Hi,
I am looking for a good design for a bidirectional logic translator. I want a super safe design because the 3.3v board is much more expensive than the 5v board which will typically just be a display or something.
The usual way of doing this is to use a MOSFET with the drain and source in series with the 3.3v input/output and the 5v input/output, along with some pullup resistors. But with that design if the MOSFET drain to source blows short (for ANY reason under the sun) the 3.3v logic input/output is subject to the full potential of the 5v logic high, which would, of course, be 5v. 5v will easily blow out the entire 3.3v board which is typically (but not limited to) a microcontroller board.
I thought about using a regular design like with the MOSFET, but using instead a bipolar and a small series resistor like 330 ohms, along with a Schottky protection diode from the 3.3v input to the 3.3v supply line, but am looking for any other idea too. The main idea here is that the bipolar will be less susceptible to shorting collector to emitter than the MOSFET shorting from drain to source, as well as having a current limiting resistor in case of shorting anyway, and the diode clamp to +3.3v for the input with a low voltage drop Schottky.
Any other ideas?
I am looking for a good design for a bidirectional logic translator. I want a super safe design because the 3.3v board is much more expensive than the 5v board which will typically just be a display or something.
The usual way of doing this is to use a MOSFET with the drain and source in series with the 3.3v input/output and the 5v input/output, along with some pullup resistors. But with that design if the MOSFET drain to source blows short (for ANY reason under the sun) the 3.3v logic input/output is subject to the full potential of the 5v logic high, which would, of course, be 5v. 5v will easily blow out the entire 3.3v board which is typically (but not limited to) a microcontroller board.
I thought about using a regular design like with the MOSFET, but using instead a bipolar and a small series resistor like 330 ohms, along with a Schottky protection diode from the 3.3v input to the 3.3v supply line, but am looking for any other idea too. The main idea here is that the bipolar will be less susceptible to shorting collector to emitter than the MOSFET shorting from drain to source, as well as having a current limiting resistor in case of shorting anyway, and the diode clamp to +3.3v for the input with a low voltage drop Schottky.
Any other ideas?