MAX7031 Crystal-Based Fractional-N Transceiver

The MAX7031 is a crystal-based fractional-N transceiver designed to transmit and receive FSK data at factory-preset carrier frequencies of 308MHz, 315MHz, and 433.92MHz, with data rates up to 33kbps (Manchester encoding) or 66kbps (NRZ encoding). The device provides a typical output power of +10dBm into a 50Ω load and a typical sensitivity of -110dBm. The MAX7031 has independent transmit and receive pins (PAOUT and LNAIN) and provides an internal RF switch for connecting the transmit and receive pins to a common antenna.

The MAX7031's transmit frequency is generated by a 16-bit, fractional-N, phase-locked loop (PLL), and the receiver local oscillator (LO) is generated by an integer-N PLL. Because the fractional-N PLL is preset 10.7MHz above the receive LO, this hybrid architecture eliminates the need for separate transmit and receive crystal reference oscillators. The receiver has a fixed-N PLL, eliminating the current-hungry fractional-N PLL and minimizing receiver power consumption.

The MAX7031 transmitter PLL has a fractional-N frequency structure, which allows the frequency deviation of the transmitted FSK signal to be accurately preset, completely eliminating the problems associated with the oscillator pulling the FSK signal. All frequency generation components are integrated on the chip, and only a crystal oscillator, a 10.7MHz IF filter and a few discrete components are needed to form a complete antenna/digital data solution.

The MAX7031 is available in a small 5mm x 5mm, 32-pin thin QFN package and operates over the -40°C to +125°C automotive temperature range.

Key Features

Single Supply Operation: +2.1V to +3.6V or +4.5V to +5.5V

Single Crystal Transceiver

Factory preset frequencies (no serial interface required)

FSK modulation

Factory preset FSK frequency deviation

+10dBm output power into 50Ω load

Built-in TX/RX switch

Built-in transmit and receive PLL, VCO and loop filter

Image rejection > 45dB

Typical RF sensitivity*: -110dBm

IF bandwidth selectable by external filter

RSSI output with high dynamic range

Current < 12.5mA in transmit mode

Current < 6.7mA in receiving mode

Shutdown current < 800nA

Fast power-on startup, startup time < 250µs

Small 32-pin Thin QFN package