A31316 datasheet(15/61 Pages) ALLEGRO

15 / 61 page

3D Magnetic Position Sensor IC

A31316

Allegro MicroSystems

955 Perimeter Road

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

www.allegromicro.com

Signal Path

The A31316 signal path contains two min sections. The first is

two 1-D signal paths each reflecting the magnetic field in one

direction as specified in the selection guide. The second section

uses a CORDIC calculation to determine an angle from the 1-D

signals. Both sections provide customer-accessible trim registers

for end-of-line calibrations.

1-D Signal Path

FACTORY CHANNEL A / CHANNEL B INPUT SELECTION

Selects the input to Channel A and Channel B. This is pro-

grammed at factory level. Use the selection guide to determine

which axes are used.

FACTORY RANGE SELECTION

Factory range selection sets the analog pre-amplifier. The A31316

front end settings are configured for a limited field range. To

determine the field range, consult the selection guide.

CUSTOMER CONTROLLABLE DATA PATH

The data path further processing is performed as by the equations below.

NOTE: If the segment processor correction components are

changed by the customer, temperature performance may devi-

ate from specification. The customer must take care in changing

these components and assumes liability for temperature perfor-

mance deviations that come about from the changes applied.

Customer Trimming

LOW-PASS FILTER

The user low pass filter allows a noise reduction without data

update rate change using a combination of a CIC and IIR filter.

The IIR filter is a third-order low pass filter.

Equation 2:

CA1 = LPF(CA0)

CB1 = LPF(CB0)

Figure 5: Low-Pass Filter

Table 2: Selection of Customer Low-Pass Filter,

EEPROM Parameter bw_sel

bw_sel

3 dB Frequency (Hz) 90% Settling (ms)

329.1

1.666

465.8

1.172

556

0.9925

700

0.763

1000

0.554

1482

0.396

2024

0.249

Adaptive

0.135

The adaptive filter has a selectable minimum and maximum band-

width for increased customization. The minimum and maximum

bandwidths are selected via the bw_adap_min and bw_adap_max

registers respectively. The table below shows the corresponding

bandwidths for each register. bw_adap_min is by default set to

code 0 and bw_adap_max is by default set to code 7.

Table 3: bw_adapt_(min/max) Frequencies

bw_adapt_(min/max) (LSB)

Frequency (Hz)

38.9

77.8

156.3

314.8

638.7

1308.6

2672.1

4734.2

The overall filter response is given below.

Figure 6: Overall IIR filter Response

Depending on the Selected Bandwidth

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