3 Translating Up

Using the LVxT family to translate up is very simple. The input switching threshold is lowered, thus the high state voltage level (V_IH) of the input can be much lower than that used for a typical CMOS device. For example, if the V_CC is 3.3 V, the typical CMOS switching threshold would be V_CC/2, or 1.65 V. Thus the input high voltage level (V_IH) must be at least V_CC × 0.7, or 2.31 V. However, for LVxT devices the input threshold for 3.3-V V_CC is approximately 1 V. This allows a signal with a 1.8-V V_IH to be translated up to the V_CC level of 3.3 V. See an example of this in the voltage characteristic plot, Figure 1.

Common up translation possibilities with LVxT family:

• 2.5-V V_CC: from 1.8 V to 2.5 V
• 3.3-V V_CC: from 1.8 V or 2.5 V to 3.3 V
• 5-V V_CC: from 2.5 V or 3.3 V to 5 V

Because these parts are CMOS, there is additional supply current (I_CC) consumption only when the input is much less than V_CC, which is common when up-translating. The current draw for up-translation at different input values is shown in Figure 2-2.