Texas Instruments DRV8811EVM User manual

DRV8811EVM
User's Guide
Literature Number: SLVA344AJuly 2009 – Revised September 2009

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Contents
1 Introduction ......................................................................................................................... 61.1 Block Diagram ............................................................................................................. 61.2 Power Connectors ........................................................................................................ 61.3 Test Stakes ................................................................................................................ 71.4 Jumpers .................................................................................................................... 71.5 Motor Outputs ............................................................................................................. 72 Installing Drivers And Software ............................................................................................. 72.1 Installing the FTDI USB Driver .......................................................................................... 72.2 Installing the DRV8811 Evaluation Board Windows Application Software ........................................ 82.3 Running the Windows Application Software ........................................................................... 83 Windows Application ............................................................................................................ 83.1 Menu ........................................................................................................................ 93.2 DRV8811 GPIO Control Signals ........................................................................................ 93.3 Updating DAC Output for Current Control (VREF/DECAY) ........................................................ 103.4 Updating DAC Output for Decay Control (DECAY) ................................................................. 103.5 Operating the Stepper Motor ........................................................................................... 104 Schematic ......................................................................................................................... 12
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List of Figures
1 VREF SELECT Jumper ..................................................................................................... 72 DECAY SELECT Jumper ................................................................................................... 73 DRV8811_RD_EVM_R1p0.exe Main Screen ............................................................................ 84 Acknowledgement Text Box ................................................................................................ 95 Signals Frame ................................................................................................................ 96 Curent Control Frame ...................................................................................................... 107 Current Control Frame ..................................................................................................... 108 Step Rate ................................................................................................................... 119 Speed Control Frame ...................................................................................................... 1110 Step Control Frame ........................................................................................................ 12
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User's GuideSLVA344A – July 2009 – Revised September 2009
Laser and Motor Drives
This document is provided as a supplement to the DRV8811 datasheet. It details the hardwareimplementation of the DRV8811 customer evaluation module (EVM).
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1 Introduction
1.1 Block Diagram
VM Power
Test Stakes
DRV8811
Motor Outputs
MSP430F1612USB
1.2 Power Connectors
Introduction www.ti.com
The DRV8811_RD customer EVM is the complete solution to evaluating the DRV8811 microsteppingbipolar stepper driver. It houses a USB link to provide easy control from a PC computer, an MSP430microcontroller that interprets serial commands from the PC and generates control signals to the driverdevice, and the DRV8811 device with access to all signals for a complete evaluation.
The DRV8811 customer EVM uses a combination of terminal blocks and test clips for theapplication/monitoring of power. The only power rail the user must supply is VM for the device’s powerstage. VDD for logic levels is internally generated from the USB connection.
The user must apply VM according to datasheet recommended parameters.
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1.3 Test Stakes
1.4 Jumpers
1.4.1 VREF SELECT (JP1) Jumper
(a) (b)
POT INT POT INT
1.4.2 DECAY SELECT (JP6) Jumper
(a) (b)
POT INT POT INT
1.5 Motor Outputs
2 Installing Drivers And Software
2.1 Installing the FTDI USB Driver
www.ti.com Installing Drivers And Software
Every pin on the device has been brought out to a test stake. A label on the silkscreen identifies eachsignal.
Three pin jumpers can be configured independently from the other two or three pin jumpers. However, twopin jumpers must either be closed or open. Two pin jumpers (JP2 to JP5) connect the diodes to the motoroutputs and are used under asynchronous rectification (SR = LO).
Figure 1. VREF SELECT Jumper
To configure the VREF SELECT jumper: Figure 1 (a) selects an analog voltage derived from VDD througha voltage divider implemented as a potentiometer R4. Figure 1 (b) selects an analog voltage derived fromthe MSP430’s digital to analog converter channel 0 (DAC0).
Figure 2. DECAY SELECT Jumper
To configure the DECAY SELECT jumper: Figure 2 (a) selects an analog voltage derived from VDDthrough a voltage divider implemented as a potentiometer R6. Figure 2 (b) selects an analog voltagederived from the MSP430’s digital to analog converter channel 1 (DAC1).
There are three ways of connecting the bipolar stepper motor into the DRV8811 EVM: four pin header(J2), four position terminal block (J3) or test clips. Each connection style offers identical connectivity to thedevice’s output terminals. It is recommended, however, to use the header or terminal block, as the teststakes traces are of low current handling capability.
Instructions on how to install the FTDI USB driver on a Windows based computer are detailed in the“USB_Drivers_Install_Readme.pdf” file supplied with the CD inside the USB_Driver folder.
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2.2 Installing the DRV8811 Evaluation Board Windows Application Software
2.3 Running the Windows Application Software
3 Windows Application
Windows Application www.ti.com
The included CD contains a folder titled “Windows Application”. It is recommended for the contents of thisfolder to be copied to any desired folder on the computer. The reason for this is the Settings.ini file will bewritten upon software exit. This action can not take place if the application is run within the CDenvironment.
To run the application, double click the DRV8811_RD_EVM_R1p0.exe application icon found in the samefolder the application was extracted into.
The DRV8811 Windows Application is the software counterpart for the DRV8811 EVM. It is in charge ofconnecting to the MSP430 microcontroller via a USB connection which in turn selects the proper logicstate for the DRV8811 control signals.
The graphical user interface (GUI) has been designed to allow for all of the DRV8811 device’sfunctionality to be tested without having to intervene with the hardware, except for the proper configurationof jumpers when needed.
Figure 3 shows the DRV8811_RD_EVM_R1p0.exe main screen. It contains menu items to configure andenable/disable the serial port, frames with GPIO control for the DRV8811 control signals, stepper motorcontrol for start/stop and speed, and current/decay control through the MSP430 DACs.
