power-down sequencing on TMS320C6747

M E,

See comments below from a colleague:

Brief exposure to this condition (such as the short time while supplies may be discharging due to capacitive loads) is unlikely to cause any problem. However, if system faults are possible where the core supply may turn off while the 3.3V remains powered, then protection circuitry should be added to the power supply design to ensure that these supplies don’t differ by more than the difference during normal operation (2.1V).

The power management solutions on ti.com are currently being updated to include protection circuitry that performs this function.

The C6747 is built on a 1.8V transistor process. The circuitry on the 3.3V supplies is built by appropriately cascading 1.8V transistors and using special biasing to achieve 3.3V operation. When the supplies are operating normally, the internal interfaces between the 3.3V and 1.2V power domains only experience a voltage difference of 2.1V which they are designed to handle. If the core voltage is completely removed, these transistors see a much higher voltage (up to 3.3V). This exposure to higher voltage, although it may not cause short-term device damage, may have implications for long-term reliability and therefore should be avoided. There have been no reliability studies done on this case because it is considered to be out-of-spec operation.