Diodes Incorporated ZNBG3211Q20TC

Overview

ZNBG3211Q20TC from Zetex (now Diodes Incorporated) is a FET bias controller IC designed for satellite LNBs, providing regulated negative rail generation (-3 V), three-channel GaAs/HEMT FET gate/drain biasing, 22 kHz tone detection, and polarization switching via 0 V gate control. It operates from a single 5–10 V supply, delivers 2.0 V nominal drain voltage per FET (ZNBG3211 variant), supports 0–15 mA user-set drain current, and integrates dynamic FET protection across -40°C to +70°C.

For engineers reviewing the ZNBG3211Q20TC datasheet, ZNBG3211Q20TC pinout, ZNBG3211Q20TC application in LNB polarisation switching or 22 kHz tone detection, or ZNBG3211Q20TC equivalent for GaAs FET bias control, this page delivers verified functional context, validated pin roles, real-world LNB circuit integration details, and direct alternatives with documented electrical and application-level differences.

Technical Context

The ZNBG3211Q20TC implements a fully integrated bias management architecture: an on-chip oscillator (200–800 kHz) drives a charge-pump-based negative rail generator (VSUB ≈ −3.0 V) using two external 47 nF capacitors; three independent current-sense amplifier loops regulate FET drain current via RCAL (33 kΩ typical); and VPOL input enables zero-volt-gate switching between two FETs (Q1/Q2) while Q3 remains permanently active.

Tone detection uses a dedicated Sallen-Key filter stage (centered at 22 kHz, rejection of DiSEqC™ bursts and low-frequency interference), followed by rectification and comparator logic to drive LB/HB outputs; LOV pin configures output polarity-grounded for −2.6 V/0 V switching or biased to VOSC for supply-voltage-level band switching-enabling compatibility with both MMIC and discrete oscillator topologies.

Key Specifications

Pinout & Package

Package: QSOP20 - 20-pin, gull-wing, surface-mount package with recessed pin 1 marker; dimensions per Zetex drawing (A = 8.55–8.74 mm, B = 0.635 mm, E = 3.81–3.99 mm).

Key Features

Applications

Equivalent & Alternatives

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

Compared with ZNBG3210Q20TC and MAX2380ETP+, the ZNBG3211Q20TC offers optimal integration for cost-sensitive universal LNBs needing fixed 2.0 V FET bias and self-contained −3 V generation-reducing BOM count and eliminating external filter components required by the MAX2380.

Availability

ZNBG3211Q20TC is available at Aetrix Electronics and suitable for satellite LNB manufacturing, PMR base station production, and cellular infrastructure transceiver development requiring stable component supply, guaranteed long-term sourcing, and full traceability.

Supply support for ZNBG3211Q20TC 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 (acquired by Diodes Incorporated in 2008) was a UK-based designer of high-performance analog and mixed-signal ICs focused on RF, power management, and interface solutions for communications and industrial markets.

The ZNBG series was developed specifically for satellite LNB bias control-integrating negative rail generation, multi-FET regulation, polarisation switching, and 22 kHz detection into a single QSOP20 package to replace 15+ discrete components in mass-market receiver designs.

FAQ

What external components are mandatory for basic ZNBG3211Q20TC operation?

Four components are mandatory: two 47 nF capacitors (CNB, CSUB) for the internal negative rail generator; one resistor (RCAL) setting drain current (e.g., 33 kΩ for 10 mA); and a 10 kΩ resistor on VPOL for polarisation switching. Gate (CG = 4.7 nF) and drain (CD = 10 nF) capacitors are required for RF stability but may be omitted only in non-RF evaluation setups.

How does the ZNBG3211Q20TC handle fault conditions like short-circuited FETs?

Under negative rail overload or short circuit, the device shuts down all drain outputs (D1–D3) to prevent excessive current flow through external FETs. Gate outputs remain within −3.5 V to +1.0 V limits during all transients-including power-up/down-ensuring FET gate oxide integrity is preserved even if the substrate voltage collapses.

Can the ZNBG3211Q20TC drive FETs without external gate or drain capacitors?

No. CG (4.7 nF) and CD (10 nF) capacitors are required for unconditional RF stability across −40°C to +70°C with connected FETs. Omitting them risks oscillation, increased noise injection into adjacent circuits, and potential instability in multi-stage LNB designs-per Zetex's absolute stability guarantee and test conditions.

Is the 22 kHz tone detection sensitive to supply ripple or DiSEqC™ commands?

No. The internal Sallen-Key filter and comparator are specifically designed to reject DiSEqC™ tone bursts (22 kHz square-wave modulated at 1.5 kHz) and low-frequency supply ripple (<1 kHz). Test data confirms >46 dB rejection at 1.5 kHz and full immunity to standard DiSEqC™ command sequences without any external filtering.