MPXY8300 datasheet(80/164 Pages) FREESCALE

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MPXY8300 Series

Sensors

Freescale Semiconductor

10.4

Temperature Measurements

The MPXY8300 Series measures temperature in all members of the family. The temperature is measured from a

ΔVB sensor

built into channel 1 of the ADC10. Obtaining a temperature measurement is done using the REIMS_READ_COMP_TEMP_8

firmware subroutine as described in Section 14. This subroutine sequences the correct bits to obtain a temperature dependent

voltage and convert it to the transfer function specified in Section 17.

The output of this measurement can be used as an over temperature shutdown to prevent RF transmissions and save power

during very high temperature conditions which might over stress the battery. This over temperature shutdown software can also

set up a restart when the temperature is once again less than the temperature restart level, TNORM, using the temperature restart

circuit as described in Section 10.7.2.

The output values of $00 or $FF from the calculated temperature measurement are considered fault codes. Further, any

calculated value of temperature below -40

°C or above 125°C will be converted to the $00 or $FF fault code respectively. The

transfer function for temperature versus an 8-bit result from the REIMS_READ_COMP_TEMP_8 firmware is:

NOTE

The accuracy, power consumption and timing specified for a temperature measurement in the electrical

specifications in Section 17 are only guaranteed if the user obtains a temperature reading using the firmware

subroutine call, REIMS_READ_COMP_TEMP_8.

Faults in the temperature sensor that result in a reading less than the minimum level (-40

°C) or greater than the maximum level

(125

°C) will result in the firmware making the output value zero. An output code of zero or 255 are considered fault codes.

Another cross check is that there should be a change in pressure in the presence of a change in temperature. Therefore the user

software should cross check the pressure and temperature readings to determine if the device is responding to the Ideal Gas

Law:

The temperature within the tire will rise after the tire has been in motion for some period of time. Lack of a temperature rise during

the first few minutes of tire motion may be an indication of a failed temperature sensor.

10.5

Voltage Measurements

Voltage measurements can be made on the internal bandgap to estimate the supply voltage on VDD.

10.5.1

Internal Bandgap

An internal bandgap voltage reference is provided to take measurements of a supply voltage. This voltage measurement is taken

directly by the ADC10 converter using channel 2 as the bandgap reference is always powered up during any ADC10 conversion.

Obtaining a calculated VDD voltage measurement based on the bandgap reference is done using the

REIMS_READ_COMP_VOLTAGE firmware subroutine as described in Section 14. This subroutine sequences the correct bits

to obtain a voltage measurement and convert it to the transfer function specified in Section 17.

The output values of $00 or $FF from the calculated voltage measurement are considered fault codes. Further, any calculated

value of voltage below 2.1V or above 3.6V will be converted to the $00 or $FF fault code respectively. The transfer function for

voltage versus an 8-bit result from the REIMS_READ_COMP_VOLTAGE firmware is:

NOTE

The accuracy, power consumption and timing specified for a voltage measurement in the electrical specifications

in Section 17 are only guaranteed if the user obtains a voltage reading using the firmware subroutine call,

REIMS_READ_COMP_VOLTAGE.

CODE

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T0.01

CODE

1.22

MPXY8300 Datasheet(PDF) 80 Page - Freescale Semiconductor, Inc

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