A group select matrix is added to an implantable stimulator device to allow current sources to be dedicated to particular groups of electrodes at a given time. The group select matrix can time multiplex the current sources to the different groups of electrodes to allow therapy pulses to be delivered at the various groups of electrodes in an interleaved fashion. Each of the groups of electrodes may be confined to a particular electrode array implantable at a particular non-overlapping location in a patients body. A switch matrix can be used in conjunction with the group select matrix to provide further flexibility to couple the current sources to any of the electrodes.
