Diodes Incorporated ZMDC953TA

Overview

ZMDC953TA from Zetex Semiconductors is a dual silicon hyperabrupt varactor diode optimized for voltage-controlled frequency tuning in low-voltage RF systems. It delivers 45 pF nominal capacitance at 0.5 V, 30–37 pF at 1.5 V, capacitance ratio C_0.5/C_2.5 ≥ 2.0, Q ≥ 250 at 0.5 V/50 MHz, and reverse leakage ≤ 20 nA at 8 V - enabling precise, low-phase-noise tuning in 3 V VCXO and DAB band-selection circuits.

For engineers reviewing the ZMDC953TA datasheet, ZMDC953TA pinout, ZMDC953TA application, or ZMDC953TA equivalent, key selection criteria include its banded capacitance tolerance (Band A/B/C), SOT323 dual-die packaging, hyperabrupt CV profile, low-voltage tuning range (0.5–2.5 V), and verified performance in TCXO loop filters and digital radio front-ends.

Technical Context

This dual varactor integrates two matched ZV953V2-type junctions in a single SOT323 package, sharing common cathode connection and independent anodes - enabling differential or switched tuning topologies. Its hyperabrupt doping profile ensures linearized frequency vs. voltage response in oscillator control loops.

Designed for operation from −55°C to +85°C, it maintains stable capacitance temperature coefficient (< ±100 ppm/°C) and sub-20 nA reverse leakage across the full tuning range, directly supporting low-phase-noise requirements in DAB and mobile radio synthesizers.

Key Specifications

Pinout & Package

SOT323 package: 3-terminal surface-mount outline with exposed thermal pad (non-electrical), 0.65 mm lead pitch, and cathode-common dual-anode configuration.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZV953V2TA, ZMDC953TA saves PCB space and improves VCO linearity via integrated dual junctions; compared with FSD273TA, it offers broader capacitance flexibility at the cost of post-reel binning effort.

Availability

ZMDC953TA is available at Aetrix Electronics and suitable for DAB band-selection filters, TCXO pulling circuits, mobile radio VCOs, and pager synthesizers requiring stable component supply across automotive, industrial, and consumer RF programs.

Supply support for ZMDC953TA 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) specialized in high-performance analog and RF discretes, with emphasis on low-noise, high-Q, and precision-tolerance semiconductor devices.

The 950 series varactors were developed specifically for low-voltage, high-stability frequency control in portable digital radio and wireless infrastructure - prioritizing CV linearity, phase noise immunity, and SMT manufacturability.

FAQ

What is the cathode connection configuration in ZMDC953TA?

ZMDC953TA uses a common-cathode dual-anode structure: Pin 2 is the shared cathode, while Pins 1 and 3 are independent anodes. This allows either parallel, series, or differential connection without external wiring - critical for minimizing stray inductance in VCO tank circuits.

Does ZMDC953TA require derating at elevated temperatures?

No derating is required up to +85°C ambient: its 300 mW power dissipation rating and ≤100 ppm/°C capacitance drift are specified across −55°C to +85°C. Reverse leakage remains ≤20 nA at 8 V up to +85°C, preserving phase noise integrity in thermally stressed TCXOs.

Can ZMDC953TA be substituted for ZV953V2TA in existing layouts?

Yes, with minor footprint adaptation: both use SOT323, but ZMDC953TA has three terminals (Anode1-Cathode-Anode2) versus ZV953V2TA's two (Anode-Cathode). Layout must accommodate the extra anode pad and isolate both anodes - no change needed to schematic if only one anode is used.

Is banded capacitance guaranteed per reel for ZMDC953TA?

No - unlike FSD273TA, ZMDC953TA is supplied unbanded. Reels contain mixed capacitance values across the full 30–37 pF range at 1.5 V. For banded material, order FSD273TA with suffix -55 (Band A), -56 (Band B), or -57 (Band C) per the datasheet ordering table.