Patent ID: 8139433

Claim:
Apparatus comprising a memory controller for controlling a memory device having a clock enable (CKE) input, the memory controller comprising: first circuitry adapted to apply a first CKE signal to the CKE input during a normal operating mode; and second circuitry adapted to apply a second CKE signal to the CKE input during a self-refresh operating mode, wherein, during the self-refresh operating mode: the first circuitry is powered off; and the second circuitry is powered on to drive the second CKE signal to a self-refresh signal level for the memory device, wherein: the first circuitry comprises (i) a first output buffer connected to drive the first CKE signal to the CKE input and (ii) first logic circuitry connected to control operations of the first output buffer; the second circuitry comprises (i) a second output buffer connected to drive the second CKE signal to the CKE input and (ii) second logic circuitry connected to control operations of the second output buffer; and the memory controller is adapted to support a power-down transition from the normal operating mode to the self-refresh operating mode, wherein: before the power-down transition: the first circuitry is powered on; the first logic circuitry controls the first output buffer to drive the CKE input for the normal operating mode; and the second output buffer is disabled; during the power-down transition: (1) the first logic circuitry controls the first output buffer to drive the CKE input to the self-refresh signal level; (2) the second logic circuitry then enables and controls the second output buffer to drive the CKE input to the self-refresh signal level in parallel with the first output buffer driving the CKE input to the self-refresh signal level; and (3) the first circuitry is then powered down; and after the power-down transition: the first circuitry is powered off; the second circuitry is powered on; and the second logic circuitry controls the second output buffer to drive the CKE input to the self-refresh signal level.