PCA9306: Tying EN to 1.8V

Austin Allen

Part Number: PCA9306
Other Parts Discussed in Thread: TCA9406, LSF0002

Tool/software:

Hey team,

Engineer is trying to use PCA9306 as a 1.8V to 3.3V translator for I2C. Issue is, the 3.3V supply will be up before the 1.8V supply.

Ideally, we would like to isolate the 3.3V supply from the 1.8V supply until EN comes up.

In the PCA9306 "normal setup" (figure 8-1 in the datasheet) we see EN tied to VREF2 which is tied through resistor to VCC2 = 3.3V

Is it possible to instead tie EN to VCC1 = 1.8V such that the TRX is not enabled until 1.8V comes up? Or is it possible to connect VREF1 to 3.3V and VREF2 to 1.8V?

If it is not possible to achieve what we are looking for with PCA9306, is it preferable to use TCA9406 here?

Thanks!

Austin Allen

4 months ago

0 Clemens Ladisch 4 months ago

Guru 318050 points

Then EN/200 kΩ biasing circuit must be connected to the higher voltage.

But for a low-speed protocol like I²C, the biasing circuit is not needed. Connect EN directly to 1.8 V, and leave VREF1/VREF2 open. (Or just use the LSF0002.)

0 Tyler Townsend 4 months ago

TI__Guru 50688 points

HI Austin,

I agree with Clemens here.

Regards,

Tyler

0 Austin Allen 4 months ago in reply to Tyler Townsend

TI__Intellectual 2555 points

Thank you both for the feedback.

I may not require the biasing, but if we are trying to do level translation between 1.8V and 3.3V wouldn't I need to tie VREF2 to 3.3V?

In any case, the customer has opted to utilize the PG output of their 1.8V VR (pulled up to 3.3V) as the input to the EN pin. Would this work okay? Also, in this case, would it be acceptable for VREF2 to come up after VREF1? Is it okay for the chip to be supplier with VREF1 in the absence of VREF2?

Thanks,

Austin Allen

0 Tyler Townsend 3 months ago in reply to Austin Allen

TI__Guru 50688 points

Hi Austin,

Best practice is to have smaller voltage on VCC1 = VREF1 = 1.8V, and VCC2 = 3.3V. This ensures best case prop delays and proper level translation. The level translation circuit connection that includes the 200k PU resistor will ensure that EN voltage is properly biased to 1.8V + VTH. See the application diagram.

Austin Allen said:
In any case, the customer has opted to utilize the PG output of their 1.8V VR (pulled up to 3.3V) as the input to the EN pin. Would this work okay?

So is the output of the VR 1.8V to the EN pin or is the output 3.3V to the EN pin?

If EN = 3.3V, this will not work

Regards,

Tyler

0 Austin Allen 3 months ago in reply to Tyler Townsend

TI__Intellectual 2555 points

Hey Tyler, I'm sending you and email with clarifications

0 Tyler Townsend 3 months ago in reply to Austin Allen

TI__Guru 50688 points

Hi Austin,

Let me continue our discussion over email.

Regards,

Tyler

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PCA9306: Tying EN to 1.8V