A3984: 带转换器的 DMOS 微步驱动器

A3984 是一款完全的微步电动机驱动器,带有内置转换器,易于操作。该产品可在完整、1/2、1/4 及 1/16 步进模式时操作双极步进电动机,输出驱动性能为 35 伏特及 ± 2 安培。A3984 包括一个固定停机时间电流稳压器,该稳压器可在慢或混合衰减模式下操作。

转换器是 A3984 易于实施的关键。只要在“步进”输入中输入一个脉冲,即可驱动电动机产生微步。该程序中没有相位顺序表、高频率控制行或复杂的界面。A3984 界面非常适合复杂的微处理器不可用或过载的应用。

A3984 内的斩波控制可自动选择电流衰减模式(慢或混合)。当一个信号出现在“步进”输入引脚处,A3984 会确定该步进是否会在每个电动机相位中产生较高或较低的电流。如果电荷产生较高的电流,则将该衰减模式设置为“慢”衰减。如果电荷产生较低的电流,则电流衰减设置成混合(开始对周期达到固定停机时间的 31.25% 设置为快速衰减,然后将截止剩余周期设置为慢衰减。)此电流衰减控制方案能减少可听到的电动机噪音、增加步进精确度并减少功率耗散。

内部同步整流控制电路用来改善脉宽调制 (PWM) 操作时的功率消耗。

内部电路保护包括:因滞后引起的过热关机、欠压锁定 (UVLO) 及交叉电流保护。不需要特别的通电排序。

A3984 采用低厚度(1.2 毫米,最大值)、带外露隔热盘(封装 LP)的 24 引脚 TSSOP 封装。该产品也是无铅版本(后缀为–T),且引脚框采用 100% 雾锡电镀。

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样品和购买

Astrorep Inc. (Allegro and Sanken Semiconductors, Sanken Power Supplies)
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  • 小型 24 个引脚 TSSOP 封装(7.8 x 4.4 x 1.2 毫米)
    与我们最接近的竞争者的 PC 主板空间的三分之一相比还要少。多种应用情况下,PC 主板空间是有限的,因此越小越好。热阻:RθJA 28C/W。
  • “步进”与“方向”界面
    两个控制行与竞争器件的 8、10 或更多控制行进行比较。附加的 I/O 行可加至系统成本中。不需要整流表。客户可以转换至其他的 Allegro 步进/方向界面器件,而不需要改变软件。所有应用的共用界面。
  • 同步整流
    减少功率耗散,并无需昂贵的肖特基二极管。一般可节约 20% 的功率
  • 低 Ron DMOS 输出
    减少功率耗散。可因较低的裸片温度上升而产生较高的平均输出电流。
  • 自驱慢、快速及混合衰减
    改善微步精确度并减少可闻噪音,这是 Allegro 专有的特性。
  • 2 安培峰值输出电流
    2 安培额定值比大多数竞争对手高出 0.5 安培。可靠性设计产生额外的安全优势。
  • 至少 10 毫安睡眠模式电流
    新设计禁用时要求低电流汲取。A3983/84 的大多数双极竞争者禁用时要求 10 至 1000 倍的电流汲取。
  • 有竞争力的价格
    A3983/84 的定价可以与任何有相同输出率的步进电动机驱动器相抗衡。
 

A3984 采用低厚度(1.2 毫米,最大值)、带外露隔热盘(封装 LP)的 24 引脚 TSSOP 封装。该产品也是无铅版本(后缀为–T),且引脚框采用 100% 雾锡电镀。

LP TSSOP 24 pin

Frequently Asked Questions


Q1: Is there an application note for the A3982/83/84?

Q2: What type of microstepping can be performed with the A3982/83/84?

Q3: Are there drop-in, or pin-for-pin replacements for the A3982/83/84?

Q4: What is the advantage of having the translator and driver in one package?

Q5: Do I need pull-up/pull-down resistors on the input pins?

Q6: What type of protection features do the A3982/83/84 offer?

Q7: What is the maximum allowable motor supply voltage?

Q8: The datasheet states an output current of ±2.0 A. Is this total current for the device, or current per phase?

Q9: What type of external components are required?

Q10: What is the best way to determine a value for RS, so as not to exceed 0.5 V on the SENSE pin?

Q11: Are there any layout concerns I should be aware of?

Q12: Are the A3982/83/84 constant-current or constant-voltage controlled devices?

