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This article will explain in detail how to achieve two-way level conversion in NMOS. The content of the article is of high quality, so the editor shares it for you as a reference. I hope you will have a certain understanding of the relevant knowledge after reading this article.

Principle analysis

To simplify, leave a line of I2C for analysis, as shown in the following figure.

There are four situations:

1. When the SDA1 output is high, the Vgs of the MOS transistor Q1 is turned off and the SDA2 is pulled to 5V by the resistor R3.

2. When the SDA1 output low level: the Vgs of the MOS transistor Q1 is 3.3 V, which is larger than the turn-on voltage, the MOS transistor turns on, and the SDA2 is pulled to the low level through the MOS transistor.

3. When the SDA2 output is high, the Vgs of the MOS transistor Q1 remains unchanged, the MOS remains off, and the SDA1 is pulled to 3.3V by the resistor R2.

4. When the SDA2 output is low, the MOS tube does not turn on, but it has a body diode! The body diode in the MOS tube pulls the SDA1 down to a low level, and the Vgs is about 3.3V MOS transistor on, further lowering the voltage of the SDA1.

Note: low level refers to equal to or close to 0V. High level is equal to or close to the supply voltage. Therefore, the high level of the device in 3.3V voltage domain is equal to or close to 3.3V / 5V voltage domain, and its high level is equal to or close to 5V. Specific requirements to see how the chip data manual describes this limited range, for example, 0.3 times the "chip power supply voltage" below the low level, 0.7 times the "chip power supply voltage" above the high level. In other words, when the "chip supply voltage" is 5V, the level below 5 x 0.3 = 1.5V is low and the level above 5 x 0.7 = 3.5V is high.

Matters needing attention

The above is the case between 3.3V and 5V, if you switch to the conversion between other voltage domains, such as 3.3V, 2.5V, 1.8V and so on, you should pay attention to the Vgs turn-on voltage of the MOS tube. Too high Vgs to MOS tube will cause MOS tube to burn out! Too low Vgs will cause the MOS tube not to open! Different types of MOS tube this parameter value is not the same!

Multisim simulation results at this time, whether the other side is high-level, the other side is also output high-level.

At this point, the 5v terminal inputs a low level, and the 3.3v terminal is correspondingly low.

On how to achieve two-way level conversion in NMOS to share here, I hope that the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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