NXP Semiconductors UM11227 - Tab. 209. ADC10 Channel Assignments; Pressure Measurement

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
186 / 205
When making measurements of the various analog voltages the individual blocks will
first be powered up long enough to stabilize their outputs before a conversion is started.
The ADC channels are connected in hardware. Conversions are started and ended
synchronously with the sampling of the voltages.
The accuracy, power consumption, and timing specifications given in the data sheet are
based on using the assigned firmware subroutines in the firmware user guide to make
these measurements and convert them into an 8-bit, 9-bit or 10-bit transfer function.
These measurement accuracy specifications cannot be guaranteed if the user creates
custom software routines to convert these measurements. For additional information,
contact your NXP sales representative.
Table 209. ADC10 channel assignments
ADC10
Channel
Input Select Firmware Call(s) Characteristic
Pressure Sensor TPMS_READ_COMP_PRESSURE P
CODE
Optional X-axis Acceleration
Sensor
TPMS_READ_COMP_ACCEL_X A
XCODE
AD0
Optional Z-axis Acceleration
Sensor
TPMS_READ_COMP_ACCEL_Z A
ZCODE
AD1 Temperature Sensor TPMS_READ_COMP_TEMP T
CODE
AD2 Band gap Reference TPMS_READ_COMP_VOLTAGE V
CODE
AD3 GPIO PTA0 TPMS_READ_V0 G0
CODE
AD4 GPIO PTA1 TPMS_READ_V1 G1
CODE
AD5 V
REG
Monitor TPMS_WIRE_CHECK
10.26.1 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)
The transfer equation of the 100-900 kPa range is:
(2)
The transfer equation of the 100-1500 kPa range is:
(3)
Due to calibration routines and parameters stored in the NTM88, 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,