UC3845BD Equivalent & Substitute Parts

Part Overview

The UC3845BD 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 package 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 product is currently obsolete, making equivalent and substitute parts necessary for ongoing design support, maintenance, and new production requirements.

Key Parameters

Parameter	Value
Manufacturer Part Number	UC3845BD
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 Configuration	Positive, Isolation Capable
Voltage - Supply (Vcc/Vdd)	7.6V ~ 30V
Frequency - Switching	Up to 500kHz
Duty Cycle (Max)	48%
Operating Temperature	0°C ~ 70°C (TA)
Mounting Type	Surface Mount
Output Type	Transistor Driver
Number of Outputs	1
Control Features	Frequency Control
RoHS Status	RoHS non-compliant

Substitute Part Grouping Explanation

Substitution eligibility for the UC3845BD is determined by strict alignment with the following critical parameters:

Primary Substitution Criteria:

Package / Case: 14-SOIC (0.154", 3.90mm Width)
Topology: Boost, Flyback
Function: Step-Up, Step-Up/Step-Down
Output Configuration: Positive
Voltage - Supply (Vcc/Vdd): 7.6V ~ 30V
Operating Temperature: 0°C ~ 70°C (TA)
Output Type: Transistor Driver
Number of Outputs: 1
Duty Cycle (Max): 48%

Substitute parts are classified into two categories:

Direct Substitutes maintain identical electrical and mechanical specifications with the UC3845BD, differing only in packaging format (tube vs. tape & reel) or manufacturer source. These include UC3845AD, UC3845ADTR, UC3845D, and UC3845DTR.

Similar Substitutes share the same base topology, package, and core functional parameters but may differ in switching frequency specification or product status. These include TL3845BD, TL3845BDR, TL3845D, and TL3845DR, all manufactured by Texas Instruments.

Parameter Comparison

Parameter	UC3845BD (onsemi)	UC3845AD (TI)	UC3845ADTR (TI)	UC3845D (Fairchild)	UC3845DTR (TI)	TL3845BD (TI)	TL3845BDR (TI)	TL3845D (TI)	TL3845DR (TI)
Package / Case	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC	14-SOIC
Topology	Boost, Flyback	—	—	—	—	Boost, Flyback, Forward Converter	Boost, Flyback, Forward Converter	Boost, Flyback, Forward Converter	Boost, Flyback, Forward Converter
Function	Step-Up, Step-Up/Step-Down	—	—	—	—	Step-Up, Step-Up/Step-Down	Step-Up, Step-Up/Step-Down	Step-Up, Step-Up/Step-Down	Step-Up, Step-Up/Step-Down
Output Configuration	Positive, Isolation Capable	—	—	—	—	Positive	Positive	Positive	Positive
Voltage - Supply (Vcc/Vdd)	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	—	12V ~ 28V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V	7.6V ~ 30V
Frequency - Switching	Up to 500kHz	—	—	—	—	100kHz	100kHz	100kHz	100kHz
Duty Cycle (Max)	48%	—	—	—	—	48%	48%	48%	48%
Operating Temperature	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	0°C ~ 70°C	0°C ~ 70°C
Output Type	Transistor Driver	—	—	—	—	Transistor Driver	Transistor Driver	Transistor Driver	Transistor Driver
Number of Outputs	1	—	—	—	—	1	1	1	1
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Product Status	Obsolete	Active	Active	Obsolete	Active	Last Time Buy	Last Time Buy	Active	Active

Engineering Selection Recommendations

For Direct Substitution (Preferred):

UC3845ADTR and UC3845DTR are the primary recommendations for direct replacement. Both are manufactured by Texas Instruments, carry Active product status, and maintain full electrical compatibility with the UC3845BD. UC3845ADTR is supplied in Tape & Reel packaging with 5092 units in stock, while UC3845DTR is also in Tape & Reel format with 7322 units available. Both comply with ROHS3 standards, addressing the RoHS non-compliance limitation of the original UC3845BD.

UC3845AD provides an alternative direct substitute in tube packaging with 2414 units in stock, suitable for applications where tape & reel format is not required.

For Similar Substitution (Extended Compatibility):

TL3845D and TL3845DR represent active product alternatives with extended topology support (Boost, Flyback, Forward Converter). TL3845D is available in tube packaging with 2002 units in stock and carries AEC-Q100 automotive qualification. TL3845DR is available with 6940 units in stock and also includes AEC-Q100 qualification. Both maintain the 7.6V to 30V supply voltage range and 48% maximum duty cycle.

TL3845BD and TL3845BDR carry Last Time Buy status and should be considered only when existing inventory commitments require their use. TL3845BDR offers 3172 units in stock in Cut Tape & Digi-Reel packaging.

Compliance Consideration:

All substitute parts listed are ROHS3 compliant, providing regulatory advantage over the RoHS non-compliant UC3845BD for new designs and production transitions.

Frequently Asked Questions (FAQ)

Q: Can UC3845ADTR directly replace UC3845BD in existing designs?

A: Yes. UC3845ADTR maintains identical electrical specifications including 7.6V to 30V supply voltage, 48% maximum duty cycle, and 14-SOIC package format. The primary difference is packaging format (Tape & Reel vs. tube) and ROHS3 compliance status.

Q: What is the difference between UC3845 and TL3845 series parts?

A: Both series share the same 14-SOIC package, 7.6V to 30V supply voltage range, and 48% duty cycle specification. TL3845 variants support an additional Forward Converter topology beyond the Boost and Flyback topologies of UC3845. TL3845 parts specify 100kHz switching frequency, while UC3845BD supports up to 500kHz.

Q: Are TL3845D and TL3845DR suitable for automotive applications?

A: Yes. Both TL3845D and TL3845DR carry AEC-Q100 automotive qualification and are suitable for automotive-grade designs. Other substitute parts listed do not include automotive qualification.

Q: What packaging options are available for direct substitutes?

A: UC3845ADTR and UC3845DTR are supplied in Tape & Reel (TR) format. UC3845AD is supplied in tube packaging. All three maintain identical electrical specifications and 14-SOIC package dimensions.

Q: Why is UC3845D (Fairchild) listed as a substitute if it is obsolete?

A: UC3845D is included for reference in applications where existing inventory or legacy supply chains require its use. However, Active product alternatives (UC3845ADTR, UC3845DTR, TL3845D, TL3845DR) are preferred for new designs and ongoing production.

Q: Does switching frequency difference between UC3845BD (500kHz) and TL3845 variants (100kHz) affect substitution?

A: Switching frequency is a design parameter that affects circuit performance and component selection. While TL3845 parts operate at lower switching frequency, they maintain the same maximum duty cycle and supply voltage range. Circuit redesign may be required to accommodate frequency differences in applications sensitive to switching speed.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. All substitute parts listed (UC3845AD, UC3845ADTR, UC3845D, UC3845DTR, TL3845BD, TL3845BDR, TL3845D, TL3845DR) are ROHS3 compliant, providing regulatory compliance advantage over the RoHS non-compliant UC3845BD.

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