NEGATIVE CURRENT PROTECTION SYSTEM FOR LOW SIDE SWITCHING CONVERTER FET

摘要

A negative current protection system for a low side switching converter FET, for use with a switching converter arranged to operate high and low side FETs connected to an output inductor to produce an output voltage. The negative current protection system comprises a current sensing circuit which produces an output Vcs that varies with the current in the high side FET, a negative current threshold generator which produces a threshold signal −Ith which represents the maximum negative current to which the low side FET is to be subjected, and a comparison circuit arranged to compare the valley portion of Vcs and −Ith and to set a flag if Vcs<−Ith at a predetermined time in the switching cycle—typically after the converter's blanking time. When the flag is set, the system preferably responds by adjusting the operation of the switching FETs to reduce the negative current.

主权项

1. A system for protecting the low side switching element of a switching converter arranged to operate high and low side switching elements connected to an output inductor using a switching cycle having associated ‘on’ and ‘off’ times to produce an output voltage, said system comprising:
a current sensing circuit arranged to produce an output which varies with the current in said high side switching element; a negative current threshold generator arranged to produce a first threshold signal which represents the maximum negative current to which said low side switching element is to be subjected; and a comparison circuit arranged to compare the valley portion of said current sensing circuit output and said first threshold signal and to set a ‘maximum negative current limit exceeded’ flag if said current sensing circuit output is below said first threshold signal at a predetermined time in said switching cycle.