Datasheet

TMC2209 DATASHEET (Rev. 1.03 / 2019-JUN-26) 52
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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 voltages below about 0.5V to 1V for full scale, because relative analog noise caused by
digital circuitry and power supply ripple has an increased impact on the chopper precision at low
VREF voltages. For best precision, choose the sense resistors in a way that the desired maximum
current is reached with VREF in the range 2V to 2.4V. Be sure to optimize the chopper settings for the
normal run current of the motor.
DRIVING VREF
The easiest way to provide a voltage to VREF is to use a voltage divider from a stable supply voltage
or a microcontroller’s DAC output. A PWM signal also allows current control. The PWM becomes
transformed to an analog voltage using an additional R/C low-pass at the VREF 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. VREF additionally
provides an internal low-pass filter with 3.5kHz bandwidth.
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. Adapt the sense resistors to fit the desired motor
current for the best result.
VREF
8 Bit DAC
Digital
current
control
2.5V
precision
reference
0-2.4V for
current scaling
VREF
PWM output
of µC with
>20kHz
0-2.4V for
current scaling
22k
1µ
Precision current scaler Simple PWM based current scaler
VREF
1-2.4V for fixed
current scaling
R1
Fixed resistor divider to set current scale
(use external reference for enhanced precision)
R2
5VOUT or precise
reference voltage
R1+R2»10K
R3
100k
Optional
digital
control
BC847
Analog ScalingAnalog Scaling Analog Scaling
Figure 9.1 Scaling the motor current using the analog input