SG3845DM Equivalent & Substitute Parts

Part Overview

The SG3845DM is a Flyback Regulator Controller IC manufactured by Microchip Technology, designed for positive output, isolation-capable DC-DC conversion applications. This 8-SOIC surface mount device operates as a transistor driver for step-up/step-down topologies with a single output phase. The part is currently in active product status with 1037 units in stock.

Equivalent and substitute parts are necessary when the primary SG3845DM becomes unavailable, when alternative packaging formats are required for manufacturing processes, or when sourcing from multiple suppliers is required for supply chain resilience. Substitute controllers must maintain electrical compatibility across critical parameters including supply voltage range, switching frequency capability, duty cycle specifications, and output configuration.

Key Parameters

Parameter	Value
Manufacturer	Microchip Technology
Part Number	SG3845DM
Category	Power Management (PMIC)
Package / Case	8-SOIC (0.154", 3.90mm Width)
Topology	Flyback
Output Type	Transistor Driver
Function	Step-Up/Step-Down
Output Configuration	Positive, Isolation Capable
Voltage - Supply (Vcc/Vdd)	7.6V ~ 30V
Frequency - Switching	1Hz ~ 500kHz
Duty Cycle (Max)	48%
Synchronous Rectifier	Yes
Operating Temperature	0°C ~ 70°C (TA)
Mounting Type	Surface Mount
RoHS Status	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)
Product Status	Active

Substitute Part Grouping Explanation

Substitute parts for the SG3845DM are classified into two categories based on electrical and mechanical compatibility:

Direct Substitutes maintain full functional equivalence across all critical parameters. These parts share identical or compatible specifications for supply voltage range (7.6V ~ 30V), maximum duty cycle (48%), package format (8-SOIC), output configuration (positive output), and topology support (flyback operation). Direct substitutes are pin-compatible and require no circuit modifications.

Similar Substitutes provide functional capability within the same product category but with variations in specific parameters. These variations may include different topology support (boost, forward converter in addition to flyback), different switching frequency specifications, different synchronous rectifier implementation, or different operating temperature ranges. Similar substitutes require design verification to confirm compatibility with the target application.

The following parameters determine substitution eligibility:

Package / Case format (8-SOIC required)
Supply voltage range (minimum 7.6V, maximum 30V)
Maximum duty cycle (48% or higher)
Output configuration (positive output required)
Topology support (flyback capability required)
Mounting type (surface mount required)
RoHS3 compliance status

Parameter Comparison

Parameter	SG3845DM (Main)	TL3845BD-8	TL3845BDR-8	UC3845BD1013TR	UC3845BD1G	UC3845BD1R2G	UC3845BVD1R2G	UC3845AD8	UC3845AD8TR
Manufacturer	Microchip Technology	Texas Instruments	Texas Instruments	STMicroelectronics	onsemi	onsemi	onsemi	Texas Instruments	Texas Instruments
Package / Case	8-SOIC	8-SOIC	8-SOIC	8-SOIC	8-SOIC	8-SOIC	8-SOIC	8-SOIC	8-SOIC
Voltage - Supply (Vcc/Vdd)	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V
Duty Cycle (Max)	48%	48%	48%	48%	48%	48%	48%	Not specified	Not specified
Output Type	Transistor Driver	Transistor Driver	Transistor Driver	Transistor Driver	Transistor Driver	Transistor Driver	Transistor Driver	Transistor Driver	Transistor Driver
Output Configuration	Positive, Isolation Capable	Positive	Positive	Positive, Isolation Capable	Positive, Isolation Capable	Positive, Isolation Capable	Positive, Isolation Capable	Not specified	Not specified
Topology	Flyback	Boost, Flyback, Forward Converter	Boost, Flyback, Forward Converter	Boost, Flyback	Boost, Flyback	Boost, Flyback	Boost, Flyback	Not specified	Not specified
Frequency - Switching	1Hz ~ 500kHz	100kHz	100kHz	Up to 500kHz	Up to 500kHz	Up to 500kHz	Up to 500kHz	Not specified	Not specified
Synchronous Rectifier	Yes	No	No	No	No	No	No	Not specified	Not specified
Operating Temperature	0°C ~ 70°C (TA)	0°C ~ 70°C (TA)	0°C ~ 70°C (TA)	-40°C ~ 150°C (TJ)	0°C ~ 70°C (TA)	0°C ~ 70°C (TA)	-40°C ~ 105°C (TA)	0°C ~ 70°C (TA)	0°C ~ 70°C (TA)
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Product Status	Active	Last Time Buy	Active	Active	Active	Active	Active	Last Time Buy	Active

Engineering Selection Recommendations

Direct Substitutes (Recommended Priority Order)

UC3845BD1013TR (STMicroelectronics) - Active product status with highest inventory availability (287,800 units). Maintains full electrical compatibility with SG3845DM including 7.6V ~ 30V supply range, 48% maximum duty cycle, positive isolation-capable output, and boost/flyback topology support. Extended operating temperature range (-40°C ~ 150°C TJ) provides additional thermal margin. Switching frequency capability extends to 500kHz. ROHS3 compliant with MSL 1 rating.
UC3845BD1R2G (onsemi) - Active product status with substantial inventory (88,972 units). Identical electrical specifications to SG3845DM with 7.6V ~ 30V supply, 48% duty cycle, positive isolation-capable output, and boost/flyback topology. Standard operating temperature range (0°C ~ 70°C TA). Cut Tape & Digi-Reel packaging format. ROHS3 compliant.
UC3845BD1G (onsemi) - Active product status with 2,900 units available. Matches all critical electrical parameters of SG3845DM. Tube packaging format. ROHS3 compliant with MSL 1 rating.
UC3845BVD1R2G (onsemi) - Active product status with 4,091 units in stock. Provides extended operating temperature range (-40°C ~ 105°C TA) compared to SG3845DM. Maintains all electrical compatibility requirements. Tape & Reel packaging. ROHS3 compliant.

