The SMBus interface uses Write Word protocol to setup the registers and to turn the DC/DC converters on or off. Read Word protocol is used to verify register contents and to return the On/Off status of the converters. The LTC1699-80, LTC1699-81 and LTC1699-82 incorporate safeguards against errors due to bus conflicts. Three open-drain N-channel outputs (CPU_ON, IO_ON and CLK_ON) are provided to turn DC/DC converter supplies on or off via their RUN/SS inputs. A global control pin, VRON is used to turn the converters on or off simultaneously. An internal timer pulls the PGOOD pin low for 50s if the divider setting changes or the converters are turned on via the SMBus and the VRON pin.