A31316 datasheet(41/61 Pages) ALLEGRO

41 / 61 page

3D Magnetic Position Sensor IC

A31316

Allegro MicroSystems

955 Perimeter Road

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

www.allegromicro.com

error flag can be cleared by a read of the device register, or

through reporting in the applicable output protocol.

Overall, the SAT flag is constructed as follows:

• SAT can be caused by saturation at multiple points of the

signal path. Each point is lumped in with a sub-flag which can

be individually masked to customize the saturation detection

flag. Provided in order of the signal path the individual sub-

flags are: SAT_FILT, SAT_CHAN, SAT_COR, and SAT_LIN.

Alternatively if no saturation detection is required, the entire

SAT error can be masked by setting sat_mask = 1

□ SAT_FILT is set when saturation occurs in the ACD or low-

pass filter. This sub-flag can be disabled by setting sat_filt_

mask = 1. Possible causes are:

◦ Too high of input field on the device.

◦ A digital or analog error in the ADC or filter circuitry.

□ SAT_CHAN is saturation caused by channel A/B 1-D offset/

gain corrections. This sub-flag can be disabled by setting

sat_chan_mask = 1. Possible causes are:

◦ Too high of an input field on the device.

◦ A digital error in the factory or customer 1-D trims

◦ Customer 1-D trim is set incorrectly for the input field

used.

□ SAT_COR is set when saturation would occur within the

angle offset and gain corrections. This sub-flag can be

disabled by setting sat_cor_mask = 1. Possible causes are:

◦ Output value of pre-gain offset is outside of the ang_

thresh_low / ang_thresh_high limits. This check is only

performed if ang_thresh_en bit is set.

◦ Output value of angle gain is outside of the signal path

range. This check is only performed if ang_gain_sat_en is

set. Otherwise the output will rollover to a valid output.

◦ Output value of the post-gain offset is outside of the signal

path range. This check is only performed if the ang_offs_

sat_en bit is set.

□ SAT_LIN is set when the output of linearization would

cause saturation. This sub-flag can be disabled by sat_lin_

mask = 1. Possible causes are:

◦ Linearization correction applies a correction which results

in a value beyond the range.

The SAT error is updated with every angle update. However, the

error can be suppressed for up to 16 tupdate based on the fault_filt

EEPROM setting.

Oscillator Frequency Error (OFE)

The A31316 contains a low frequency oscillator to act as a watch-

dog of the main oscillator. If these two oscillators deviate beyond

comparison threshold (20%), the device will go into a state as

defined in Table 32. This error is considered critical and cannot be

cleared by any action besides a device reset (POR). To mask OFE

errors, the ofe_mask bit can be set. It is not recommended to set this

bit for normal operation but is provided for debugging purposes.

The OFE error detection starts every 10 tupdate.

Signal Processing Logic Failure (SLF)

To help check the main signal path logic in the device during

operation, a set of known inputs will periodically be run through

key parts of the data path and compared to known outputs. This

allows the user to have confidence in the accuracy of the digital

signal path without need for running the LBIST which interrupts

the device operation. Additionally, a watchdog checks that the

output angle is updated at the expected delay after the input sig-

nals are available. In case of unexpected test outputs, or missed

watchdog timer, the SLF flag will be set as shown in Table 32.

If the error condition is removed the error flag can be cleared by

a read of the device register or by reporting through the output

modes so normal operation can resume. The SLF error is deter-

mined every 10 tupdate.

Signal Radius Out of Range (SRR)

The A31316 has an internal check on the two dimensions that

are used to calculate angle (called sine and cosine) by calculating

the radius and comparing to user defined diagnostic boundar-

ies. These boundaries are set by the magnetic_thresh_min and

magnetic_thresh_max EEPROM parameters. The condition for

no error is calculated by the equation below:

Equation 19:

magnetic_thresh_min2 < radius_sq_17b < magnetic_thresh_max2

with

The brackets [x] denote the floor function, which rounds x down

to the nearest integer. The current value of radius_out_sq_17b

can be read directly from the appropriate register.

The SRR check helps ensure the accuracy of the ATAN2 by the

assumption the magnitude of the two dimensions will remain

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