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DRV8889-Q1 Datasheet(PDF) 58 Page - Texas Instruments

Part No. DRV8889-Q1
Description  DRV8889-Q1, DRV8889A-Q1 Automotive Stepper Driver with Integrated Current Sense, 1/256 Micro-Stepping, and Stall Detection
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Maker  TI [Texas Instruments]
Homepage  http://www.ti.com
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DRV8889-Q1 Datasheet(HTML) 58 Page - Texas Instruments

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8.2.2 Detailed Design Procedure
8.2.2.1 Stepper Motor Speed
The first step in configuring the device requires the desired motor speed and microstepping level. If the target
application requires a constant speed, then a square wave with frequency ƒstep must be applied to the STEP pin.
If the target motor speed is too high, the motor does not spin. Make sure that the motor can support the target
speed. Use Equation 2 to calculate ƒstep for a desired motor speed (v), microstepping level (nm), and motor full
step angle (θstep)
step
step
m
v (rpm)
360 ( / rot)
¦
VWHSV V
( / step) n
(steps / microstep)
60 (s / min)
u
q
T
q
u
u
(2)
The value of θstep can be found in the stepper motor data sheet, or written on the motor.
For example, the motor in this adaptive headlight application is required to rotate at 15°/step for a target of 300
rpm at 1/8 microstep mode. Using Equation 2, ƒstep can be calculated as 960 Hz.
The microstepping level is set by the MICROSTEP_MODE bits in the SPI register and can be any of the settings
listed in Table 8-2. Higher microstepping results in a smoother motor motion and less audible noise, but
increases switching losses and requires a higher ƒstep to achieve the same motor speed.
Table 8-2. Microstepping Indexer Settings
MICROSTEP_MODE
STEP MODE
0000b
Full step (2-phase excitation) with 100%
current
0001b
Full step (2-phase excitation) with 71%
current
0010b
Non-circular 1/2 step
0011b
1/2 step
0100b
1/4 step
0101b
1/8 step
0110b
1/16 step
0111b
1/32 step
1000b
1/64 step
1001b
1/128 step
1010b
1/256 step
8.2.2.2 Current Regulation
In a stepper motor, the full-scale current (IFS) is the maximum current driven through either winding. This quantity
depends on the VREF voltage and the TRQ_DAC setting.
The maximum allowable voltage on the VREF pin is 3.3 V. DVDD can be used to provide VREF through a
resistor divider.
During stepping, IFS defines the current chopping threshold (ITRIP) for the maximum current step.
(3)
8.2.2.3 Decay Modes
The device supports eight different decay modes, as shown in Table 7-7. The current through the motor windings
is regulated using an adjustable fixed-time-off scheme which means that after any drive phase, when a motor
DRV8889-Q1
SLVSEE9C – APRIL 2020 – REVISED AUGUST 2020
www.ti.com
58
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