Diodes Incorporated FSD270TA

Overview

FSD270TA from Zetex (now Diodes Incorporated) is a hyperabrupt SOT-23 dual common-cathode varactor diode optimized for VHF/UHF tuning in DAB receiver modules, VCXOs, and TCXOs. It delivers 33 pF nominal capacitance at 2 V, 25 V reverse breakdown, <20 nA leakage at 20 V, 6.5:1 capacitance ratio (2 V/20 V), and minimum Q of 200 at 50 MHz.

For engineers reviewing the FSD270TA datasheet, FSD270TA pinout, FSD270TA application, or FSD270TA equivalent, key selection criteria include matched dual-diode CV characteristics, tight 3-band capacitance grading (A/B/C), low-phase-noise suitability via sub-200 pA IR at 20 V, and SOT-23 footprint compatibility with high-density RF filter and oscillator designs.

Technical Context

The FSD270TA integrates two monolithic varactor junctions sharing a common cathode terminal, enabling symmetrical voltage-controlled capacitance tuning without inter-diode conduction skew. Its hyperabrupt doping profile yields a steep, linearized C–V slope ideal for wide-tuning-range oscillators and tracking filters.

Designed specifically for DAB front-end channel selection, it replaces discrete single varactors to suppress RF-induced forward conduction in PLL loop filters-reducing harmonic distortion and bias drift under high-swing VHF/UHF signals.

Key Specifications

Pinout & Package

SOT-23 package (JEDEC TO-236AB), 3-pin surface-mount outline with gull-wing leads. Dimensions: 2.9 mm × 1.3 mm × 1.0 mm (L × W × H); thermal pad not present.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMV2023-011LF and BBY58-02V, the FSD270TA uniquely combines dual symmetry, 33 pF baseline capacitance, and 6.5:1 ratio-enabling compact, high-rejection DAB filters and wide-pull VCXOs without performance trade-offs in Q or leakage.

Availability

FSD270TA is available at Aetrix Electronics and suitable for DAB receiver modules, voltage-controlled crystal oscillators (VCXOs), and mobile radio transceiver filters requiring stable component supply, matched dual-varactor performance, and SOT-23 manufacturability.

Supply support for FSD270TA 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

Zetex plc (acquired by Diodes Incorporated in 2008) specialized in high-performance analog and RF semiconductors for communications and consumer electronics.

The FSD270 series belongs to Zetex's precision varactor diode product line, engineered specifically for digital broadcast and frequency-agile oscillator applications demanding tight CV matching and ultra-low phase noise.

FAQ

What does the 'TA' suffix indicate in FSD270TA?

The 'TA' suffix denotes tape-and-reel packaging: 3000 units per 8 mm embossed carrier tape on a 180 mm reel. Devices are pre-tested and binned into capacitance bands (A/B/C) at 2 V, with each reel containing only one band. The part marking on the device body identifies its band (e.g., '70A').

Can FSD270TA be used in place of a single varactor diode?

Yes-but only if the circuit topology accommodates dual-anode/common-cathode configuration. Replacing a single diode requires rewiring to use one anode and the shared cathode, leaving the second anode unconnected or grounded. Performance may differ due to parasitic coupling between integrated junctions.

Is thermal derating required for continuous operation?

Yes. At ambient temperatures above 25°C, power dissipation must be linearly derated at 3 mW/°C. For example, at 85°C ambient, maximum allowable PD drops to 150 mW. Mounting on 25 mm × 25 mm FR4 with full 1 oz copper improves thermal resistance by ~40% versus bare board.

How is capacitance matching verified across the dual diodes?

Each FSD270TA device undergoes final test at 2 V reverse bias; both diodes are measured and binned together. Band A devices have Cd = 29.7–32.1 pF, Band B = 31.9–34.1 pF, Band C = 33.9–36.3 pF. Matching tolerance between anodes on the same die is typically ≤±0.3 pF.