There are provided a DC/DC converter control circuit and a DC/DC converter
system having high degree of freedom of mounting and achieving the
following matters: (1) housing a DC/DC converter control circuit in a
package miniaturized by reducing the number of terminals; and (2)
starting-up a power saving mode in response to an input of an external
control signal to a DC/DC converter system. A frequency setting terminal
(RT) is connected to a resistance element RT and a switching section 1 in
series, between the terminal and ground voltage. An external control
signal CTL is inputted to the switching section 1. When an external
control signal CTL turns off the switching section 1, connection to the
ground voltage is opened and an oscillation driving section 4 does not
operate. Thereby, power saving mode is kept. When the switching section 1
is turned on, connection to the ground voltage is closed and the
oscillation driving section 4 starts up. Subsequently, a bias control
section 5 starts up and bias condition toward the resistance element RT is
controlled. Thereby oscillation frequencies approximate to a setting
value. Control of power saving mode can be thus carried out without a
dedicated terminal for an external control signal CTL.
