Diodes Incorporated ZC931TC

Overview

ZC931TC from Zetex Semiconductors is a silicon hyperabrupt varactor diode optimized for voltage-controlled oscillator (VCO) and VCXO/TCXO tuning circuits. It delivers 13.5 pF capacitance at 1 V, 6.5 pF at 2.5 V, and 4.0 pF at 4 V reverse bias, with minimum Q of 300 at 50 MHz and typical reverse leakage of 200 pA - enabling low-phase-noise frequency synthesis in wireless transceivers.

For engineers reviewing the ZC931TC datasheet, ZC931TC pinout, ZC931TC application, or ZC931TC equivalent, key selection criteria include its octave-tuning range (0–6 V), tight C-V tolerance, SOD323 package compatibility, and verified performance in mobile radio and pager reference oscillators.

Technical Context

This hyperabrupt junction varactor exhibits a steep, linearized C–V slope over 0–6 V, supporting wideband frequency pulling in crystal oscillator loops. Its 300–400 ppm/°C temperature coefficient of capacitance and 12 V maximum reverse voltage ensure stable tuning under thermal variation and supply margin.

Designed for RF tuning applications, it operates with reverse bias only; forward current rating is 100 mA but not intended for conduction. The device's high Q (>300 @ 50 MHz) and ultra-low IR (<100 nA @ 8 V) directly suppress phase noise in oscillator tank circuits.

Key Specifications

Pinout & Package

Package: SOD323 - 2-pin surface-mount plastic package (2.67 × 1.20 × 0.37 mm), cathode-banded, compatible with standard reflow profiles and automated placement.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SMV1232-011 and BBY52-02W, ZC931TC uniquely balances octave tuning range, sub-nA leakage, and Q ≥ 300 - making it optimal for production TCXOs where calibration repeatability and long-term bias stability are mandatory.

Availability

ZC931TC is available at Aetrix Electronics and suitable for VCXO modules, pager RF front-ends, and mobile radio transmitters requiring stable component supply across extended product lifecycles.

Supply support for ZC931TC 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 Semiconductors (now part of Diodes Incorporated) was a UK-based designer of high-performance analog and RF semiconductors, specializing in discrete devices for precision signal conditioning and frequency control.

The ZC930/ZC931 series belongs to Zetex's hyperabrupt varactor product line, engineered specifically for low-phase-noise oscillator tuning in portable and infrastructure wireless equipment.

FAQ

What is the recommended PCB pad layout for ZC931TC in SOD323?

Use IPC-7351B compliant SOD323 footprint: 1.4 mm × 0.9 mm solder pads with 0.5 mm spacing, 0.2 mm solder mask opening, and thermal relief on cathode pad only. Avoid copper pours under the device body to prevent warpage during reflow.

Can ZC931TC be used in forward bias?

No - ZC931TC is strictly a reverse-biased varactor. Forward conduction degrades junction integrity and permanently alters C–V characteristics. Absolute maximum forward current is 100 mA, but operation must remain in reverse bias (VR ≥ 0 V) at all times.

How does temperature affect ZC931TC's tuning linearity?

Its capacitance temperature coefficient is 300–400 ppm/°C at 3 V, causing measurable C–V curve shift. For TCXO use, this requires compensation via thermistor network or digital lookup table - uncorrected, it contributes ±0.5% frequency drift over –20°C to +70°C.

Is ZC931TC RoHS-compliant and halogen-free?

Yes - per Zetex Issue 7 (2004) documentation and Diodes Incorporated's legacy compliance archive, ZC931TC meets RoHS Directive 2002/95/EC and contains no brominated flame retardants or chlorine-based solvents in packaging or die attach materials.