* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Simple Way to Achieve Changeable Holding Current of DRV8x
Electrical ballast wikipedia , lookup
Three-phase electric power wikipedia , lookup
Power inverter wikipedia , lookup
Brushless DC electric motor wikipedia , lookup
History of electric power transmission wikipedia , lookup
Commutator (electric) wikipedia , lookup
Mains electricity wikipedia , lookup
Stray voltage wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Voltage optimisation wikipedia , lookup
Electric machine wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Electric motor wikipedia , lookup
Distribution management system wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Surge protector wikipedia , lookup
Two-port network wikipedia , lookup
Power electronics wikipedia , lookup
Current source wikipedia , lookup
Induction motor wikipedia , lookup
Buck converter wikipedia , lookup
Brushed DC electric motor wikipedia , lookup
Alternating current wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Opto-isolator wikipedia , lookup
Application Report SLVA640 – July 2014 Achieving Changeable Holding Current of a DRV88x Stepper Motor Driver Alvin Zheng, Anda Zhang Motor Driver Business Unit ABSTRACT This document is provided as a supplement to the DRV88x stepper motor drivers using external VREF to realize output current control (DRV8818, DRV8812, DRV8813, DRV8821, DRV8823, DRV8824, DRV8825, DRV8828, and DRV8829; hereafter in this document referred to as DRV88x). The application report details a method to provide the changeable holding current function for a stepper motor. 1 2 3 4 Contents Introduction .................................................................................................................................. 1 Current Regulation Principle ....................................................................................................... 2 Changeable Holding Current Circuit ........................................................................................... 3 Application Example Based on DRV8818 ................................................................................... 4 Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figures Current Regulation Analog Block ................................................................................... 2 Changeable Holding Current Circuit .............................................................................. 3 Output of Normal Operation............................................................................................ 4 Output of Holding State................................................................................................... 4 Normal Operation Waveform .......................................................................................... 4 Holding State Waveform ................................................................................................. 4 Schematic Application Example Based on DRV8818 .................................................... 5 1 Introduction In some applications, stepper motors are expected to stop at a particular position and hold that position until the next step input. To ensure the position is not moved, the holding torque should be stronger than the load. For those stepper motors whose mechanical holding function can’t provide enough holding torque when facing heavy loads, extra holding current is necessary. This is called electric holding. Also, stepper motors can only be locked at a mechanical stepping angle (electric full step) when no current flows through windings during the holding state. For applications expecting to stop and restart at same position, electric holding is an ideal solution. 1 SLVA640 When performing electric holding, the stepper motor is still powered on in the holding state, there is a big current flowing through the windings. When the stepper motor stops, all the current turns into heat in the motor windings. Although a large holding current can generate enough torque to hold the load, it also produces high heat in the motor windings. In fact, the minimum current needed to hold the load is smaller than the current above. It is necessary to cut down the holding current to decrease the dissipation and meanwhile keep enough holding torque. So in a practical application, changeable holding current is preferred. For chips using external VREF to realize output current (DRV8818, DRV8812, DRV8813, DRV8821, DRV8823, DRV8824, DRV8825, DRV8828, and DRV8829), the current of the motor windings is set by the external VREF pin, and the holding current can be changed using an external circuit. 2 Current Regulation Principle The current regulation of DRV88x chips is achieved by the external VREF. Figure 1 depicts the typical analog block utilized to sample current information and disable the H-bridge accordingly. Figure 1. Current Regulation Analog Block The current regulation block continuously monitors motor winding current by sampling the voltage across the SENSE resistor which is proportional with the winding current. The voltage is amplified and then compared against the reference voltage. When the amplified SENSE resistor voltage is greater than the reference voltage, this signifies winding current is larger than the target current. Then, the device’s logic disables the H-bridge and allows the current to decay through the internal structure. This process is repeated on a continuous basis thus obtaining a regulated current output. The typical regulated current (ITRIP) is in the form of: Where: ITRIP = VREF GAIN × R SENSE ITRIP - the current regulation set point VREF - the analog reference voltage at the device’s VREF input GAIN - the internal amplifier gain RSENSE - the SENSE resistor in Ohms 2 Achieving Changeable Holding Current of a DRV88x Stepper Motor Driver (1) SLVA640 3 Changeable Holding Current Circuit The circuit in Figure 2 can realize changeable holding current