HMC5843 Honeywell Microelectronics & Precision Sensors, HMC5843 Datasheet - Page 6

• Manufacturer Part Number: HMC5843
• Description: Magnetic Sensor
• Manufacturer: Honeywell Microelectronics & Precision Sensors

Specifications of HMC5843

• Msl: MSL 3 - 168 Hours
• Sensitivity Range: +/- 10 %
• Sensor Terminals: PCB
• Magnetic Field Max: 4G
• Axis Configuration: Three
• Sensor Output: Digital

HMC5843
BASIC DEVICE OPERATION
Anisotropic Magneto-Resistive Sensors
The Honeywell HMC5843 magnetoresistive sensor circuit is a trio of sensors and application specific support circuits to
measure magnetic fields. With power supply applied, the sensor converts any incident magnetic field in the sensitive axis
directions to a differential voltage output. The magnetoresistive sensors are made of a nickel-iron (Permalloy) thin-film
deposited on a silicon wafer and patterned as a resistive strip element. In the presence of a magnetic field, a change in
the bridge resistive elements causes a corresponding change in voltage across the bridge outputs.
These resistive elements are aligned together to have a common sensitive axis (indicated by arrows on the pinouts) that
will provide positive voltage change with magnetic fields increasing in the sensitive direction. Because the output only is in
proportion to the one-dimensional axis (the principle of anisotropy) and its magnitude, additional sensor bridges placed at
orthogonal directions permit accurate measurement of arbitrary field direction. The combination of sensor bridges in two
and three orthogonal axis permit applications such as compassing and magnetometry.
Offset Strap
The offset strap is a spiral of metallization that couples in the sensor element’s sensitive axis. The offset strap measures
nominally 13 ohms, and requires 10mA for each gauss of induced field. The straps will easily handle currents to buck or
boost fields through the ±6 gauss linear measurement range, but designers should note the extreme thermal heating on
the sensor die when doing so.
With most applications, the offset strap is not utilized and can be ignored. Designers can leave one or both strap
connections (Off- and Off+) open circuited, or ground one connection node. Do not tie both strap connections together to
avoid shorted turn magnetic circuits.
Set/Reset Strap
The set/reset strap is another spiral of metallization that couples to the sensor elements easy axis (perpendicular to the
sensitive axis on the sensor die. Each set/reset strap has a nominal total resistance of 2.25 ohms with a nominal required
peak current of 800mA for reset or set pulses. With rare exception, the set/reset strap must be used to periodically
condition the magnetic domains of the magneto-resistive elements for best and reliable performance.
ASIC Description
The ASIC has inputs for three differential signals from Honeywell’s magneto-resistive sensors. The sensors’ signals are
multiplexed (MUX) into the instrumentation amplifier (AMP), which is then fed into an analog to digital converter (ADC).
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The logic block controls system timing, I
C interface, Set/Reset function, and bias current generator. The ASIC is
developed by Honeywell for use specifically for our magnetoresistive sensors.
Instrumentation Amplifier (AMP)
The Instrumentation amplifier is used to amplify differential signals from the magnetic sensors. The output impedance
from each channel of the sensor is typically 1kO. Differential signal into the instrumentation amplifier is in the mV range
and common mode signal is near AVDD / 2. Typical operation for the sensors is near DC.
Multiplexer (MUX)
The multiplexer is used to MUX the signals from the sensors. The MUX is a low noise device, and the power-on default
state for the MUX is channel 1.
Analog to Digital Converter (ADC)
The ADC converts the analog signals from the amplifier into digital signals. The ADC resolution is 12 bits.
Power Management
This device is capable of operating with a single supply (AVDD) or dual supplies (AVDD and DVDD). Pin VREN makes
this selection by enabling the internal digital supply voltage regulator. When VREN is tied to AVDD, the device is in single
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