Protecting the power supply from drawing higher
current or potential voltage overshoots is
important in battery operated applications or
applications that do not have an internal
overcurrent or overvoltage protection built into
the power supply.
- When the load on the motor increases, the
device draws higher current from the power supply.
To limit the current drawn from the power supply,
enable bus current limit
[BUS_CURRENT_LIMIT_ENABLE] and configure the bus
current limit [BUS_CURRENT_LIMIT] to protect the
power supply from drawing higher current.
For
example, limiting the current drawn from power
supplies such as batteries is required because the
battery life depends on the charge and discharge
cycles. Enabling the bus current limit limits the
power supply current by limiting the speed of the
motor.
- When a command is issued for the motor to
decelerate, based on the deceleration rate, energy
from the motor can be pumped back to the power
supply, increasing the supply voltage to levels
that are possibly unsafe for electronics. Enable
the antivoltage surge [AVS] to protect the power
supply from voltage overshoots that override any
deceleration limit set by any other register and
automatically apply a safe deceleration rate.
Figure 7-2 shows overshoot in power supply voltage when
AVS is disabled. Motor decelerates from 100% duty
cycle to 10% duty cycle at a deceleration rate of
70000Hz/s. Figure 7-3 shows no overshoot in power supply voltage when
AVS is enabled.
Figure 7-2 Power Supply Voltage and Phase Current Waveform
When AVS is Disabled Figure 7-3 Power Supply Voltage and Phase Current Waveform
When AVS is Enabled