UC3845BVD Equivalent & Substitute Parts

Part Overview

The UC3845BVD is a boost and flyback regulator controller IC manufactured by onsemi, designed for step-up and step-up/step-down DC-DC conversion applications. This 14-SOIC surface mount device operates across a 7.6V to 30V supply voltage range with switching frequencies up to 500kHz and a maximum duty cycle of 48%. The part is classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and production continuity.

Key Parameters

Parameter	Value
Manufacturer Part Number	UC3845BVD
Manufacturer	onsemi
Category	Power Management (PMIC)
Package / Case	14-SOIC (0.154", 3.90mm Width)
Topology	Boost, Flyback
Function	Step-Up, Step-Up/Step-Down
Output Type	Transistor Driver
Output Configuration	Positive, Isolation Capable
Number of Outputs	1
Voltage - Supply (Vcc/Vdd)	7.6V ~ 30V
Frequency - Switching	Up to 500kHz
Duty Cycle (Max)	48%
Operating Temperature	-40°C ~ 105°C (TA)
Mounting Type	Surface Mount
Control Features	Frequency Control
Product Status	Obsolete
RoHS Status	RoHS non-compliant

Substitute Part Grouping Explanation

Substitution for the UC3845BVD is determined by strict alignment of electrical and mechanical parameters. The critical substitution criteria are:

Primary Compatibility Parameters:

Package type: 14-SOIC (0.154", 3.90mm Width) — all substitutes must match this footprint
Topology: Boost and/or Flyback capability
Output configuration: Positive output
Supply voltage range: 7.6V ~ 30V minimum overlap
Switching frequency capability: Up to 500kHz
Duty cycle maximum: 48%
Output type: Transistor Driver
Control features: Frequency Control

Substitute Categories:

Direct Equivalents (UC3845 Base Series): UC3845AD, UC3845ADTR, UC3845D, and UC3845DTR maintain the UC3845 base product number with identical topology and electrical specifications. These parts are pin-compatible and functionally equivalent within their operating temperature and supply voltage ranges.

Similar Alternatives (TL2845 and TL3845 Series): TL2845BD, TL2845BDR, TL3845BD, TL3845BDR, TL3845D, and TL3845DR share the same 14-SOIC package, topology support (Boost, Flyback, Forward), and core electrical parameters. These parts operate at fixed switching frequencies (500kHz for TL2845, 100kHz for TL3845) and support the same duty cycle and supply voltage specifications.

Parameter Comparison

Parameter	UC3845BVD	UC3845AD	UC3845ADTR	UC3845D	UC3845DTR	TL2845BD	TL2845BDR	TL3845BD	TL3845BDR	TL3845D	TL3845DR
Package / Case	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC
Topology	Boost, Flyback	Boost, Flyback	Boost, Flyback	Boost, Flyback	Boost, Flyback	Boost, Flyback, Forward	Boost, Flyback, Forward	Boost, Flyback, Forward Converter	Boost, Flyback, Forward Converter	Boost, Flyback, Forward Converter	Boost, Flyback, Forward Converter
Output Type	Transistor Driver	Transistor Driver	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	Positive	Positive	Positive	Positive	Positive	Positive	Positive
Number of Outputs	1	1	1	1	1	1	1	1	1	1	1
Voltage - Supply (Vcc/Vdd)	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	12V ~ 28V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V
Frequency - Switching	Up to 500kHz	Up to 500kHz	Up to 500kHz	Up to 500kHz	Up to 500kHz	Up to 500kHz	Up to 500kHz	100kHz	100kHz	100kHz	100kHz
Duty Cycle (Max)	48%	48%	48%	48%	48%	48%	48%	48%	48%	48%	48%
Operating Temperature	-40°C ~ 105°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	-40°C ~ 85°C	-40°C ~ 85°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C
Control Features	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control	Frequency Control
Product Status	Obsolete	Active	Active	Obsolete	Active	Last Time Buy	Active	Last Time Buy	Last Time Buy	Active	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

For Active Production (Recommended Primary Choices):

UC3845ADTR and UC3845DTR are the preferred direct substitutes. Both are manufactured by Texas Instruments, maintain active product status, and provide ROHS3 compliance. UC3845ADTR offers the full 7.6V to 30V supply range with 0°C to 70°C operating temperature. UC3845DTR operates within a narrower 12V to 28V supply range but maintains the same switching frequency capability and duty cycle specifications. Both are available in Tape & Reel packaging for production volumes.

