DRV10983ZPWPR datasheet(25/58 Pages) TI1

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BEMF = kt × speed

U = BEMF + I × Rm

Limit

Speed Hz

Time

Speed

Close loop

Op2ClsThr

AlignTime

Accelerate Time

Accelerate Time is determined by

Op2ClsThr and A1, A2.

Speed =

t + 0.5

DRV10983

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SLVSCP6C – JULY 2014 – REVISED MAY 2016

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Figure 17. Motor Start-Up Process

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

velocity up to the closed loop threshold in the shortest time possible. Using a slow accelerate rate 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 motor’s velocity constant based on the relationship

described in Equation 1.

BEMF = KtPH × speed (Hz)

(1)

9.4.4 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.

The start current is set by programming the OpenLCurr[1:0] bits. The current should be selected to allow the

motor to reliably accelerate to the handoff threshold. Heavier loads may require a higher current setting, but it

should be noted that the rate of acceleration will be limited by the acceleration rate (StAccel[2:0], StAccel2[2:0]).

If the motor is started with more current than necessary to reliably reach the handoff threshold, it results in higher

power consumption.

The start current is controlled based on the relationship shown in Equation 2 and Figure 18. The duty cycle

applied to the motor is derived from the calculated value for ULimit and the magnitude of the supply voltage, Vcc,

as well as the drive state of the motor.

where

•

ILimit is configured by OpenLCurr[1:0]

•

Rm is configured by Rm[6:0]

•

Speed is variable based motor’s open loop acceleration profile

•

Kt is configured by Kt[6:0]

(2)

Figure 18. Motor Start-Up Current

DRV10983ZPWPR Datasheet(PDF) 25 Page - Texas Instruments

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