NXP Semiconductors
FXTH87E
FXTH87E, Family of Tire Pressure Monitor Sensors
ADC10
Channel
Input Select
Firmware Call(s)
Characteristic
Optional Z-axis Acceleration TPMS_READ_COMP_ACCEL_Z
Sensor
AZCODE
AD1
AD2
AD3
AD4
AD5
Temperature Sensor
Band gap Reference
GPIO PTA0
TPMS_READ_COMP_TEMP_8
TPMS_READ_COMP_VOLTAGE
TPMS_READ_V0
TCODE
VCODE
G0CODE
G1CODE
GPIO PTA1
TPMS_READ_V1
VREG Monitor
TPMS_WIRE_CHECK
12.1 Pressure measurement
The pressure measurement consists of an interface to a pressure sensing element.
Control bits on the MCU operate the SMI to power up the P-Cell and capture a voltage
which is converted by the ADC10. The resulting pressure transfer equation for the
100-500 kPa range:
(1)
(2)
(3)
The transfer equation of the 100-900 kPa range is:
The transfer equation of the 100-1500 kPa range is:
Due to calibration routines and parameters stored in the FXTH87E, the pressure range is
selected at production and cannot be changed in the field.
Note: Lack of change of the pressure measurement over time may indicate the package
pressure port to be blocked or the internal section of the sensor to be contaminated.
User application should maintain either locally or at the system data receiver a record of
pressure measurements along with temperature and/or accelerometer measurements,
and possibly identify the pressure port as blocked or contaminated if no changes are
recorded over time.
12.2 Temperature measurements
The temperature is measured from a ΔVB sensor built into channel 1 of the ADC10 in the
same manner as is done in the FXTH87E devices with the resulting transfer equation:
(4)
12.3 Voltage measurements
Voltage measurements can be made on the internal band gap to estimate the supply
voltage on VDD
.
FXTH87ERM
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2019. All rights reserved.
Reference manual
Rev. 5.0 — 4 February 2019
100 / 183
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