CDST-21-G Equivalent & Substitute Parts Reference

Part Overview

The CDST-21-G is a general-purpose rectifier diode manufactured by Comchip Technology, rated for 250V DC reverse voltage with 200mA average rectified current in a surface mount SOT-23-3 package. This component is classified as obsolete, making identification of compatible substitute parts essential for ongoing design support and production continuity. The part operates as a small-signal rectifier with 50ns reverse recovery time, suitable for standard switching applications requiring compact form factors.

Substiute Parts

CDST-21-G

Comchip TechnologyIn Stock: 783CDST-21-G Datasheet

Current PartRFQ

BAS21-HF

Comchip TechnologyIn Stock: 42748BAS21-HF Datasheet

DirectRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the CDST-21-G is determined by the following critical parameters:

Mandatory Matching Criteria:

• Voltage - DC Reverse (Vr) (Max): 250V minimum
• Package / Case: SOT-23-3 (physical and electrical compatibility)
• Mounting Type: Surface Mount
• Operating Temperature - Junction: 150°C or higher
• RoHS Status: ROHS3 Compliant

Allowable Parameter Variations:

• Current - Average Rectified (Io): Equal to or greater than 200mA
• Voltage - Forward (Vf): Equal to or less than 1.25V @ 200mA
• Reverse Recovery Time (trr): Equal to or less than 50ns
• Current - Reverse Leakage @ Vr: Equal to or less than 1µA @ 200V
• Capacitance @ Vr, F: Equal to or less than 5pF @ 0V, 1MHz

The BAS21-HF meets all mandatory criteria and exceeds performance in current capacity and leakage characteristics, qualifying it as a direct substitute.

Parameter Comparison

Engineering Selection Recommendations

BAS21-HF as Direct Substitute:

The BAS21-HF is qualified as a direct substitute for the CDST-21-G based on the following engineering factors:

1. Product Status Alignment: The BAS21-HF carries Active product status, ensuring continued availability and manufacturing support, whereas the CDST-21-G is obsolete.

2. Regulatory Compliance: Both components maintain ROHS3 compliance and identical moisture sensitivity ratings (MSL 1), ensuring compatibility with current manufacturing and environmental standards.

3. Electrical Performance: The BAS21-HF meets or exceeds all critical electrical parameters. The increased current rating (400mA versus 200mA) and reduced reverse leakage (100nA versus 1µA) provide enhanced performance margins without introducing incompatibility.

4. Physical Compatibility: Identical package designation (SOT-23-3) and mounting type (Surface Mount) ensure direct PCB-level compatibility without layout modifications.

5. Thermal Characteristics: Matching maximum junction temperature (150°C) confirms thermal design compatibility.

Selection of BAS21-HF eliminates obsolescence risk while maintaining full electrical and mechanical compatibility with existing circuit designs.

Frequently Asked Questions (FAQ)

Q: Can BAS21-HF replace CDST-21-G in all applications?

A: Yes. The BAS21-HF meets all mandatory electrical and mechanical parameters of the CDST-21-G. The higher current rating and lower leakage current represent performance improvements that do not create incompatibility.

Q: Are there any package differences between these parts?

A: No. Both components use the SOT-23-3 package (also designated TO-236-3 or SC-59). Pin configuration and physical dimensions are identical, enabling direct PCB substitution.

Q: What is the significance of the current rating difference?

A: The CDST-21-G is rated for 200mA average rectified current, while the BAS21-HF is rated for 400mA. In applications requiring 200mA or less, the BAS21-HF operates well within its design envelope, providing additional thermal and reliability margin.

Q: How do the reverse leakage specifications compare?

A: The CDST-21-G specifies 1µA reverse leakage at 200V, while the BAS21-HF specifies 100nA at the same voltage. The BAS21-HF exhibits superior leakage performance, which is beneficial for high-impedance circuit applications.

Q: Are both parts RoHS compliant?

A: Yes. Both CDST-21-G and BAS21-HF are ROHS3 compliant with MSL 1 (unlimited moisture sensitivity level), confirming compatibility with current manufacturing and environmental regulations.

Q: What is the difference between "Small Signal" and "Fast Recovery" speed classifications?

A: The CDST-21-G is classified as Small Signal (≤200mA, Any Speed), while the BAS21-HF is classified as Fast Recovery (≤500ns, >200mA). Both share identical 50ns reverse recovery time specifications. The classification difference reflects the current rating category, not a functional incompatibility.