WEBENCH® Tools: Level Translator solution

SHYAM THILLAINATHAN61

Other Parts Discussed in Thread: PCA9306, TCA9517

Tool/software: WEBENCH® Design Tools

Hi,

We are looking to design a level shifter for an I2C bus between our system and a target device. The
specifications for each are as follows:

System:
 3.3V I2C bus (2 data lines – SDA and SCL)
 3.3V power supply capable of sourcing 1A
 5.0V power supply capable of sourcing 1A

Target:
 Unknown voltage I2C bus between 1.8V – 5.0V
 Target voltage reference capable of sourcing 10uA
 Common ground with the host system

Please do provide a solution.

over 6 years ago

0 Miguel Robertson over 6 years ago

TI__Guru 62920 points

Hi Shyam,

We are looking into recommendations, but I want to make sure I understand the application. When you say the target reference voltage can only support 10 uA, is that the maximum current draw from the 1.8-V to 5-V rail?

Regards,
Max

0 SHYAM THILLAINATHAN61 over 6 years ago in reply to Miguel Robertson

Prodigy 70 points

Hi Max,

Yes, that is right.

0 BOBBY over 6 years ago in reply to SHYAM THILLAINATHAN61

TI__Guru 73331 points

EDITING my response, I think I misunderstood what you were asking. Check in later.....

Thanks,
-Bobby

0 SHYAM THILLAINATHAN61 over 6 years ago in reply to BOBBY

Prodigy 70 points

Thank you, Bobby.

0 BOBBY over 6 years ago in reply to SHYAM THILLAINATHAN61

TI__Guru 73331 points

Hey Shyam,

Is my understanding correct?

Currently if the image is correct, then the pull up resistor on side 2 will likely always try to sink more than 10uA of current in this configuration. Another power supply on Vcc2 would be a simpler solution to this problem. If not, then the I2C communication frequency would need to be slowed down to try to support a really slow rise time on side 2. (we would likely need to violate the maximum rise time allowed in the I2C standard to do this)

Is it possible to add an adjustable LDO on Vcc2 instead of relaying on the target I2C subsystem?

Thanks,

-Bobby

0 SHYAM THILLAINATHAN61 over 6 years ago in reply to BOBBY

Prodigy 70 points

We also have a 5V supply. I think then I will have to use a separate LDO for the VCC2 supply then.

0 BOBBY over 6 years ago in reply to SHYAM THILLAINATHAN61

TI__Guru 73331 points

Hey Shyam,

In that case, you can use PCA9306 and have Vref2 shorted to the enable pin and pulled up by a 200k pull up to the LDO output. This device will allow for Vref2 to be larger or lower than Vref1.

The other alternative device you can do this with is TCA9517. (set B side to the 3.3V side so we meet the VccB level requirements and support 1.8V to 5V on A side)

Thanks,
-Bobby

0 SHYAM THILLAINATHAN61 over 6 years ago in reply to BOBBY

Prodigy 70 points

Thank you, Bobby. I think then I will have to go this route.

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WEBENCH® Tools: Level Translator solution