I need connect 3V3 powered MSP430 family processor and PW0268 ultrasonic sonar IC. PW0268 is powered Vcc 5-11V and is connected with MCU via bidirectional IO pin which is internally pulled up (3.5-6.5k) to Vcc as there is an open colector transistor. When Vcc 10V I can measure Vio 7.7V (or 8.7V/6.7V). The function is: MCU generates short pulse, releases IO and sonar IC pull down when response is received. I cannot use my "standard" 74LVC shifter method as they are not tolerant to voltage above 5V. I'm uncertain about common base FET method used for I2C 5/3V3 shifting.


simulate this circuit – Schematic created using CircuitLab

My only idea is to use resistor and 3V3 zener diod but it will leak current which I dislike as it's battery powered circuit, use MOSFET transistor used with Vgs=5-10V, Vds=3V3 (but FET Vgsmax is normally 8V and I'm not sure about Vgs/Vds/Id diagram) or use an operating amplifier powered 3V3 with 12V tolerant inputs (if any).

Any idea how to do it simply and efficiently ?

Edit: Level shift with Schottky diode blocking higher voltage in high state and small enough forward voltage (Vf@D2 + open Vce@Q2) to fill requirment for low state at input pin.

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    \$\begingroup\$ There are specialized chips for bi-directional level conversion. Google is your friend. \$\endgroup\$ – Wouter van Ooijen Oct 18 '15 at 18:02
  • \$\begingroup\$ Absolutely, there are tons of specialized chips for any conversion in 1.8-5V range. But I'm asking for high-to-low shift beyond this range. \$\endgroup\$ – TMa Oct 18 '15 at 20:14
  • \$\begingroup\$ good point. if the timing permits, you could make the 11V->3V shifter much higher in impedance (say 100k/100k), with a (schottky) diode to the 3V power instead of the zener? If you choose an opamp, why not power it with the5-11V? \$\endgroup\$ – Wouter van Ooijen Oct 18 '15 at 21:47
  • \$\begingroup\$ @WoutervanOoijen: I've added Schottky option in original schema (do you meand this way?). I agree with opamp power but I believe opamp is too "complicated" for such a simple case. \$\endgroup\$ – TMa Oct 18 '15 at 22:16
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    \$\begingroup\$ Seems to me like the ancient CD40109 would work here. Still made. ti.com/lit/ds/symlink/cd40109b-q1.pdf \$\endgroup\$ – Fizz Oct 18 '15 at 22:16

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