Analog Devices Inc. LTC6948IUFD-3

Overview

LTC6948IUFD-3 from Analog Devices is an ultralow-noise 3.84GHz to 5.79GHz fractional-N PLL synthesizer with integrated VCO, featuring a 4th-order ΔΣ modulator, 18-bit fractional denominator, –225 dBc/Hz normalized in-band phase noise floor, and programmable output divider (1–6). It serves as the core frequency generation engine in microwave data links and secure radio transceivers.

For engineers reviewing the LTC6948IUFD-3 datasheet, LTC6948IUFD-3 pinout, LTC6948IUFD-3 application, or LTC6948IUFD-3 equivalent, key selection criteria include its guaranteed VCO range (3.84–5.79 GHz), O_DIV-dependent output frequency coverage (0.64–2.895 GHz), integrated charge pump current tuning (1–11.2 mA), and QFN-28 (4mm × 5mm) package with exposed thermal pad.

Technical Context

The LTC6948IUFD-3 implements a fully integrated PLL architecture comprising a reference divider (R = 1–31), phase-frequency detector, ultralow-noise charge pump (ICP = 1–11.2 mA), 4th-order fractional-N ΔΣ modulator (Numerator = 1–262143), and VCO with tunable output divider (O = 1–6). Its loop bandwidth supports fast frequency switching with <170 ns mute disable time.

It operates with three independent supply domains: 3.3V for digital/RF/reference circuitry (VREF+, VD+, VRF+), 5V for VCO and charge pump (VVCO+, VCP+), and includes LDO regulation for the ΔΣ modulator. The device supports SPI interface (CS/SCLK/SDI/SDO) with configurable status output (STAT) and hardware RF muting (MUTE).

Key Specifications

Pinout & Package

Package: 28-lead (4mm × 5mm) plastic QFN (UFD) with exposed thermal pad (Pin 29 = GND, must be soldered to PCB ground plane).

Key Features

Applications

Equivalent & Alternatives

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

Compared with HMC830LP6GE and ADF4371BCPZ, the LTC6948IUFD-3 delivers superior phase noise floor (–225 dBc/Hz) within its 3.84–5.79 GHz VCO band and simplifies layout with integrated LDO and calibrated output divider-making it optimal for space-constrained microwave radios where jitter and spurs dominate system SNR.

Availability

LTC6948IUFD-3 is available at Aetrix Electronics and suitable for wireless basestations, microwave data links, military secure radio, and test & measurement equipment requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LTC6948IUFD-3 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 is a global leader in high-performance analog, mixed-signal, and RF ICs, serving precision instrumentation, communications, and defense markets since 1965.

The LTC6948 product line delivers ultralow-noise, wideband fractional-N synthesizers with integrated VCOs for demanding RF signal generation in microwave and secure communications systems.

FAQ

What is the guaranteed VCO frequency range for the LTC6948IUFD-3?

The LTC6948IUFD-3 is factory-configured for a VCO frequency range of 3.84 GHz to 5.79 GHz. This range is fixed per variant and verified during production test; it does not overlap with LTC6948IUFD-2 (3.08–4.91 GHz) or LTC6948IUFD-4 (4.20–6.39 GHz). Operation outside this band is not characterized or guaranteed.

How does the output divider setting affect the usable output frequency range of the LTC6948IUFD-3?

For the LTC6948IUFD-3, the output divider (O_DIV) scales the VCO output linearly: O=1 yields 3.84–5.79 GHz, O=2 yields 1.92–2.895 GHz, O=3 yields 1.28–1.93 GHz, O=4 yields 0.96–1.448 GHz, O=5 yields 0.768–1.158 GHz, and O=6 yields 0.64–0.965 GHz. All settings maintain 50% duty cycle and matched phase noise scaling.

What are the supply voltage requirements for the LTC6948IUFD-3?

The LTC6948IUFD-3 requires three distinct supply rails: VREF+/VD+/VRF+ = 3.15–3.45 V (3.3 V nominal), VVCO+ = 4.75–5.25 V (5 V nominal), and VCP+ = 4.0–5.25 V (5 V nominal). Each rail must be independently bypassed per datasheet layout guidelines; mixing supplies violates absolute maximum ratings.

Does the LTC6948IUFD-3 support hardware RF muting, and what is its timing performance?

Yes, the LTC6948IUFD-3 supports active-low hardware muting via Pin 9 (MUTE). When asserted, RF output power drops to ≤–80 dBm while internal bias remains active. Mute enable time is 110 ns; mute disable time is 170 ns-enabling rapid TDD slot transitions without re-locking delays.

What SPI interface features does the LTC6948IUFD-3 provide for register access and status monitoring?

The LTC6948IUFD-3 uses a 4-wire SPI interface (CS, SCLK, SDI, SDO) supporting both write and read operations. The STAT pin provides configurable logical OR of lock (LOK), unlock (UNLOK), and alarm bits. Register readback enables real-time verification of N-divider, R-divider, O-divider, and status flags without interrupt overhead.