【NXP】 Basic introduction to PJF7992 chip

I. Overview

      PEPS system RF radio frequency scheme, the system uses ultra-high frequency signals in the 434 MHz frequency band combined with the low frequency in the 125KHz frequency band, through the response and interaction of the PEPS system, to realize the functions of automobile tire pressure monitoring, remote control door lock, one-key start and so on.

(Image source Internet)

2. Introduction

      PJF7992 is NXP's second-generation ABIC2 (Advanced Basestation IC 2), a fully integrated base station IC. The IC is designed to provide read and write access to the responder, with a high degree of integration and a small number of external components.

      The IC can be used in the NXP transponder series HT2, HT2-extended, HT3 and HT-Pro (PCF7xxx) and similar transponder types. It operates at a frequency of 125KHz and supports FSK frequency modulation and ASK amplitude modulation.

      As the second generation, PJF7992 provides many enhanced functions on the basis of PCF7991 ABIC, such as on-chip voltage regulator, support for single-wire communication, integrated LIN transceiver and antenna drive signal waveform shaping, specifically, the IC has a wide supply voltage range, allowing direct from the vehicle battery (12V)Supply, and no external voltage regulator is required, an on-chip temperature sensor is provided to protect the device from overheating.

2.1 Features

• Integrated single-chip base station
• Integrated powerful programmable antenna driver/modulator
• Integrated LIN transceiver (physical layer compatible with 0 and SAE J2602, compatible with lin1.3)
• Support single-line communication
• High-performance adaptive sampling time AM/PM demodulator
• On-chip clock oscillator and divider in the case of external clock reference
• Antenna open circuit and short circuit detection
• Low-power and ultra-low-power standby modes

2.2 Application

      The advancement of semiconductor technology has provided automobile manufacturers with intelligent, safer and more convenient automotive technology. PCF7991 is suitable for reading and writing operations and has a stable frequency. This chip is used as an RFID front-end circuit to successfully apply RFID electronic tag technology to automobile electronic locks. Through the 125KHz wireless connection between the car and the key, the RFID electronic tag technology is successfully applied to automobile electronic locks.Communication to achieve electronic identification.

3. Introduction to the main functional pins

(Image source "PJF7992A_DataSheet. pdf》)

4. Introduction to PJF7992 communication

4.1 Overview of communication modes

      PJF7992 can communicate with the device via SPI or single-wire mode. Depending on the needs of the application, the device configuration uses a set of commands to control and modify the corresponding device registers.

      Configure the serial interface as a transparent transmission or buffered transponders communication mode through commands to enable read/write access to the transponders. In the transparent transmission mode, the data line (LIN, DI, DO) is used to provide direct control of the antenna driver and direct access to the demodulated received signal, providingThe demodulated received signal binary pulse length modulation (BPLM) encoder and Manchester decoder transmit and receive transponder data in 8-bit blocks.

4.2 Communication mode selection

       For architectures with embedded base stations, SPI operation is the most appropriate because it provides fast and direct access to the device. For an architecture with a remote base station, the single-wire mode is advantageous because it only requires three interconnection lines (VBAT, GND and LIN), and has the excellent signal-to-noise ratio characteristics of serial data communication.

       The pin IOREF determines the operating mode of the serial interface, and the SPI operation is selected. If the voltage level is IOREF, it exceeds a certain threshold value (VIOREF, IMS). In this case, the voltage level on pin IOREF is also used to match the interface I/O voltage level specification with the power supply provided to the external microcontroller. In this case, the microcontroller and pin IOREF must be provided by an external voltage regulator (VIOREF). Otherwise, if the pin IOREF is below a certain threshold value (VIOREF, IMS), single-wire operation is selected.

4.2.1 SPI communication mode

      The SPI communication mode is set by setting the value of VIOREF to be greater than VIOREF. In this mode, the interface operates synchronously during command reception and response, using dedicated data input DI, data output DO, and data clock and CLK lines.

4.2.2 Single-line communication mode

      By setting VIOREF to be smaller than VIOREF, in this mode, the data input and data output share the same line, and the interface operates asynchronously, avoiding a dedicated data clock line. On the contrary, the data clock comes from the system clock.

      In the process of transparent communication with the transponder, the actual data rate is irrelevant. The timing is determined by the transponder protocol. The single-line mode uses an on-chip LIN transceiver to communicate remotely with the device. No external microcontroller is required. The LIN transceiver is controlled by an internal state machine. The CSN, DI, and CLK pins have no functions, so they can be grounded.

(Image source "PJF7992A_DataSheet. pdf》)

V. Reference materials

【NXP PEPS 方案深入浅出（一）-系统结构与选型】

https://www.wpgdadatong.com/blog/detail/41423

【【 NXP 】PCF7991 芯片基础介绍 - 大大通】
https://www.wpgdadatong.com/blog/detail/43478