PCA9306: PCA9306

Franco Gaetano Cartolano

Part Number: PCA9306

Hello,

I am working on a user interface module project for a home appliance. The EMS in China has designed the circuitry with a PCA9306 for bidirectionl I2C level convertion between 5V and 3.3V. On the schematics, I noticed that VREF1 that should be 5V, has been connected to 3.3V, and VREF2 that should be 3.3V has been left floating. The prototype works but I wanted to check if this configuration may lead to noise sensitivity or to reduced long term reliability. Thank you.

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 317320 points

What is important is the EN bias voltage. Please show the schematic.

0 Franco Gaetano Cartolano over 2 years ago in reply to Clemens Ladisch

Prodigy 10 points

EN is connected to 3.3V directly.

0 Franco Gaetano Cartolano over 2 years ago in reply to Franco Gaetano Cartolano

Prodigy 10 points

So I have 5V I2C but power supply is 3.3V. I am not sure about what happens when the host microcontroller on the SDA1 side needs to receive signal from SDA2 side, which has no power supply at all.

+1 BOBBY over 2 years ago in reply to Franco Gaetano Cartolano

TI__Guru 73871 points

Hi Franco,

We technically recommend the EN and Vref2 be shorted together and then a 200k resistor go from that connection to Vcc2.

The configuration you currently have looks like it isn't using the standard set up we recommend. For this set up to work you would need to make sure the signals you are translating on both sides be greater than ~2.7V.

Franco Gaetano Cartolano said:
I am not sure about what happens when the host microcontroller on the SDA1 side needs to receive signal from SDA2 side, which has no power supply at all.

It technically could receive the signal. If you are trying to level translate though both sides would need to be larger than about 2.7V. The Vref2 pin helps with level translation when you tie it to the EN pin with a 200k resistor to Vcc2. Having EN directly at 3.3V loses some of that 'help' but it technically does not need a supply voltage on Vref to work.

-Bobby

0 Clemens Ladisch over 2 years ago in reply to Franco Gaetano Cartolano

Guru 317320 points

With EN connected directly to the lower voltage, you have a plain I²C level shifter as specified in NXP's AN10441. (In this case, the VREF1/2 pins are not used, and the VREF1 connection to 3V3 is superfluous, but harmless.) This will work fine.

The VREF2+EN+200kΩ biasing circuit in the PCA9306 datasheet would allow higher speeds, but is not necessary for I²C.

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PCA9306: PCA9306