LMX2485_14 Datasheet, PDF (1/43 Pages) Texas Instruments – 50 MHz - 3.0 GHz High Performance Delta-Sigma Low Power Dual PLLatinum™ Frequency Synthesizers with 800 MHz Integer PLL

LMX2485, LMX2485E
www.ti.com
SNAS236E – OCTOBER 2005 – REVISED FEBRUARY 2008
LMX2485/LMX2485E 50 MHz - 3.0 GHz High Performance Delta-Sigma Low Power Dual
PLLatinum™ Frequency Synthesizers with 800 MHz Integer PLL
Check for Samples: LMX2485, LMX2485E
FEATURES
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•23 Quadruple Modulus Prescalers for Lower
Divide Ratios
– RF PLL: 8/9/12/13 or 16/17/20/21
– IF PLL: 8/9 or 16/17
• Advanced DeltaSigma Fractional
Compensation
– 12 bit or 22 bit selectable fractional
modulus
– Up to 4th order programmable delta-sigma
modulator
• Features for Improved Lock Times and
Programming
– Fastlock / Cycle slip reduction
– Integrated time-out counter
– Single word write to change frequencies
with Fastlock
• Wide Operating Range
– LMX2485 RF PLL: 500 MHz to 3.0 GHz
– LMX2485E RF PLL: 50 MHz to 3.0 GHz
• Useful Features
– Digital lock detect output
– Hardware and software power-down control
– On-chip crystal reference frequency
doubler.
– RF phase comparison frequency up to 50
MHz
– 2.5 to 3.6 volt operation with I_CC = 5.0 mA at
3.0 V
APPLICATIONS
• Cellular phones and base stations
– CDMA, WCDMA, GSM/GPRS, TDMA, EDGE,
PDC
• Direct digital modulation applications
• Satellite and cable TV tuners
• WLAN Standards
DESCRIPTION
The LMX2485 is a low power, high performance delta-sigma fractional-N PLL with an auxiliary integer-N PLL.
The device is fabricated using National Semiconductor’s advanced process.
With delta-sigma architecture, fractional spurs at lower offset frequencies are pushed to higher frequencies
outside the loop bandwidth. The ability to push close in spur and phase noise energy to higher frequencies is a
direct function of the modulator order. Unlike analog compensation, the digital feedback technique used in the
LMX2485 is highly resistant to changes in temperature and variations in wafer processing. The LMX2485 delta-
sigma modulator is programmable up to fourth order, which allows the designer to select the optimum modulator
order to fit the phase noise, spur, and lock time requirements of the system.
Serial data for programming the LMX2485 is transferred via a three line high speed (20 MHz) MICROWIRE
interface. The LMX2485 offers fine frequency resolution, low spurs, fast programming speed, and a single word
write to change the frequency. This makes it ideal for direct digital modulation applications, where the N counter
is directly modulated with information. The LMX2485 is available in a 24 lead 4.0 X 4.0 X 0.8 mm LLP package.
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Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PLLatinum is a trademark of Texas Instruments.
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All other trademarks are the property of their respective owners.
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PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2005–2008, Texas Instruments Incorporated