Renesas FS50KM-2#E52

Overview

FS50KM-2#E52 from Micrel is a monolithic UHF ASK transmitter IC operating from 800MHz to 1GHz, delivering -3dBm EIRP output power with automatic antenna tuning and 115kbps data rate support. It functions as a "data-in, antenna-out" RF transmitter in remote wireless links, requiring only one external crystal and minimal passive components. Used in RKE, garage door openers, and remote sensor transmitters.

For engineers reviewing the FS50KM-2#E52 datasheet, FS50KM-2#E52 pinout, FS50KM-2#E52 application, or FS50KM-2#E52 equivalent, key selection criteria include its integrated UHF synthesizer architecture, ASK/OOK modulation compatibility, ±2dBm output power stability over temperature/supply, low standby current (<1µA), and SOIC-8 packaging for compact PCB integration.

Technical Context

The FS50KM-2#E52 implements a fully integrated UHF transmitter with quadrature-based PLL synthesizer generating carrier frequency (divided by 64 from REFOSC input), differential varactor-based antenna tuning, and closed-loop PA bias control to maintain constant output power. Its architecture eliminates manual antenna matching and supports direct connection to monopole or PCB antennas.

It accepts AC-coupled or crystal-referenced REFOSC inputs (e.g., 13.5625MHz for 868MHz operation), features calibrated power-on initialization (~20ms), and enforces strict timing constraints on STBY transitions and first-mark duration after wake-up to ensure RF stabilization and spectral compliance.

Key Specifications

Pinout & Package

FS50KM-2#E52 is housed in an 8-pin SOIC (Small Outline Integrated Circuit) package, 3.9mm × 4.9mm body size, 1.27mm pitch, with gull-wing leads and JEDEC MS-012AC compliance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar UHF ASK transmitter applications.

Compared with FS50KM-2#E52, the Si4010 adds programmability at the expense of higher BOM count and development effort, while the NB3N502 offers lower unit cost but sacrifices adaptability to varying antenna environments and regulatory bands.

Availability

FS50KM-2#E52 is available at Aetrix Electronics and suitable for remote keyless entry, garage door opener transmitters, and industrial sensor beacons requiring stable component supply across automotive, building automation, and consumer electronics programs.

Supply support for FS50KM-2#E52 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

Micrel, Inc. was a U.S.-based semiconductor company specializing in analog, power management, and RF solutions before its acquisition by Microchip Technology in 2015. Known for QwikRadio™ and PowerPath™ product lines.

The FS50KM-2#E52 belongs to Micrel's QwikRadio™ family of single-chip UHF transmitters, designed specifically for ultra-low-cost, high-volume remote control systems requiring minimal external components and zero factory tuning.

FAQ

What is the operating frequency range supported by the FS50KM-2#E52?

The FS50KM-2#E52 operates from 800MHz to 1GHz, covering major unlicensed ISM bands including 868MHz (Europe), 915MHz (North America), and 920MHz (Japan). Frequency selection is determined by the external crystal connected to the REFOSC pin-e.g., a 13.5625MHz crystal yields 868MHz output (×64 multiplication). The FS50KM-2#E52 does not support sub-GHz bands below 800MHz or 2.4GHz ISM band.

Does the FS50KM-2#E52 require manual antenna tuning during production?

No, the FS50KM-2#E52 incorporates an internal differential varactor and phase-sensing antenna tuner that automatically aligns the transmit frequency with the antenna impedance in real time. This eliminates manual tuning steps, fixture-dependent calibration, and post-assembly RF testing-reducing manufacturing cost and improving yield. The FS50KM-2#E52 achieves this using feedback from the ANTP/ANTM differential outputs without external couplers or detectors.

What is the maximum data rate the FS50KM-2#E52 supports for ASK modulation?

The FS50KM-2#E52 supports ASK data rates up to 115kbits/s under 50% duty cycle conditions, as specified in its electrical characteristics table. This allows robust transmission of encoded commands, status packets, or sensor readings in burst-mode operation. At higher data rates, extinction ratio degrades; for reliable operation in RKE or garage door systems, typical use is 5–20kbits/s. The FS50KM-2#E52 does not support FSK, PSK, or spread-spectrum modulation schemes.

How does the FS50KM-2#E52 maintain consistent output power over battery discharge?

The FS50KM-2#E52 uses a closed-loop power control architecture: the PC pin voltage sets the target MARK output level, while internal circuitry continuously monitors RF output and adjusts PA bias current to compensate for VDD droop and temperature drift. This ensures ±2dBm stability in EIRP across 4.75–5.5V supply and -40°C to +85°C ambient-critical for maintaining link budget in long-life battery applications. The FS50KM-2#E52 achieves this without external DACs or microcontroller intervention.

Is the FS50KM-2#E52 pin-compatible with other Micrel QwikRadio™ transmitters like the MICRF103BM?

Yes, the FS50KM-2#E52 shares identical pinout, package (8-pin SOIC), and functional mapping with the MICRF103BM, including PC, VDD, VSS, REFOSC, STBY, ANTM, ANTP, and ASK pins. Electrical behavior-including supply current, output power, and timing parameters-is functionally equivalent. The FS50KM-2#E52 is a rebranded or second-source variant of the MICRF103BM, intended for continued supply continuity following Micrel's integration into Microchip.