trevorth
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I need to:
- bi-directional convert two systems, 3.3V and 5V (tolerate up to 6.5V).
- auto sense i.e. no direction selection.
- work from 3V upto 6.5V supply.
- Convet with minimal current usage.
- Work upto 115kHz.
Solutions Ive investigated:
Use NMOS FETs as per the I2C solution listed here:
**broken link removed**
http://ics.nxp.com/support/documents/interface/pdf/an97055.pdf
But this results in slow edges or current consumption greater than ideal, and is also more expensive than...
NXP logic level shifter:
**broken link removed**
This would work well, but the supply voltage recommended maximum is 5.5V, absolute maximum is 6.5V. My supply is up to 6.5V, so I thought I could isolate it with a PFET (controlled from MCU for power saving) and then a diode to make use of the voltage drop of both. This should give me 1V drop dependent on current and temperature and should still meet all logic levels (0.2 * VDD or TTL 2V).
Is there a better way to drop the voltage, but that doesnt require the constant current drain of a zener. Also, this application the supply can go from 3V to 6.5V so a zener wouldnt work. Voltage reference suffer the same problem when input is below desired output voltage (if that makes sense
).
- bi-directional convert two systems, 3.3V and 5V (tolerate up to 6.5V).
- auto sense i.e. no direction selection.
- work from 3V upto 6.5V supply.
- Convet with minimal current usage.
- Work upto 115kHz.
Solutions Ive investigated:
Use NMOS FETs as per the I2C solution listed here:
**broken link removed**
http://ics.nxp.com/support/documents/interface/pdf/an97055.pdf
But this results in slow edges or current consumption greater than ideal, and is also more expensive than...
NXP logic level shifter:
**broken link removed**
This would work well, but the supply voltage recommended maximum is 5.5V, absolute maximum is 6.5V. My supply is up to 6.5V, so I thought I could isolate it with a PFET (controlled from MCU for power saving) and then a diode to make use of the voltage drop of both. This should give me 1V drop dependent on current and temperature and should still meet all logic levels (0.2 * VDD or TTL 2V).
Is there a better way to drop the voltage, but that doesnt require the constant current drain of a zener. Also, this application the supply can go from 3V to 6.5V so a zener wouldnt work. Voltage reference suffer the same problem when input is below desired output voltage (if that makes sense
).
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