Datasheet

TMC4671 Datasheet • IC Version V1.3 | Document Revision V2.00 • 2020-Apr-17
37 / 142
4.5 Analog Signal Conditioning
The range of measured coil currents, resp. the measured voltages of sense resistors, needs to be mapped
to the valid input voltage range of the delta sigma ADC inputs. This analog preprocessing is the task of the
analog signal conditioning.
4.5.0.1 Chain of Gains for ADC Raw Values
An ADC raw value is a result of a chain of gains that determine it. A coil current I_SENSE flowing through a
sense resistor causes a voltage difference according to Ohm’s law. Finally, a current is mapped to an ADC
raw value
ADC_RAW = (I_SENSE · ADC_GAIN) + ADC_OFFSET. (16)
The ADC_GAIN is a result of a chain of gains with individual signs. The sign of the ADC_GAIN is positive
or negative, depending on the association of connections between sense amplifier inputs and the sense
resistor terminals. The ADC_OFFSET is the result of electrical offsets of the phase current measurement
signal path. For the TMC4671, the maximum ADC_RAW value is ADC_RAW_MAX = (2
16
− 1) and the minimum
ADC raw value is ADC_RAW_MIN = 0.
ADC_GAIN = ( I_SENSE_MAX · R_SENSE )
· SENSE_AMPLIFIER_GAIN
· ( ADC_RAW_MAX/ADC_U_MAX )
(17)
Rsense [mΩ] Isense [A] Usense [mV ] GAIN[V/V ] ADC_GAIN[A/V ] Sense Amplifier
5 10 50 20 10 AD8418
10 5 50 20 5 AD8418
Table 17: Example Parameters for ADC_GAIN
For the FOC, the ADC_RAW is scaled by the ADC scaler of the TMC4671 together with subtraction of offset
to compensate it. Internally, the TMC4671 FOC engine calculates with s16 values. So, the ADC scaling needs
to be chosen so that the measured currents fit into the s16 range. With the ADC scaler, the user can choose
a scaling with physical units like [ mA ]. A scaling to [ mA ] covers a current range of − 32 A . . . + 32 A with
m [ A ] resolution. For higher currents, the user can choose unusual units like centi Ampere [ cA ] covering
−327A . . . + 327A or deci Ampere −3276A . . . + 3276A.
ADC scaler and offset compensators are for mapping raw ADC values to s16 scaled and offset cleaned
current measurement values that are adequate for the FOC.
4.5.1 FOC3 - Stator Coil Currents I_U, I_V, I_W and associated Voltages U_U, U_V, U_W
The correct association between stator terminal voltages U_U, U_V, U_W and stator coil currents I_U, I_V,
I_W is essential for the FOC.
For three-phase motors with three terminals U, V, W, the voltage U_U is in phase with the current I_U, U_V
is in phase with I_V, and U_W is in phase with I_W according to equations (18) and (19) for FOC3.
©2020 TRINAMIC Motion Control GmbH & Co. KG, Hamburg, Germany
Terms of delivery and rights to technical change reserved.
Download newest version at www.trinamic.com