SMD packaging, eliminating layout concerns.

Operating Temperature Limitation:

HCPL-4701 variants operate within 0°C to 70°C range, narrower than the 6N138SD specification (-40°C to 85°C). Applications requiring extended temperature operation below 0°C or above 70°C must use the 6N138SDM.

Frequently Asked Questions (FAQ)

Q: Can the 6N138SDM directly replace the 6N138SD without PCB modification?

A: Yes. The 6N138SDM maintains identical 8-SMD Gull Wing package and pin configuration. No PCB layout changes are required. The enhanced 5000Vrms isolation and extended temperature range (-40°C to 100°C) provide improved performance margins.

Q: What are the key differences between onsemi 6N138 series and Broadcom HCPL-4701 series?

A: Both provide single-channel Darlington output with base connection and 60mA output current. The HCPL-4701 series offers higher current transfer ratios (600% vs. 300% minimum) and increased output voltage (18V vs. 7V maximum). Operating temperature range differs: 6N138SDM supports -40°C to 100°C while HCPL-4701 variants operate 0°C to 70°C. Isolation voltage options range from 3750Vrms to 5000Vrms across the HCPL-4701 lineup.

Q: Are all HCPL-4701 variants pin-compatible with the 6N138SD?

A: All HCPL-4701 variants maintain identical pin configuration and Darlington output with base connection. However, the supplier device package designation (8-DIP Gull Wing) differs from the 6N138SD (8-SMD). Physical package dimensions and PCB footprint compatibility must be confirmed before substitution.

Q: Which substitute part is recommended for applications operating below 0°C or above 70°C?

A: The 6N138SDM is the only substitute supporting the extended temperature range of the original 6N138SD (-40°C to 85°C). HCPL-4701 series variants are limited to 0°C to 70°C operation.

Q: What is the isolation voltage difference between 6N138SDM and HCPL-4701 variants?

A: The 6N138SDM provides 5000Vrms isolation. HCPL-4701 variants offer either 3750Vrms (HCPL-4701#300, HCPL-4701-300E, HCPL-4701-360E, HCPL-4701-500E, HCPL-4701-560E) or 5000Vrms (HCPL-4701-320E, HCPL-4701-520E). All exceed the original 6N138SD specification of 2500Vrms.

Q: Are RoHS3-compliant variants available across all substitute options?

A: The 6N138SDM is ROHS3 compliant. Among HCPL-4701 variants, HCPL-4701-300E, HCPL-4701-320E, HCPL-4701-360E, HCPL-4701-500E, HCPL-4701-520E, and HCPL-4701-560E are ROHS3 compliant. The HCPL-4701#300 is RoHS non-compliant.

Q: What packaging options are available for substitute parts?

A: The 6N138SDM is supplied in Tape & Reel (TR) format. HCPL-4701 variants are available in both Tube and Tape & Reel packaging depending on part number designation. Verify packaging availability with supplier before design finalization.

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