How can I achieve level shifting from 1.8V to 3.3V and vice versa?

Step-down (3.3V→1.8V) and step-up (1.8V→3.3V) voltage translation can be achieved by using a CMOS logic IC with input-tolerant function, single- or dual-supply level shifters (Buffer type), and dual-supply bus switches.

The following is a brief example.
For detailed selection methods, please use the following application notes.
→ Tips for Selecting Level Shifters(Voltage Translation ICs) (PDF:2.62MB)

Fig. 1 Step-down voltage translation using an input-tolerant function
Fig. 1 Step-down voltage translation using an input-tolerant function

Step-down voltage conversion:
The input-tolerant function allows level shifting from a higher voltage to a lower voltage such as from 3.3V to 1.8V. For example, the input-tolerant function allows 3.3V to be applied to an input without drawing extra current even when VCC = 0V. (Fig. 1）
For Step-down voltage translation using the input-tolerant function of a CMOS logic IC, ensure that the maximum low-level input voltage is within the VIL range. (Table-1)

Table-1 input voltage specification (7UL1G08）
Characteristics Symbol Test Condition Vcc(V) Min Typ. Max Unit
High-level input voltage VIH - 0.9 Vcc - - V
1.1 to 1.3 Vcc x 0.70 - -
1.4 to 1.6 Vcc x 0.65 - -
1.65 to 1.95 Vcc x 0.65 - -
2.3 to 2.7 1.7 - -
3.0 to 3.6 2.0 - -
Low-level input voltage VIL - 0.9 - - GND V
1.1 to 1.3 - - Vcc x 0.30
1.4 to 1.6 - - Vcc x 0.35
1.65 to 1.95 - - Vcc x 0.35
2.3 to 2.7 - - 0.7
3.0 to 3.6 - - 0.8
Fig.2 Step-up voltage translation using a CMOS logic IC with a TTL
Fig.2 Step-up voltage translation using a CMOS logic IC with a TTL

Step-up voltage translation:
Level shifting from a lower voltage to a higher voltage such as from 1.8V to 2.5V can be performed if the high-level output voltage (VOH) of the preceding IC satisfies the high-level input voltage (VIH) of level translation IC because VOH is almost equal to the supply voltage (VCC).
(Fig. 2)

Table-2 Example of TTL input specifications of a CMOS logic IC（74UL1T08）
Characteristics Symbol Test Condition Vcc(V) Min Typ. Max Unit
High-level input voltage VIH - 2.3 to 2.7 1.1 - - V
3.0 to 3.6 1.2 - -
Low-level input voltage VIL - 2.3 to 2.7 - - 0.35 V
3.0 to 3.6 - - 0.5

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