Simple power down

This circuit adds a power down function to analog I/O ports (for example, the AD7769 and AD7774). Moreover, the diodes ordinarily needed to protect the devices against power-supply missequencing can be
eliminated
In the circuit, MOSFETs Q1 and Q2 switch the +5- and +12-V supplies, respectively, in a sequence controlled by two cross-coupled CD4001 CMOS NOR gates (U1C and U1D). The sequence in which power isapplied is important: The controlled circuits may be damaged anytime Vcc exceeds Vdd+0.3V. Consequently, the NOR gates must be powered from a 12-V supply throughout the power-down sequence. [...]