Datasheet

HMC5883L

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H-Bridge for Set/Reset Strap Drive

The ASIC contains large switching FETs capable of delivering a large but brief pulse to the Set/Reset strap of the sensor.

This strap is largely a resistive load. There is no need for an external Set/Reset circuit. The controlling of the Set/Reset

function is done automatically by the ASIC for each measurement. One half of the difference from the measurements

taken after a set pulse and after a reset pulse will be put in the data output register for each of the three axes. By doing

so, the sensor’s internal offset and its temperature dependence is removed/cancelled for all measurements. The set/reset

pulses also effectively remove the past magnetic history (magnetism) in the sensor, if any.

For each “measurement”, the ASIC:

1. Sends a “Set” pulse

2. Takes one measurement (Mset)

3. Sends a “Reset” pulse

4. Takes another measurement (Mreset)

5. Puts the following result in sensor’s data output register:

Output = [Mset – Mreset] / 2

Charge Current Limit

The current that reservoir capacitor (C1) can draw when charging is limited for both single supply and dual supply

configurations. This prevents drawing down the supply voltage (VDD).

MODES OF OPERATION

This device has several operating modes whose primary purpose is power management and is controlled by the Mode

Continuous-Measurement Mode

During continuous-measurement mode, the device continuously makes measurements, at user selectable rate, and

places measured data in data output registers. 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 data

output registers are updated with the new measurement. To conserve current between measurements, the device is

placed in a state similar to idle mode, but the Mode Register is not changed to Idle Mode. That is, MD[n] bits are

unchanged. Settings in the Configuration Register A affect the data output rate (bits DO[n]), the measurement

configuration (bits MS[n]), when in continuous-measurement mode. All registers maintain values while in continuous-

measurement mode. The I

C bus is enabled for use by other devices on the network in while continuous-measurement

mode.

Single-Measurement Mode

This is the default power-up mode. During single-measurement mode, the device makes a single measurement and

places the measured data in data output registers. After the measurement is complete and output data registers are

updated, the device is placed in idle mode, and the Mode Register is changed to idle mode by setting MD[n] bits. Settings

in the configuration register affect the measurement configuration (bits MS[n])when in single-measurement mode. All

registers maintain values while in single-measurement mode. The I

C 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 I

C bus, but major sources of power consumption are disabled,

such as, but not limited to, the ADC, the amplifier, and the sensor bias current. All registers maintain values while in idle

mode. The I

C bus is enabled for use by other devices on the network while in idle mode.