TL3845DR and TL3845D are active alternatives from Texas Instruments with ROHS3 compliance. These parts operate at a fixed 100kHz switching frequency compared to the UC3845's configurable up to 500kHz. TL3845DR includes automotive-grade qualification (AEC-Q100) and operates across the full 0°C to 70°C temperature range. Selection of TL3845 variants is appropriate when fixed 100kHz operation meets application requirements.

For Extended Temperature Range Applications:

TL2845BD and TL2845BDR support -40°C to 85°C operating temperature, exceeding the standard 0°C to 70°C range of most UC3845 direct substitutes. These parts maintain 500kHz switching frequency capability and are suitable for industrial or automotive environments requiring extended temperature performance.

For Legacy System Maintenance:

UC3845D (Fairchild Semiconductor) and UC3845AD (Texas Instruments, Tube packaging) are available as direct equivalents for systems already deployed with UC3845 controllers. Both maintain obsolete or active status with ROHS3 compliance, though UC3845AD operates within 0°C to 70°C temperature limits.

Compliance Considerations:

All recommended substitutes are ROHS3 compliant, addressing environmental regulatory requirements. The original UC3845BVD is RoHS non-compliant; substitution with any listed alternative provides compliance improvement for new designs or production transitions.

Frequently Asked Questions (FAQ)

Q: Can UC3845AD directly replace UC3845BVD in existing designs?

A: UC3845AD is electrically and mechanically compatible, sharing the same 14-SOIC package, topology support, and core electrical parameters. However, UC3845AD operates within 0°C to 70°C, while UC3845BVD supports -40°C to 105°C. Verify that your application's operating temperature range does not exceed 0°C to 70°C before substitution.

Q: What is the difference between UC3845ADTR and UC3845AD?

A: Both parts are identical electrically and functionally. The difference is packaging: UC3845ADTR is supplied in Tape & Reel format for automated assembly and high-volume production, while UC3845AD is supplied in Tube packaging for lower volumes or manual handling.

Q: Why do TL3845 parts operate at 100kHz instead of 500kHz?

A: TL3845 is a fixed-frequency variant of the UC3845 family, designed with 100kHz switching frequency as a standard specification. This is not a limitation but a design choice. Select TL3845 variants when your application requires or benefits from fixed 100kHz operation, such as in specific power supply topologies or EMI management strategies.

Q: Are TL2845 and TL3845 parts pin-compatible with UC3845?

A: Yes. All parts in this comparison share the 14-SOIC package with identical pin assignments, enabling direct PCB-level substitution. Functional differences (topology support, switching frequency) do not affect physical compatibility.

Q: Which substitute offers the best long-term availability?

A: UC3845ADTR and TL3845DR both carry Active product status from Texas Instruments, indicating ongoing production and long-term availability. TL3845DR additionally includes automotive-grade qualification (AEC-Q100), supporting extended lifecycle in automotive and industrial applications.

Q: Can I use TL3845 in a design originally specified for UC3845?

A: Yes, provided your circuit design accommodates the fixed 100kHz switching frequency. The TL3845 supports the same topologies (Boost, Flyback, Forward Converter), output configuration (Positive), and supply voltage range (7.6V ~ 30V). Verify that your transformer, inductor, and filter component designs function correctly at 100kHz instead of the variable frequency up to 500kHz.

Q: What is the significance of "Last Time Buy" status for TL2845BD and TL3845BD?

A: Last Time Buy status indicates that these parts are in their final production phase. Existing inventory is available, but no new production runs are planned. For new designs, select Active status parts such as UC3845ADTR, UC3845DTR, TL3845D, or TL3845DR to ensure long-term supply continuity.

Q: Does RoHS3 compliance affect electrical performance?

A: No. RoHS3 compliance addresses material composition and environmental safety, not electrical specifications. All ROHS3-compliant substitutes maintain identical electrical performance to the original UC3845BVD within their specified operating parameters.

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