Technical tips and hints

We offer two level shifters to allow interfacing CMOS switching levels in mixed 3-volt and 5-volt systems. One device is the LVC4245A and the other is the ALVC164245. These devices feature two supply rails.

On the LVC4245A, the A port is powered by V_CCA and operates from 1.5V to 5.5V. The A port's inputs are TTL level compatible when V_CCA is between 4.5V to 5.5V. The B port is powered by V_CCB and operates from 1.5V to 3.6V. The B port's inputs are TTL level compatible when V_CCB is between 2.7V to 3.3V. Both port's outputs swing between the ground and V_CC rails. The enable and direction pins are powered by the 3.3V V_CC. These control pins are 5V tolerant while the I/O pins can handle 0.5V above V_CC.

The ALVC164245 has the same type of characteristics as the LVC4245A, but the A port is powered by V_CC2 and operates from 1.5V to 3.6V, while the B port is powered by V_CC1 and operates from 1.5V to 5.5V.

Besides 3V to 5V translation, these devices can also be used to interface in systems with supply voltages ranging from 1.5V to 5V. On the LVC4245A for instance, V_CCA may be 3.3V or 5V while V_CCB is 1.8V or 2.5V. When V_CC is outside of the range to guarantee TTL input switching levels, the inputs operate at CMOS switching levels which equal 30% V_CC for a LOW and 70% V_CC for a HIGH.

During power-up sequencing of the supply rails, no current flows between the supply voltages. This is also true when either the 5V or 3.3V supply is grounded.