Texas Instruments LMX2531LQ1570E/NOPB

Overview

LMX2531LQ1570E/NOPB from Texas Instruments is a high-performance fractional-N delta-sigma PLL frequency synthesizer with integrated VCO, operating in the 1530–1636 MHz high-band and 765–818 MHz low-band ranges. It delivers ultra-low phase noise (–93 dBc/Hz @ 10 kHz offset at 1583 MHz), supports 1.8-V MICROWIRE serial interface, and integrates LDOs for PLL/VCO supply-noise immunity. It serves as a local oscillator in wireless radios and broadband access equipment.

For engineers reviewing the LMX2531LQ1570E/NOPB datasheet, LMX2531LQ1570E/NOPB pinout, LMX2531LQ1570E/NOPB application, or LMX2531LQ1570E/NOPB equivalent, key selection criteria include its dual-band VCO tuning range, FastLock capability with timeout, programmable fourth-order delta-sigma modulator, integrated loop filter support, and 36-pin WQFN package with dedicated Vtune, CPout, and Ftest/LD monitoring pins.

Technical Context

The LMX2531LQ1570E/NOPB implements a fully integrated delta-sigma PLL architecture with a programmable fourth-order modulator to suppress fractional spurs and enable fine frequency resolution. Its VCO includes an on-die tank inductor and adjustable third/fourth poles for optimized loop stability across its 1530–1636 MHz high-band output range.

It features three independent LDOs-VregPLL1, VregVCO, and VregBUF-each internally regulated and externally bypassed, providing supply-noise rejection critical for low-phase-noise RF synthesis. The MICROWIRE interface (DATA/CLK/LE/CE) enables register configuration with precise timing requirements (e.g., tCS ≥25 ns, tCWH ≥25 ns).

Key Specifications

Pinout & Package

The LMX2531LQ1570E/NOPB is housed in a 36-pin 6 mm × 6 mm × 0.8 mm WQFN package (NJG0036A variant), with exposed thermal pad for enhanced heat dissipation and GND connections on pins 3, 19, 20, and 34.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar frequency synthesizer applications.

Compared with LMX2531LQ1515E/NOPB and LMX2531LQ1650E/NOPB, the LMX2531LQ1570E/NOPB fills the 1530–1636 MHz gap with identical architecture, enabling seamless band coverage across 1.45–1.70 GHz without changing PCB layout or firmware.

Availability

LMX2531LQ1570E/NOPB is available at Aetrix Electronics and suitable for cellular base stations, wireless LAN infrastructure, and broadband wireless access equipment requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LMX2531LQ1570E/NOPB 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

Texas Instruments is a global semiconductor leader delivering analog and embedded processing solutions, with over 90 years of innovation in precision analog, RF, and power management technologies.

The LMX2531 product line delivers highly integrated, low-noise PLL+VCO synthesizers for wireless infrastructure and test equipment, designed to replace discrete PLL/VCO modules while maintaining superior phase noise and supply rejection.

FAQ

What frequency bands does the LMX2531LQ1570E/NOPB support?

The LMX2531LQ1570E/NOPB supports two distinct bands: a low-band range of 765–818 MHz and a high-band range of 1530–1636 MHz. These ranges are fixed per device variant and cannot be extended beyond specification. The high-band output is generated directly by the integrated VCO, while the low-band is achieved using an internal divider. Both bands are validated across –40°C to +85°C ambient temperature with full electrical characterization in the official TI datasheet SNAS252S.

Does the LMX2531LQ1570E/NOPB require external loop filter components?

Yes, the LMX2531LQ1570E/NOPB requires an external passive loop filter between CPout (Pin 24) and Vtune (Pin 23). Although the device integrates adjustable third and fourth poles, the primary RC network-including resistors and capacitors-is external and must be designed based on the target loop bandwidth, phase margin, and VCO gain (KVtune = 4–7 MHz/V). TI provides design tools and reference schematics to calculate optimal component values for specific stability and settling-time requirements.

What is the function of the Ftest/LD pin on the LMX2531LQ1570E/NOPB?

The Ftest/LD pin (Pin 30) on the LMX2531LQ1570E/NOPB is a multiplexed CMOS output that defaults to lock-detect functionality. When configured via register settings, it asserts a high signal once the PLL achieves frequency and phase lock, providing real-time status for system initialization and fault monitoring. It can also be repurposed as a general-purpose test output for internal node observation during debug, but lock detection is its primary operational mode in production systems.

Can the LMX2531LQ1570E/NOPB operate with a 1.8-V digital interface supply?

Yes, the LMX2531LQ1570E/NOPB supports 1.8-V MICROWIRE serial interface operation on DATA (Pin 8), CLK (Pin 9), LE (Pin 10), and CE (Pin 11). Input voltage thresholds are specified for VIH ≥1.6 V and VIL ≤0.4 V, ensuring reliable communication with 1.8-V microcontrollers without level-shifting circuitry. All timing parameters-including tCS ≥25 ns and tCWH ≥25 ns-are guaranteed under these conditions, as verified in the SNAS252S datasheet Section 7.6.

How does temperature affect lock stability in the LMX2531LQ1570E/NOPB?

The LMX2531LQ1570E/NOPB maintains continuous lock across ±90 °C ambient temperature drift from the point of last R0 register programming. Beyond this drift, the VCO calibration routine must be re-executed by reloading R0 to retain lock-this is not a failure but a defined operational behavior. The device remains functional across the full –40°C to +85°C range; however, exceeding the ±90 °C drift threshold triggers a required recalibration step to compensate for VCO center-frequency drift due to temperature-dependent varactor capacitance.