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參數(shù)資料
| 型號： | ML4428 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Sensorless Smart-Start BLDC PWM Motor Controller(無傳感智能啟動無刷直流PWM電機控制器) |
| 中文描述： | 智能傳感器啟動無刷電機控制器的PWM（無傳感智能啟動無刷直流脈寬調(diào)制電機控制器） |
| 文件頁數(shù)： | 7/16頁 |
| 文件大小： | 151K |
| 代理商： | ML4428 |
ML4428
REV. 1.0 11/17/2000
7
RES1, RES2 and RES3
Operating motors at greater than 12V requires attenuation
resistors in series with the sense inputs (PHI1, PHI2, PHI3)
to keep the voltage less than 12V. The phase sense input
impedance is 8700y. This requires the external resistor to
be set as follows and results in the given attenuation.
RES1 = RES2 = RES3
RESI = 725 (V
MOTOR
– 10)
Atten
RES
=
2900
1 8700
A larger value for RES1 may be required if the peak motor
phase voltage exceds V
MOTOR
.
ISENSE FILTER
The I
SENSE
filter consists of an RC lowpass filter in series
with the current sense signal. The purpose of this filter is to
filter out noise spikes on the current, which may cause false
triggering of the one shot circuit. It is important that this
filter not slow down the current feedback loop, or
destruction of the output stage may result. The
recommended values for this circuit are R = 1Ky and C=
300pF. This gives a time constant of 300ns, and will filter
out spikes of shorter duration. These values should suffice for
most applications. If excessive noise is present on the
I
SENSE
pin, the capacitor may be increased at the expense
of speed of current loop response. The filter time constant
should not exceed 500ns or it will have a significant impact
on the response speed of the one shot current limit.
CIOS
The one shot capacitor determines the off time after the
current limit is activated, i.e. the voltage on the I
SENSE
pin exceeded 0.5V. The following formula ensures that the
motor current is stable in current limit:
C
V
IOS MAX
(
MOTOR
)
.
=
×
1 11 10
11
CIOS is in Farads
This is the maximum value that C
IOS
should be. Higher
average torque during the current limit cycle can be
achieved by reducing this value experimentally, while
monitoring the motor current carefully, to be sure that a
runaway condition does not occur. This runaway condition
occurs when the current gained during the on time
exceeds the current lost during the off time, causing the
motor current to increase until damage occurs. For most
motors this will not occur, as it is usually a self limiting
phenomenon. (See Figure 7)
Component Selection Guide
In order to properly select the critical components for the
ML4428 you should know the following things:
1. The motor operating voltage, V
MOTOR
(V).
2. The maximum operating current for the motor,
I
MAX
(A).
3. The number of poles the motor has, N.
4. The back-EMF constant of the motor, K
e
(V
∞
s/rad).
5. The torque constant of the motor, K
e
(N
∞
m/A). (This
is the same as the back-EMF constant, only in
different units.)
6. The maximum desired speed of operation, RPM
MAX
(rpm).
7. Line to line resistance, R
L-L
(Ohms).
8. Line to line inductance, L
L-L
(Henries).
9. The motor should have at least 15% line-to-line
inductance variation during rotation for proper start-
up sensing. (Air core motors will not run using the
ML4428.) Examine the motor to determine if there is
any iron in the core. If the stator coils are not wound
around an iron form, the ML4425 or ML4426 may be
a better choice.
If you do not know one or more of the above values, it is
still possible to pick components for the ML4428, but some
experimentation may be necessary to determine the
optimal value. All quantities are in SI units unless other
wise specified. The formulas in the following section are
based on linear system models. The following formulas
should be considered a starting point from which you can
optimize your application.
Note: Refer to Application Note 43 for details on loop
compensation.
RSENSE
The function of R
SENSE
is to provide a voltage
proportional to the motor current, for current limit/
feedback purposes. The trip voltage across R
SENSE
is 0.5V
so:
R
I
SENSE
MAX
=
0 5
Imax is the maximum motor current.
The power dissipation in the resistor is I
MAX
squared times
R
SENSE
, so the resistor should be sized appropriately. For
very high current motors, a smaller resistor can be used,
with an op-amp to increase the gain, so that power
dissipation in the sense resistor is minimized.
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| ML4428直流電機控制芯片 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述: |
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