LMX2485SQ/NOPB Integrated Circuits (ICs)

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1. Describe

The LMX2485SQ/NOPB device is a low-power, high-performance delta-sigma fractional-N PLL with an auxiliary integer-N PLL. The device is manufactured using Texas Instruments' advanced processes. With a delta-sigma architecture, fractional spurs at lower offset frequencies are pushed to higher frequencies outside the loop bandwidth. The ability to push spurious 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 LMX2485SQ/NOPB is highly resistant to temperature variations and wafer processing variations. The LMX2485 delta-sigma modulator is programmable up to fourth order, allowing designers to select the optimal modulator order to suit the system's phase noise, spurs, and lock-time requirements. Serial data used to program the LMX2485SQ/NOPB is transmitted over a three-wire high-speed (20-MHz) MICROWIRE interface. The LMX2485SQ/NOPB offers fine frequency resolution, low spurious, fast programming speed and single word write to change frequency. This makes it ideal for direct digital modulation applications, where the N counter is modulated directly with the information. The LMX2485 is available in a 24-pin 4.0 × 4.0 × 0.8 mm WQFN package.

2. Feature

    1. Quadruple analog-to-digital prescaler for low frequency division

        – RF PLL: 8/9/12/13 or 16/17/20/21

        – IF PLL: 8/9 or 16/17

    2. Advanced Delta-Sigma fractional compensation

        – 12-bit or 22-bit optional fractional modulus

        – Up to 4th order programmable Delta-Sigma modulator

    3. Improved lock time functionality

        – Fastlock/Cycle Slip reduction with integrated timeout counter, requires only a single word write

    4. Wide working range

        – LMX2485 RF PLL: 500 MHz to 3.0 GHz

        – LMX2485E RF PLL: 50 MHz to 3.0 GHz

    5. Useful features

        – Digital lock detection output

        – Hardware and software power-down control

        – On-chip input multiplier.

        – RF phase detector frequency up to 50 MHz

        – 2.5 to 3.6 V operating at ICC = 5.0 mA

3. Application

    1. Cell Phones and Base Stations

    2. Direct digital modulation applications

    3. Satellite and cable TV tuners

    4. WLAN standard

4. Pin configuration

5. Pin Description

6. Application Information

This device is ideal for use in a wide range of applications, especially those requiring low current consumption and Low score spurs. For applications requiring only one PLL, unused PLLs can be powered down, Does not consume any extra current or generate any spurious or crosstalk.