TMC2100 DATASHEET (Rev. 1.07 / 2017-MAY-15)
25
voltages below about 0.5V to 1V, because analog noise caused by digital circuitry has an increased
impact on the chopper precision at low AIN voltages. For best precision, choose the sense resistors in
a way that the desired maximum current is reached with AIN in the range 2V to 2.4V. Be sure to
optimize the chopper settings for the normal run current of the motor.
DRIVING AIN
The easiest way to provide a voltage to AIN is to use a voltage divider from a stable supply voltage
or a microcontroller’s DAC output. A PWM signal can also be used for current control. The PWM
becomes transformed to an analog voltage using an additional R/C low-pass at the AIN pin. The PWM
duty cycle controls the analog voltage. Choose the R and C values to form a low pass with a corner
frequency of several milliseconds while using PWM frequencies well above 10 kHz. AIN additionally
provides an internal low-pass filter with 3.5kHz bandwidth. The integration of an NTC into the voltage
divider feeding AIN allows the realization of temperature dependent motor current scaling. When a
precise reference voltage is available (e.g. from TL431A), the precision of the motor current regulation
can be improved when compared to the internal voltage reference.
Hint
Using a low reference voltage (e.g. below 1V), for adaptation of a high current driver to a low current
motor will lead to reduced analog performance. Adapting the sense resistors to fit the desired motor
current gives a better result.
2.5V
precision
reference
1-2.4V for fixed
current scaling
0-2.4V for
current scaling
0-2.4V for
current scaling
Digital
current
control
PWM output
of µC with
>20kHz
5VOUT or precise
reference voltage
8 Bit DAC
R1
22k
R2
R3
1µ
R1+R2»10K
Optional
digital
control
BC847
100k
DAC Reference
IREF
DAC Reference
IREF
DAC Reference
IREF
Fixed resistor divider to set current scale
(use external reference for enhanced precision)
Precision current scaler
Simple PWM based current scaler
Figure 8.1 Scaling the motor current using the analog input
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
