BZX585-B51,115 Equivalent & Substitute Parts

Part Overview

The BZX585-B51,115 is an active Zener diode manufactured by Nexperia USA Inc., rated at 51 V nominal with 300 mW maximum power dissipation in a surface mount SOD-523 package. This component is designed for voltage regulation and protection applications requiring precise Zener characteristics at 51 V. The part carries AEC-Q100 automotive qualification and is ROHS3 compliant. Substitute parts are identified when equivalent electrical performance can be achieved within the specified parameter tolerances while maintaining functional compatibility in the target application circuit.

Key Parameters

Parameter	Value	Unit
Voltage - Zener (Nom)	51	V
Tolerance	±2%	%
Power - Max	300	mW
Impedance (Max)	180	Ohms
Current - Reverse Leakage @ Vr	50	nA @ 35.7 V
Voltage - Forward (Vf) (Max) @ If	1.1	V @ 100 mA
Operating Temperature Range	-65 to 150	°C
Package / Case	SOD-523	—
Mounting Type	Surface Mount	—
Grade	Automotive	—
Qualification	AEC-Q100	—
RoHS Status	ROHS3 Compliant	—

Substitute Part Grouping Explanation

Substitution of the BZX585-B51,115 is determined by the following critical electrical and mechanical parameters:

Electrical Equivalence Criteria:

Zener voltage (Nom): 51 V ±2% tolerance
Operating temperature range: -65°C to 150°C minimum
Surface mount technology compatibility
RoHS3 compliance and REACH unaffected status

Mechanical Compatibility Criteria:

Surface mount package format (SOD-523 or equivalent footprint)
Tape & Reel packaging for automated assembly

The substitute part MM3Z51VB meets the electrical specification for Zener voltage and tolerance. However, the power rating differs (200 mW vs. 300 mW), which affects maximum dissipation capability. The package format differs (SOD-323F vs. SOD-523), requiring PCB layout verification for physical fit. Both parts maintain identical operating temperature range, automotive-grade qualification, and regulatory compliance status.

Parameter Comparison

Parameter	BZX585-B51,115 (Main)	MM3Z51VB (Substitute)	Match Status
Voltage - Zener (Nom)	51 V	51 V	Equivalent
Tolerance	±2%	±2%	Equivalent
Power - Max	300 mW	200 mW	Substitute Lower
Impedance (Max)	180 Ohms	169 Ohms	Substitute Lower
Current - Reverse Leakage @ Vr	50 nA @ 35.7 V	45 nA @ 35.7 V	Substitute Lower
Voltage - Forward (Vf) (Max) @ If	1.1 V @ 100 mA	1 V @ 10 mA	Different Test Condition
Operating Temperature Range	-65°C to 150°C	-65°C to 150°C	Equivalent
Package / Case	SOD-523	SOD-323F	Different Package
Mounting Type	Surface Mount	Surface Mount	Equivalent
Grade	Automotive	Automotive	Equivalent
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	Equivalent
Moisture Sensitivity Level	1 (Unlimited)	1 (Unlimited)	Equivalent

Engineering Selection Recommendations

Primary Part Selection (BZX585-B51,115): The BZX585-B51,115 is the specified component with active product status, AEC-Q100 automotive qualification, and ROHS3 compliance. This part is suitable for applications requiring 300 mW power dissipation at 51 V Zener voltage with SOD-523 package constraints.

Substitute Part Selection (MM3Z51VB): The MM3Z51VB is an active substitute with equivalent Zener voltage and tolerance specifications. This part maintains automotive-grade qualification and ROHS3 compliance. The substitute is applicable only when the following conditions are met:

Circuit design permits maximum power dissipation of 200 mW (not 300 mW)
PCB layout accommodates SOD-323F package footprint (smaller than SOD-523)
Forward voltage test conditions at 10 mA (not 100 mA) are acceptable for the application

Both parts are manufactured by established suppliers with active product status and unlimited moisture sensitivity rating, ensuring long-term availability and reliability.

Frequently Asked Questions (FAQ)

Q: Can MM3Z51VB directly replace BZX585-B51,115 in all applications?

A: No. The MM3Z51VB has a lower maximum power rating (200 mW vs. 300 mW) and a different package format (SOD-323F vs. SOD-523). Substitution is valid only when circuit power dissipation does not exceed 200 mW and the PCB layout supports the smaller SOD-323F footprint.

Q: Are the Zener voltage specifications identical between these parts?

A: Yes. Both parts specify 51 V nominal Zener voltage with ±2% tolerance and identical operating temperature range (-65°C to 150°C). The Zener voltage regulation characteristics are equivalent.

Q: What is the significance of the different package formats?

A: BZX585-B51,115 uses SOD-523 package while MM3Z51VB uses SOD-323F package. These are different physical footprints requiring different PCB pad layouts. Physical substitution requires PCB redesign or verification that the smaller SOD-323F component fits the existing SOD-523 footprint space.

Q: Do both parts meet automotive qualification requirements?

A: Yes. Both parts carry automotive-grade designation and AEC-Q100 qualification, suitable for automotive applications. Both are ROHS3 compliant and REACH unaffected.

Q: What is the impact of the power rating difference?

A: The BZX585-B51,115 dissipates up to 300 mW while MM3Z51VB dissipates up to 200 mW. In applications where the Zener diode must dissipate more than 200 mW, the substitute part will exceed its thermal limits. Circuit analysis must confirm that actual power dissipation remains within the 200 mW limit.

Q: Are the impedance values significant for substitution?

A: The impedance values are similar (180 Ohms vs. 169 Ohms), with the substitute showing slightly lower impedance. This difference is within normal manufacturing variation and does not prevent substitution from an impedance perspective.

Q: What inventory considerations apply to these parts?

A: BZX585-B51,115 has 819 pieces in stock while MM3Z51VB has 3200 pieces in stock. The substitute offers higher inventory availability if supply chain considerations are relevant to component selection.

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