HMC5843 Datasheet, PDF (9/19 Pages) Honeywell Solid State Electronics Center – 3-Axis Digital Compass IC

HMC5843
Charge Current Limit
The current that reservoir capacitor (C1) can draw when charging is limited. When using dual supplies this device shall
limit the current drawn from DVDD source to charge this capacitor. When only a single supply is used, Pin DVDD is
externally tied to pin C1. In this configuration, current is still limited. For example, the internal voltage regulator will limit
this current draw.
Bias Current Generator
The bias current generator is used to apply a bias current to the offset strap of the magneto-resistive sensor, which
creates an artificial magnetic field bias on the sensor. This function is enabled and the polarity is set by bits MS[n] in the
configuration register. The bias current generator generates dc current supplied from the AVDD supply.
MODES OF OPERATION
This device has several modes whose primary purpose is power management. This section describes these modes.
Continuous-Measurement Mode
During continuous-measurement mode, the device continuously makes measurements and places measured data in data
output registers. Settings in the configuration register affect the data output rate (bits DO[n]), the measurement
configuration (bits MS[n]), and the gain (bits GN[n]) when in continuous-measurement mode. To conserve current
between measurements, the device is placed in a state similar to idle mode, but the mode is not changed to idle mode.
That is, MD[n] bits are unchanged. Data can be re-read from the data output registers if necessary; however, if the
master does not ensure that the data register is accessed before the completion of the next measurement, the new
measurement may be lost. All registers maintain values while in continuous-measurement mode. The I²C bus is enabled
for use by other devices on the network in while continuous-measurement mode.
Single-Measurement Mode
This is the default single supply power-up mode. In dual supply configuration this is the default mode when AVDD goes
high. During single-measurement mode, the device makes a single measurement and places the measured data in data
output registers. Settings in the configuration register affect the measurement configuration (bits MS[n]), and the gain
(bits GN[n]) when in single-measurement mode. After the measurement is complete and output data registers are
updated, the device is placed sleep mode, and the mode register is changed to sleep mode by setting MD[n] bits. All
registers maintain values while in single-measurement mode. The I²C bus is enabled for use by other devices on the
network while in single-measurement mode.
Idle Mode
During this mode the device is accessible through the I²C bus, but major sources of power consumption are disabled,
such as, but not limited to, the ADC, the amplifier, the SVDD pin, and the sensor bias current. All registers maintain
values while in idle mode. The I²C bus is enabled for use by other devices on the network while in idle mode.
Sleep Mode
This is the default dual supply power-up mode when only DVDD goes high and AVDD remains low. During sleep mode
the device functionality is limited to listening to the I²C bus. The internal clock is not running and register values are not
maintained while in sleep mode. The only functionality that exists during this mode is the device is able to recognize and
execute any instructions specific to this device but does not change from sleep mode due to other traffic on the I²C bus.
The I²C bus is enabled for use by other devices on the network while in sleep mode. This mode has two practical
differences from idle mode. First this state will create less noise on system since the clock is disabled, and secondly this
state is a lower current consuming state since the clock is disabled.
Off Mode
During off mode device is off. No device functionality exists. Both AVDD and DVDD are low. The I²C bus is enabled for
use by other devices on the network in off mode. In this mode the I²C pins shall be in a high impedance state.
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