A3981 Allegro Micro Systems, Inc., A3981 Datasheet
A3981
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A3981 Summary of contents
Page 1
... The A3981 is a flexible microstepping motor driver with built-in translator for easy operation single-chip solution, designed to operate bipolar stepper motors in full-, half-, quarter- and sixteenth-step modes and ±750 mA. The A3981 can be controlled by simple Step and Direction inputs, or through the SPI-compatible serial interface that also can be used to program many of the integrated features and to read diagnostic information ...
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... A3981 Selection Guide Part Number A3981KLP-T A3981KLPTR-T *Contact Allegro ® for additional packing information. Absolute Maximum Ratings With respect to GND Characteristic Load Supply Voltage Logic Supply Voltage Pin CP1 Pins CP2, VCP Pins STEP, DIR, ENABLE, DIAG Pin VREG Pin RESETn ...
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... A3981 3.3V VDD REF DAC 6-bit DAC STEP DIR MS1 MS0 RESETn System ENABLE Control and Registers SDI SDO SCK STRn 6-bit DAC Cold Warning, Hot Warning, Overtemperature DIAG A G Automotive, Programmable Stepper Driver Functional Block Diagram OSC VREG Oscillator Regulator REF ...
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... A3981 ELECTRICAL CHARACTERISTICS Characteristics Supplies Load Supply Voltage Range 3 Load Supply Quiescent Current Logic Supply Voltage Range Logic Supply Quiescent Current Charge Pump Voltage Internal Regulator Voltage Internal Regulator Dropout Voltage Motor Bridge Output High-Side On-Resistance High-Side Body Diode Forward Voltage ...
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... A3981 ELECTRICAL CHARACTERISTICS Characteristics Current Control (continued) Reference Input Current Maximum Sense Voltage Current Trip Point Error 5 Logic Input And Output – DC Parameters Input Low Voltage Input High Voltage Input Hysteresis Input Current (Except RESETn) Input Pull-Down Resistor (RESETn) Output Low Voltage ...
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... A3981 ELECTRICAL CHARACTERISTICS Characteristics Diagnostics and Protection VBB Overvoltage Threshold VBB Overvoltage Hysteresis V VREG Undervoltage Threshold VREG Undervoltage Hysteresis VDD Undervoltage Threshold VDD Undervoltage Hysteresis V OSC Timeout High-Side Overcurrent Threshold High-Side Current Limit Low-Side Overcurrent Sense Voltage Overcurrent Fault Delay Open Load Current Threshold Error ...
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... A3981 STEP STRn C SCK J SDI X F SDO Z Figure 1. Serial Interface Timing Diagram Key A Clock High Time B Clock Low Time C Strobe Lead Time D Strobe Lag Time E Strobe High Time F Data Out Enable Time G Data Out Disable Time STEP DIR, MS0, MS1 RESETn ...
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... A3981 The A3981 is an automotive stepper motor driver suitable for high temperature applications such as headlamp bending and leveling, throttle control, and gas recirculation control also suitable for other low current stepper applications such as air con- ditioning and venting. It provides a highly flexible microstepping motor driver that can be configured via the SPI-compatible serial interface ...
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... PWM switching. The full-bridge con- figuration provides full control over the current direction during the PWM on-time, and over the current decay mode during the PWM off-time. Due to the flexibility of the A3981 these control techniques can be completely transparent to the user or can be Automotive, Programmable Stepper Driver partially- or fully-programmed through the serial interface ...
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... Phase Current table and the intended direction of rotation of the motor. Diagnostics The A3981 integrates a number of diagnostic features to protect the driver and load as far as possible from fault conditions and extreme operating environments. At the system level the supply voltages and the chip temperature are monitored ...
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... The fault bits in the diag- nostic registers remain set until cleared by a diagnostic registers reset. • If the logic supply voltage, V voltage threshold, the A3981 will be completely disabled except Latched to monitor the V DD rises above the VDD undervoltage threshold, a power-on reset No will take place and all registers will be reset to the default state ...
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... Fault flag will go high but the Thermal Shutdown bits remain set in the diagnostic registers until reset. Bridge and Output Diagnostics The A3981 includes monitors that can detect a short to supply or a short to ground at the motor phase connections. These condi- tions are detected by monitoring the current from the motor phase connections through the bridge to the motor supply and to ground ...
