The TMS37157 or PaLFI (Passive Low Frequency Interface Device) combines a 134.2kHz low frequency transponder with a SPI interface and provides power management for use with a connected microcontroller. The transponder EEPROM memory is accessible through the SPI and low frequency wireless interface. The use of the low frequency band enables communication in harsh environments and ensures a well defined read zone. The long wavelength of the 134.2kHz signal also allows for penetration through most materials including liquids with almost no reduction in range. The EEPROM memory is accessible over the LF interface without support from the battery or through SPI by a microcontroller if a battery is connected. The TMS37157 also offers a wireless battery charge mode which can be used to power a microcontroller wirelessly.