ADuM415x Maximum injected current on output pins

Hi Jacob, 

I'm not clear if the ADuM4153 is powered already while the MCU is starting up, so let me explain it both scenarios.

The ESD protection is effectively a diode from MI to VDD1 and another to GND1. The Abs Max Ratings (Table 18) restrict the voltages applied to an I/O to a diode drop below GNDx and above VDDx.

With VDD1 unpowered and a voltage on MI, power will backfeed to the VDD1 rail. This backfeed through the ESD diode will power up the ADuM4153 and may well make the circuit behave strangely. The same thing will happen with a voltage on the MO, MCLK or any of the other I/O while VDDx is unpowered.  

If the ADuM4153 is powered while the MCU is starting up, it sounds like there is a contention issue with both the MCU and the ADuM4153's MI pin driving the bus line. In this case the Average Current per Output Pin spec in the Abs Max Ratings limit the average current to +/-10mA. 

Is this MCU the master? Or is it a slave device? 

Regards,

Jason 

Hi Jason,

Thank you for your reply. The MCU is master.

The AduM4153 will be powered up when this condition would happen which is only during production and initial programming of the MCU. For some reason ST designed their MCU to enter bootloader when the flash is empty. This BL sets some pins high until it has been programmed and can cause all kinds of havoc - not documented
I will add some current limit to 10mA, thanks for this information.

Regards,

Jacob