Hardware Reference
3-8 Copyright ©2001-2003. All rights reserved. ARM DUI 0163B
3.5 Stepper motor interfaceThe IM-AD1 provides four stepper motor interfaces. Two of these, Step 1 and Step 2,
are provided with on-board motor drivers for bipolar motors. The remaining two, Step
3 and Step 4, provide logic-level signals that are connected to two 10-pin headers. This
enables you to connect to off-board motor drivers.
3.5.1 Functional description
The on-board stepper motor drivers comprise a L6506 current controller and L298
bridge drivers. These are controlled directly by outputs from the logic module and are
configured to drive bipolar motors. Figure3-5 shows the architecture of one stepper
motor driver.
Figure 3-5 Stepper motor drivers (Step 1)
The L298 contains driver circuitry for two bridges, and each bridge has separate enable
signals. The enable signals and four phase drive signals are supplied by a stepper motor
controller instantiated in the logic module FPGA (see Chapter 4 Reference Design
Example). The controller logic uses the 4MHz IM_CLK signal divided to provide a
step clock.
The L6506 uses a chopper circuit, operating at a frequency of 21kHz, to control the
current on the phase drive signals to the stepper motor. A 0.1Ω sense resistor is provided
to generate a voltage drop that is proportional to the motor current. The sense voltage is
compared against a reference voltage of 0.15V that is supplied to the L6506 by a
resistive divider. When the reference voltage is reached, the phase drive signals are
turned off until the start of the next chopper period.
IM Socket
L6506
(U23)
L298
(U24)
STEP1_ENA
STEP1_ENB
STEP1_PH1
STEP1_PH2
STEP1_PH3
STEP1_PH4
STEP1_O1
STEP1_O2
STEP1_O3
STEP1_O4
J19
Stepper motor
windings
STEP1_VSS
STEP_GND