DRV10975ZPWPR datasheet(39/66 Pages) TI2

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MotorSpeed[15:8]

Motor Speed Read Back

Read

MotorSpeed[7:0]

Read

MotorSpeed[15:8]

I C send out motor speed.

MotorSpeed[7:0]

MotorSpeed

Buffer[7:0]

ecycles

1 mechcycle

sec ond

1530 RPM

sec ond

ecycle

minute

DRV10975, DRV10975Z

www.ti.com

SLVSCP2F – JANUARY 2015 – REVISED JUNE 2020

Product Folder Links: DRV10975

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8.4.11.2 Motor Speed Readback

The motor operation speed is automatically updated in register MotorSpeed1 and MotorSpeed2 while the motor

is spinning. MotorSpeed1 contains the 8 most significant bits and MotorSpeed2 contains the 8 least significant

bits. The value is determined by the period for calculated BEMF zero crossings on phase U. The electrical speed

of the motor is denoted as Velocity (Hz) and is calculated as shown in Equation 8.

Velocity (Hz) = {MotorSpeed1:MotorSpeed2} / 10

(8)

As an example consider the following:

MotorSpeed1 = 0x01;

MotorSpeed2 = 0xFF;

Velocity = 512 (0x01FF) / 10 = 51 Hz

For a 4-pole motor, this translates to:

The electrical speed of the motor (Hz) readback from MotorSpeed1 and MotorSpeed2 is not accurate and has up

to 6% error. For accurate results, it is recommended to read the Motor electrical period (see Motor Electrical

Period Readback) and then calculate the electrical speed of the motor (Hz) manually by calculating the inverse of

Motor electrical period or measure the frequency of the FG signal output (see FG Output Frequency).

8.4.11.2.1

Two-Byte Register Readback

Several of the registers such as MotorSpeed report data that is contained in two registers.

To make sure that the data does not change between the reading of the first and second register reads, the

DRV10975 implements a special scheme to synchronize the reading of MSB and LSB data. To ensure valid data

is read when reading a two register value, use the following sequence.

1. Read the MSB.

2. Read the LSB.

Figure 37 shows the two-register readback circuit. When the MSB is read, the controller takes a snapshot of the

LSB. The LSB data is stored in one extra register byte, which is shown as MotorSpeedBuffer[7:0]. When the LSB

is read, the value of MotorSpeedBuffer[7:0] is sent.

Figure 37. Two-Byte Register Readback

8.4.11.3 Motor Electrical Period Readback

The motor operation electrical period is automatically updated in register MotorPeriod1 and MotorPeriod2 while

the motor is spinning. MotorPeriod1 is the MSB and MotorPeriod2 is the LSB. The electrical period is measured

as the time between calculated BEMF zero crossings for phase U. The electrical period of the motor is denoted

as d as tELE_PERIOD (µs) and is calculated as shown in Equation 9.

tELE_PERIOD (µs) = {MotorPeriod1:MotorPeriod2} × 10

(9)

As an example consider the following:

MotorPeriod1 = 0x01;

DRV10975ZPWPR Datasheet(PDF) 39 Page - Texas Instruments

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