Example of Application of the Power-Down Protection Function (Partial Power-Down)

Example of application of the power-down protection function (partial power-down)

Partial power-down is possible if an IC with a power-down protection function is used.

To reduce power consumption, a system with two voltage domains (VCC1 and VCC2) might provide partial power-down mode in which the subsystem operating from VCC1 is shut down. Suppose, for example, that the 74VHC Series is used in the VCC1 domain. The 74VHC Series has an unintended parasitic diode between the output and power supply. Therefore, when VCC2 > VCC1, this parasitic diode turns on. In this case, the IC might be destroyed by the resulting large current. Device destruction can be prevented by using an IC with neither an input nor output parasitic diode (e.g., 74VHCT, 74LCX, and 74VCX Series). These series provide power-down protection.

Usage Considerations of CMOS Logic ICs

Handling of Unused Input Pins
Input Rise and Fall Time Specifications
Multiple Outputs from a General-Purpose CMOS Logic IC Come Into Conflict (Short-Circuiting)
Connecting a Load Capacitance to a CMOS Output Pin
Calculating the Operating Supply Current and Power Dissipation
Level Shifting Using an Input-Tolerant Function
Input-Tolerant and Output Power-Down Protection Functions Available with Each Series
Types of Noise to be Noted
Countermeasures for Reducing Switching Noise
Countermeasures for Signal Reflection
Countermeasures for Crosstalk
Countermeasures for Hazards
Countermeasures for Metastability
Countermeasures for Latch-Up
Countermeasures for ESD Protection


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