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| 型号： | A8904SLP-T |
| 元件分类： | 运动控制电子 |
| 英文描述： | BRUSHLESS DC MOTOR CONTROLLER, 1.4 A, PDSO28 |
| 封装： | 1.20 MM HEIGHT, LEAD FREE, TSSOP-28 |
| 文件页数： | 7/18页 |
| 文件大小： | 736K |
| 代理商： | A8904SLP-T |
3-Phase Brushless DC Motor Controller/Driver
with Back EMF Sensing
A8904
15
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Braking.
A dynamic braking feature of the A8904 shorts
the three motor windings to ground. This is accomplished by
turning the three source drivers OFF and the three sink drivers
ON. Activation of the brake can be implemented through the
BRAKE input or through the D2 bit in the serial port.
During braking, the motor is effectively acting as three
sine-wave voltage generators, 120° out of phase, where the
voltage developed by each of the windings is proportional to the
motor speed and constant. The current through any sink driver is
simply the generated voltage divided by the center tap to OUT
resistance plus the sink driver resistance. As the motor tends to
slow during the braking process, both the generated voltage and
the corresponding current decreases.
When selecting a motor to use where braking will be ap-
plied, it is important to characterize the application to ensure
that when braking is applied, the peak current in the sink drivers
does not exceed 3A and the period from the peak current to the
maximum current limit of the drivers does not exceed 800 ms.
Another consideration is the thermals of the solution, where
repeated spin-up followed by brake cycles could cause excessive
junction temperatures.
The supply voltage for the brake circuit is derived from the
charge pump supply capacitor, CRES. With CRES chosen to be
220 nF, the brake circuit will function for at least 100 ms after a
power failure.
In certain applications such as disk drives, it is desirable to
include a brake delay to allow sensitive circuitry such as the disk
head to retract before activating the spindle motor brake. The
brake delay can be simply implemented by using an external RC
and diode to control the brake terminal.
The brake delay can be set using the equation:
tBRK = –RBCB x ln (VBRK / [VFAULT – VD]).
Once the brake is activated, the three sink drivers will re-
main active until the supply rails fall below the operating range.
It is recommended that the part is reset before restarting.
Centertap.
It is recommended that the centertap connec-
tion of the motor be connected to the CENTERTAP terminal. If
the centertap of the motor is not connected to the CENTERTAP
terminal, the A8904 internally emulates the centertap voltage of
Functional Description (cont’d)
the motor through a series of 10 k
Ω resistors connected between
each output and CENTERTAP. This technique does not provide
ideal commutation points.
External component selection.
All capacitors should
be rated to at least 25 V and the dielectric should be X7R, apart
from the start-up capacitor CST, which can be Z5U dielectric
or equivalent and the input capacitor Clter, which should be an
electrolytic type of value greater than 100 μF, 35 V, Iripple > 100
mA. If the solution experiences ambient temperatures of greater
than 70°C then Clter should be rated for 105°C.
All resistors are at least 1/8 W and have a tolerance of ±5%.
In noise-sensitive systems where electromagnetic interfer-
ence is an issue, or to stabilize the current waveforms with cer-
tain motors, it may be necessary to add RC snubbers across the
motor windings as shown in the application circuit on the next
page. The A8904 solution should be relatively noise immune
from the effects of switching voltage spikes etc. if the correct
watchdog capacitor has been selected for optimum blanking and
good layout practices are implemented.
At the range of operating frequencies that the current pulses
are drawn out of the load supply, it is the capacitance reactance
as opposed to the ESR that dominates the overall impedance of
the input lter, Clter. Therefore, it is possible to reduce conduct-
ed electromagnetic emissions further, by simply increasing the
value of Clter. In extremely sensitive systems, it may be neces-
sary to introduce a differential mode inductor in series with the
load supply line.
Layout considerations.
The TSSOP part (A8904SLP)
has three separate ground connections, analog, digital, and pow-
er that must be connected together externally. A ground plane
should be used to provide heat sinking for the power switches
and the reduction of potential noise pick-up through inductive
loops and radiated emissions. The ground plane should cover the
area beneath the A8904 and extend beyond the outline to form a
plane around all the external components. The exposed thermal
pad of the TSSOP part should be connected to the ground plane.
Filter components, especially Clter, timing, and delay
capacitors should be positioned as close as possible to the device
terminals. It is also imperative that the traces to the serial port
and oscillator are as short and as wide as possible to reduce stray
inductance and prevent potential data corruption. In addition,
these traces should be positioned well away from any noisy
signals.
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相关代理商/技术参数 |
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| A8904SLPTR | 功能描述:IC CTRLR/DRVR DC MOTOR 28TSSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 电机和风扇控制器，驱动器 系列:- 标准包装:1 系列:- 应用:直流电机驱动器，步进电机驱动器 评估套件:- 输出数:1 或 2 电流 - 输出:750mA 电压 - 负载:10 V ~ 40 V 电源电压:4.5 V ~ 5.5 V 工作温度:-20°C ~ 70°C 安装类型:表面贴装 封装/外壳:24-BFSOP（0.295"，7.50mm 宽） 供应商设备封装:24-SOP 包装:Digi-Reel® 其它名称:MTS62C19A-HS105DKR |
| A8904SLPTR-T | 功能描述:IC CTRLR/DRVR DC MOTOR 28TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 电机和风扇控制器，驱动器 系列:- 标准包装:1 系列:- 应用:直流电机驱动器，步进电机驱动器 评估套件:- 输出数:1 或 2 电流 - 输出:750mA 电压 - 负载:10 V ~ 40 V 电源电压:4.5 V ~ 5.5 V 工作温度:-20°C ~ 70°C 安装类型:表面贴装 封装/外壳:24-BFSOP（0.295"，7.50mm 宽） 供应商设备封装:24-SOP 包装:Digi-Reel® 其它名称:MTS62C19A-HS105DKR |
| A8905CLB | 制造商:ALLEGRO 制造商全称:Allegro MicroSystems 功能描述:3-PHASE BRUSHLESS DC MOTOR CONTROLLER/DRIVER WITH BACK-EMF SENSING |
| A8906CLB | 制造商:ALLEGRO 制造商全称:Allegro MicroSystems 功能描述:BIDIRECTIONAL 3-PHASE BRUSHLESS DC MOTOR CONTROLLER/DRIVER WITH BACK-EMF SENSING |
| A8909CLB | 制造商:ALLEGRO 制造商全称:Allegro MicroSystems 功能描述:3-PHASE BRUSHLESS DC MOTOR CONTROLLER/DRIVER WITH BACK-EMF SENSING AND POWER DMOS OUTPUTS |
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