The MAX7044 from Maxim Integrated (now part of Analog Devices) is a low-cost crystal-referenced phase-locked-loop (PLL) VHF/UHF transmitter designed to transmit OOK/ASK data in the 300 MHz to 450 MHz frequency range - the ISM bands used by most short-range remote and sensor links. MAX7044AKA+T is the RoHS ("+"), tape-and-reel ("T") 8-pin SOT23 option.

Its defining feature is the crystal-based architecture. Where a SAW-based transmitter suffers from shallow modulation depth, slow frequency settling, loose transmit-frequency tolerance and temperature drift, the MAX7044 references a small, low-cost crystal through an on-chip PLL. This gives greater modulation depth, faster frequency settling, much tighter transmit-frequency tolerance and reduced temperature dependence - so the receiver can use a narrower bandwidth and recover more range from the same power.

The MAX7044 delivers up to +13 dBm output into a 50 Ω load and supports data rates to 100 kbps, yet draws only 7.7 mA at 2.7 V (50% duty cycle). A fast-on oscillator reaches operation in about 250 µs, which matters for the burst, duty-cycled transmissions typical of battery RKE fobs and sensors. It runs from a single +2.1 V to +3.6 V supply over -40 °C to +125 °C in the 3 mm x 3 mm 8-pin SOT23.

Note: Values are taken from the Maxim MAX7044 datasheet. Confirm every parameter (and the crystal/PLL multiplication for your target channel) against the latest official documentation before committing a design.

MAX7044AKA+T ships in the tiny 8-pin SOT23 (3 mm x 3 mm) - small enough for a key fob, a tire-pressure sensor module or a compact sensor node, where board area and height are at a premium. Keep the PAOUT matching network compact and the PAGND/GND returns short for a clean output spectrum, and place the crystal close to XTAL1/XTAL2. The package is shown below.

The 8-pin SOT23 carries the crystal, supply, power-amplifier and data pins (per the MAX7044 datasheet):

• Pin 1 - XTAL1: Crystal connection 1 (reference oscillator).
• Pin 2 - VDD: Supply input, +2.1 V to +3.6 V; bypass to GND.
• Pin 3 - PAGND: Power-amplifier ground (keep this return short).
• Pin 4 - PAOUT: Power-amplifier output to the 50 Ω antenna matching network.
• Pin 5 - CLKOUT: Buffered clock output to clock the encoder / microcontroller.
• Pin 6 - DATA: OOK/ASK data input (the modulating bitstream).
• Pin 7 - XTAL2: Crystal connection 2.
• Pin 8 - GND: Ground.

The MAX7044 is the +13 dBm crystal-based ASK transmitter for 300-450 MHz. The parts below are Maxim companions that commonly share a wireless node board - the supply, reference, supervisor and input conditioning around the RF link.

Selection Tips: Choose the MAX7044 for a rugged, crystal-referenced +13 dBm OOK/ASK transmitter at 300-450 MHz. Pair it with the MAX604 (supply), MAX6071 (reference), MAX705 (MCU supervision) and MAX6816 (debounced button input) to complete a battery wireless-remote or sensor node.

Maxim Integrated, now part of Analog Devices, Inc. (ADI), designed the MAX7044 to give short-range OOK/ASK links the stability of a crystal reference instead of a SAW resonator - deeper modulation, tighter frequency and better temperature behavior in a SOT23.

ADI maintains the datasheet, the PLL/crystal and PA-matching application guidance, and the regulatory (ISM-band) notes for the family - the basis for a reliable 300-450 MHz transmitter design.