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Current Loop
Juno Step Motor Control IC User Guide
57
9
9.2.1
Typical Current Signal Processing Circuitry
Figure 9-2:
Typical Current
Signal
Processing
Circuitry
shows a typical leg sensing processing circuit for the current signal inputs. Q1 and Q2 are the half-bridges
for one motor phase, and R6 is the current sensing resistor. U1A with R1~R4 is a differential amplifier for signal
conditioning; it is capable of measuring bidirectional current and has an output of 1.65V at zero current. R5 and C1
form a low pass filter, and they should be placed close to the pins on the Juno IC. R1~R4 should be 1% or higher
grade. The power rating of R6 should match the winding current with 50% power margin recommended.
Section 15.7, “PWM High/Low Motor Drive With Leg Current Sensing/Control”
for complete example
schematics for various Juno-based amplifier designs with current control.
9.2.2
Current Signal Scaling
The value of the user’s external sense resistors and analog conditioning circuitry determine the overall controllable
current range of the step motor amplifier. The overall current sense range should be 25% to 50% above the largest
expected peak current. The user commandable current range is 80% of the current sense range.
Example
A step motor application will require a peak current in each phase of 7.5 amps. The total current sense is selected as
+/- 10.0 amps, which gives a commandable range of +/- 8.0 amps (80% of the total current sense range). A sense
resistor and op amp are used to ge/- 1.65 volts for the desired current range of +/- 10 amps, presenting a
voltage of 0.0V for a reading of -10.0A, 1.65Vfor 0.0A, and 3.3V for +10.0A at the
CurrentA-D
pins.
To determine the numerical value for the user specified drive current and holding current commands we multiply by
1/ .8 reflecting the 80% scaling within Juno’s current loop. So given a desired current in amps the command numerical
Current control only functions when the PWM output mode is set to PWM High/Low. For information on motor
output modes, refer to
Содержание Juno MC71112
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Страница 100: ...Application Notes MC74113 MC75113 100 Juno Step Motor Control IC User Guide 15 Figure 15 3 Drive Safety and Monitoring ...
Страница 103: ...Application Notes MC74113 MC75113 Juno Step Motor Control IC User Guide 103 15 Figure 15 4 Leg Current Sensing ...
Страница 114: ...Application Notes MC74113 MC75113 114 MC58113 Electrical Specifications 15 This page intentionally left blank ...