PCA9306: Device Connection

Shinichi Yokota

Part Number: PCA9306

Hello,

I'd like to ask if a connection described below is allowed for PCA9306 or not.

A PCA9306 device is used as an I²C bus switch. Pull-up resistors on the side 1 and the V_REF1 pin are mistakenly tied to +1.8 V while the I/O level of the master device is +3.3 V. If the external pull-up resistors are removed and the master device's internal pull-up resistors are enabled to fix this issue, can the PCA9306 work properly? In this configuration, the V_REF1 pin voltage stays on +1.8 V while the I²C bus signals go up to +3.3 V.

Original Circuit

Plan to Fix The Issue

Best regards,
Shinichi Yokota

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 316510 points

The VREF voltages are independent from the signal voltages; the only restriction is that VREF1 must not be higher than the lowest signal voltage.

This will work.

0 BOBBY over 3 years ago

TI__Guru 72501 points

Hi Shinichi,

Clemen's is correct. In both cases, your set up would work.

-Bobby

0 Shinichi Yokota over 3 years ago in reply to BOBBY

TI__Genius 9715 points

Bobby, Clemens,

Clemens Ladisch said:
...VREF1 must not be higher than the lowest signal voltage.

Could you elaborate on that? I can't figure out what exactly "the lowest signal voltage" means. Does it mean signal levels on the side 1 (SCL1, SDA1)?

Best regards,
Shinichi Yokota

0 Clemens Ladisch over 3 years ago in reply to Shinichi Yokota

Guru 316510 points

The lowest pull-up voltage (on either side).

For voltages below VREF1, the PCA9306 works as an analog switch, i.e., it allows such voltages from the other side to pass through. (For voltages above VREF1, the switch is open, and the voltage on the other side is determined by the pull-up resistor.)

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PCA9306: Device Connection