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PCA9306-Q1: PCA9306TDCURQ1 without pull-up resistors on the I2C lines of VREF2

Yossi Aharon1
Prodigy 190 points
Part Number: PCA9306-Q1
Other Parts Discussed in Thread: DAC53401, PCA9306

Tool/software:

Hello,

I have a design with PCA9306TDCURQ1 connected to DAC53401.

The processor is connected to the VREF1 side of PCA9306. The I2C pull-up resistor of VREF1 side are 1Kohm to 1V8_LPD supply.

The I2C signals for the DAC have no pull-up resistor. The supply of the DAC is from a 3V voltage reference.

The DAC53401 requires VIH minimum of 1.62V and scope measurements of the DAC side I2C signals show good signal shape, levels and timinig.

Is there any risk of working without the pull-up resistors on the I2C signals of the VREF2 side?

Do you think that the 180mV of margine between the 1.8V signal high to the 1.62V minimum high of the DAC is enough?

Regards,

Yossi

  • +1
    Guru 312220 points

    The DAC's digital inputs are designed to be connected to devices with a lower supply voltage. 1.8 V signals will work; check the tolerances of the 1V8_LPD supply. 0.18 V is a very small noise margin; if there is a voltage drop on the SCL line, the devices on the bus might see a false clock pulse. I do not know how likely this would be in your environment. Consider using stronger pull-up resistors (the I²C specification allows up to 3 mA on normal buses, but check the drive strength of your 1.8 V I²C devices).

    Without the pull-up up resistors on the high-voltage side, you can remove the level shifter.