Data Sheet
FS
v SENSE SENSE
xVREF(V) xVREF(V)
I (A)
A R ( ) 5 R ( )
u : u :
step
rotations µsteps
120 360 8
minute rotation step
¦ VWHSV VHF RQG
seconds
60 1.8
minute step
§ ·
q
§ · § ·
u u
¨ ¸ ¨ ¸ ¨ ¸
© ¹ © ¹
© ¹
§ ·
q
§ ·
u
¨ ¸ ¨ ¸
© ¹
© ¹
m
step
step
rotations µsteps
v 360 n
minute rotation step
¦ VWHSV VHF RQG
seconds
60
minute step
§ ·
q
§ · § ·
u u
¨ ¸ ¨ ¸ ¨ ¸
© ¹ © ¹
© ¹
§ ·
q
§ ·
u T
¨ ¸ ¨ ¸
© ¹
© ¹
DRV8825
www.ti.com
SLVSA73F –APRIL 2010–REVISED JULY 2014
If the target motor startup speed is too high, the motor will not spin. Make sure that the motor can support the
target speed or implement an acceleration profile to bring the motor up to speed.
For a desired motor speed (v), microstepping level (n
m
), and motor full step angle (θ
step
),
SPACE
(2)
SPACE
(3)
θ
step
can be found in the stepper motor data sheet or written on the motor itself.
For the DRV8825, the microstepping level is set by the MODE pins and can be any of the settings in Table 1.
Higher microstepping will mean a smoother motor motion and less audible noise, but will increase switching
losses and require a higher ƒ
step
to achieve the same motor speed.
9.2.2.2 Current Regulation
In a stepper motor, the set full-scale current (I
FS
) is the maximum current driven through either winding. This
quantity depends on the xVREF analog voltage and the sense resistor value (R
SENSE
). During stepping, I
FS
defines the current chopping threshold (I
TRIP
) for the maximum current step. The gain of DRV8825 is set for 5
V/V.
(4)
To achieve I
FS
= 1.25 A with R
SENSE
of 0.2 Ω, xVREF should be 1.25 V.
9.2.2.3 Decay Modes
The DRV8825 supports three different decay modes: slow decay, fast decay, and mixed decay. The current
through the motor windings is regulated using a fixed-frequency PWM scheme. This means that after any drive
phase, when a motor winding current has hit the current chopping threshold (I
TRIP
), the DRV8825 will place the
winding in one of the three decay modes until the PWM cycle has expired. Afterward, a new drive phase starts.
The blanking time, t
BLANK
, defines the minimum drive time for the current chopping. I
TRIP
is ignored during t
BLANK
,
so the winding current may overshoot the trip level.
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Product Folder Links: DRV8825