My question is about the shutdown mode on these power amplifiers. Power down or power off? Why would want or need to use this shutdown feature as opposed to just cutting the power?
The data sheet (I copied from TI's Lm4871) says, "
To conserve power in portable applications, the LM4871's micropower shutdown mode (IQ = 0.6µA,
typ) is activated when VDD is applied to the SHUTDOWN pin."
Circuit from LM4871 datasheet

 

The reasons for using a device shutdown input instead of switching the power are several. First, there would need to be a switching device able to carry the load current of the controlled device, which may be a fair amount. Second, the bypassing and filtering would need to be more distant from the controlled device, and third, the control logic may be switching the controlled device on and off much more rapidly than a higher powered switch can even operate. And in addition, the capacitors associated with the controlled device may cause problems during the switch-on and switch-off sequences. There are probably additional considerations that I did not mention. So you see it is far more than just connecting and disconnecting the power.

 

The reasons for using a device shutdown input instead of switching the power are several. First, there would need to be a switching device able to carry the load current of the controlled device, which may be a fair amount. Second, the bypassing and filtering would need to be more distant from the controlled device, and third, the control logic may be switching the controlled device on and off much more rapidly than a higher powered switch can even operate. And in addition, the capacitors associated with the controlled device may cause problems during the switch-on and switch-off sequences. There are probably additional considerations that I did not mention. So you see it is far more than just connecting and disconnecting the power.

In the above schematic, if the circuit was not part of a larger circuit, what would YOU use the shutoff for? Could I never turn this circuit off safely?

 

Ihe circuit can certainly be switched off safely, the shutdown is provided for the use when the amplifier is a part of a larger system and not needed all of the time. It may also prevent speaker thump, which is often a concern in higher powered systems.

 

Thanks, MisterBill2.