APGAC031 Microchip Technology, APGAC031 Datasheet - Page 2

• Manufacturer Part Number: APGAC031
• Description: KIT ACC TIRE PRESSURE MON SYSTEM
• Manufacturer: Microchip Technology
• Type: Automotive, Tire Pressure Monitorr

Specifications of APGAC031

• Frequency: 315MHz
• Processor To Be Evaluated: PIC18F2680
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: APGRD003
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

AN238
Sensor/Transmitter (S/TX) Device
There are typically five S/TX units per vehicle, one per
wheel, and the spare tire. Each unit has a unique serial
number enabling the system to distinguish between
each tire. When mounted within a vehicle tire, the S/TX
periodically measures internal tire pressure, tempera-
ture and battery condition. It then sends a RF signal
composed of the measured information to a central
receiver. The device described in this document is
based on Microchip’s rfPIC12F675 and the pressure
and temperature sensing is performed by the Sensonor
SP-13, a sensor IC (www.sensonor.com). The unit is
also equipped with a LF receiver unit, used to commu-
nicate to the S/TX device and to enable it from a Sleep
state.
RF Receiver Module
A central RF receiver module receives transmissions
from the individual S/TX devices. The receiver can also
be used as a remote keyless entry receiver, saving on
overall system cost. The design of the RF receiver
module falls beyond the intent of this document. A
functional RF receiver module is assumed.
LF Commander Device
The LF commander is designed to send specific
commands to the S/TX unit via a 125 kHz ASK modu-
lated signal. The LF link communicates over a short
distance (1 meter or less), thus making it capable of
communicating with the wheel in its immediate range.
LF magnetic communications is well suited for sending
commands to the S/TX devices. These commands,
when received by the S/TX device, instruct it to carry
out specific tasks.
Control Unit
The control unit is responsible for initiating communica-
tions, interpreting received data and reporting the
relevant information back to the vehicle. The unit will
only be treated from a system overview perspective.
Pressure Vessel
The pressure vessels (tires) are the measurement
subjects, with pressure and temperature values
measured and reported.
TPM Sensor/Transmitter
TECHNICAL SPECIFICATIONS
• Modulation Format: ASK
• Operating Voltage: 2.5-3.6V
• Low-Voltage Alert Threshold: 2.5V
• Quiescent Current: TBD
DS00238C-page 2
RF Specific:
• Transmit Frequency: 315 MHz
• Transmit Interval: 60, 15 or 5 seconds (LF
• Power Output: +9 dBm into 50 Ω load
• Operating Current – Transmit: 12.5 mA at max RF
LF Specific:
• Input Frequency: 125 kHz
• Input Sensitivity: TBD
Pressure Sensor Specific:
• Pressure Sensor Range: 50-637 kPa absolute
• Temperature Sensor Range: -40–125°C
The schematic for the TPM S/TX is shown in Appendix
A: “Schematics”.
THEORY OF OPERATION
The S/TX device comprises two integrated circuits:
• Microchip’s rfPIC12F675 MCU/RF transmitter IC
• Sensonor SP-13 (pressure, temperature and
In addition, the S/TX also includes LF input circuitry.
This circuitry allows the S/TX device to receive special
commands via the LF link. Refer to Appendix A:
“Schematics” for additional circuit detail.
rfPIC12F675 Transmitter IC
The rfPIC
was chosen as the heart of the S/TX for several rea-
sons. First, the PIC12FXXX series of microcontrollers
are widely used for transmitter applications and millions
of PIC
transmitter applications today. Second, this device fea-
tures an internal RC oscillator, thereby reducing the
external component count which, directly reduces
module cost as well as circuit board size. Third, this
device includes the RF transmitter circuitry, which
again reduces external component count, cost and
overall size of the circuit board. The rfPIC12F675 also
has an internal comparator which plays an important
role in decoding the information from the LF link. The
internal comparator helps reduce overall part count,
thereby further reducing module cost and circuit board
size. Lastly, the rfPIC12F675 features a 10-bit Ana-
log-to-Digital converter, allowing the designer to use
analog output pressure sensors.
The rfPIC microcontroller performs three functions. It
monitors the data line from the SP-13 sensor IC and
from the LF input, and assembles and transmits a RF
message at periodic intervals.
selectable)
power
low-voltage sensor IC)
®
microcontroller devices are currently used in
®
microcontroller, based on the PIC12F675,
© 2009 Microchip Technology Inc.