DRV8880_15 Datasheet, PDF (34/48 Pages) Texas Instruments – DRV8880 2-A Stepper Motor Driver With AutoTune™

DRV8880
SLVSD18A – JUNE 2015 – REVISED JULY 2015
www.ti.com
Example: If the desired full-scale current is 1.5 A
Set R_SENSE = 100 mΩ, assume TRQ = 100%.
VREF would have to be 0.99 V.
Create a resistor divider from V3P3 (3.3 V) to set VREF ≈ 0.99 V.
Set R2 = 10 kΩ, set R1 = 22 kΩ
Note that I_FS must also follow the equation below in order to avoid saturating the motor. VM is the motor supply
voltage, and R_L is the motor winding resistance.
I_FS
(A)

R_L
(:)

VM (V)
2 u R_DS(ON) (:)

R_SENSE
(:)
(5)
8.2.2.3 Decay Modes
The DRV8880 supports several different decay modes: slow decay, fast decay, mixed decay, and AutoTune. The
current through the motor windings is regulated using an adjustable fixed-time-off scheme. This means that after
any drive phase, when a motor winding current has hit the current chopping threshold (I_TRIP), the DRV8880 will
place the winding in one of the decay modes for t_OFF. After t_OFF, a new drive phase starts. For fixed decay modes
(slow, fast, and mixed), the best setting can be determined by operating the motor and choosing the best setting.
8.2.2.4 Sense Resistor
For optimal performance, it is important for the sense resistor to be:
• Surface-mount
• Low inductance
• Rated for high enough power
• Placed closely to the motor driver
The power dissipated by the sense resistor equals I_rms ² × R. For example, if the rms motor current is 1.4A and a
250 mΩ sense resistor is used, the resistor will dissipate 1.4 A² × 0.25 Ω = 0.49 W. The power quickly increases
with higher current levels.
Resistors typically have a rated power within some ambient temperature range, along with a derated power curve
for high ambient temperatures. When a PCB is shared with other components generating heat, margin should be
added. It is always best to measure the actual sense resistor temperature in a final system, along with the power
MOSFETs, as those are often the hottest components.
Because power resistors are larger and more expensive than standard resistors, it is common practice to use
multiple standard resistors in parallel, between the sense node and ground. This distributes the current and heat
dissipation.
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