Analog Devices Inc. LTC6948IUFD-4#PBF

Overview

LTC6948IUFD-4#PBF from Analog Devices is an ultralow-noise 4.20GHz to 6.39GHz fractional-N 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 synthesis engine in microwave receivers and high-speed wireless transceivers.

For engineers reviewing the LTC6948IUFD-4#PBF datasheet, LTC6948IUFD-4#PBF pinout, LTC6948IUFD-4#PBF application, or LTC6948IUFD-4#PBF equivalent, key selection criteria include its guaranteed 4.20–6.39GHz VCO range (LTC6948-4 variant), 50% duty-cycle RF output buffer, reference input support up to 425MHz, fast frequency switching, and FracNWizard™ software design tool compatibility.

Technical Context

The LTC6948IUFD-4#PBF implements a fully integrated PLL architecture with separate 3.3V digital/analog supplies (VD+, VREF+, VRF+) and 5V VCO/charge pump rails (VVCO+, VCP+). Its fractional feedback path uses a 4th-order ΔΣ modulator to suppress spurs, enabling wide loop bandwidths (up to 186kHz) while maintaining ultra-low integrated phase noise (0.14° RMS, 100Hz–40MHz).

It supports integer and fractional-N modes, with programmable R-divider (1–31), N-divider (32–1023 integer / 35–1019 fractional), and O-divider (1–6). The VCO tuning sensitivity is 4.5–6.5 %/Hz/V across its 4.20–6.39GHz range, and RF output power is configurable from –9dBm to +1.5dBm (single-ended, 50Ω load) via RFO[1:0] bits.

Key Specifications

Pinout & Package

28-lead (4mm × 5mm) plastic QFN (UFD package) with exposed thermal pad (Pin 29 = GND). Requires soldering of exposed pad to PCB ground plane for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

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

Compared with HMC703LP4E and ADF4372BCPZ, the LTC6948IUFD-4#PBF delivers superior phase noise floor (–225 dBc/Hz vs –220 dBc/Hz) and extends usable LO generation to 6.39GHz-critical for next-gen mmWave test equipment and 5G FR2 infrastructure where every 100MHz of VCO range enables new channel plans.

Availability

LTC6948IUFD-4#PBF is available at Aetrix Electronics and suitable for wireless basestations, microwave data links, military secure radios, and test & measurement equipment requiring stable component supply across extended temperature ranges (–40°C to 105°C).

Supply support for LTC6948IUFD-4#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 is a global leader in high-performance analog, mixed-signal, and RF ICs, serving precision instrumentation, communications, and defense markets.

The LTC6948 product line was designed specifically for ultralow-noise, wideband fractional-N frequency synthesis in demanding wireless infrastructure and test equipment-emphasizing phase noise, spur suppression, and software-assisted design.

FAQ

What is the guaranteed VCO frequency range for LTC6948IUFD-4#PBF?

The LTC6948IUFD-4#PBF is factory-configured for a VCO frequency range of 4.20GHz to 6.39GHz, as confirmed in the "Order Information" table and Electrical Characteristics section (fVCO parameter, LTC6948-4 row). This range is fixed per variant and cannot be extended beyond these limits by programming.

Does LTC6948IUFD-4#PBF support both integer-N and fractional-N modes?

Yes, the LTC6948IUFD-4#PBF supports both integer-N and fractional-N operation. Integer mode uses N-divider values from 32 to 1023; fractional mode supports N values from 35 to 1019 with an 18-bit fractional denominator, enabling fine frequency resolution down to 190.7Hz steps at 6.39GHz.

What is the maximum reference input frequency supported by LTC6948IUFD-4#PBF?

The LTC6948IUFD-4#PBF supports reference input frequencies up to 425MHz, as specified in the Electrical Characteristics table under "fREF Input Frequency" (MIN/TYP/MAX = 10/-/425 MHz). This allows high PFD frequencies that improve loop stability and reduce reference spurs.

How is the RF output configured for single-ended use with LTC6948IUFD-4#PBF?

For single-ended RF output, terminate the unused pin (RF+ or RF–) to 50Ω, configure RFO[1:0] bits for desired output power, and ensure VRF+ is supplied at 3.3V with 0.01µF local bypass. The internal 136Ω pull-up resistors to VRF+ provide proper DC bias and impedance matching for 50Ω systems.

What thermal management is required for LTC6948IUFD-4#PBF in continuous operation?

The LTC6948IUFD-4#PBF requires soldering of the exposed pad (Pin 29) directly to the PCB ground plane with multiple thermal vias. Its θJCbottom is 7°C/W; for junction temperatures ≤105°C at 125°C ambient, a minimum 4cm² copper pour with ≥6×0.3mm vias is recommended to maintain thermal resistance <15°C/W to ambient.