A4988-Datasheet.pdf-资料库

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A4988 DMOS Microstepping Driver with Translator And Overcurrent Protection Features and Benefits ▪ Low RDS(ON) outputs ▪ Automatic current decay mode detection/selection ▪ Mixed and Slow current decay modes ▪ Synchronous rectification for low power dissipation ▪ Internal UVLO ▪ Crossover-current protection ▪ 3.3 and 5 V compatible logic supply ▪ Thermal shutdown circuitry ▪ Short-to-ground protection ▪ Shorted load protection ▪ Five selectable step modes: full, 1/2, 1/4, 1/8, and 1/16 Package: 28-contact QFN with exposed thermal pad 5 mm × 5 mm × 0.90 mm (ET package) Description The A4988 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-, eighth-, and sixteenth-step modes, with an output drive capacity of up to 35 V and ±2 A. The A4988 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 A4988. Simply inputting one pulse on the STEP input drives the motor one microstep. There are no phase sequence tables, high frequency control lines, or complex interfaces to program. The A4988 interface is an ideal fit for applications where a complex microprocessor is unavailable or is overburdened. During stepping operation, the chopping control in the A4988 automatically selects the current decay mode, Slow or Mixed. In Mixed decay mode, the device is set initially to a fast decay for a proportion of the fixed off-time, then to a slow decay for the remainder of the off-time. Mixed decay current control results in reduced audible motor noise, increased step accuracy, and reduced power dissipation. Approximate size Continued on the next page… Typical Application Diagram VDD 0.22 μF 0.1 μF 0.1 μF 0.22 μF 5 kΩ Microcontroller or Controller Logic 4988-DS, Rev. 4 VREG ROSC CP1 CP2 VCP VBB1 VBB2 100 μF VDD SLEEP STEP MS1 MS2 MS3 DIR ENABLE RESET VREF A4988 OUT1A OUT1B SENSE1 OUT2A OUT2B SENSE2 GND GND

A4988 DMOS Microstepping Driver with Translator And Overcurrent Protection Description (continued) Internal synchronous rectification control circuitry is provided to improve power dissipation during PWM operation. Internal circuit protection includes: thermal shutdown with hysteresis, undervoltage lockout (UVLO), and crossover-current protection. Special power-on sequencing is not required. The A4988 is supplied in a surface mount QFN package (ES), 5 mm × 5 mm, with a nominal overall package height of 0.90 mm and an exposed pad for enhanced thermal dissipation. It is lead (Pb) free (suffix –T), with 100% matte tin plated leadframes. Selection Guide Part Number A4988SETTR-T 28-contact QFN with exposed thermal pad 1500 pieces per 7-in. reel Package Packing Absolute Maximum Ratings Characteristic Symbol Notes Rating Units Load Supply Voltage Output Current Logic Input Voltage Logic Supply Voltage Motor Outputs Voltage Sense Voltage Reference Voltage Operating Ambient Temperature Maximum Junction Storage Temperature VBB IOUT VIN VDD VSENSE VREF TA TJ(max) Tstg Range S 35 ±2 –0.3 to 5.5 –0.3 to 5.5 –2.0 to 37 –0.5 to 0.5 5.5 –20 to 85 150 –55 to 150 V A V V V V V ºC ºC ºC Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 2

A4988 DMOS Microstepping Driver with Translator And Overcurrent Protection Functional Block Diagram 0.22 F 0.1 F VREG ROSC CP1 CP2 Current Regulator OSC Charge Pump DMOS Full Bridge DMOS Full Bridge OCP Gate Drive OCP DAC PWM Latch Blanking Mixed Decay Translator Control Logic PWM Latch Blanking Mixed Decay DAC VREF VDD REF STEP DIR RESET MS1 MS2 MS3 ENABLE SLEEP VCP VBB1 OUT1A OUT1B SENSE1 VBB2 OUT2A OUT2B SENSE2 0.1 F RS1 RS2 Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 3