Figure 3. DRV8811_RD_EVM_R1p0.exe Main Screen
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3.1 Menu
3.2 DRV8811 GPIO Control Signals
www.ti.com Windows Application
The menu at the top of the application offers a series of quick options for how the COM port is to behave.1. File →Exit - Terminates the application2. Settings →Port - Selects from COM1 to COM4. Default is COM4.The serial port's actual port number defaults to what we have specified on“USB_Drivers_Install_Readme.pdf”. However, any port between COM 1 and COM 4 are equallyusable.
3. Connect: Opens the serial port. When this menu item is pressed, its caption changes to “Disconnect”.4. Disconnect: Closes the serial port. When this menu item is pressed, its caption changes to “Connect”.
After opening the application, the order of events should be:1. Go to Settings →Port and choose the COM port where the USB virtual COM port device has beenconfigured to work. If the COM port is 4, then this step can be skipped as application defaults toCOM4.
2. Press Connect. If the port is available, the menu changes the “Connect“ caption to “Disconnect“. PressDisconnect to disable the serial communications.
< 1> < 4> < 0> should return on the text box as an acknowledgement. The text box also changes from red togreen, as shown in Figure 4 .
Figure 4. Acknowledgement Text Box
The application is ready for use.
Once the application is communicating with the interface board, the control signals can be actuated bychecking or un-checking check boxes on the Signals frame.
Figure 5. Signals Frame
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3.3 Updating DAC Output for Current Control (VREF/DECAY)
VREF = DAC_VALUE ·
2.5 V
¾
4095
(1)
3.4 Updating DAC Output for Decay Control (DECAY)
DECAY = DAC_VALUE ·
2.5 V
¾
4095
(2)
3.5 Operating the Stepper Motor
3.5.1 Turning the Stepper Motor
Windows Application www.ti.com
A checked checkbox translates to a HI level on the respective control signal. A un-checked checkboxtranslates to a LO level on the respective control signal.
If the DRV8811 EVM has been configured to accept VREF analog voltages through the MSP430microcontroller interface (JP1 is set to INT), then the slider bar on the Current Control frame can be usedto set the VREF voltage.
Figure 6. Curent Control Frame
The MSP430F1612 12-bit DAC channel 0 is connected to the DRV8811 VREF analog input. Changing theDAC digital value from 0 to 4095, changes the analog voltage at the VREF/DECAY pin from 0 V to 2.5 Vrespectively. See Equation 1 .
Where VREF is the output voltage and DAC_VALUE is a number from 0 to 4095.
If the DRV8811 EVM has been configured to accept DECAY analog voltages through the MSP430microcontroller interface (JP6 is set to INT), then the slider bar on the Current Control frame can be usedto set the DECAY voltage.
Figure 7. Current Control Frame
The MSP430F1612 12 bit DAC channel 1 is connected to the DRV8811 DECAY analog input. Changingthe DAC digital value from 0 to 4095, changes the analog voltage at the DECAY pin from 0 V to 2.5 Vrespectively. See Equation 2 .
Where DECAY is the output voltage and DAC_VALUE is a number from 0 to 4095.
The Windows Application, in conjunction with the MSP430F1612 microcontroller, utilizes a series of timersto coordinate the rate of steps sent to the device. Once all the control signals are configured accordingly(ENABLEn = LO, SLEEPn = HI, RESETn = HI; DIR, USM0 and USM1 can be HI or LO depending onpreferred mode of operation; SRn must be L, if external diodes are not populated), the motor is ready tobe turned.
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Time
Base
Accel Rate
Pulses Per Second
www.ti.com Windows Application
The DRV8811_RD customer EVM allows for the possibility of coordinating step rates such thataccelerating and decelerating profiles are achieved. Both acceleration and deceleration are controlled bythe same parameters, acceleration rate and time base.
When the motor starts, it always starts at the slowed pulses per second (PPS) speed (62 pulses persecond). The controller will accelerate the motor in order to reach the PPS speed. Acceleration rate is an8-bit number (0 to 255) that gets added to the current PPS speed and time base is an 8-bit number (0 to255) that specifies how many milliseconds will elapse from one speed increase to the next. Once thespecified PPS speed has been achieved, the acceleration stops.
Figure 8. Step Rate
When the motor is commanded to stop, the inverse of the description above occurs.
The Windows Application frame to control speed, acceleration and deceleration, as well as motor start andstop, looks as portrayed in Figure 9 .
Figure 9. Speed Control Frame
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3.5.2 Step by Step control
4 Schematic
Schematic www.ti.com
Pressing the Start Steps button, will start the timer and pulses will be generated at the rate specified bythe decimal number at the PPS text box. Once the Start Steps button is pressed it becomes the Steppingbutton. Press the Stepping button to stop the stepper motion.
When the motor is stepping, the Update Speed button becomes enabled. Speed can be updated bymodifying the PPS text box and then pressing the Update Speed button. The Update Speed button isdisabled every time the motor is not turning because the stepping has been halted by pressing theStepping button.
The Step Control frame has a series of tools to control the stepping of the motor on a predeterminednumber of steps fashion.
The Pulse Step button allows for a single step to be issued. At the same time, the STEP Control checkbox allows the control of the STEP signal in the same fashion that other GPIO signals on the Signalsframe could be set and cleared. Checked stands for HI and unchecked for LO. Remember that a STEPtakes place when STEP goes from LO to HI.
Figure 10. Step Control Frame
To move the motor a number of steps and then stop, fill the # of Steps text box with a decimal numberfrom 0 to 65535 and the motor will move that number of steps at the speed specified on the PPS text box.No acceleration or deceleration takes place under this function.
The schematic can be found on the provided CD under the EVM Related folder.
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