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A4979GLPTR-T Datasheet(PDF) 12 Page - Allegro MicroSystems |
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A4979GLPTR-T Datasheet(HTML) 12 Page - Allegro MicroSystems |
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12 / 44 page  Microstepping Programmable Stepper Motor Driver With Stall Detect and Short Circuit Protection A4979 12 Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com When using the serial interface to control the stepper motor, a step change value (6-bit) is input through the serial interface to increase or decrease the Step Angle Number. The step change value is a two’s complement (2’sC) number, where a positive value increases the step angle and a negative value decreases the step angle. A single step change in the Step Angle Number is equivalent to a single one-sixteenth microstep. Therefore, for cor- rect motor movement, the step change value should be restricted to no greater than 16 steps, positive or negative. This facility enables full control of the stepper motor at any microstep resolution up to and including sixteenth-step, plus the ability to change microstep resolution “on-the-fly” from one microstep to the next. In both control input method cases, the resulting Step Angle Number is used to determine the phase current value and current direction for each phase, based on the Phase Current table. The decay mode is determined by the position in the Phase Current table and the intended direction of rotation of the motor. Diagnostics The A4979 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. A number of these features automatically disable the current drive to protect the outputs and the load. Others only provide an indication of the likely fault status, as shown in the Fault table (table 1). A single diagnostic output pin (DIAG) can be programmed through the serial interface to provide several different internal signals. At power-up, or after a power-on-reset the DIAG pin outputs a simple Fault Output flag which will be low if a fault is present. The Fault Output flag remains low while the fault is present or if one of the latched faults (for example, a bridge short circuit) has been detected and the outputs disabled. Alternative to the Fault Output flag, the DIAG output can be pro- grammed via the serial interface to output: the stall detect signal, which goes low when a stall is detected; the phase A PWM-on signal, which is high during the phase A PWM on-time; or an analog signal indicating the silicon temperature. If required, specific fault information can be determined by read- ing the diagnostic registers (see Serial Interface section). The first bit (bit 15) in both diagnostic registers contains a com- mon Fault Register flag which will be high if any of the fault bits in either register has been set. This allows a fault condition to be detected using the serial interface, by simply taking STRn low. As soon as STRn goes low the fist bit in the diagnostic registers can be read to determine if a fault has been detected at any time since the last diagnostic registers reset. In all cases the fault bits in the diagnostic registers are latched and only cleared after a diagnostic registers reset. Note that the Fault Register flag in the diagnostic registers, does not provide the same function as the Fault Output flag on the DIAG pin. The Fault Output flag on the DIAG pin provides an indication that either a fault is present or the outputs have been disabled due to a short circuit fault. The Fault Register flag sim- ply provides an indication that a fault has occurred since the last diagnostic registers reset and has been latched. At the system level the supply voltages and chip temperature are monitored. Supply Voltage Monitors The logic supply, the motor supply, and the regulator output are monitored: the motor supply, and the regulator output and logic supply for undervoltage. • If the motor supply voltage, VBBA and VBBB, goes below the VBB undervoltage threshold, the A4979 will indicate the fault and reduce the VREG undervoltage threshold to the low level. When the motor supply voltage goes above the VBB under- voltage threshold, the VREG undervoltage threshold will be increased to the high level and the fault flag removed. The fault Table 1. Fault Table Diagnostic Action Latched VREG Undervoltage Disable outputs, set Fault Register flag No VDD Undervoltage Power-down, full reset No Temperature Warning Set Fault Register flag No Overtemperature Disable outputs, set Fault Register flag No Bridge Short Disable outputs, set Fault Register flag Yes Bridge Open Set Fault Register flag No Stall Detect Set ST flag No |
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