A1696PKHTN-RDBPTYCD datasheet(10/14 Pages) ALLEGRO

10 / 14 page

Position Sensor IC with Speed and Direction Output

A1696PKH

Allegro MicroSystems

955 Perimeter Road

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

www.allegromicro.com

STOP & GO MODE

In certain engine management applications, it is possible for large

temperature changes to occur while the target is stationary. These

temperature changes can affect the differential magnetic signals.

The Stop & Go algorithm compensates for such shifts in the pro-

cessed signal. Once normal rotation resumes, the part will return

to running mode.

APPLICATION INFORMATION

Power Supply Protection

The A1696 contains an on-chip regulator and can operate across a

wide supply voltage range. Figure 2 shows the minimum external

circuitry needed for proper operation of the sensor IC. This ease

of use reduces design time and incremental assembly costs for

most applications. Contact Allegro MicroSystems for information

on EMC specification compliance.

Target Design

The A1696 is designed to provide highly accurate switching at

each switching feature detected, including switching at the first

switching feature after power-on, as well as at the first switching

feature after a reversal in the direction of target rotation. To sup-

port this functionality, the target must generate a trio of differen-

tial magnetic profiles, such that the two direction channels have

discernible leading/lagging characteristics. The direction of rota-

tion is determined by comparing the spatial separation between

the differential magnetic profiles of the two direction channels.

SIGNAL DIFFERENTIATION AT SWITCHING FEATURES

The optimal separation between the profiles of the two differen-

tial direction signals occurs when the corresponding magnetic

profiles are in quadrature; this is illustrated in Figure 10. Quadra-

ture profiles can be achieved when the target pitch of the switch-

ing feature is approximately equal to twice the distance between

the midpoints of the two direction channels, that is, the distance

between the midpoint of Hall elements E1 and E2 and the mid-

point of Hall elements E2 and E3. This equates to 2.5 mm.

For the A1696, a switching feature can either be magnetic north

and/or magnetic south of a ring magnet depending on the Output

Pulse Location. This translates to either a positive or negative

slope on the Speed channel magnetic signal, and the output

switching occurs at the BST point. The BST point is programma-

ble depending on target type; see Programmable Options Table.

Either differential direction channel can be leading or lagging the

other, depending on the relative direction of target rotation. When

a switching feature is adjacent to the device, i.e., the Speed chan-

nel crosses the BST point, the difference between the differential

direction signals must be at least 35% of the peak-to-peak ampli-

tude in the sequential regions, BSEQ. The difference between

the differential direction signals is programmable depending on

target type; see Programmable Options Table. The sequential

region refers to the target areas where the switching features are

periodic and of uniform configuration, and therefore generating a

consistent magnetic profile; see Figure 6.

NON-SWITCHING FEATURES

When non-switching features are adjacent to the device, the

constraints on the differential magnetic signals are less stringent,

because no output pulses are generated. However, channel signal

separation greater than zero must be maintained so that the lead-

ing/lagging relationship of the differential magnetic signals is not

reversed.

USE OF SIGNATURE REGIONS

Signature regions are target features that are disproportionately

long relative to the sequential features. As a result, they can gen-

erate differential signal peaks that differ from the peaks gener-

ated by the sequential regions; see Figure 6. The device accom-

modates these peaks and switching occurs at relatively the same

switchpoint as on the sequential features. The effect of a signature

region would be a delay in reaching the next switch point.

The extension of the signal period significantly reduces the slope

of the magnetic gradient around the midpoint of a signature fea-

ture. In fact, for relatively large signature features, the magnetic

gradient can become flat, as shown in Figure 6. The flat magnetic

signal also makes it difficult to maintain the necessary channel

separation required for a switching feature. For these reasons,

the device accommodates only signature features that are non-

switching features.

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