Diodes Incorporated ZNBG3115Q20TC

Overview

ZNBG3115Q20TC from Zetex Semiconductors is a FET bias controller IC designed for satellite LNBs, providing regulated negative gate bias (−2.8 V), user-selectable drain current (0–15 mA via RCAL), 2.2 V nominal drain voltage per FET, integrated 22 kHz tone detection, and polarization switching between two FETs with third FET permanently active - all in a QSOP20 package.

For engineers reviewing the ZNBG3115Q20TC datasheet, ZNBG3115Q20TC pinout, ZNBG3115Q20TC application, or ZNBG3115Q20TC equivalent, key selection criteria include LNB-specific tone detection accuracy, FET gate voltage clamping (−3.0 V to +1.0 V), unconditional RF stability with GaAs/HEMT FETs, and DiSEqC™-ready transient rejection during channel switching.

Technical Context

The ZNBG3115Q20TC integrates three independent FET bias stages with shared on-chip negative rail generation (−2.8 V, ±0.25 V) using an internal oscillator (180–800 kHz) and two external 47 nF capacitors. Each stage features programmable drain current (0–15 mA), fixed 2.2 V drain voltage output, and individual current limiting.

Its VPOL input enables polarity switching by sensing supply voltage thresholds (≤14 V → Q2 active; ≥15.5 V → Q1 active), while the FIN input feeds a dedicated 22 kHz tone detector with built-in op-amp gain control, rectifier-smoother-comparator, and supply-voltage-compensated threshold (100–350 mV_p-p) - rejecting DiSEqC™ bursts and power transients without external filtering.

Key Specifications

Pinout & Package

Package: QSOP20 (JEDEC MO-137AD), 8.55 × 3.81 mm body, 0.635 mm pitch, surface-mount, lead-free compatible.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar FET bias controller applications.

Compared with ZNBG3116Q20TC, the ZNBG3115Q20TC provides higher drain voltage for improved linearity in high-gain LNB stages; versus MAX2382ETA+, it delivers full LNB functionality in one device - eliminating 7+ external components and enabling drop-in replacement in Universal LNB designs.

Availability

ZNBG3115Q20TC is available at Aetrix Electronics and suitable for satellite receiver LNBs, private mobile radio (PMR) transceivers, and cellular base station low-noise amplifiers requiring stable component supply, long-lifecycle support, and guaranteed traceable sourcing.

Supply support for ZNBG3115Q20TC 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 (now part of Diodes Incorporated) is a UK-based analog semiconductor specialist focused on high-performance, application-optimized ICs for RF, power management, and signal conditioning.

The ZNBG series was developed specifically for satellite LNB biasing - integrating negative rail generation, FET current/voltage control, polarization switching, and 22 kHz tone detection into a single compact IC to replace multi-component discrete solutions.

FAQ

What external components are mandatory for basic ZNBG3115Q20TC operation?

Four components are mandatory: two 47 nF capacitors (CNB1, CNB2) for the internal negative rail oscillator; one resistor (RCAL) from pin 12 to ground to set drain current; and a 10 kΩ resistor from VPOL (pin 11) to the LNB supply to enable polarization switching. Gate and drain decoupling capacitors (4.7 nF and 10 nF) are strongly recommended for RF stability but not strictly mandatory for DC functionality.

How does the ZNBG3115Q20TC handle supply voltage transients during DiSEqC™ command bursts?

The device rejects DiSEqC™ transients via a proprietary tone detector architecture that separates 22 kHz signal detection from supply-line noise. Its internal comparator uses supply-voltage-compensated thresholds and ignores fast-rising edges typical of DiSEqC™ bursts (22 ms duration, 22 kHz carrier), ensuring band switching occurs only on valid tone presence - not on command pulses.

Can unused FET bias channels be left unconnected without affecting performance?

Yes. Drain (D1, D2, D3) and gate (G1, G2, G3) pins for unused FET stages may be left open-circuit with no impact on remaining active channels. The internal current limiters and gate clamps remain functional per active stage, and the shared negative rail generator continues operating normally. This allows flexible configuration for 1-, 2-, or 3-FET LNB designs.

What is the maximum allowable load on the CSUB (−2.8 V) output?

The CSUB pin is rated for ≤200 µA continuous load. It is intended solely for powering FET gates and small auxiliary circuits (e.g., tone detector bias). Driving loads exceeding 200 µA risks degrading the negative rail regulation accuracy and may cause shutdown if the internal current limiter activates. For higher-current external circuits, a separate charge-pump or LDO regulator must be used.