APGRD003 Microchip Technology, APGRD003 Datasheet - Page 23

• Manufacturer Part Number: APGRD003
• Description: KIT TPMS REFERENCE DESIGN
• Manufacturer: Microchip Technology
• Type: Automotive, Tire Pressure Monitorr

Specifications of APGRD003

• Frequency: 433.92MHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: PIC18F4680, PIC18F2680, MCP2030
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

3.5
3.6
© 2006 Microchip Technology Inc.
ANALOG SENSOR CALIBRATION
SENSOR CALIBRATION
3.4.3.7
• The battery measurement is implemented by comparing the difference between
The calibration method recommended by Intersema for the optimal sensor
performance is the 4-point calibration routine using the simple linear sensor model
described in the Intersema application note (AN402). Total of four independent mea-
surements performed at two different temperatures and pressures are used to calcu-
late and compensate for the variations in the performance of the sensor due to process
variations. Refer to Application Note AN402 from Intersema for more details regarding
analog sensor calibration methods.
The multiplication and division subroutines used in the sensor calibration/compensa-
tion routine are derived from the math subroutines described in Microchip’s Application
Note AN617, “Fixed Point Routines”. Refer to this application note for more descrip-
tions on the 16x16 bits multiplication and 32/16 bits division routines. The flow charts
for the addition routine (Figure 3-6) and subtraction routine (Figure 3-7) are included
for references.
the constant forward voltage drop of a diode (D3) with the battery voltage level
using the internal ADC in the microcontroller. Pin RC1 is set up as the input to
ADC for battery measurement. A threshold value of 2.3V is selected to ensure the
proper operation of the internal ADC. The Battery Low flag will be set if the battery
falls below the threshold value.
Note:
Note:
Note:
BATTERY MEASUREMENT
This method of the temperature measurement is not the most accurate way
to monitor the temperature. An external temperature sensor should be
used, if high accuracy is desired.
The internal ADC minimum required Vref voltage is 2.2V. In order to
achieve the 1LSB accuracy, Vref voltage value of 2.7V or higher is required.
This reference design provides only the typical calibration values used
during development and the calibration values will vary from unit to unit.
Therefore, the accuracy of the measurements is not guaranteed. The user
is responsible for performing the calibration routine for their applications.
Please contact sensor manufacturing for additional information regarding
this topic.
DS51624B-page 19