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... In addition to using the integrated features of the A3981 also possible to perform stall detection by examining the PWM on-time for a single phase using an external microcontroller. In the A3981 the PWM-on signal for phase A can be selected as the output on the DIAG pin, by using the serial interface. 13 Allegro MicroSystems, Inc ...
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... A3981 A three wire synchronous serial interface, compatible with SPI, can be used to configure and control all the features of the A3981. A fourth wire can be used to provide diagnostic feedback. The registers that are accessible through the serial interface are defined in table 2. The A3981 can be operated without using the serial interface, by using the default configuration and control register settings and the STEP and DIR logic inputs for motor control ...
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... This is one of the configuration and control registers, accessed when both address bits are 1. It can be used to write a sequence of values to the phase current table in the A3981. This allows the current at each Step Angle Number to be tailored to suit the microstep current profile requirements of a specific motor. ...
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... PTP, to ensure an odd number the transmission. This is checked by the A3981 and if a the number the value plus parity bit is not odd, the FF bit will be set and the SDO pin will go high the next time STRn is taken low, indicating a parity error. That data will still be written to the next phase table value address ...
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... A3981 15 14 CONFIG Configuration Register 0 Synchronous rectification SYR SYR Synchronous Rectification 0 Diode recirculation 1 Synchronous Microstep mode for external STEP input control MS[1..0] MS1 MS0 Microstep Mode 0 0 Full Step 0 1 Half Step 1 0 Quarter Step 1 1 Sixteenth Step Max phase current as a percentage of I MXI[1 ...
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... A3981 15 14 CONFIG RUN 1 0 Configuration Register 1 Selects clock source OSC OSC Clock Source 0 Internal 1 External Overcurrent fault delay Assumes 4-MHz clock TSC[1..0] TSC1 TSC0 Detect Delay Time 0 0 0.5 μ μ μ μs PWM count difference for ST detection Default to 8 CD[3 ...
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... A3981 15 14 TBLLD 1 1 Fault 0 FF TW1 Fault 1 FF TW1 Table Load Register Parity bit (odd parity) PTP Phase Table Value PT(0..15)[5..0] Table Load Register Mapping Step Angle Number Phase PT( PT( PT( PT( ...
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... Figure 3. A3981 Phase Current table as a phase diagram; values shown are referred to as the Step Angle Number Automotive, Programmable Stepper Driver Application Information the phase angle within the full 360° electrical cycle and is called the Step Angle Number. This is illustrated in figure 3. ...
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... Note that each phase current in the A3981 is defined by a 6-bit DAC. This means that the smallest resolution of the DAC is 100 / 64 = 1.56% of the full scale, so the A3981 cannot produce a resultant motor current of exactly 100% at each microstep. Nor can it produce an exact microstep angle. However, as can be seen from the calculations above, the results for both are well within the specified accuracy of the A3981 current control ...
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... The A3981 provides the ability to directly control the motor movement using only the serial interface. In fact, all features 0 of the A3981, except sleep mode, can be controlled through the I B serial interface thus removing the requirement for individual control inputs. This can reduce the interface requirement from multiple I/O signals to a single four wire interface ...
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... A3981 arithmetic operators to be used, within the microcontroller, to determine the size of the next step increment. Table 6 shows the binary equivalent of each decimal number between –16 and +16. Each increase in the Step Angle Number represents a forwards movement of one-sixteenth microstep. Each decrease in the Step Angle Number represents a reverse movement of one-sixteenth microstep ...
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... The current at each Step Angle Number can be set to suit the microstep current profile requirements of a specific motor. Note: This is an advanced feature of the A3981, which will not be required for most applications. In general the default sinusoidal profile will suffice and therefore the phase current table does not have to be loaded ...
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... A3981 (forwards) 23 (DAC value (reverse) 40 (DAC value Step Angle Number (forwards) 23 (DAC value ...
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... A is highlighted in figure 12 (and shown in table 7). This single value is used in a total of eight locations. The same distribution of values applies to all the values in steps 1 to 15. These values are defined in the A3981 as PT(0) to PT(14), respectively. There are two exceptions to this data distribution principal. These ...
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... A3981 Each of the 16 values written to the phase table is a 6-bit num- ber that determines the current trip point for the associated step. The highest value, 63, represents the maximum phase current defined in the section of the specification on phase cur- PMAX rent control. Other numbers represent a percentage of I example, the number 23 sets the phase current trip point to 23/ ...
