Questions about level conversion circuit in I2C

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Questions about level conversion circuit in I2C [Copy link]

The schematic diagram is as above: A1 connects to the SDA of the 3.3V MCU, and B1 connects to the SDA of the 5V MCU

Sometimes when A1 is at a low level, the S level of NMOS still has 1.5V.

But if R17 is changed to 0R, the S-level voltage of NMOS can basically reach 0V.

It feels like R15 is not big enough, but according to the voltage division of the resistance value, it is not right.

呜呼哀哉

If your NMOS drive is not enough and Rds=100r, wouldn’t it be just right to use resistors to divide the voltage?

jimtien

It is best if R17/R18 is equal to 0. There should be no resistor in series on the signal line.

beijk

R17 and R18 are totally unnecessary.

The problem is that B1 is configured to output a high level.

se7ens

After careful analysis, the 1.5V should be caused by Vgsth. At this time, the DS current is very small, resulting in Vgs only needing to maintain the turn-on voltage.