Q13: What is the recommended minimum copper ground plane area for reducing power dissipation at high currents?

Q14: Are there special techniques to reduce the package power dissipation when running at high currents?

Q15: Are the A3982/83/84 capable of being used in portable applications?

Q16: Can you change the step resolution while running?

Q17: What does automatic current decay mode detection/selection mean?



Q1: Is there an application note for the A3982/83/84?

At this time, no. However, there is one for the A3977, which is a similar device in the Step and Direction family. The difference would be in the output current (A3977 = 2.5 A and the 3982/83/84 = 2.0 A peaks). See application note STP01-2, "A New Microstepping Motor-Driver IC with Integrated Step & Direction Translator Interface".


Q2: What type of microstepping can be performed with the A3982/83/84?

The A3982 offers full and half step modes, the A3983 offers full, half, quarter, and eighth step modes, and the 3984 offers full, half, quarter, and sixteenth step modes.


Q3: Are there drop-in, or pin-for-pin replacements for the A3982/83/84 ?

No. The A3982/83/84 are generally a more cost-effective solution than most typical motor driver ICs. These devices, as well as the entire Step and Direction family, can replace two or more devices in many designs, thereby reducing overall system cost.


Q4: What is the advantage of having the translator and driver in one package?

The advantage of having the translator and driver in one package is minimizing the number of control lines. The A3983/83/84 can be controlled using 2 control lines: step and direction. Typical motor drivers can have as many as 6 to 8 control lines to achieve the same functionality.


Q5: Do I need pull-up/pull-down resistors on the input pins?

If the logic inputs are pulled up to VDD, it is good practice to use a 1 to 5 kΩ pull-up resistor in order to limit current to the logic inputs, should an overvoltage event occur.


Q6: What type of protection features do the A3982/83/84 offer?

  • Thermal shutdown (TSD)
  • Undervoltage lockout (UVLO)
  • Crossover current protection
  • VREG and charge pump monitors

Q7: What is the maximum allowable motor supply voltage?

35 V. This must not be exceeded under any circumstances.


Q8: The datasheet states an output current of ±2.0 A. Is this total current for the device, or current per phase?

The value ±2 A defines the maximum current that each phase of the driver can support continuously. This is independent of temperature rise.

Caution should be taken to never exceed a junction temperature of 150°C when running the device.


Q9: What type of external components are required?

The following components are required for correct operation of the A3982/83/84:

  • RSENSE1 and RSENSE2, the external sense resistors required for the PWM current control circuit. These should be noninductive type resistors. The value for RS can be calculated using the formula: ITRIP(max) = VREF / (8 x RS). When selecting a value for RS it is very important not to exceed the 0.5 V limit on the SENSE pin over the full expected current range. For very short time durations during switching, transient voltages larger than 0.5 V may be observed. Using a reasonably smaller value for RS will dissipate less power in RS and provide headroom.
  • A 0.1 µF mono/ceramic capacitor must be placed between the CP1 and CP2 pins.
  • The VREG pin should be decoupled with a 0.22 µF capacitor to ground.
  • A logic supply decoupling capacitor; a 10 µF ceramic capacitor is recommended.
  • A load supply decoupling capacitor; a value of > 47 µF electrolytic capacitor is recommended. In addition, a 0.1 µF ceramic capacitor should be placed in parallel.
  • A 0.1 µF capacitor is required on the VREF pin.

Q10: What is the best way to determine a value for Rs, so as not to exceed 0.5 V on the SENSE pin?

By using the formula:

RS = 0.5 / ITRIP(max),

where:

  • RS is the sense resistor,
  • 0.5 is the absolute maximum allowable voltage on the SENSE pin, and
  • ITRIP(max) is the maximum expected current.

This will ensure that the 0.5 V limit on the SENSE pin is never exceeded.


Q11: Are there any layout concerns I should be aware of?

Yes. The printed circuit board should use a heavy groundplane. For optimum electrical and thermal performance, the exposed pad on the underside of the device 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 singlepoint ground, known as a star ground, located very close to the device. By making the connection between the exposed thermal pad and the groundplane directly under the device, that area becomes an ideal location for a star ground point.

The two input capacitors (electrolytic and ceramic) should be placed in parallel, and as close to the device supply pins as possible. The ceramic capacitor should be closer to the pins than the bulk capacitor. 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 supporting 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 accurately measure the current in the windings.


