參數(shù)資料
型號(hào): 55VDMOSFULL-BRIDGEMOTORDRIVER
英文描述: (647.67 k)
中文描述: (647.67十一)
文件頁(yè)數(shù): 9/18頁(yè)
文件大?。?/td> 647K
代理商: 55VDMOSFULL-BRIDGEMOTORDRIVER
Applications Information
POWER SUPPLY BYPASSING
Step changes in current drawn from the power supply occur
repeatedly during normal operation and may cause large
voltage spikes across inductance in the power supply line.
Care must be taken to limit voltage spikes at V
to less than
the 60V Absolute Maximum Rating. At a change in the direc-
tion of the load current, the initial load current tends to raise
the voltage at the power supply rail (Figure 3) again. Current
transients caused by the reverse recovery of the clamp di-
odes tend to pull down the voltage at the power supply rail.
Bypassing the power supply line at V
is required to protect
the device and minimize the adverse effects of normal op-
eration on the power supply rail. Using both a 1 μF high fre-
quency ceramic capacitor and a large-value aluminum elec-
trolytic capacitor is highly recommended. A value of 100 μF
per ampere of load current usually suffices for the aluminum
electrolytic capacitor. Both capacitors should have short
leads and be located within one half inch of V
CC
.
OVERCURRENT PROTECTION
If the forward current in either source switch exceeds a 12A
threshold, internal circuitry disables both source switches,
forcing a rapid decay of the fault current (Figure 5). Approxi-
mately 3 μs after the fault current reaches zero, the device
restarts.Automatic restart allows an immediate return to nor-
mal operation once the fault condition has been removed. If
the fault persists, the device will begin cycling into and out of
thermal shutdown. Switching large fault currents may cause
potentially destructive voltage spikes across inductance in
the power supply line; therefore, the power supply line must
be properly bypassed at V
for the motor driver to survive
an extended overcurrent fault.
In the case of a locked rotor, the inductance of the winding
tends to limit the rate of change of the fault current to a value
easily handled by the protection circuitry. In the case of a low
inductance short from either output to ground or between
outputs, the fault current could surge past the 12A shutdown
threshold, forcing the device to dissipate a substantial
amount of power for the brief period required to disable the
source switches. Because the fault power must be dissi-
pated by only one source switch, a short from output to
ground represents the worst case fault. Any overcurrent fault
is potentially destructive, especially while operating with high
supply voltages (
30V), so precautions are in order. Sinking
V
for heat with 1 square inch of 1 ounce copper on the
printed circuit board is highly recommended. The sink
switches are not internally protected against shorts to V
CC
.
THERMAL SHUTDOWN
Internal circuitry senses the junction temperature near the
power bridge and disables the bridge if the junction tempera-
ture exceeds about 155C. When the junction temperature
cools past the shutdown threshold (lowered by a slight hys-
teresis), the device automatically restarts.
UNDERVOLTAGE LOCKOUT
Internal circuitry disables the power bridge if the power sup-
ply voltage drops below a rough threshold between 8V and
5V. Should the power supply voltage then exceed the thresh-
old, the device automatically restarts.
The Typical Application
Figure 6 shows the typical application, the power stage of a
chopper drive for bipolar stepper motors. The 20 k
resistor
and 2.2 nF capacitor connected between RC and ground set
the off-time at about 48 μs, and the 20 k
resistor connected
between CS OUT and ground sets the gain at about 200 mA
per volt of the threshold for chopping. Digital signals control
the thresholds for chopping, the directions of the winding
currents, and, by extension, the drive type (full step, half
step, etc.). A μprocessor or μcontroller usually provides the
digital control signals.
DS011878-15
Trace: Fault Current at 5A/div
Horizontal: 20 μs/div
FIGURE 5. Fault Current with V
CC
= 30V, OUT 1 Shorted to OUT 2, and CS OUT Grounded
9
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