DRV8886AT Datasheet, PDF (18/40 Pages) Texas Instruments – 2-A Stepper Motor Driver With Integrated Current Sense and AutoTune Technology

DRV8886AT
SLVSDO1 – JANUARY 2017
www.ti.com
7.3.5 Controlling RREF With an MCU DAC
In some cases, the full-scale output current may need to be changed between many different values, depending
on motor speed and loading. The reference current of the RREF pin can be adjusted in the system by tying the
RREF resistor to a DAC output instead of GND.
In this mode of operation, as the DAC voltage increases, the reference current decreases and therefore the full-
scale regulation current decreases as well. For proper operation, the output of the DAC should not rise above
V_RREF.
DVDD
IREF
Controller
DAC
RREF
RREF
RREF
Analog
Input
Figure 15. Controlling RREF with a DAC Resource
Use Equation 2 to calculate the full-scale regulation current as controlled by a controller DAC.
I_FS (A)
$_RREF
N$:
>u 9_RREF
9
± 9_DAC
9@
u TRQ (%)
V_RREF (V) u RREF (k :)
(2)
For example, if a 20-kΩ resistor is connected from the RREF pin to the DAC, and the DAC outputs 0.74 V, the
chopping current is 600 mA (TRQ at 100%)
The RREF pin can also be adjusted using a PWM signal and low-pass filter.
Controller
DVDD
IREF
PWM
RREF
R1
RREF
R2
C1
RREF
Analog
Input
Figure 16. Controlling RREF With a PWM Resource
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