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L6480 Stepper Motor Power Supplies Question

Question asked by Jensen.Brad on Feb 21, 2017
Latest reply on Mar 2, 2017 by Enrico Poli



I am looking at using the L6480 in the externally supplied modes, where my system will be supplying:
VS = +24V DC




The +24V supplied to VS by the system is removed (floating) during an emergency stop condition.


Can the L6480 handle this situation where VS and thus VBOOT is removed, but the other rails are still supplied with the +12V and +3.3V respectively?


On page 34 of the data sheet there is a note that states "VSREG must be always less than VBOOT in order to avoid related ESD protection diode turnon"



When VS is removed due to an emergency stop condition, VSREG will be +12V greater than VBOOT (floating), causing the internal protection diode turnon.


It goes on to say "The device can be protected from this event by adding an external low drop diode between the VSREG and VS pins" however there is no detail of direction, rating nor if this will cause undesired operation with such a large difference in voltage.


This is where I am confused about the diode. Regarding direction, the diode would have the anode connected to VSREG and the cathode to VS.

During the emergency stop condition this would pass the +12V, less the forward voltage drop of the diode, to the VS pins and charge pump, and try to continue to power the motor from the +12V supply via the diode.


With the diode in the reversed orientation, VS less the diode forward voltage would be applied to the VSREG +12V which violates the 7.5-15V limit of VSREG.


So can I SAFELY use the L6480 without diodes when VS is removed?

Or the L6480 cannot be used in a system where VS is removed?