Original question:
Dear Sir,
In datasheet PCA9548A,
• Allows Voltage-Level Translation Between 1.8-V, 2.5-V, 3.3-V, and 5-V Buses
Does it means SDx/SCx can be pulled up to different Volatge, such like 1.2V ,1.8V, 3.3V individually?
if so, it can reduce I2C level shiffter iC instead.
Best regards.
David
Tiger,
Thanks for reaching out.
Mostly yes. Each bus channel SD0/SC0 through SD7/SC7 can independently be operated at different voltage levels; however, it is not intended for use with 1.2 V buses.
Your selection for VCC of the device (pin 24) is driven by the lowest operating voltage out of all of the connected buses. This is because Vpass must be equal to or below the lowest overall bus voltage. You can use this graph (section 9.2.3 of the PCA9548A datasheet) to determine maximum VCC using Vpass(max):
Note that the minimum supply voltage (VCC) for this device is 2.3 V, which can be found under Recommended Operating Conditions. Using the graph above, it can be seen that this minimum supply voltage does not allow a Vpass of 1.2 V. For design purposes, the “maximum” curve should be used, as it is considered the worst-case. This is why, as you noted in your question, the datasheet lists 1.8 V for any secondary but not 1.2 V. See the markup below, showing this:
The main channel will depend if the reference is above VIH if it is lower than VCC as well. Section 9 of the datasheet provides a thorough set of recommendations for the application of this device.
Regards,
Danny Bacic
