Data Sheet

AN1012 Supervisor products
Doc ID 6395 Rev 4 19/33
6 Supervisor products
STMicroelectronics also has a family of ZEROPOWER
®
and TIMEKEEPER
®
supervisor
devices. Supervisors are self-contained units that allow standard low-power SRAMs to be
turned into non-volatile memory devices. They monitor and provide V
CC
input for one or
more external SRAMs the same way ZEROPOWER and TIMEKEEPER products do. They
use a precision voltage reference and comparator to monitor the V
CC
input for going out-of-
tolerance.
When V
CC
becomes invalid, the supervisor’s conditioned chip-enable outputs (E
CON
) are
forced to their “inactive” state, thereby putting each external SRAM into its own write-protect
state. During the power failure, the supervisor provides the power for the SRAM from the
lithium cell within its SNAPHAT top. The supervisor switches the power source back to the
V
CC
supply as soon as the voltage returns to specified levels.