A4988 DMOS Microstepping Driver with Translator And Overcurrent Protection ELECTRICAL CHARACTERISTICS1 at TA = 25°C, VBB = 35 V (unless otherwise noted) Test Conditions Characteristics Symbol Output Drivers Load Supply Voltage Range Logic Supply Voltage Range Output On Resistance Body Diode Forward Voltage Motor Supply Current Logic Supply Current Control Logic Logic Input Voltage Logic Input Current Microstep Select Logic Input Hysteresis Blank Time Fixed Off-Time Reference Input Voltage Range Reference Input Current Current Trip-Level Error3 Crossover Dead Time Protection Overcurrent Protection Threshold4 Thermal Shutdown Temperature Thermal Shutdown Hysteresis VDD Undervoltage Lockout VDD Undervoltage Hysteresis VBB VDD RDSON VF IBB IDD VIN(1) VIN(0) IIN(1) IIN(0) RMS1 RMS2 RMS3 VHYS(IN) tBLANK tOFF VREF IREF errI tDT Operating Operating Source Driver, IOUT = –1.5 A Sink Driver, IOUT = 1.5 A Source Diode, IF = –1.5 A Sink Diode, IF = 1.5 A fPWM < 50 kHz Operating, outputs disabled fPWM < 50 kHz Outputs off VIN = VDD0.7 VIN = VDD0.3 MS1 pin MS2 pin MS3 pin As a % of VDD OSC = VDD or GND ROSC = 25 kΩ VREF = 2 V, %ITripMAX = 38.27% VREF = 2 V, %ITripMAX = 70.71% VREF = 2 V, %ITripMAX = 100.00% IOCPST TTSD TTSDHYS VDDUVLO VDDUVLOHYS VDD rising Min. Typ.2 Max. Units 8 3.0 – – – – – – – – VDD0.7 – –20 –20 – – – 5 0.7 20 23 0 –3 – – – 100 2.1 – – 2.7 – – – 320 320 – – – – – – – – <1.0 <1.0 100 50 100 11 1 30 30 – 0 – – – 475 – 165 15 2.8 90 35 5.5 430 430 1.2 1.2 4 2 8 5 – VDD0.3 20 20 – – – 19 1.3 40 37 4 3 ±15 ±5 ±5 800 – – – 2.9 – V V mΩ mΩ V V mA mA mA mA V V μA μA kΩ kΩ kΩ % μs μs μs V μA % % % ns A °C °C V mV 1For input and output current specifications, negative 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 individual units, within the specified maximum and minimum limits. 3VERR = [(VREF/8) – VSENSE] / (VREF/8). 4Overcurrent protection (OCP) is tested at TA = 25°C in a restricted range and guaranteed by characterization. Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 4

A4988 DMOS Microstepping Driver with Translator And Overcurrent Protection THERMAL CHARACTERISTICS Characteristic Package Thermal Resistance Symbol RθJA Four-layer PCB, based on JEDEC standard Test Conditions* Value Units ºC/W 32 *Additional thermal information available on Allegro Web site. Power Dissipation versus Ambient Temperature 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 ) W ( D P , n o i t a p i s s D i r e w o P 0 20 R J A = 3 2 º C/ W 40 60 100 80 120 Temperature, TA (°C) 140 160 Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 5

A4988 DMOS Microstepping Driver with Translator And Overcurrent Protection t A t B STEP MS1, MS2, MS3, RESET, or DIR t C t D Time Duration Symbol STEP minimum, HIGH pulse width STEP minimum, LOW pulse width Setup time, input change to STEP Hold time, input change to STEP tA tB tC tD Typ. 1 1 200 200 Unit μs μs ns ns Figure 1. Logic Interface Timing Diagram Table 1. Microstepping Resolution Truth Table MS1 MS2 MS3 Microstep Resolution Excitation Mode L H L H H L L H H H L L L L H Full Step Half Step Quarter Step Eighth Step Sixteenth Step 2 Phase 1-2 Phase W1-2 Phase 2W1-2 Phase 4W1-2 Phase Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 6

