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參數(shù)資料
| 型號(hào)： | A3933SEQ |
| 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)： | 8/12頁 |
| 文件大?。?/td> | 168K |
| 代理商： | A3933SEQ |
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
3933
THREE-PHASE POWER
MOSFET CONTROLLER
Applications Information
bootstrap capacitor. When the bootstrap capacitor has been
properly charged, the high side is turned back ON. The circuit
will allow three faults of this type within one commutation
cycle before signaling a fault and coast the motor (all gate
outputs go low).
2)
Bootstrap Monitor.
The bootstrap capacitor is charged
whenever a sink-side MOSFET is ON, Sx output goes low, and
the load current recirculates. This happens constantly during
normal operation. A 60
μ
s timer is started at the beginning of
this cycle and the capacitor is charged with typically 100 mA.
The bootstrap capacitor voltage is clamped at approximately
87% of V
CCOUT
. If the capacitor is not charged to the clamp
voltage in 60
μ
s, a fault is signaled and the motor will coast.
3)
Undervoltage.
The internal V
CCOUT
regulator supplies the
low-side gate driver and the bootstrap charge current. It is
critical to ensure that the voltages are at a proper level before
enabling any of the outputs. The undervoltage circuit is active
during power up and will force a motor coast condition until
V
CCOUT
is greater than approximately 10 V.
4)
Hall Invalid.
Illegal codes for the HALL inputs (000 or
111) will force a fault and coast the motor.
Faults are cleared at the beginning of each commutation. If a
stalled motor results from a fault, the fault can only be cleared
by toggling the RESET terminal or by a power-up sequence.
Current Control.
Internal fixed off-time PWM circuitry is
implemented to limit load current to a desired value. The
external sense resistor combined with the applied analog
voltage to REF terminal will set the peak current level
approximately
I
TRIP
≈
V
REF
/R
S
.
After the peak level is reached, the sense comparator trips and
the load current will decay for a fixed off time.
An external resistor (R
T
) and capacitor (C
T
) are used to set the
fixed off-time period (t
off
= R
T
x C
T
). The t
off
should be in the
range of 10
μ
s to 50
μ
s. Longer values for t
off
can result in
audible noise problems.
Torque control can be implemented by varying the REF input
voltage as long as the PWM input stays high. If direct control
of the torque/current is desired by PWM input, a voltage can be
applied to the REF input to set an absolute maximum current
limit.
Bootstrap Capacitor Selection.
The high-side bootstrap
circuit operates on a charge-transfer principle. The gate charge
(Q
g
) specification of the external power MOSFET must be
taken into consideration. The bootstrap capacitor must be large
enough to turn on the MOSFET without losing significant gate
voltage. If the bootstrap capacitor is too large, it would take too
long to charge up during the off portion of the PWM cycle. The
capacitor value must be selected with both of these constraints
in mind.
1)
Minimum bootstrap capacitor value to transfer charge. The
charge on the bootstrap capacitor should be 20x greater than the
gate charge (Q
g
) of the power MOSFET.
Example: For Q
g
= 0.025
μ
C, select
C
boot
= 20 x Q
g
/10.5 V = 0.047
μ
F.
Check for maximum V
g
drop at turn on: dq = C
boot
x dV
g
, where
Q
g
= dq.
dV
g
= dq/C
boot
= 0.025
μ
C/0.047
μ
F = 532 mV.
2) Calculate minimum PWM “OFF” cycle with C
boot
= 0.047
μ
F.
dt = r
o
x C
boot
x ln(0.036/[Q
g
/C
boot
+ 0.036])
where r
o
= 20 ohms, the equivalent internal series resistance of
the bootstrap capacitor monitor circuit.
The sink-side MOSFET will be held OFF for this minimum
time such that the bootstrap capacitor can be recharged
independently of the PWM input frequency.
The above equation is valid for PWM cycles after the bootstrap
capacitor has been charged once. For the first cycle after a
motor phase commutates from Hi-Z to GHx ON, or during the
first charging cycle at power-up, the circuit will ignore PWM
signals until it has been charged.
The time required to charge up at power up and at commutation
change is approximately:
t = C
boot
x 7 V/0.1 A
Protection Circuitry.
The A3933 will protect the external
MOSFETs by shutting down the gate drive if any of the
following conditions are detected:
1)
Gate Source Monitor (high side only).
The voltage on
the GHx terminals must stay 7 V higher than the source. If this
voltage droops below the threshold, the high side turns OFF,
and the low-side gate will turn ON in an attempt to recharge the
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