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... A3981 32/63=50.8% and so on. The value at each Step Angle Number is then assigned to its corresponding phase table values as follows: 1 where DI represents the digitized value of the current at Step n Angle Number n. A selection of the values and the corresponding phase current table entries is shown in figure12 ...
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... The A3981 is a power circuit, therefore careful consideration must be given to power dissipation and the effects of high cur- rents on interconnect and supply wiring. A first order approximation of the power dissipation in the A3981 can be determined by examining the power dissipation in each of the two bridges during each of the operation modes. When syn- Synchronous Fast Decay • ...
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... A3981 The total power dissipation for each of the four decay modes the average power for the drive current ramp por- D(TOT) XX tion and the drive current decay portion cycle. For slow decay the current will be rising for approximately 20% of the cycle and decaying for approximately 80%. For fast decay the ratio will be approximately 50% ...
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... The ceramic capacitor should have a value of 100 nF and should be placed as close as pos- sible to the associated supply and ground pins of the A3981. The electrolytic capacitor connected to VBB should be rated at least 1.5 times the maximum circuit voltage, and selected to support the maximum ripple current provided to the motor ...
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... A3981 Terminal List Table Name Number Description AGND 7 Analog reference ground CP1 24 Charge pump capacitor terminal CP2 23 Charge pump capacitor terminal DIAG 16 Diagnostic output DIR 3 Direction select input ENABLE 26 Bridge enable input MS0 13 Microstep select input MS1 12 Microstep select input OAM ...
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... A3981 9.70±0. 5.08 NOM 28X 0.10 C 0.30 0.65 BSC 0.19 Automotive, Programmable Stepper Driver Package LP, 28-Pin TSSOP with Exposed Thermal Pad 8º 0º 0.20 0.09 3 NOM 4.40±0.10 6.40±0.20 0.60 ±0.15 1.00 REF 0.25 BSC Branded Face SEATING PLANE C GAUGE PLANE SEATING PLANE For Reference Only; not for tooling use (reference MO-153 AET) 1 ...
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... A3981 A stepper motor is a particular form of brushless DC motor. As for any electric motor, motion is created by magnetic interaction between the stationary part of the motor, known as the stator, and the moving part of the motor, known as the rotor. The information presented here concentrates on a specific type of motor known as a hybrid stepper motor ...
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... A3981 Stator Rotor Stator Rotor Stator Rotor Stator Rotor Figure A1. Basic principle of bipolar stepper motor operation ...
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... A3981 In the next panel, panel (b), the current is flowing down through the phase B winding from top to bottom and there is no current in phase A. The result pole on the B electromagnets and an S pole on the B-bar electromagnets. These magnetic poles will attract and repel the permanent magnets on the rotor producing a ...
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... A3981 in the first instance, by the resistance of the winding and the applied voltage. From figure A2( also apparent that varying the relative current in each phase will make it possible to move the rotor to any intermediate position between the four positions of figure A1, which occur when only a single phase is energized. When there is one intermediate position this is known as half step ...
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... A3981 Improved Half Step Figure A5 shows a circle superimposed on the phase diagram. This circle represents the required locus of the resultant phase cur- rent vectors to maintain 100% current magnitude. At the full-step positions and 6, only one phase is active and the magni- tude of the phase current is at 100%. At the half-step positions and 7, both phases are active ...
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... A system to drive a stepper motor with microstep capability requires sequencers, current reference generators, and current controllers. Developing such a system from discrete components, Phase A or even using a fast microcontroller complex task. The A3981 is one of several fully integrated stepper drivers that are – I – I ...
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... The magnitude of the currents at each microstep may then require a relationship other than sinusoidal. The A3981 and a few other integrated driv- ers are able to accommodate this by allowing the phase current values for each microstep position to be reprogrammed. In most ...
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... A3981 100% 99% 98% 96% 92% 88% 83% 77% 70% 63% 56% 47% 38% 29% 19% 10 10% 19% 29% 38% 47% 56% 63% 70% 77% 83% 88% 92% 96% 98% 99% 100% 100% 99% 98% 96% 92% 88% 83% 77% 70% 63% 56% 47% 38% 29% 19% 10 10% 19% 29% 38% 47% 56% 63% 70% 77% 83% 88% 92% 96% 98% 99% 100% Figure A11. Phase current sequence for sixteenth step ...
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... A3981 Copyright ©2010-2011, Allegro MicroSystems, Inc. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec tions as may be required to per- mit improvements in the per for mance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro’ ...