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AMT49413 bảng dữ liệu(PDF) 9 Page - Allegro MicroSystems |
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AMT49413 bảng dữ liệu(HTML) 9 Page - Allegro MicroSystems |
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9 / 21 page  3-Phase BLDC Controller and MOSFET Driver AMT49413 9 Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com ally be the direction of mechanical rotation. With a motor that has a high inertial load, the DIR input can be used to apply a con- trolled breaking torque, when fast decay is used (MODE = 0). BRAKE. An active-low input that provides a braking function. WhenBRAKE=0(seeTable3),allthelow-sideFETsareturned on and the high-side FETs are turned off. This effectively short- circuits the back EMF in the windings, and brakes the motor. The braking torque applied depends on the speed. RESET = 0 or COAST=0overridesBRAKEandcoaststhemotor.Notethat whenBRAKEisusedtodynamicallybrakethemotor,thewind- ings are shorted with no control over the winding current. ESF. The state of the enable stop on fault (ESF) pin determines the action taken when a short is detected. See the Diagnostics section for details. TEST. Test is for Allegro production use and must be connected to AGND. Current Regulation Load current can be regulated by an internal fixed frequency PWM control circuit or by external input on the PWM pin. Current Sense Amplifier: CSP, CSN, and CSOUT. A dif- ferential current sense amplifier with a gain, AV, of 19 typical, is provided to allow the use of low-value sense resistors or current shunts as the current sensing elements. Because the output of this sense amplifier is available at CSOUT, it can be used for either internal or external current sensing. With the sense resistor, RSENSE, connected between CSP and CSN, the output of the sense amplifier will be approximately: VCSOUT≈(ILOAD×AV×RSENSE)+VOOS , where VOOS is the output offset voltage (the voltage at zero load current), and AV is the differential voltage gain of the sense amplifier, 19 typical. Internal Current Control: REF. A fixed reference voltage can be applied to provide a maximum current limit. A variable reference voltage will provide a variable torque control. The output voltage of the current sense differential amplifier, VCSOUT, is compared to the reference voltage available on the REF pin. When the outputs of the MOSFETs are turned on, current increases in the motor winding until it reaches a trip point value, ITRIP, given by: ITRIP = (VREF – VOOS) / (RSENSE×AV) . At the trip point, the sense comparator resets the source enable latch, turning off the source driver. At this point, load inductance causes the current to recirculate until the start of the next PWM period. The current path during recirculation is determined by the configuration of the MODE pin. Torque control can therefore be implemented by varying the voltage on the REF pin, provided that the PWM input remains high. If direct control of the torque or current by PWM input is desired, a voltage can be applied to the REF pin to set an absolute maximum current limit. The REF input is internally limited to 4 V, which allows the use of a simple pull-up resistor to V5, RREF, to set the maximum reference voltage, avoiding the need for an externally generated reference voltage.RREFshouldhaveavaluebetween20and200kΩ. Internal PWM Frequency. The internal oscillator frequency, fOSC, is determined by an external resistor, RT, and capacitor, CT, connected in parallel from the RC pin to AGND. The frequency is approximately: fOSC≈1/(RTCT+tBLANK+tDEAD) . where fOSCintherange20to50kHz. PWM Input. Can be used to control the motor torque by an external control circuit signal on the PWM pin. Referring to Table 3, when PWM = 0, the selected drivers are turned off and the load inductance causes the current to recirculate. The current path during recirculation is determined by the configuration of the MODE pin. Setting PWM = 1 will turn on selected drivers as determinedbytheHxinputlogic.HoldingPWM=1allowsspeed and torque control solely by the internal current-limit circuit, using the voltage on the REF pin. In some circumstances, it may be desirable to completely disable the internal PWM control. This can be done by pulling the RC pin directly to AGND. This will disable the internal PWM oscil- lator and ensure that the output of the PWM latch is always high. Blank Time. When the source driver is turned on, a current spike occurs due to the reverse-recovery currents of the clamp diodes and switching transients related to distributed capaci- tance in the load. To prevent this current spike from erroneously resetting the source enable latch, the current-control comparator output is blanked for a short period of time, tBLANK, when the source driver is turned on. The length of tBLANKis different for internal versus external PWM. It is set by the value of the timing capacitor, CT, according to the following formulas: |
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