TMC2100 DATASHEET (Rev. 1.07 / 2017-MAY-15)
24
8 Motor Current Control
The basic motor current is set by the resistance of the sense resistors. Several possibilities allow
scaling down motor current, e.g. to adapt for different motors, or to reduce motor current in standstill
or low load situations.
Three modes of current setting can be chosen using the CFG3 pin:
CFG3: SETS MODE OF CURRENT SETTING
CFG3
GND
VCC_IO
Current Setting
Internal reference voltage. Current scale set by sense resistors, only.
Internal sense resistors. This setting gives best results when combined with
stealthChop voltage PWM chopper. Tie BRA and BRB directly to GND. See chapter
9 for details.
open
External reference voltage on pin AIN. Current scale set by sense resistors and
scaled by AIN. This allows fine tuning of current setting using a simple voltage
divider.
Select the sense resistor to deliver enough current for the motor at full current scale (VREF=2.5V).
RMS RUN CURRENT CALCULATION:
ꢉ
ꢄ
ꢊꢋ
∗
+ꢈꢎ푚Ω ꢈ
√
퐼ꢇ푀푆
=
ꢇ
ꢋꢌꢍꢋꢌ
STANDBY HOLD CURRENT CALCULATION:
ꢄꢈ
ꢏꢈ
ꢉ
ꢄ
ꢊꢋ
퐼ꢇ푀푆
=
∗
∗
+ꢈꢎ푚Ω ꢈ
√
ꢇ
ꢋꢌꢍꢋꢌ
with VFS = full scale voltage (see VSRT)
CURRENT REDUCTION BY ANALOG SCALING:
When analog scaling of VFS is enabled, the resulting voltage VFS‘ is calculated by:
ꢉ
ꢐꢑꢍ
푉′ = 푉
∗
퐹푆
퐹푆
ꢈ.ꢒꢉ
with VAIN the voltage on pin AIN_IREF in the range 0V to V5VOUT/2
For best precision of current setting, it is advised to measure and fine tune the current in the
application.
8.1 Analog Current Scaling AIN
When a high flexibility of the output current scaling is desired, the analog input of the driver can be
enabled for current control, rather than choosing a different set of sense resistors. This way, a simple
voltage divider can be used for the adaptation of a board to different motors. Therefore, leave the
CFG3 pin open.
AIN SCALES THE MOTOR CURRENT
The TMC2100 provides an internal reference voltage for current control, directly derived from the
5VOUT supply output. Alternatively, an external reference voltage can be used. This reference voltage
becomes scaled down for the chopper comparators. The chopper comparators compare the voltages
on BRA and BRB to the scaled reference voltage for current regulation. If analogue scaling is enabled
(CFG3 open), the external voltage on AIN is amplified and filtered and becomes used as reference
voltage. A voltage of 2.5V (or any voltage between 2.5V and 5V) gives the same current scaling as the
internal reference voltage. A voltage between 0V and 2.5V linearly scales the current between 0 and
the current scaling defined by the sense resistor setting. It is not advised to work with reference
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