I have two STM32 chips, one as Master and one as Slave on separate power domains of 3.3V each. My problem is that when the Slave is turned off and power is removed, it is still being powered from the SPI Master. The voltage on the power pins of the SPI Slave when the power is removed from it is 2.65V. If I remove NSS (Chip Select) from the Slave the voltage drops to 1.1V on the slave power pins and the device finally shuts off.
The layout is as follows:
The Master always receives 3.3V on its own Voltage Regulator. The Slave has a switched 3.3V Source on its own Voltage Regulator. The only connections between the two are the SPI Pins MISO, MOSI, SCK and CS.
Does anyone know of a solution? Is it normal for the SPI Slave to be powered entirely through SPI?
Thanks in Advance,