3.3V to 5V level shifter with high impedance (no control input)
Created: Oct 05, 2017
Logic level shifter with HiZ output when input is HiZ. Many voltage combinations can be programmed by adjusting the resistor divider, given that the current and voltage requirements of active components are meet.
This circuit can only shift from a lower or equal voltage to a higher voltage output.
High frequency can be archived by removing C1 and C2 and selecting high-frequency capable transistors Q1, Q2, Q3 and Q5. Useful when charlieplexing with a controller with few pins.
In order to make Y1 to a higher voltage, you must:
- Put the X1 input in HiZ
- Adjust the R4 to R5 relation so that in HiZ the voltage in R3 to GND is 0 and R2 to Vdd is 0.
Selecting a MOSFET:
- Read the voltage in R2 and R3 in all three modes
- The minimum value read is the minimum Vgs(th). Select a fairly higher Vgs(th).
- The maximum value is the maximum Vgs. Select a MOSFET capable of handling such voltage.
- For higer currents, select a low Rds(on) MOSFET
- For higer frequencies, select a low Qg MOSFET
- Try to use matched, paired or array MOSFETs
Selecting a Transistor:
- \beta should be at least 10 (depending on the shifter voltage)
- Select a low Vce(sat) transistor