AK8973 Datasheet, PDF (2/31 Pages) Asahi Kasei Microsystems – 3-axis Electronic Compass

ASAHI KASEI
[AK8973]
2. Overview
AK8973 is a geomagnetism detection type electronic compass IC.
The small package of AK8973 integrates magnetic sensors for detecting geomagnetism in the X-axis, Y-axis,
and Z-axis, and arithmetic circuit for processing the signal from each sensor. AK8973 outputs four data in total
as 8-bit digital values respectively: 3-axis magnetic sensor measured values and temperature sensor read value.
By processing the magnetic sensor measured values with an external CPU, azimuth data can be obtained.
By using AK8973 integrated into the system, a navigation system is achieved with reduced space in portable
equipment such as PDA or mobile phone incorporating the GPS function.
Specifically, AK8973 has the following features:
(1) Due to the built-in 8-bit ADC and serial interface, geomagnetism of the X-axis, Y-axis, and Z-axis can be
detected as digital data.
(2) The serial interface corresponds to the I²C bus.
(3) A dedicated power supply is used for the serial interface, so the low-voltage specification can also be
supported by applying 1.85V.
(4) Due to the built-in DAC for compensating the offset magnetic field, the position restraint with parts
which generate the offset magnetic field such as speakers is reduced, and the degree of freedom about
layout is expanded. Note 1)
(5) An EEPROM for storing the individual adjustment values of sensor sensitivity is built-in. The
adjustment values are stored in factory at the time of shipment from AKM.
(6) The built-in temperature sensor as an accessory generates the 8-bit digital A/D-converted value.
The temperature information is not used for azimuth calculation.
(7) The major circuit blocks of AK8973 are activated by the measurement request command from the
controller, and transit to the power-down mode automatically at the end of measurement. That
characteristic realizes the low power consumption required for mobile phones.
(8) The interrupt function for posting the completion of sensor signal measurement to the external CPU is
built-in.
(9) The master clock oscillator is built-in. It is unnecessary to supply the clock from the outside.
Note 1) For AK8973, the offset magnetic field compensation range is approximately ±2.0mT (typical
geomagnetism range is approximately 0.05mT). Depending on usage or required accuracy, use with
the full-range is available. However, for the azimuth measurement by the mobile phones, it is
important to regard the following in the design phase: the magnetic field intensity of offset magnetic
field source (e.g. magnet of speaker) is not fully controlled, and the temperature characteristic
dispersion is noted. With AK8973, it is recommended that the design be performed with the parts
layout where the offset magnetic field of each measurement axis is ±0.8mT or less.
MS0561-E-01 <Preliminary>
-2-
2007/01