Analog Devices Inc. LTC6946IUFD-2#PBF

Overview

LTC6946IUFD-2#PBF from Analog Devices (formerly Linear Technology) is an ultralow-noise integer-N PLL synthesizer with integrated VCO, operating across 3.08GHz to 4.91GHz (VCO range) and delivering RF output from 0.513GHz to 2.455GHz via programmable 1–6 divider. It features –226dBc/Hz normalized in-band phase noise floor, 11.2mA adjustable charge pump current, and SPI-compatible serial control - deployed in LTE/W-CDMA base station local oscillators.

For engineers reviewing the LTC6946IUFD-2#PBF datasheet, LTC6946IUFD-2#PBF pinout, LTC6946IUFD-2#PBF application, or LTC6946IUFD-2#PBF equivalent, key selection criteria include its guaranteed VCO frequency band (LTC6946-2), integrated loop filter interface (CP, TUNE), differential RF output architecture (RF+/RF–), and temperature-stable operation from –40°C to 105°C in the 4mm × 5mm QFN package.

Technical Context

The LTC6946IUFD-2#PBF implements a fully integrated PLL architecture with reference divider (R = 1–1023), phase-frequency detector (PFD), ultralow-noise charge pump (ICP = 0.25–11.2mA), integer feedback divider (N = 32–65535), and on-die VCO calibrated for 3.08–4.91GHz operation. Its output divider (O = 1–6) enables precise sub-GHz to mid-GHz RF synthesis without external components.

It supports dual-mode VCO tuning sensitivity (4.7–7.0%Hz/V), configurable lock window width (3–90ns), and low-jitter RF output with 50% duty cycle. The device uses separate supply domains (3.3V for digital/reference/RF, 5V for VCO/charge pump) and integrates status reporting via STAT pin and SPI-accessible register.

Key Specifications

Pinout & Package

Package: 28-lead (4mm × 5mm) plastic QFN (UFD), exposed pad (Pin 29) soldered to ground plane for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar integer-N PLL synthesizer applications.

Compared with HMC830LP6GE and ADF4355BCPZ, the LTC6946IUFD-2#PBF delivers superior in-band phase noise (–226dBc/Hz) in its designated band, eliminates external VCO components, and fits into a smaller 4mm × 5mm footprint - making it the preferred choice for high-density, noise-critical wireless infrastructure designs where integer-N performance suffices.

Availability

LTC6946IUFD-2#PBF is available at Aetrix Electronics and suitable for wireless infrastructure, military radio, and test equipment applications requiring stable component supply, long-term lifecycle support, and guaranteed performance across –40°C to 105°C.

Supply support for LTC6946IUFD-2#PBF 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

Analog Devices acquired Linear Technology in 2017 and maintains its high-performance analog IC portfolio, including precision timing, RF, and power management products for demanding industrial and communications markets.

The LTC6946 product line delivers ultralow-noise, fully integrated PLL synthesizers targeting wireless base stations, secure radios, and instrumentation - emphasizing phase noise performance, integration density, and robust operation in harsh thermal environments.

FAQ

What is the guaranteed VCO frequency range for the LTC6946IUFD-2#PBF?

The LTC6946IUFD-2#PBF is the LTC6946-2 variant, with a guaranteed VCO frequency range of 3.08GHz to 4.91GHz. This range is factory-characterized and specified over the full –40°C to 105°C operating temperature range. Output frequencies from 0.513GHz to 2.455GHz are achieved using the internal 1–6 output divider, as confirmed in the "Available Options" table of the datasheet.

Does the LTC6946IUFD-2#PBF require external VCO components?

No, the LTC6946IUFD-2#PBF does not require external VCO components. It integrates a fully self-contained VCO core with internal calibration circuitry that automatically adjusts tuning voltage post-power-up to achieve the target frequency. No external inductors, varactors, or resonators are needed - only the external loop filter (R, C) between CP and TUNE pins is required for PLL operation.

How is the RF output configured on the LTC6946IUFD-2#PBF?

The LTC6946IUFD-2#PBF provides differential RF output on pins RF+ and RF–, each with a 136Ω internal pull-up to VRF+. For single-ended use, one pin is terminated to 50Ω while the other drives the load; for differential use, both pins connect to a balun or differential receiver. Output frequency is set by the VCO frequency divided by O (1–6), and output power ranges from –9.7dBm to 2.3dBm depending on O and RFO[1:0] register setting.

What supply voltages does the LTC6946IUFD-2#PBF require?

The LTC6946IUFD-2#PBF requires two distinct supply domains: 3.3V (±150mV) for VREF+, VREFO+, VD+, and VRF+ pins, and 5.0V (±250mV) for VVCO+ and VCP+ pins. These rails must be independently bypassed - 0.1µF ceramics near VREF+/VD+/VCP+, 0.01µF + 1µF ceramics near VVCO+, and 0.01µF near VRF+. Mixing or sharing these supplies degrades phase noise and may cause functional failure.

Can the LTC6946IUFD-2#PBF be used with a 100MHz reference input?

Yes, the LTC6946IUFD-2#PBF supports reference input frequencies from 10MHz to 250MHz, including 100MHz. The REF+/REF– inputs are high-impedance differential, self-biased, and require 1µF AC-coupling capacitors. For 100MHz operation, the FILT[1:0] bits should be set to '0' per Table 1, and BST should be set to '0' since VREF ≥2.0VP-P is expected - ensuring optimal reference buffer linearity and noise performance.