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This is what I'm trying to do:

I have an MSP430G2553 chip and I'd like to write an ADC program to translate some input from an arduino sensor (I have a few analog sensors that use 5.5v - some work between 3.3 and 5.5 volts).

I realized that my MSP430 can not connect directly to these 5.5v sensors so I decided to get the PCA9306DCTR voltage leveler from TI to bridge the gap.

My problem:

I'm not sure I understand how these voltage levelers work and if I'm thinking about this connection correctly.

My MCU is powered by a debugger (the MSP-FET) to the DVCC and DVSS and to pin 17 & 16 (for the Spy-By-Wire) protocol. MSP430G2553 Pinout

Considering the fact that the voltage on my MCU pin (say A0 - pin 2) is ~1.4v and the needed voltage into my sensor (say the: ultrasonic distance sensor) is ~5v, I connected the VREF1 pin on thePCA9306 PCA9306 pin description

PCA9306 Pinout

to an external 3.3V supply coming from 2 AA batteries and the GND pin to the DVSS of the MCU (attempting to create a common-ground). In my mind the PCA9306 does not need a 5.5V supplier for the sensor.

Questions:

  1. Do both VREF pins (both sides) have to be provided? Can I just add the ~1.2 - 1.4V from the MCU into VREF1 and expect ~5V coming out of the PCA9306?

  2. Since most application designs include one single voltage power-source (be it 3.3V or 5V, etc.) can I assume that the voltage-leveler will raise the voltage from 1.4V to 5V without an external 5V power-source?

  3. How are the serial-clock and serial-data ports used in my case? After connecting the GND and VREF1 to 3.3V, do I connect my A0 (MCU pin 2) into the SDA1 and the ultrasonic sensor into the SDA2 of the voltage-leveler?

  4. Am I going about this the right way? If not, what am I missing?

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The PCA9306 is a voltage translator for I²C, which is a purely digital protocol. In other words, it translates a voltage of 0 V to 0 V, and a voltage of VREF1 to/from VREF2, and any other voltages are forbidden.

If you have an analog signal that can be anywhere between 0 V and 5 V, you need to use an analog amplifier (with an amplification factor of less than one) to proportionally reduce all possible voltages; see, e.g., Analog voltage level conversion (level shift).

If your sensor output has a very low impedance (which is unlikely), a voltage divider would be a simpler alternative.

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  • \$\begingroup\$ Thanks, @CL. So, if I understand you correctly, a voltage-leveler would not be the way to go here \$\endgroup\$ – Nactus Sep 24 '18 at 17:24
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    \$\begingroup\$ It's not called a "voltage leveler" but a "level translator", and the circuit with an opamp is also called a "level translator". The important thing is that you need an analog level translator. \$\endgroup\$ – CL. Sep 24 '18 at 18:00

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