DRV10975ZPWPR datasheet(28/66 Pages) TI2

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BEMF = Kt × speed

V = BEMF + I × Rm

Limit

Speed Hz

DRV10975, DRV10975Z

SLVSCP2F – JANUARY 2015 – REVISED JUNE 2020

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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 3 and Figure 19. 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 open-loop acceleration profile of the motor

•

Kt is configured by Kt[6:0]

(3)

Figure 19. Motor Start-Up Current

8.4.4.1 Start-Up Current Ramp-Up

A fast change in the applied drive current may result in a sudden change in the driving torque. In some

applications, this could result in acoustic noise. To avoid this, the DRV10975 allows the option of limiting the rate

at which the current is applied to the motor. OpLCurrRt[2:0] sets the maximum voltage ramp up rate that will be

applied to the motor. The waveforms in Figure 20 show how this feature can be used to gradually ramp the

current applied to the motor.

Start driving with fast current ramp

Start driving with slow current ramp

Figure 20. Motor Startup Current Ramp

8.4.5 Closed Loop

In closed loop operation, the DRV10975 continuously samples the current in the U phase of the motor and uses

this information to estimate the BEMF voltage that is present. The drive state of the motor is controlled based on

the estimated BEMF voltage.

DRV10975ZPWPR Datasheet(PDF) 28 Page - Texas Instruments