Taiwan Semiconductor Corporation 1SMA5945

Overview

1SMA5945 from Taiwan Semiconductor is a surface-mount 1.5W Zener diode with nominal zener voltage of 68V, ±5% tolerance, 5.5Ω dynamic impedance at 5.5mA test current, and maximum leakage current of 0.5µA at 51.7V reverse voltage. It operates within -55°C to +150°C junction temperature range and is used for precision voltage regulation in DC/DC converters and power supply feedback loops.

For engineers reviewing the 1SMA5945 datasheet, 1SMA5945 pinout, 1SMA5945 application, or 1SMA5945 equivalent, key selection criteria include its DO-214AC (SMA) package compatibility, 68V regulation stability under 5.5mA I_ZT, low 0.5µA IR at VR = 51.7V, JEDEC Class 3B ESD rating, and moisture sensitivity level 1 handling requirements.

Technical Context

The 1SMA5945 functions as a single-die, glass-passivated Zener diode optimized for stable voltage reference and overvoltage clamping in compact power circuits. Its 68V nominal breakdown voltage is guaranteed at thermal equilibrium with ±5% tolerance, and it maintains low dynamic impedance (1700Ω at I_ZK = 0.25mA) for sharp knee characteristics.

Designed for surface-mount assembly on 5mm × 5mm Cu pads, the device supports automated placement and exhibits low inductance and typical reverse leakage <0.5µA above 11V. It meets JESD201 Class 2 whisker resistance and UL 94V-0 flammability standards for reliability in industrial-grade power systems.

Key Specifications

Pinout & Package

Package: DO-214AC (SMA), surface-mount, single-anode/single-cathode configuration. Cathode indicated by band; matte tin-plated leads compliant with J-STD-002 solderability.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Zener diode applications.

Compared with 1N4748A and BZX84-C68, the 1SMA5945 delivers 50% higher power capability in an SMT-optimized package with superior moisture resilience and tighter low-current regulation-making it the preferred choice for modern, high-density power supply designs requiring long-term reliability.

Availability

1SMA5945 is available at Aetrix Electronics and suitable for switching mode power supplies, on-board DC/DC converters, and lighting applications requiring stable component supply, full traceability, and extended lifecycle support.

Supply support for 1SMA5945 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Taiwan Semiconductor Corporation (TSC) is a vertically integrated semiconductor manufacturer specializing in discrete power devices, analog ICs, and protection components for industrial and consumer markets.

The 1SMA59xx series was developed to deliver high-reliability, surface-mount Zener diodes with enhanced thermal performance and JEDEC-compliant robustness for next-generation power conversion systems.

FAQ

What is the exact zener voltage tolerance and test condition for 1SMA5945?

The 1SMA5945 has a nominal zener voltage of 68V with ±5% tolerance, verified at I_ZT = 5.5 mA and thermal equilibrium per datasheet Note 2. The guaranteed range is 64.6V to 71.4V, measured under stabilized junction temperature conditions-not ambient temperature alone.

Can 1SMA5945 be used in place of 1SMA5944 or 1SMA5946 in existing designs?

Yes, 1SMA5945 can substitute for adjacent family members like 1SMA5944 (62V) or 1SMA5946 (75V) only if the circuit's regulation window accommodates ±5V shift and power dissipation remains within 1.5W limits. However, each part has unique Z_ZT and I_ZK values-verify loop stability and leakage impact before interchange.

Does 1SMA5945 meet lead-free reflow requirements per J-STD-020?

Yes, the 1SMA5945 is rated Moisture Sensitivity Level 1 per J-STD-020 and supports standard lead-free reflow profiles (peak 260°C, 10-second dwell). Its matte tin-plated leads comply with J-STD-002 for solderability, and the UL 94V-0 molding compound withstands multiple reflow cycles without delamination.

What is the maximum DC zener current (I_ZM) for 1SMA5945 at 25°C ambient?

The maximum DC zener current for 1SMA5945 is 22 mA at T_A = 25°C, derived from P_D = 1.5 W and V_Z = 68V. At elevated ambient temperatures, I_ZM must be reduced per the 20 mW/°C derating curve-e.g., 15.6 mA at 75°C ambient on a 5 mm × 5 mm Cu pad.

How does the 1SMA5945's leakage current compare to other 68V Zeners in the same package?

The 1SMA5945 specifies maximum leakage current of 0.5 µA at V_R = 51.7V (75% of V_Z), which is 2–5× lower than typical industry-standard 68V SMA Zeners. This low IR enables accurate biasing in high-impedance feedback networks where leakage-induced offset would otherwise degrade regulation accuracy.