PDF A3987 Data sheet ( Hoja de datos )

Número de pieza	A3987
Descripción	DMOS Microstepping Driver
Fabricantes	Allegro MicroSystems
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No Preview Available ! www.DataSheet4U.com A3987 DMOS Microstepping Driver with Translator Features and Benefits ▪ Low RDS(on) outputs ▪ Short-to-ground protection ▪ Shorted load protection ▪ Automatic current decay mode detection/selection ▪ Mixed and slow current decay modes ▪ Synchronous rectification for low power dissipation ▪ Internal UVLO and thermal shutdown circuitry ▪ Crossover-current protection Package: 24 pin TSSOP with exposed thermal pad (suffix LP) Approximate scale Description The A3987 is a complete microstepping motor driver with built-in translator for easy operation. It is designed to operate bipolar stepper motors in full, half, quarter, and sixteenth step modes, with output drive capability of 50 V and ±1.5 A. The A3987 includes a fixed off-time current regulator, which has the ability to operate in slow or mixed decay modes. The translator is the key to the easy implementation of the A3987. Simply inputting one pulse on the step input drives the motor to take one microstep.There are no phase sequence tables, high frequency control lines, or complex interfaces to program. The A3987 interface is an ideal fit for applications where a complex microprocessor is unavailable or over-burdened. The A3987 chopping control automatically selects the current decay mode (slow or mixed). When a STEP signal occurs, the translator determines if that step results in a higher or lower current in each of the motor phases. If the change is to a higher current, then the decay mode is set to slow decay. If the change is to a lower current, then the decay mode is set to 30.1% fast decay. This current decay control scheme results in reduced audible motor noise, increased step accuracy, and reduced power dissipation. Continued on the next page… Typical Application Diagram Microcontroller or Controller Logic 10 μF 5 kΩ 0.22 μF VREG VDD 0.1 μF X7R CP1 CP2 VCP ROSC A3987 STEP DIR SLEEP/RESET ENABLE MS1 MS2 REF VBB1 VBB2 OUT1A OUT1B SENSE1 OUT2A OUT2B SENSE2 0.1 μF X7R 100 μF 3987DS, Rev.1 1 page A3987 DMOS Microstepping Driver with Translator ELECTRICAL CHARACTERISTICS1 (continued) valid at TA = 25°C, VBB = 50 V, unless noted otherwise Characteristics Symbol Test Conditions Min. Typ.2 Max. Units Protection Circuitry Overcurrent Protection Threshold4 Iocpst 2 – –A Overcurrent Blanking tocp 1 3 μs Thermal Shutdown Temperature TTSD – 165 – °C Thermal Shutdown Hysteresis TTSDhys – 15 – °C 1Negative current is defined as coming out of (sourcing) the specified device pin. 2Typical data are for initial design estimations only, and assume optimum manufacturing and application conditions. Performance may vary for indi- vidual units, within the specified maximum and minimum limits. 3VERR = [(VREF / 8) – VSENSE ] / (VREF / 8). 4OCP is tested at TA = 25°C in a restricted range and guaranteed by characterization. tA tB STEP MS1, MS2, RESET/SLEEP, or DIR tC tD Time Duration STEP minimum, HIGH pulse width STEP minimum, LOW pulse width Setup time, input change to STEP Hold time, input change to STEP Figure 1. Logic Interface Timing Diagram Symbol tA tB tC tD Typ. 1 1 200 200 Unit μs μs ns ns Allegro MicroSystems, Inc. 5 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 5 Page A3987 DMOS Microstepping Driver with Translator Layout. The printed circuit board should use a heavy ground- plane. For optimum electrical and thermal performance, the A3987 must be soldered directly onto the board. On the under- side of the A3987 package is an exposed pad, which provides a path for enhanced thermal dissipation. The thermal pad should be soldered directly to an exposed surface on the PCB. Thermal vias are used to transfer heat to other layers of the PCB. In order to minimize the effects of ground bounce and offset issues, it is important to have a low impedance single-point ground, known as a star ground, located very close to the device. By making the connection between the pad and the ground plane directly under the A3987, that area becomes an ideal location for a star ground point. A low impedance ground will prevent ground bounce during high current operation and ensure that the supply voltage remains stable at the input terminal. The recom- mended PCB layout, shown in figure 8, illustrates how to create a star ground under the device, to serve both as a low impedance ground point and thermal path. The two input capacitors should be placed in parallel, and as close to the device supply pins as possible. The ceramic capaci- tor (CIN1) should be closer to the pins than the bulk capacitor (CIN2). This is necessary because the ceramic capacitor will be responsible for delivering the high frequency current components. The sense resistors, RSx , should have a very low impedance path to ground, because they must carry a large current while sup- porting very accurate voltage measurements by the current sense comparators. Long ground traces will cause additional voltage drops, adversely affecting the ability of the comparators to accu- rately measure the current in the windings. As shown in figure 8, the SENSEx pins have very short traces to the RSx resistors and very thick, low impedance traces directly to the star ground underneath the device. If possible, there should be no other com- ponents on the sense circuits. A3987 PCB Thermal Vias Solder Trace (2 oz.) Signal (1 oz.) Ground (1 oz.) Thermal (2 oz.) OUT1A GND OUT1B VIN RS1 U1 CCP CVCP CREF CVDD RS2 ROSC CIN2 CREG CIN1 VREF OUT2A OUT2B Figure 8. Printed circuit board layout with typical application circuit, shown at right. The copper area directly under the A3987 (U1) is soldered to the exposed thermal pad on the underside of the device. RS1 CREF RS2 OUT1A OUT1B VIN 1 SENSE1 OUT1A NC MS1 DIR STEP GND REF ENABLE VDD OUT2A SENSE2 VBB1 MS2 A3987 OUT1B CP2 CP1 PAD VCP GND ROSC SLEEP/RESET VREG OUT2B VBB2 CCP CVCP ROSC CREG CIN2 CIN1 VREF OUT2A CVDD OUT2B The thermal vias serve also as electrical vias, connecting it to the ground plane on the other side of the PCB , so the two copper areas together form the star ground. Allegro MicroSystems, Inc. 11 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 www.allegromicro.com 11 Page

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