Alternative Substitutes (Conditional Use)

TL3845BDR-8 (Texas Instruments) - Active product status with highest inventory among Texas Instruments options (17,222 units). Supports boost, flyback, and forward converter topologies with positive output configuration. Supply voltage range matches (7.6V ~ 30V) and duty cycle specification (48%). Switching frequency fixed at 100kHz (lower than SG3845DM capability). Tape & Reel packaging. ROHS3 compliant. Suitable for applications not requiring switching frequencies above 100kHz.
TL3845BD-8 (Texas Instruments) - Last Time Buy product status with 1,166 units available. Electrical specifications match TL3845BDR-8. Tube packaging format. Not recommended for new designs due to Last Time Buy status.

Not Recommended for Direct Substitution

UC3845AD8 and UC3845AD8TR - Last Time Buy and Active status respectively, but duty cycle specification not provided in documentation, creating uncertainty for applications requiring 48% duty cycle operation.
LT1243CS8#PBF and LT1244CS8#PBF - Buck topology only (step-down function). Incompatible with SG3845DM flyback topology requirement. Different supply voltage ranges and duty cycle specifications.

Frequently Asked Questions (FAQ)

Q: Can TL3845BDR-8 replace SG3845DM in all applications?

A: TL3845BDR-8 is electrically compatible for supply voltage (7.6V ~ 30V), duty cycle (48%), and package format (8-SOIC). However, TL3845BDR-8 has a fixed switching frequency of 100kHz, while SG3845DM supports 1Hz ~ 500kHz. Applications requiring switching frequencies outside the 100kHz specification require design verification or selection of alternative substitutes with wider frequency range support.

Q: What is the difference between UC3845BD1013TR and UC3845BD1R2G?

A: Both parts maintain identical electrical specifications for supply voltage, duty cycle, topology, and output configuration. The primary differences are: (1) UC3845BD1013TR operates across -40°C ~ 150°C (TJ), providing extended high-temperature capability; (2) UC3845BD1R2G operates across 0°C ~ 70°C (TA), matching SG3845DM temperature range; (3) UC3845BD1013TR has higher inventory availability (287,800 units vs. 88,972 units). Selection depends on thermal requirements and supply chain preferences.

Q: Are all substitute parts pin-compatible with SG3845DM?

A: All recommended direct substitutes share the 8-SOIC package format with identical pin pitch (0.154", 3.90mm width). Pin-level compatibility is confirmed by the UC3845 base product number shared across multiple manufacturers. However, circuit-level verification is required for applications with specific frequency, topology, or temperature requirements.

Q: Why do some substitutes show "Synchronous Rectifier: No" while SG3845DM shows "Yes"?

A: The SG3845DM includes integrated synchronous rectifier capability. Substitute parts without this feature (TL3845 series, UC3845 variants from onsemi and STMicroelectronics) function as standard PWM controllers without integrated synchronous rectification. Applications utilizing synchronous rectification must implement external rectification circuits when using these substitutes, or select UC3845BD1013TR which maintains compatibility with the SG3845DM architecture.

Q: What is the significance of "Last Time Buy" product status?

A: Parts designated as Last Time Buy (TL3845BD-8, UC3845AD8) indicate the manufacturer will discontinue production after a specified date. These parts remain available for current orders but are not recommended for new product designs. Active status parts (UC3845BD1013TR, UC3845BD1R2G, TL3845BDR-8) are preferred for long-term supply chain stability.

Q: Can LT1243CS8#PBF or LT1244CS8#PBF substitute for SG3845DM?

A: No. LT1243CS8#PBF and LT1244CS8#PBF implement buck (step-down) topology only, while SG3845DM implements flyback topology. These parts are functionally incompatible despite sharing the 8-SOIC package format and PMIC category. Buck topology controllers cannot perform the step-up or isolation functions required in flyback applications.

Q: What packaging formats are available for substitute parts?

A: Substitute parts are available in three packaging formats: (1) Tube - for manual handling and lower-volume applications; (2) Cut Tape (CT) & Digi-Reel - for semi-automated pick-and-place equipment; (3) Tape & Reel (TR) - for fully automated high-volume manufacturing. Selection depends on manufacturing process requirements and volume specifications.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. All recommended substitute parts maintain ROHS3 compliance status, matching the SG3845DM environmental certification. All parts also maintain MSL 1 (Unlimited) moisture sensitivity level rating, indicating no special moisture handling requirements during storage or assembly.

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