FXTH870xD
Sensors
Freescale Semiconductor, Inc.
91
12
LF Receiver
The low-frequency receiver (LFR) is a very low-power, low-frequency, receiver system for short-range communication in TPMS.
The module allows an external coil to be connected to two dedicated differential input pins. In TPMS systems a single coil may
be oriented for optimal coupling between the receiver in the tire or wheel and a transmitter coil on the vehicle body or chassis.
This LFR system minimizes power consumption by allowing flexibility in choosing the ratio of on to off times and by turning off
power to blocks of circuitry until they are needed during signal reception and protocol recognition. In addition, this LFR system
can autonomously listen for valid LF signals, check for protocol and ID information so the main MCU can remain in a very low
power standby mode until valid message data has been received.
The LFR can be configured for various message protocols and telegrams to allow it to be used in a broad range of applications.
The message preamble must be a series of Manchester coded bits at the nominal 3.906-kbps data rate. A synchronization pattern
is used to mark the boundary between the preamble and the beginning of Manchester encoded information in the message body.
The synchronization pattern is a non-Manchester specific TPMS pattern. Messages can optionally include none, an 8-bit or a 16-
bit ID value. Messages may contain any number of data bytes with the end-of-message indicated by detecting an illegal
Manchester bit at a data byte boundary.
It is not intended that LFR may be actively receiving/decoding LF signals while physical parameter measurements are being
made; or during the time that the RFM may be actively powered up and/or transmitting RF data. The resulting interactions will
degrade the accuracy of the LF detection.
Figure 65. Block Diagram
For definitions of the acronyms and detailed descriptions of the bits and/or byte registers, please refer to
Rectifier3
Data
Slicer
1kHz_clock
Carrier
Detector
MFO
32kHz
Clamp
R
V
R
V
R
V
LFA
LFB
1 kHz_clock Typ
129 kHz
Typ
Clamp
Rectifier0
Rectifier1
Rectifier2
Amp1
Sensitivity
Buff1
Amp3
Amp2
Buff3
Buff2
Vref_sensitivity
Carrier
Detector
Logic Block 1:
- On/Off cycling
- Carrier Detection
Logic Block 2:
- Data decoding
Data
Slicer
Average
Filter
Summator
Содержание FXTH870 D Series
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