NXP Semiconductors UM11227 - Temperature Measurements; Voltage Measurements; Internal Band Gap; External Voltages

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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and possibly identify the pressure port as blocked or contaminated if no changes are
recorded over time.
Refer to the specific data sheet for reference descriptions of the equation terms, which
differ by part number variants.
10.26.2 Temperature measurements
The temperature is measured from a ΔV
B
sensor built into channel 1 of the ADC10 in the
same manner as is done in the NTM88 devices with the resulting transfer equation:
(4)
Refer to the specific data sheet for reference descriptions of the equation terms, which
differ by part number variants.
10.26.3 Voltage measurements
Voltage measurements can be made on the internal band gap to estimate the supply
voltage on V
DD
.
Refer to the specific data sheet for reference descriptions of the equation terms, which
differ by part number variants.
10.26.3.1 Internal band gap
An internal band gap voltage reference is provided to take measurements of the supply
voltage. The resulting transfer equation:
(5)
10.26.3.2 External voltages
Measurements of an external voltage on either the PTA0 or PTA1 pins can be made and
referenced to the internal band gap voltage. The resulting transfer equation:
(6)
where x = 0, 1 refers to PTA0 or PTA1.
10.26.4 Optional acceleration measurements
The acceleration measurement consists of an interface to an optional acceleration
sensing element. Control bits on the MCU operate the SMI to power up the g-Cell and
capture a voltage which is converted by the ADC10. The data from the ADC10 is then
pre-processed by a dynamic range firmware routine that will return the two values
necessary to calculate the acceleration, A
y
, (y = X-axis or Z-axis, depending on selection)
in conjunction with values taken from the tables in the data sheet.
Acceleration sensitivity, ΔA
MAX-MIN
, varies between each offset step, and should be
calculated by dividing the range of g’s for each offset step by the usable A
yCODE
range:
(7)