ALS31313 datasheet(15/25 Pages) ALLEGRO

15 / 25 page

Automotive Grade, 3-D Linear Hall-Effect Sensor

with I2C Output and Advanced Low Power Management

ALS31313

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

APPLICATION INFORMATION

Magnetic Sensor(s) Output

The ALS31313 provides a 12-bit digital output value that is pro-

portional to the magnetic field applied normally to any of the Hall

elements. The most and least significant bits for X, Y, and Z chan-

nels are separated across two primary registers: 0x28 and 0x29.

The process begins with a full 8-byte read of MSB and LSB reg-

isters to construct a 12-bit 2’s complement signed value. All data

must be read in a single 8-byte read when combining registers,

or the result will be the combination of two separate samples in

time. The 12 bits of data are combined per Table 8.

Table 8: Combined MSBs and LSBs for Magnetic Data

BIT

11 10

DATA

MSB Data

LSB Data

Assume that a full 8-byte read returns the following binary data

for a single axis:

MSB = 1100_0000

LSB = 0110

The combined data {MSB;LSB} = 1100_0000_0110, or the

decimal equivalent = –1018. This value can then be converted to

gauss by dividing by the sensitivity of the ALS31313.

An ALS31313 with 500 gauss full-scale input range will have a

typical sensitivity of 4 LSB/gauss. The 12-bit magnetic data value

can be converted to gauss using the equation:

gauss = –1018 LSB ÷ 4 LSB⁄G = –254 gauss

Example source code for combining MSB and LSB data is avail-

able in the 3D Linear and 2D Angle Sensing Application Note.

Temperature Sensor Output

The ALS31313 provides a 12-bit digital output that is propor-

tional to the junction temperature of the IC. Similar to magnetic

data, the most and least significant bits for temperature are sepa-

rated across two primary registers: 0x28 and 0x29. Temperature

is a 12-bit signed value where 25°C is expressed as 12’b0, with a

temperature slope ≈ 8 LSB/°C.

After power-on, the temperature sensor is stable within 8 ms and it

is updated every 8 ms after that. In low-power duty cycle mode, the

temperature sensor is updated once every 10 low power cycles.

Power Modes

Power management on the ALS31313 is user-selectable and

highly configurable, allowing for system-level optimization of

current consumption and performance. The ALS31313 supports

three different power modes: Active Mode, Sleep Mode, and

Low-Power Duty Cycle Mode (LPDCM). The operating mode of

the ALS31313 will be determined by the value in Sleep, Address

0x27, bits 1:0, described in Table 9.

Table 9: Sleep

Address

Bits

Value

Operating Mode

0x27

1:0

Active Mode

Sleep Mode

Low-Power Duty Cycle Mode

SLEEP MODE

In Sleep Mode, the ALS31313 enters a near powered-off state

where it consumes the minimum amount of current (14 nA typical).

In this mode, the device will still respond to I2C commands, but

will not update magnetic or temperature data. Sleep mode is valu-

able in applications where the supply voltage cannot be disabled

but minimal power consumption is required. The time it takes to

exit sleep mode is equivalent to Power-On Delay Time (tPOD).

LOW-POWER DUTY CYCLE MODE (LPDCM)

In Low-Power Duty Cycle Mode (LPDCM), the ALS31313 tog-

gles between Active and Inactive states, reducing overall current

consumption. The average ICC for the ALS31313 during Low-

Power Duty Cycle Mode will vary based on the settings used, and

may range anywhere from 2 mA to 12 µA (typical).

The diagram in Figure 4 shows the profile of ICC as the

ALS31313 toggles between Active and Inactive states during

Low-Power Duty Cycle Mode.

3.5

2.5

1.5

0.5

Time

VCC

ICC

tINACTIVE

tACTIVE

ICC(INACTIVE)

ICC (mA)

VCC (V)

ALS31313 Low-Power Duty Cycle Mode

Figure 4: ICC in Low-Power Duty Cycle Mode

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