Smart shutdown function

L6491

16/24

DocID024832 Rev 1

In common overcurrent protection architectures, the comparator output is usually connected

to the SD input and an RC network is connected to this SD/OD line in order to provide

a monostable circuit, which implements a protection time following the fault condition.

Differently from the common fault detection systems, the L6491 smart shutdown

architecture allows immediate turn-off of the output gate driver in case of fault, by minimizing

the propagation delay between the fault detection event and the current output switch-off. In

fact the time delay between the fault and the output turn-off is no longer dependent on the

RC value of the external network connected to the SD/OD pin. In the smart shutdown

circuitry, the fault signal has a preferential path which directly switches off the outputs after

the comparator triggering. At the same time, the internal logic turns on the open-drain output

such threshold is reached, the open-drain output is turned off, allowing the external pull-up

to recharge the capacitor. The driver outputs restart following the input pins as soon as the

voltage at the SD/OD pin reaches the higher threshold of the SD logic input. The smart

shutdown system gives the possibility to increase the time constant of the external RC

network (that determines the disable time after the fault event) up to very large values

without increasing the delay time of the protection.

Any external signal provided to the SD pin is not latched and can be used as control signal

in order to perform, for instance, PWM chopping through this pin. In fact when a PWM signal

is applied to the SD input and the logic inputs of the gate driver are stable, the outputs

switch from the low level to the state defined by the logic inputs and vice versa.