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mcf52259 cs0 cs1 draw current when power off

Question asked by RICK BOURGEOIS on Mar 26, 2013
Latest reply on Mar 27, 2013 by RICK BOURGEOIS

My previous project used a multiplexer to select one of 8 SRAM's used for battery back up storage.

When powered off a coin cell provided power to the external SRAM and the multiplexer so that the SRAM would not be accessed.

The multiplexer enable signal was disabled by the reset.

My new project only uses two SRAM's so I eliminated the multiplexer and drove each SRAM with its own chip selects.

The chip selects have a 4.7K resistor pulling up from VSTBY to prevent memory from being accessed.

On one side of the 4.7K I have 2.77V and on the other side 1.25V.

This means that 322 uA is flowing to each chip select output causing the coin cell to drain rapidly.

Is there anything I can do to make the chip selects power down?

Should I re-spin and put diodes in series?

Any suggestions out there would be appreciated.

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