In order to perform level shift bidirectional 245 type.
1 power supply type level shift TC74LCX/VCX and 2 power supply type level shift are described below:
For TC74LCX/VCX245, bidirectional, single power supply level shift such as 3.3V↔5V,1.8V↔3.3V,1.8V↔2.5V is available.
Level shift is available if the output voltage VOH of the IC in the previous stage satisfies the input voltage VIH level of the IC in the subsequent stage.
Because TC74VHC245 does not have the output tolerant function and therefore the voltage that is higher than VCC cannot be applied to the input/output pin, level shift is not available.
[Figure: 1 power supply type level shift]
* Output at lower voltage. Consumption current ICC increases at the first input of the IC in the subsequent stage.
| IC in the previous stage | IC in the subsequent stage | |||
|---|---|---|---|---|
| VCCA≈VOUTA | series | VCCB=5V VIH=2.0V |
VCCB=3.3V VIH=2.0V |
VCCB=2.5V VIH=1.6V |
| 3.3V | LCX，VCX | OK | - | - |
| 2.5V | VCX | OK | OK | - |
| 1.8V | VCX | NG | NG | OK |
Bidirectional 2 power supply type level shift is available in ICs that have built-in level converter circuit such as 3.3V↔5V,1.8V↔3.3V,and 1.8V↔2.5V.
Take TC7MP3245 (8-bit) for example. Any level shift between VCCA=1.1 - 2.7 and VCCB=1.65 - 3.6V is available.
Because it fully swings to the output voltage VOH≈VCC, quick switching operation is possible with low consumption current.
There are types of low and high power supply of the control circuit. The power supply of the control circuit must be turned on earlier or at the same time. In 8-bit products and 16-bit products, note that voltages of the power supply of the control circuit are VCCA and VCCB respectively.
[Figure: 2 power supply type level shift
lower voltage (VCCA) ↔ higher power supply (VCCB) bidirectional 2 power supply type]