Q12: Are the A3982/83/84 constant-current or constant-voltage controlled devices?

The A3982/83/84 provide constant-current control. Motor winding current is controlled by an internal PWM current-control circuit. Off-time is set by a resistor from the ROSC pin to ground and is defined by the formula: tOFF  = ROSC / 825. If the ROSC pin is tied directly to VDD, the off-time defaults to 30 µs.


Q13: What is the recommended minimum copper ground plane area for reducing power dissipation at high currents?

A ground plane area at least two times larger than the package outline is a good place to start. For further layout considerations, please refer to Package Thermal Characteristics.

NOTE: The datasheet also defines RθJA with various copper areas. See page 4 of the datasheet.


Q14: Are there special techniques to reduce the package power dissipation when running at high currents?

In a typical stepper-motor application, the motor driver IC is in current-decay (recirculation) mode for a higher percentage of the PWM cycle compared to the on-time. This means that most of the power dissipation is a result of the forward-voltage drop of the internal body diode of the power DMOS. However, the A3982/83/84 offers synchronous rectification (SR). This feature turns on the appropriate DMOS devices during current decay and effectively shorts out the body diodes with the low RDS(on) of the driver. The power dissipation reduction in the SR feature can eliminate the need for external Schottky diodes in most stepper-motor applications, thereby saving the cost and board space for these components. Heat sinks are also a possibility. For additional information, please refer to application note AN29504.8, Power Drive Circuits.


Q15: Are the A3982/83/84 capable of being used in portable applications?

Absolutely. The A3983/84 has Sleep mode, which minimizes power consumption when not in use. During Sleep mode, the device will only draw a maximum of 10 µA. The logic supply voltage range of 3.0 to 5.5 V makes it compatible with typical battery operated equipment.


Q16: Can you change the step resolution while running?

Yes, as long as the timing requirements are met. The easiest way to change sequencing modes, to higher or lower resolution, is to do it at the HOME position (HOME is low). Otherwise, when going from a lower resolution to a higher resolution mode (half-step to quarter-step, etc.) both sequences have identical output currents. (Both sequences fall on the same row of table 2 in the datasheet.) The translator will keep the output current levels unchanged until the next step, at which time it will begin the smaller steps.

To keep the motor moving at a constant speed while changing sequencing modes, the step frequency must be multiplied by 2, 4, or 8, depending on the modes you jump from and to. Going from a higher-resolution mode to a lower-resolution mode should only be done when both modes appear on the same row of table 2 from the datasheet (Eighth Step #5 and Full Step #1, etc.). This is only important if position must be maintained or if there is no position control loop.

It should be mentioned that changing the MSx pins at any time will not cause damage to the device. To keep the motor moving at a constant speed while changing sequencing modes, the step frequency must be divided by 2, 4, or 8, depending on the modes you jump from and to. If you go from a higher resolution mode to a lower resolution mode and do it at a position that is not a valid possibility for the lower resolution mode in table 2 of the datasheet, then the sequencer will advance to first possibility without actually changing the output currents. When the next step arrives, the device will go from the position the translator was at before the sequencing mode was changed, to the next position of the new sequencing mode. For example, with direction low, if you changed from Eighth Step mode to Full Step mode when you were at Eighth Step #2, the translator will advance to Full Step #2 (but not change the output currents). When the next step occurs, the position will go to Full Step #3. The effect would be that the motor would move by 11 eighth-steps. This would make keeping the motor at constant speed very tricky.


Q17: What does automatic current decay mode detection/selection mean?

The A3982/83/84 automatically selects the decay modes suitable for optimum performance, if the output current at the previous step was higher than the output current for the present step. If the output current at the previous step was lower than the output current for the present step, then the decay mode is fixed to slow decay (rising current, away from zero). When first powering-up the device, coming out of reset, or coming out of Sleep mode, the device sets both bridges to mixed-decay.

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功能方框图 Pinout Diagram

完整型号

型号 封装类型 温度 遵循 RoHS规范 部件 构成/RoHS 数据 评论 样品 分销商库存
A3984SLPTR-T 24-lead TSSOP -20°C to 85°C 查看数据 联系本地销售代表 检查库存
APEK3984SLP-01-T DEMO BOARD -20°C to 85°C -- 联系本地销售代表 检查库存

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