7.3.5 Current Limit

A current limit circuit is provided to protect the system in the event of an overcurrent condition, such as what would be encountered if driving a DC motor at start-up or with an abnormal mechanical load (stall condition).

The motor current is sensed by monitoring the voltage across an external sense resistor. When the voltage exceeds a reference voltage of 200 mV for more than approximately 3 µs, the PWM duty cycle is reduced to limit the current through the motor to this value. This current limit allows for starting the motor while controlling the current.

If the current limit condition persists for some time, it is likely that a fault condition has been encountered, such as the motor being run into a stop or a stalled condition. An overcurrent event must persist for approximately
275 ms before the fault is registered. After approximately 275 ms, a fault signaled to the host by driving the FAULTn signal low. Operation of the motor driver will continue.

The current limit fault condition is self-clearing and will be released when the abnormal load (stall condition) is removed.

The resistor used to set the current limit must be less than 1 Ω. Its value may be calculated as follows:

Equation 1.

where

• R_ISENSE is the current sense resistor value
• I_LIMIT is the desired current limit (in mA)

If the current limit feature is not needed, the ISENSE pin may be directly connected to ground.