function by using the CD74HC123. The CD74HC123 is a dual, retriggerable, monostable multivibrator, with reset. In this application, the input STEP comes from the step signal of the motor driver ICs, such as DRV8818. The output VREF is applied to the VREF pin of the motor driver ICs to achieve changeable holding current. According to the principle of CD74HC123, when a pulse is applied to pin 1, there is a high output on pin 13, with a pulse width of 0.45 RX × CX starting at the falling edge of the signal on pin 1. When the signal frequency on pin 1 is bigger than 1 / (0.45 RX × CX), the high level on pin 13 maintains all the time. Figure 3 shows that by this time, the voltage on pin 13 stays high (Vcc), through a potential-divider network, an R4 × Vcc / (R4 + R2 // R3) output voltage is applied to the VREF pin of the motor driver IC. When the stepper motor is in holding state, there will be no pulse on the STEP, the level on pin 1 will be low so the output voltage on pin 13 will be driven low (GND), hence the VREF voltage becomes Vcc × (R2 // R4) / (R2 // R4 + R3), as shown in Figure 4. In this way, the holding current of the stepper motor can be set by choosing suitable resistors. So the VREF can be automatically changed when the stepper motor enters into holding state. Note: to get a good performance of normal operation, adjust the value of RX and CX based on a target STEP signal to achieve a constant high level on pin 13 when the stepper motor is in normal operation. For example, if the frequency of the step signal is 1/15 Hz, that is, there are only four steps in one minute, then 1/15 > 1 / (0.45 RX × CX), so RX × CX must be larger than 33.3, so 10M can be selected for RX, 10 µF can be selected for CX. Vcc Vcc STEP 1 2 3 4 5 6 7 8 U2 1/A Vcc 1B 1RxCx 1/R 1Cx 1/Q 1Q 2Q 2/Q 2Cx 2/R 2RxCx 2B GND 2/A 16 15 14 R1 10M C1 10uF R3 3K 13 12 GND R2 11 3K 10 9 Vref R4 1K CD74HC123 GND Figure 2. GND Changeable Holding Current Circuit Achieving Changeable Holding Current of a DRV88x Stepper Motor Driver 3 SLVA640 VCC VCC R3 3K GND R2 R3 3K Vref=0.2VCC VCC 3K R2 Vref=0.4VCC 3K R4 1K R4 1K GND Figure 3. 4 Output of Normal Operation GND Figure 4. Output of Holding State Application Example Based on DRV8818 This example is a total solution of a stepper motor with changeable holding current function using the DRV8818. When the stepper is in normal operation, the VREF of DRV8818 is about 2 V, when the stepper enters into the holding state, the VREF automatically drops down to 1 V. Figure 5 and Figure 6 show the test results. Figure 5 and Figure 6 are the VREF and STEP waveforms of two-operation state, Figure 5 is a normal operation waveform and Figure 6 is the holding-state waveform. It can be found that VREF is cut down to half in holding state compared to the normal operation. Figure 5. 4 Normal Operation Waveform Figure 6. Holding State Waveform Achieving Changeable Holding Current of a DRV88x Stepper Motor Driver SLVA640 Figure 7 shows the detailed schematic of the application example. C3 Vin 4 2 C2 47uF/50V CB /SHDN SW GND FB 1 6 Vcc 22uH 1 5 VM 10nF 2 U3 L1 D3 2A R6 3 C4 22uF 11k LM2841 R5 2K GND Vcc C6 10nF R7 3k R14 100R GND C7 1.6nF R9 GND C8 1.6nF R12 47k GND Vcc 47k S1 1 GND 2 S2 1 2 GND C9 R13 10nF 100R R10 10k R11 10k U1 VMA ISENA SLEEPn HOME ENABLEn DIR AOUT1 AOUT2 CP2 DECAY RCA CP1 GND VCP VREF GND RCB VGD VCC STEP BOUT2 BOUT1 USM1 RESETn SRn USM0 ISENB VMB 28 27 26 25 24 23 22 21 20 19 18 17 16 15 VM Vcc EN AOUT2 C10 0.22uF STEP BOUT2 C12 10nF DRV8818 GND P1 Vcc VM 1 STEP 2 3 4 5 6 7 8 U2 1/A Vcc 1B 1RxCx 1/R 1Cx 1/Q 1Q 2Q 2/Q 2Cx 2/R 2RxCx 2B GND 2/A 16 15 14 R1 10M C1 10uF R3 3K AOUT1 12 GND R2 11 3K 9 EN 4 13 10 DIR 3 Stepper Motor 1 Vref R4 1K STEPPER AOUT2 2 3 1 R15 10K VM 2 STEP C11 0.22uF C14 0.22uF GND GND Vcc Vcc 4 R8 3k C5 1nF 1 2 3 DIR AOUT1 4 5 6 7 8 Vref 9 10 Vcc BOUT1 11 12 13 14 CD74HC123 GND Figure 7. GND BOUT1 BOUT2 Schematic Application Example Based on DRV8818 Achieving Changeable Holding Current of a DRV88x Stepper Motor Driver 5 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily performed. TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide adequate design and operating safeguards. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the third party, or a license from TI under the patents or other intellectual property of TI. Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional restrictions. Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements. Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use of any TI components in safety-critical applications. In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and requirements. Nonetheless, such components are subject to these terms. No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties have executed a special agreement specifically governing such use. Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and regulatory requirements in connection with such use. TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of non-designated products, TI will not be responsible for any failure to meet ISO/TS16949. Products Applications Audio www.ti.com/audio Automotive and Transportation www.ti.com/automotive Amplifiers amplifier.ti.com Communications and Telecom www.ti.com/communications Data Converters dataconverter.ti.com Computers and Peripherals www.ti.com/computers DLP® Products www.dlp.com Consumer Electronics www.ti.com/consumer-apps DSP dsp.ti.com Energy and Lighting www.ti.com/energy Clocks and Timers www.ti.com/clocks Industrial www.ti.com/industrial Interface interface.ti.com Medical www.ti.com/medical Logic logic.ti.com Security www.ti.com/security Power Mgmt power.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video RFID www.ti-rfid.com OMAP Applications Processors www.ti.com/omap TI E2E Community e2e.ti.com Wireless Connectivity www.ti.com/wirelessconnectivity Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265 Copyright © 2014, Texas Instruments Incorporated