NFC interface chip offers energy harvesting

22nd May 2015

Jordan Mulcare

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ams has launched the AS3955, an NFC interface Chip (NFiC), which offers energy harvesting and data transfer capabilities. Like its predecessor the AS3953, the AS3955 provides a contactless bridge between an NFC reader and any MCU. However, the AS3955 can also act as a power supply for the host device, harvesting as much as 5mA at 4.5V (enough to charge a Li-ion cell battery) from the RF energy radiated by an NFC reader.

The AS3955 also offers the designer a choice of two bi-directional data transfer modes. The Extended mode allows the use of standard NFC tag commands to transfer data with minimum processing overhead on the host MCU. The Tunneling mode, which is the second mode, provides a transparent and fully flexible channel between the reader and the host MCU, leaving the user free to implement any standard or proprietary communication protocol. Neither mode requires data buffering in the AS3955’s internal EEPROM memory, resulting in faster data transfers.

The AS3955 features a high performance RF front end, which connects to a simple external NFC antenna without additional external components required. It also includes an EEPROM memory (of 2 or 4kb) and an SPI or I²C interface for communication with an external MCU.

The device is fully compliant with ISO14443A standard up to level 4, NFC Forum specifications, supporting both Type 2 Tag stand-alone functionality, and Type 4 Tag emulation in combination with an external MCU.

The AS3955 offers unrivaled performance and flexibility thanks to energy and data management features that are superior to those of existing interface tags on the market. The energy that the AS3955 harvests from an NFC reader enables it to operate with no external power supply.

A unique data management feature provided by the AS3955 is its new Stealth mode: this enables the host MCU to deactivate the NFiC’s RF channel via the I²C or SPI interface after an operation such as Bluetooth pairing has been completed successfully. This provides for guaranteed user control of NFC operation. The AS3955 also offers 32-bit password protection of its EEPROM memory.

The AS3955 adds a new Silent mode for fail-safe Bluetooth pairing. If the host’s battery has insufficient remaining charge to power its Bluetooth module, the AS3955 NFiC automatically disables its RF circuitry to prevent the device from initiating a pairing procedure.