The LPSRAM typically draws less than 1 micro-amp when powered
by a battery and can retain its data for years when powered by
only a small, lithium cell.
The Battery Switchover Circuit switches the LPSRAM from system
power (Vcc) to the battery (Vbat). It monitors Vcc and when it
begins to fall, the battery is connected to the LPSRAM.
When Vcc begins to fall, a micro-processor can behave erratically;
it could inadvertently overwrite and corrupt the LPSRAM's contents.
The Write Protect Circuit cuts off access to the LPSRAM to prevent
this.
All of ST's ZEROPOWER NVRAMs include these features. No other
special circuits are required. At densities of 256K-bits and below,
the NVRAM Supervisor is integrated into the silicon with the LPSRAM.
For higher densities, the two are separate ICs. |
