These pitfalls can be avoided by paying close attention to a few key issues. These include the maximum voltages applied to the input and output pins, the current flowing between the power supplies, and the input-switching threshold levels that must be met. Some circuits have limitations on the voltage that can be applied to an input or output pin. These circuits can have current paths to through diodes or parasitic elements. If the voltage is high enough, current will flow into the device to the 3-V supply.
Excessive current can also damage the diodes and circuitry.
Either of these situations will cause data disruption and may damage components. A mixture of TTL and CMOS switching levels can exist too. The driver must meet the receiver's input switching level with enough margin and do it without damaging the circuitry. This circuit is present between the physical input pin and the active circuit. Some low-voltage circuits may still use two ESD diodes connected to ground.