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參數(shù)資料
| 型號： | A3933 |
| 廠商： | Allegro MicroSystems, Inc. |
| 英文描述： | THREE-PHASE POWER MOSFET CONTROLLER |
| 中文描述： | 三相功率MOSFET控制器 |
| 文件頁數(shù)： | 9/12頁 |
| 文件大?。?/td> | 168K |
| 代理商： | A3933 |
3933
THREE-PHASE POWER
MOSFET CONTROLLER
www.allegromicro.com
Applications Information (cont’d)
PWM Blank.
The capacitor (C
T
) also serves as the means to
set the blank time duration. After the off time expires, the
selected gates are turned back ON. At this time, large current
transients can occur during the reverse recovery time (t
rr
) of the
intrinsic body diodes of the external MOSFETs. To prevent the
current-sense comparator from thinking the current spikes are a
real overcurrent event, the comparator is blanked:
t
blank
= 1.9 x C
T
/(1 mA-2/R
T
)
The user must ensure that C
T
is large enough to cover the
current-spike duration.
Load Current Recirculation.
If MODE has been set for
slow decay, the high-side (source) driver will turn OFF forcing
the current to recirculate through the pair of sink MOSFETs. If
MODE has been selected for fast decay, both the selected high-
and low-side gates are turned OFF, which will force the current
to recirculate through one sink MOSFET and the high-side
clamp diode. Synchronous rectification (only on the low side)
allows current to flow through the MOSFET, rather than the
clamp diode, during the decay time. This will minimize power
loss during the off period. It is important to take into account
that, when switching, the intrinsic diodes will conduct during
the adjustable deadtime.
Braking.
The A3933 will dynamically brake by forcing all
sink-side MOSFETs ON. This will effectively short out the
BEMF. During braking, the load current can be approximated
by:
I
BRAKE
= V
BEMF
/R
L
Power Loss Brake.
The BRKCAP and BRKSEL terminals
provide a power-down braking option. By applying a logic
level to input BRKSEL, the system can control if the motor is
dynamically braked or is allowed to coast during an
undervoltage event. The reservoir capacitor on the BRKCAP
terminal provides the power to hold the sink-side gates ON after
supply voltage is lost. A logic high on BRKSEL will brake the
motor, a logic low and it will coast.
Layout.
Careful consideration must be given to PCB layout
when designing high-frequency, fast-switching, high-current
circuits.
1)
The analog ground (AGND), the power ground (PGND),
and the high-current return of the external MOSFETs (the
negative side of the sense resistor) should return separately to
the negative side of the motor supply filtering capacitor. This
will minimize the effect of switching noise on the device logic
and analog reference.
2)
Minimize stray inductances by using short, wide copper
runs at the drain and source terminals of all power MOSFETs.
This includes motor lead connections, the input power buss, and
the common source of the low-side power MOSFETs. This will
minimize voltages induced by fast switching of large load
currents.
3)
Kelvin connect the SENSE terminal PC trace to the
positive side of the sense resistor.
Dwg. EP-006-50
RS
BB
V
DRIVE CURRENT
RECIRCULATION
(SLOW-DECAY MODE)
RECIRCULATION
(FAST-DECAY MODE)
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相關代理商/技術參數(shù) |
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|---|---|
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| A3934-2000T | 制造商:3M 制造商全稱:3M Electronics 功能描述:100 x 100, PCB Two Row |
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