DRV8461SPWPR datasheet(24/117 Pages) TI

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Table 7-11. STEP frequency filtering

FRQ_CHG

STEP_FRQ_TOL

Filtering

0b (default)

00b

01b (default)

10b

11b

Don't care

No filtering

7.3.5 Indexer Output

The DRV8461 features the INDEX registers to indicate the expected microstep current and position of the motor

to the user.

• CUR_A_POS register and CUR_A_SIGN bit indicate the position of coil A current in the indexer table.

• CUR_B_POS register and CUR_B_SIGN bit indicate the position of coil B current in the indexer table.

• CUR_A register indicates the value of expected coil A current, which is sin (90° x CUR_A_POS / 255).

• Current will be positive if the corresponding sign bit is 1b and negative if the sign bit is 0b.

Table 7-12 shows the outputs of the CUR_A_POS and CUR_B_POS registers for a current waveform

corresponding to 1/256 microstepping.

Table 7-12. Indexer Output Table

Current Quadrant

CUR_A_POS

CUR_A_SIGN

CUR_B

CUR_B_SIGN

First (0° -> 90°)

0 -> 255

255 -> 0

Second (90° -> 180°)

255 -> 0

0 -> 255

Third (180° -> 270°)

0 -> 255

255 -> 0

Fourth (270° -> 360°)

255 -> 0

0 -> 255

The Indexer outputs together with the nHOME signal allow determination of the motor position within the

electrical wave. They can be compared with an encoder output to detect discrepancies in the movement of the

motor - such as detecting step loss.

7.3.5.1 nHOME Output

For the DDW package, when the microstepping indexer reaches the home position (electrical angle of 45°),

corresponding to 71% of full-scale current in both coils, the open-drain nHOME output is pulled low. At all other

times, the nHOME output will be pulled high. When the device operates with SPI interface, additionally the

NHOME bit in SPI register becomes 0b when the indexer reaches home position.

Therefore, the nHOME output gives one low pulse per electrical rotation, i.e. one pulse per each four fullsteps,

as shown in Figure 7-6. The nHOME low pulse thus corresponds to a defined position of the motor for every four

fullsteps. A more precise homing of the motor can be achieved by combining nHOME with a mechanical home

switch.

DRV8461

SLOSE98 – DECEMBER 2022

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