Analog Devices Inc. LTC6948IUFD-3#TRPBF

Overview

LTC6948IUFD-3#TRPBF from Analog Devices is an ultralow-noise 3.84GHz to 5.79GHz fractional-N PLL synthesizer with integrated VCO, 18-bit fractional denominator, –225 dBc/Hz normalized in-band phase noise floor, and programmable output divider (1–6). It serves as the local oscillator core in microwave receiver front-ends for wireless infrastructure.

For engineers reviewing the LTC6948IUFD-3#TRPBF datasheet, LTC6948IUFD-3#TRPBF pinout, LTC6948IUFD-3#TRPBF application, or LTC6948IUFD-3#TRPBF equivalent, key selection criteria include its guaranteed VCO frequency range (3.84–5.79 GHz), integer/fractional mode spurious performance (–98 dBc), 6.39 GHz maximum RF output capability via O_DIV=1, and QFN-28 (4mm × 5mm) package thermal and layout constraints.

Technical Context

The LTC6948IUFD-3#TRPBF implements a 4th-order ΔΣ modulator for fractional-N synthesis, enabling wide loop bandwidths while suppressing fractional spurs. Its charge pump delivers 1–11.2 mA with ±3.5% matching and supports fast frequency switching with <20 µs calibration time for 126 MHz steps.

It integrates a reference divider (1–31), N-divider (32–1019 integer / 35–1019 fractional), and output divider (1–6) with 50% duty cycle. The VCO tuning sensitivity is 4.0–6.0 %/V across its 3.84–5.79 GHz band, and RF outputs are differential with internal 136 Ω pull-ups to VRF+.

Key Specifications

Pinout & Package

Package: 28-lead (4 mm × 5 mm) plastic QFN (UFD), exposed pad (Pin 29) must be soldered 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 ADF4371BCPZ, the LTC6948IUFD-3#TRPBF offers superior integrated phase noise floor (–225 dBc/Hz) and lower typical supply current (119.6 mA at RFO=3), making it optimal for power-sensitive, high-spectral-purity 3.84–5.79 GHz LO generation where VCO integration reduces component count and layout complexity.

Availability

LTC6948IUFD-3#TRPBF is available at Aetrix Electronics and suitable for wireless basestations, microwave data links, military SATCOM terminals, and test equipment requiring stable component supply over extended production lifecycles.

Supply support for LTC6948IUFD-3#TRPBF 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 digital signal processing semiconductors, serving precision instrumentation, communications, and industrial markets.

The LTC6948 product line delivers ultralow-noise, wideband fractional-N synthesizers with integrated VCOs for demanding RF signal generation in wireless infrastructure, defense, and test equipment-designed to replace discrete PLL/VCO solutions with single-chip reliability and repeatable performance.

FAQ

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

The LTC6948IUFD-3#TRPBF is factory-configured and guaranteed for VCO operation from 3.84 GHz to 5.79 GHz. This range is fixed per variant and cannot be extended beyond these limits-even with O_DIV settings-without violating specification compliance. Operation outside this band may result in degraded phase noise, increased spurs, or loss of lock.

Does the LTC6948IUFD-3#TRPBF support both integer-N and fractional-N modes?

Yes, the LTC6948IUFD-3#TRPBF supports both integer-N and fractional-N synthesis. Integer mode uses N-divider values from 32 to 1023, while fractional mode extends resolution using an 18-bit denominator and 4th-order ΔΣ modulator. Mode selection is controlled via the INTN register bit, and both modes deliver specified phase noise and spur performance per datasheet conditions.

How does the MUTE function behave on the LTC6948IUFD-3#TRPBF during RF output disable?

When the MUTE pin is asserted low, the LTC6948IUFD-3#TRPBF disables RF± differential outputs within 110 ns while maintaining internal VCO and bias circuitry fully powered and stabilized. This preserves lock state and enables RF re-enable in 170 ns-critical for TDD systems. Output power drops to –80 dBm (single-ended), and no recalibration is required upon unmuting.

What is the purpose of the LDO pin (Pin 7) on the LTC6948IUFD-3#TRPBF?

The LDO pin (Pin 7) on the LTC6948IUFD-3#TRPBF provides a dedicated bypass node for the internal ΔΣ modulator's low-dropout regulator. It must be decoupled to ground with a 0.1 µF ceramic capacitor (low ESR < 0.8 Ω) placed adjacent to the pin. This minimizes supply-induced noise coupling into the fractional modulator, directly improving fractional spur suppression and in-band phase noise stability.

Can the LTC6948IUFD-3#TRPBF generate output frequencies below 3.84 GHz?

Yes-the LTC6948IUFD-3#TRPBF can generate RF outputs as low as 0.64 GHz using its programmable output divider (O_DIV = 6). Although the VCO itself operates only from 3.84–5.79 GHz, dividing the VCO output by integers 1–6 yields RF frequencies from 0.64 GHz (3.84 GHz ÷ 6) to 5.79 GHz (5.79 GHz ÷ 1), all with 50% duty cycle and specified phase noise performance.