Diodes Incorporated ZDC834ATC

Overview

ZDC834ATC from Zetex Semiconductors is a silicon hyperabrupt varactor diode optimized for voltage-controlled frequency tuning in precision oscillators. It delivers 47.0 pF nominal capacitance at VR = 2 V, 5.0–6.5 capacitance ratio (C₂/C₂₀), ≥200 Q at 50 MHz, and ultra-low reverse leakage (200 pA typ.), enabling low-phase-noise VCXO/TCXO designs in wireless infrastructure and mobile radio front-ends.

For engineers reviewing the ZDC834ATC datasheet, ZDC834ATC pinout, ZDC834ATC application, or ZDC834ATC equivalent, key selection criteria include its SOT23 package compatibility, hyperabrupt CV slope for steep tuning response, 25 V reverse breakdown rating, and verified performance in RF filter and VCO bias networks under −55°C to +150°C operating conditions.

Technical Context

ZDC834ATC operates as a voltage-dependent capacitor with hyperabrupt doping profile, yielding nonlinear C–V response ideal for wide-range frequency pulling. Its capacitance varies from 42.3 pF (min) to 51.7 pF (max) at VR = 2 V and f = 1 MHz, with C₂/C₂₀ ratio ≥5.0 ensuring stable tuning across 2–20 V control range.

The device achieves ≥200 Q factor at 50 MHz and VR = 3 V, minimizing insertion loss in resonant tank circuits. Low IR (≤20 nA at VR = 20 V) and tight ±5% capacitance tolerance (Grade B) support phase noise <−150 dBc/Hz at 10 kHz offset in oscillator loops.

Key Specifications

Pinout & Package

Supplied in SOT23 package (JEDEC TO-236AB), 3-terminal surface-mount configuration with anode, cathode, and case (cathode-connected substrate). Standard marking "C5A" identifies ZDC834ATC on top surface.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZMV834ATA and ZC834BTA, ZDC834ATC offers the tightest capacitance tolerance and highest C₂/C₂₀ ratio in SOT23, making it optimal for phase-noise–critical VCXOs and TCXOs where tuning linearity and stability are prioritized over footprint minimization or unit cost.

Availability

ZDC834ATC is available at Aetrix Electronics and suitable for VCXO design, RF filter tuning, and mobile radio VCO development requiring stable component supply, traceable lot control, and long-term lifecycle assurance.

Supply support for ZDC834ATC 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 plc was a UK-based ISO 9001 and TS16949 certified manufacturer specializing in high-performance analog and RF discrete semiconductors before its acquisition by Diodes Incorporated in 2008.

ZDC834ATC belongs to the 830 series hyperabrupt varactor family, engineered specifically for low-phase-noise frequency control in wireless infrastructure, precision timing, and reconfigurable RF filtering applications.

FAQ

What is the maximum recommended reverse voltage for continuous operation?

The absolute maximum reverse voltage is 25 V, but for reliable long-term operation with margin, Zetex specifies 20 V as the maximum continuous reverse bias. Operating above 20 V increases risk of parametric drift and accelerated aging due to field-enhanced leakage, especially above 85°C ambient.

Does ZDC834ATC require special PCB layout considerations?

Yes - keep the cathode pad connected to a solid ground plane with minimal trace length to reduce parasitic inductance. Avoid routing RF traces near the anode; use guard rings around the SOT23 footprint to suppress coupling. Thermal vias under the case (Pin 3) improve heat dissipation during high-bias transient conditions.

How does the temperature coefficient affect TCXO compensation accuracy?

With a measured 300–400 ppm/°C capacitance tempco, ZDC834ATC closely tracks the negative tempco of AT-cut crystals (≈−20 ppm/°C²). When combined with a thermistor network, it enables first-order cancellation, achieving ±0.5 ppm stability over −40°C to +85°C without digital calibration.

Is ZDC834ATC RoHS compliant and lead-free?

Yes - Zetex confirmed full RoHS compliance for the 830 series in Issue 11 (January 2007), including lead-free terminations and halogen-free molding compound. The SOT23 package uses matte tin plating over copper leadframe, meeting JEDEC J-STD-020 moisture sensitivity level 1.