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Analog Devices LTC6948IUFD-4#PBF — Clock & Timing ICs
Analog Devices

LTC6948IUFD-4#PBF Analog Devices 6.39 GHz Fractional-N PLL

MPNLTC6948IUFD-4#PBF
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Analog Devices LTC6948IUFD-4#PBF — Fractional-N Clock/Frequency Synthesizer (RF/IF), PLL Yes, 6.39 GHz max output, 28-QFN (4x5) exposed pad, -40°C to 105°C, ROHS3 Compliant.

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LTC6948IUFD-4#PBF datasheet
Packaging28-WFQFN Exposed Pad
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Specifications

LTC6948IUFD-4#PBF Technical Specifications
ParameterValue
TypeClock/Frequency Synthesizer (RF/IF), Fractional N
Mounting typeSurface Mount
Voltage3.15V ~ 5.25V
Frequency6.39GHz
Operating temperature-40°C ~ 105°C
PLLYes
InputClock
OutputClock
PackageTube
Case28-WFQFN Exposed Pad
Divider (Multiplier)Yes/No
Number of circuits1
Ratio - Input:Output1:1
Differential - Input:OutputYes/Yes

Product details

6.39 GHz Fractional-N Synthesizer for Microwave Links

The LTC6948IUFD-4#PBF is a Fractional-N PLL capable of synthesizing clock outputs up to 6.39 GHz. That puts it in the band for Ku-band downconverters, microwave point-to-point radios, and satellite IF stages—applications where a 5.79 GHz sibling (LTC6948IUFD-3#PBF) would run out of headroom. The Fractional-N architecture means the phase-detector frequency can stay high (reducing in-band phase noise) while the feedback divider steps through fine frequency increments.

Industrial Temperature and 28-QFN Exposed Pad

The 28-QFN (4x5) package has an exposed pad that must be soldered to a thermal via array on the PCB—without it the charge-pump and VCO die temperature rises above the junction limit under sustained 6.39 GHz operation. The 3.15V to 5.25V supply range gives flexibility for 3.3V or 5V PLL rails, but the VCO tuning sensitivity shifts with supply voltage, so the loop filter design should be tuned for the chosen rail.

Frequently asked questions

What is the closest functional second-source to the LTC6948IUFD-4#PBF?

Within the same LTC6948 family, the LTC6948IUFD-3#PBF (5.79 GHz max) and LTC6948IUFD-2#PBF (4.91 GHz max) share the same package, supply range, and temperature grade. The difference is the VCO frequency range: the -4 variant tops out at 6.39 GHz versus 5.79 GHz for the -3. If your application runs below 5.8 GHz, the -3 is a direct pin-compatible drop-in. No second-source outside the LTC6948 family is officially cross-referenced.

What does the 6.39 GHz max frequency mean for loop filter design?

At 6.39 GHz, the VCO tuning sensitivity is high—small control-voltage noise translates into significant phase noise at the output. The Fractional-N architecture lets you run the phase detector at a higher frequency (up to 125 MHz typical), which pushes the loop bandwidth out and reduces in-band noise contribution. The trade-off: the loop filter must suppress the fractional spurs at the phase-detector frequency offset. Analog Devices' FracNWizard tool (free download) calculates the filter component values for your target loop bandwidth and spur rejection.