VCAP Pin Connection when Not Using the Storage Capacitor (VCAP) on nvSRAM - KBA83043

Version: *A

 

Question:

What should be done with the VCAP pin if the AutoStore feature is not required and I do not use the storage capacitor, VCAP?

 

Answer:

If the AutoStore feature is not required, the VCAP pin can be left unconnected. However, you must perform the following sequence of operations to prevent NV data corruption:

 

  1. Leave the VCAP pin unconnected
  2. Perform a soft sequence for AutoStore Disable
  3. Perform a soft sequence for software STORE
      

 

Perform Soft sequence for AutoStore Disable

 

You must disable the AutoStore feature by sending an AutoStore Disable soft sequence. If this is not done, data corruption in NV memory will happen when the nvSRAM device tries to perform an AutoStore operation in the absence of VCAP. The data corruption occurs because the device will initiate an AutoStore operation when power fails, but there would be no charge available at the VCAP pin in the absence of the storage capacitor, resulting in the NV data getting corrupted.

 

Perform Soft Sequence for Software STORE

 

After AutoStore is disabled, you must perform a software STORE operation. This operation is required to sustain the disabled state of the AutoStore feature through power cycles. If the software STORE operation is not done, the device will not perform the AutoStore operation during the first power down; but will boot up with the AutoStore feature enabled when it is powered up again. Therefore, the AutoStore Disable status must be STOREd by performing the software STORE sequence.

 

Note: If a storage capacitor is not connected to the VCAP pin, a power failure during a software STORE (the software STORE operation takes tSTORE to complete) could cause data corruption. However, if a capacitor is connected to the VCAP pin, the software STORE operation during a power failure gets completed even though the AutoStore feature is disabled.