DRV10975ZPWPR datasheet(27/66 Pages) TI2

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Time

Speed

Close loop

Op2ClsThr

AlignTime

Accelerate Time

Accelerate Time is determined by

Op2ClsThr and A1, A2.

Speed =

t + 0.5

DRV10975, DRV10975Z

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SLVSCP2F – JANUARY 2015 – REVISED JUNE 2020

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8.4.3.5.3

Motor Start

After it is determined that the motor is stationary and after completing the motor initialization with either align or

IPD, the DRV10975 begins to accelerate the motor. This acceleration is accomplished by applying a voltage

determined by the open loop current setting (OpenLCurr[1:0]) to the appropriate drive state and by increasing the

rate of commutation without regard to the real position of the motor (referred to as open loop operation). The

function of the open loop operation is to drive the motor to a minimum speed so that the motor generates

sufficient BEMF to allow the commutation control logic to accurately drive the motor.

Table 4 lists the configuration options that can be set in register to optimize the initial motor acceleration stage

for different applications.

Table 4. Configuration Options for Controlling Open Loop Motor Start

Description

Reg Name

ConfigBits

Min Value

Max Value

Open to closed loop threshold

SysOpt4

Op2ClsThr[4:0]

0.8 Hz

204.8 Hz

Align time

SysOpt4

AlignTime[2:0]

40 ms

5.3 s

First order accelerate

SysOpt3

StAccel[2:0]

0.3 Hz/s

76 Hz/s

Second order accelerate

SysOpt3

StAccel2[2:0]

0.22 Hz/s2

57 Hz/s2

Open loop current setting

SysOpt2

OpenLCurr[1:0]

200 mA

1.6 A

Open loop current ramping

SysOpt2

OpLCurrRt[2:0]

0.23 VCC/s

6 VCC/s

8.4.3.6 Start-Up Timing

Start-up timing is determined by the align and accelerate time. The align time can be set by AlignTime[2:0], as

described in Register Definition . The accelerate time is defined by the open-to-closed loop threshold

Op2ClsThr[4:0] along with the first order StAccel[2:0](A1) and second order StAccel2[2:0](A2) acceleration

coefficient. Figure 18 shows the motor start-up process.

Figure 18. Motor Start-Up Process

Select the first order and second order acceleration coefficient to allow the motor to reliably accelerate from zero

velocity up to the closed loop threshold in the shortest time possible. Using a slow acceleration coefficient during

the first order accelerate stage can help improve reliability in applications where it is difficult to accurately

initialize the motor with either align or IPD.

Select the open-to-closed loop threshold to allow the motor to accelerate to a speed that generates sufficient

BEMF for closed loop control. This is determined by the velocity constant of the motor based on the relationship

described in Equation 2.

BEMF = Kt × speed (Hz)

(2)

8.4.4 Start-Up Current Setting

The start-up current setting is to control the peak start-up during open loop. During open loop operation, it is

desirable to control the magnitude of drive current applied to the motor. This is helpful in controlling and

optimizing the rate of acceleration. The limit takes effect during reverse drive, align, and acceleration.

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