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| 型号： | A4975SB-T |
| 厂商： | Allegro Microsystems Inc |
| 文件页数： | 8/13页 |
| 文件大小： | 0K |
| 描述： | IC PWM MICROSTEP DVR FULL 16DIP |
| 特色产品： | A4975 Microstepping Drivers |
| 标准包装： | 7,500 |
| 应用： | PWM 电机驱动器，步进电机驱动器 |
| 输出数： | 1 |
| 电流 - 输出： | 1.5A |
| 电压 - 负载： | 5 V ~ 50 V |
| 电源电压： | 4.5 V ~ 5.5 V |
| 工作温度： | -20°C ~ 85°C |
| 安装类型： | 通孔 |
| 封装/外壳： | 16-DIP（0.300"，7.62mm） |
| 供应商设备封装： | 16-DIP |
| 包装： | 管件 |
| 其它名称： | 620-1435-5 A4975SB-T-ND |
A4975
Full-Bridge PWM Microstepping Motor Driver
Mixed Current-Decay Mode . If V PFD is between 1.1 V
and 3.1 V, the device will be in a mixed current-decay mode.
Mixed-decay mode allows the user to achieve good current
regulation with a minimum amount of ripple current and
motor/driver losses by selecting the minimum percentage of fast
decay required for their application (see also the Stepper Motor
Applications section).
As in fast current-decay mode, mixed-decay starts with the
sink and source drivers disabled and the opposite pair turned
on after the load current reaches I TRIP . When the voltage at the
RC terminal decays to a value below V PFD , the sink drivers are
re-enabled, placing the device in slow current-decay mode for
the remainder of the ? xed off-time ( ? gure 2). The percentage
of fast decay (PFD) is user determined by V PFD or two external
resistors.
PFD = 100 ln (0.6[R 1 +R 2 ]/R 2 )
again. The PWM cycle repeats, maintaining the peak load current
at the desired value.
With increasing values of t OFF, switching losses will decrease,
low-level load-current regulation will improve, EMI will be
reduced, the PWM frequency will decrease, and ripple current
will increase. A value of t OFF can be chosen for optimization
of these parameters. For applications where audible noise is a
concern, typical values of t OFF are chosen to be in the range of
15 to 35 μ s.
RC Blanking. In addition to determining the ? xed off-time of
the PWM control circuit, the C T component sets the comparator
blanking time. This function blanks the output of the current-
sense comparator when the outputs are switched by the internal
current-control circuitry (or by the PHASE input, or when the
device is enabled with the DAC data inputs). The comparator
output is blanked to prevent false over-current detections due to
V
where:
CC
R1
R2
PFD
reverse recovery currents of the clamp diodes, and/or switching
transients related to distributed capacitance in the load.
During internal PWM operation, at the end of the t OFF time, the
comparator ’s output is blanked and C T begins to be charged
from approximately 0.22V CC by an internal current source of
approximately 1 mA. The comparator output remains blanked
until the voltage on C T reaches approximately 0.6V CC . The
blanking time, t BLANK , can be calculated as:
t BLANK = R T C T ln (R T /[R T – 3 k Ω ]).
Dwg. EP-062-1
Fixed Off-Time. The internal PWM current-control circuitry
uses a one shot to control the time the driver(s) remain(s) off.
The one-shot off-time, t OFF , is determined by the selection of
an external resistor (R T ) and capacitor (C T ) connected from the
RC timing terminal to ground. The off-time, over a range of
values of C T = 470 pF to 1500 pF and R T = 12 k Ω to 100 k Ω , is
approximated by:
t OFF ≈ R T C T .
When the load current is increasing, but has not yet reached the
sense-current comparator threshold (I TRIP ), the voltage on the
RC terminal is approximately 0.6V CC . When I TRIP is reached,
the PWM latch is reset by the current-sense comparator and
the voltage on the RC terminal will decay until it reaches
approximately 0.22V CC . The PWM latch is then set, thereby
re-enabling the driver(s) and allowing load current to increase
When a transition of the PHASE input occurs, C T is discharged
to near ground during the crossover delay time (the crossover
delay time is present to prevent simultaneous conduction of
the source and sink drivers). After the crossover delay, C T is
charged by an internal current source of approximately 1 mA.
The comparator output remains blanked until the voltage on C T
reaches approximately 0.6V CC .
Similarly, when the device is disabled, via the DAC data inputs,
C T is discharged to near ground. When the device is re-enabled,
C T is charged by an internal current source of approximately 1
mA. The comparator output remains blanked until the voltage on
C T reaches approximately 0.6V CC . The blanking time, t BLANK ,
can be calculated as:
t BLANK = R T C T ln ([R T - 1.1 k Ω ]/R T - 3 k Ω ).
The minimum recommended value for C T is 470 pF ± 5 %.
This value ensures that the blanking time is suf ? cient to avoid
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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