A4988 DMOS Microstepping Driver with Translator And Overcurrent Protection Functional Description Functional Description Device Operation. The A4988 is a complete microstepping motor driver with a built-in translator for easy operation with minimal control lines. It is designed to operate bipolar stepper motors in full-, half-, quarter-, eighth, and sixteenth-step modes. The currents in each of the two output full-bridges and all of the N-channel DMOS FETs are regulated with fixed off-time PWM (pulse width modulated) control circuitry. At each step, the current for each full-bridge is set by the value of its external current-sense resistor (RS1 and RS2), a reference voltage (VREF), and the output voltage of its DAC (which in turn is controlled by the output of the translator). At power-on or reset, the translator sets the DACs and the phase current polarity to the initial Home state (shown in figures 8 through 12), and the current regulator to Mixed Decay Mode for both phases. When a step command signal occurs on the STEP input, the translator automatically sequences the DACs to the next level and current polarity. (See table 2 for the current-level sequence.) The microstep resolution is set by the combined effect of the MSx inputs, as shown in table 1. When stepping, if the new output levels of the DACs are lower than their previous output levels, then the decay mode for the active full-bridge is set to Mixed. If the new output levels of the DACs are higher than or equal to their previous levels, then the decay mode for the active full-bridge is set to Slow. This auto- matic current decay selection improves microstepping perfor- mance by reducing the distortion of the current waveform that results from the back EMF of the motor. Microstep Select (MSx). The microstep resolution is set by the voltage on logic inputs MSx, as shown in table 1. The MS1 and MS3 pins have a 100 kΩ pull-down resistance, and the MS2 pin has a 50 kΩ pull-down resistance. When changing the step mode the change does not take effect until the next STEP rising edge. If the step mode is changed without a translator reset, and abso- lute position must be maintained, it is important to change the step mode at a step position that is common to both step modes in order to avoid missing steps. When the device is powered down, or reset due to TSD or an over current event the translator is set to the home position which is by default common to all step modes. Mixed Decay Operation. The bridge operates in Mixed decay mode, at power-on and reset, and during normal running according to the ROSC configuration and the step sequence, as shown in figures 8 through 12. During Mixed decay, when the trip point is reached, the A4988 initially goes into a fast decay mode for 31.25% of the off-time, tOFF . After that, it switches to Slow decay mode for the remainder of tOFF. A timing diagram for this feature appears on the next page. Typically, mixed decay is only necessary when the current in the winding is going from a higher value to a lower value as determined by the state of the translator. For most loads automatically-selected mixed decay is convenient because it minimizes ripple when the current is rising and prevents missed steps when the current is falling. For some applications where microstepping at very low speeds is necessary, the lack of back EMF in the winding causes the current to increase in the load quickly, resulting in missed steps. This is shown in figure 2. By pulling the ROSC pin to ground, mixed decay is set to be active 100% of the time, for both rising and falling currents, and prevents missed steps as shown in figure 3. If this is not an issue, it is recommended that automatically-selected mixed decay be used, because it will produce reduced ripple currents. Refer to the Fixed Off-Time section for details. Low Current Microstepping. Intended for applications where the minimum on-time prevents the output current from regulating to the programmed current level at low current steps. To prevent this, the device can be set to operate in Mixed decay mode on both rising and falling portions of the current waveform. This feature is implemented by shorting the ROSC pin to ground. In this state, the off-time is internally set to 30 μs. Reset Input (¯R¯ ¯E¯ ¯S¯ ¯E¯ ¯T¯ ). The ¯R¯ ¯E¯ ¯S¯ ¯E¯ ¯T¯ input sets the translator to a predefined Home state (shown in figures 8 through 12), and turns off all of the FET outputs. All STEP inputs are ignored until the ¯R¯ ¯E¯ ¯S¯ ¯E¯ ¯T¯ input is set to high. Step Input (STEP). A low-to-high transition on the STEP input sequences the translator and advances the motor one incre- ment. The translator controls the input to the DACs and the direc- Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 7

A4988 DMOS Microstepping Driver with Translator And Overcurrent Protection Slow Decay Mixed Decay Slow Decay Mixed Decay Slow Decay Mixed Decay Slow Decay Mixed Decay Missed Step Voltage on ROSC terminal 2 V/div. Step input 10 V/div. t → , 1 s/div. Figure 2. Missed steps in low-speed microstepping ILOAD 500 mA/div. Mixed Decay No Missed Steps Step input 10 V/div. t → , 1 s/div. Figure 3. Continuous stepping using automatically-selected mixed stepping (ROSC pin grounded) Allegro MicroSystems, LLC 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 8

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A4988-Datasheet.pdf

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