PCA9548A: Voltage Translator function

Lisa Xu

Intellectual 305 points

Part Number: PCA9548A
Other Parts Discussed in Thread: TCA9548A

Dear TI Team:

Checked from PCA9548A datasheet, It shows it also supports voltage Translator function.

There are some items need your help.Thanks!

Pls check the picture as below, The PCA9548A is powered with 3.3V,

The main I2C is pulled up with 3.3V,

I2C7 is pulled up with 1.8V, I2C6 is pulled up with 3.3V,

1. This design is ok or not?

2. Main I2C switch to I2C6/I2C7 just with a transistor, how the PCA9548A guarantee the correct isolation between main I2C(3.3V) and I2C7(1.8V)?

3. Is there any relationship between the I2C0-I2C7 pull up voltage and PCA9548A power voltage?

Best Regards!

Lisa

6 months ago

+1 Clemens Ladisch 6 months ago

Guru 260910 points

For voltages between 0 V and about V_CC − 1.2 V, the PCA9548A works as an analog switch. For voltages above about V_CC − 1.2 V, the switch is always open, and the output voltage is determined by the pull-up resistor.

So you cannot use a V_CC of 3.3 V with 1.8 V devices. Connect V_CC to 1.8 V instead.

+1 Nir Gilgur 6 months ago

TI__Expert 4925 points

Hello Lisa,

1. For your application, if you need to drive a signal of 1.8V on the bus. You will need to also power the device with 1.8V (Vcc = 1.8V). Which the PCA9548A is not capable of. I recommend the TCA9548A: https://www.ti.com/lit/ds/symlink/tca9548a.pdf

It is a drop-in replacement to the PCA device, also capable to be powered by 1.8V.

Thanks,

Nir

0 Lisa Xu 6 months ago in reply to Nir Gilgur

Intellectual 305 points

Dear Nir:

Thanks for your comment.

Lisa

0 Lisa Xu 6 months ago in reply to Clemens Ladisch

Intellectual 305 points

Dear Clemens:

Thanks for your commnets.

Lisa

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PCA9548A: Voltage Translator function