NXP Semiconductors
UM11227
NTM88 family of tire pressure monitor sensors
UM11227 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2020. All rights reserved.
User manual Rev. 6 — 24 April 2020
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10.15.1 Features
Major features of the LFR module include:
• Differential input LF detector (two dedicated pins):
– Selectable sensitivity (two levels: Low Sens (LS) and High Sens (HS)).
– Thresholds trimmed at the factory with trim setting saved in nonvolatile memory.
– LFR has a reference oscillator (LFRO) trimmed at the factory with trim setting saved
in nonvolatile memory.
– Selectable signal sampling time interval and on-time.
– Sample interval and on times controlled by LFR state machine or directly by the
MCU.
• Configurable receive mode:
– Simple LF carrier detection/Telegram decode. (CARMOD)
• Configurable message protocol (telegram structure):
– Various SYNC decoding (SYNC[1:0])
6-bit time SYNC requirements
7.5-bit time SYNC requirements
9-bit time SYNC requirements
– Optional ID (ID[1:0])
8-bit or 16-bit ID
On or off
– 0-n bytes of message data. End-of-data marked by loss of Manchester at a byte
boundary.
• Optional continuous monitoring and decode of the LF detector.
• Selectable MCU interrupt when a received data byte is ready in an LFR buffer, when
a Manchester error is detected in the frame, when an ID is received or when a valid
carrier has been detected.
10.15.2 Modes of operation
The LFR is a peripheral module on an MCU. After being configured by application
software, the LFR can operate autonomously to detect and verify incoming LF messages.
When a valid message or carrier pulse is received and verified the LFR can wake the
MCU from standby modes to read received data or act upon a carrier detection.
The primary modes of operation for the LFR are:
• Disabled. Everything off and drawing minimal leakage current. LFR register contents
will be retained.
• Carrier detect/listen. Minimum circuitry enabled to detect any incoming LF signal, check
it for the appropriate signal level, frequency, and duration.
• TPMS protocol verification.
• Data reception.
10.15.3 Power management
In addition to using low power circuit design techniques, the LFR module provides
system-level features to minimize system energy requirements. In an MCU that includes
the LFR module, all MCU circuitry except a very low current 1 kHz oscillator (LFO) and
minimum regulator circuitry can be disabled. After a reset, the MCU would initialize the
LFR module and then enter a very low power standby mode (depending upon the MCU,
this could be lower than 1 μA for the MCU portion). The LFR module includes everything
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