RF platform replaces IR and RF discrete designs with low-power radio solution for remote keyless entry applications

RF platform replaces IR and RF discrete designs with low-power radio solution for remote keyless entry applications

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The new SX1240 and SX1242 ISM-band RF transmitters give designers a fully integrated solution, to enable true data-in/RF-out capability, with only an external crystal and antenna impedance matching network needed. They simplify design, reduce system size and lower costs by integrating “power-and-go modes,” which are pre-set for 434 MHz and 868 MHz (SX1240) or 345 MHz (SX1242), eliminating  the need for a microcontroller (MCU). They also can be used with a wide variety of low-cost antenna technologies that do not require active antenna re-tuning, further simplifying design.

The SX1240 and SX1242 can be paired with Semtech’s low-power SX1239 RF receiver for a complete radio solution. All three devices feature very high operating efficiency and low sleep-mode current consumption, which extends battery life and makes them an ideal solution for use with small, coin-cell battery chemistries and energy harvesting sensors.

The SX1240 transmitter operates in the 418, 434 and 868 MHz, license-free ISM bands and works with FSK and OOK modulation formats up to 100 kb/s. For design flexibility, the SX1240 offers two application modes. In “power-and-go” mode, it can be pre-configured as either a 434 MHz OOK transmitter or an 868 MHz FSK transmitter, without the need for an MCU, by simply setting the control pin. In “advanced” mode, the SX1240 can be used with an MCU and programmed via a two-wire interface for designs requiring custom configuration of output power, modulation format, operating channel and other communication parameters.

The SX1240 extends battery life with an ultra-low, 16.5 mA (typ) current consumption, which is configurable at +10 dBm output power or 9 mA (typ) current consumption at 0 dBm output power, combined with a 500 nA (typ) sleep mode current. The low current consumption of the SX1240 makes it ideal for coin-cell batteries, which are current limited at 20 mA. The SX1240 combined with SX1239 RF receiver features a high link budget of 130 dBm, allowing use of a very small antenna to further reduce the total design footprint.

The SX1242 transmitter offers similar features to the SX1240, but operates in the 345 MHz ISM band and works with OOK modulation formats up to 10 kb/s. The SX1242 also offers both “power-and-go” mode (preconfigured to operate without a microcontroller at 345 MHz) and “advanced” mode. The device provides an ultra-low, 22 mA (typ) current consumption configurable at +12 dBm output power, 500 nA (typ) sleep mode current, and a high link budget of 132 dBm when combined with SX1239 RF receiver.

Both the SX1240 and SX1242 transmitters can be paired with Semtech’s SX1239 RF receiver. This device operates over a wide frequency range, including the 345 MHz, 418 MHz, 434 MHz, 868 MHz and 915 MHz ISM bands and works with FSK, GFSK, MSK, GMSK and OOK modulation formats. The SX1239 provides constant RF performance over the 1.8 V to 3.6 V operating range. Additionally, the highly linear receiver chain and high order digital channel filters eliminate the need for an external SAW filter, enabling a low-cost external component count while still satisfying ETSI and FCC regulations. The receiver also integrates the VCO tank, PLL loop filter and an RF switch, further reducing the overall bill-of-materials. The SX1239 is software and hardware compatible with Semtech’s SX1231 and SX1233 transceivers for easy migration to two-way remote keyless entry and remote control applications.

The SX1240, SX1242 and SX1239 are certified for worldwide radio regulations. The SX1240 and SX1242 come in small form-factor, 8-pin SOIC packaging and the SX1239 is offered in a 24-lead QFN package.


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Availability and Pricing

The SX1240 and SX1242 transmitter ICs are available immediately in production quantities and are priced at $0.58 each in 2,500-piece lots. The SX1239 receiver IC is available immediately in production quantities and is priced at $1.37 each in 3,000-piece lots. Starter kits are available for all three devices. Semtech offers comprehensive design assistance, including field- and factory-based support.

Visit Semtech at

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