19-3707; Rev 0; 5/05
Low-Cost, 308MHz, 315MHz, and 433.92MHz
FSK Transceiver with Fractional-N PLL
www.dTathaeshMeeAt4Xu7.c0o3m1 crystal-based, fractional-N transceiver is
designed to transmit and receive FSK data at factory-
preset carrier frequencies of 308MHz†, 315MHz, or
433.92MHz with data rates up to 33kbps (Manchester
encoded) or 66kbps (NRZ encoded). This device gen-
erates a typical output power of +10dBm into a 50Ω
load, and exhibits typical sensitivity of -110dBm. The
MAX7031 features separate transmit and receive pins
(PAOUT and LNAIN) and provides an internal RF switch
that can be used to connect the transmit and receive
pins to a common antenna.
The MAX7031 transmit frequency is generated by a 16-
bit, fractional-N, phase-locked loop (PLL), while the
receiver’s local oscillator (LO) is generated by an inte-
ger-N PLL. This hybrid architecture eliminates the need
for separate transmit and receive crystal reference
oscillators because the fractional-N PLL is preset to be
10.7MHz above the receive LO. Retaining the fixed-N
PLL for the receiver avoids the higher current-drain
requirements of a fractional-N PLL and keeps the
receiver current drain as low as possible.
The fractional-N architecture of the MAX7031 transmit
PLL allows the transmit FSK signal to be preset for
exact frequency deviations, and completely eliminates
the problems associated with oscillator-pulling FSK sig-
nal generation. All frequency-generation components
are integrated on-chip, and only a crystal, a 10.7MHz IF
filter, and a few discrete components are required to
implement a complete antenna/digital data solution.
The MAX7031 is available in a small, 5mm x 5mm, 32-
pin, thin QFN package, and is specified to operate in
the automotive -40°C to +125°C temperature range.
†Consult factory for availability.
2-Way Remote Keyless Entry
Local Telemetry Systems
♦ +2.1V to +3.6V or +4.5V to +5.5V Single-Supply
♦ Single-Crystal Transceiver
♦ Factory-Preset Frequency (No Serial Interface
♦ FSK Modulation
♦ Factory-Preset FSK Frequency Deviation
♦ +10dBm Output Power into 50Ω Load
♦ Integrated TX/RX Switch
♦ Integrated Transmit and Receive PLL, VCO, and
♦ > 45dB Image Rejection
♦ Typical RF Sensitivity*: -110dBm
♦ Selectable IF Bandwidth with External Filter
♦ RSSI Output with High Dynamic Range
♦ < 12.5mA Transmit-Mode Current
♦ < 6.7mA Receive-Mode Current
♦ < 800nA Shutdown Current
♦ Fast-On Startup Feature, < 250µs
♦ Small, 32-Pin, Thin QFN Package
*0.2% BER, 4kbps Manchester-encoded data, 280kHz IF BW
32 Thin QFN-EP** T3255-3
**EP = Exposed paddle.
Note: The MAX7031 is available with factory-preset operating
frequencies. See the Selector Guide for complete part num-
Pin Configuration, Selector Guide, Typical Application
Circuit, and Functional Diagram appear at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.