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Tool/software:
Wanted to double check that I am using the TXS0102 part correctly and get some input.
I am currently designing a system in which a set of I2C devices on a device are selectively powered on/off through a load switch (all same 3.3V voltage) and therefore some devices might be powered on, and some might be powered off on the bus at a time.
To provide isolation on the powered down I2C bus, I am using the TXS0102 device as these support partial powered down operation and are not as significant as opto. isolators, since high voltage isolation is in no way needed for my application.
The devices that are on the selectively powered down portion of the bus are tied to the VCCA side of the translator. (EXT PWR and EXT I2C in schematic image). This ensures that VCCA <= VCCB all times and then I tie the OE to VCCA through a pull up.That way when I enable the power to powered down devices (those connected to EXT_PWR), the device is up and fully enabled.
I had a question with regards to pull up resistors. In the https://www.ti.com/lit/an/scea044/scea044.pdf app. note I found in section 4, that the internal pull up resistors are disabled when the device is disabled. Therefore on the still powered portion of the bus (3V3_RAIL/VCCB) I have to use external pull ups, but will not require them for the powered down portion.
Two questions:
1. Is this correct, that for partial power down scenarios where VCCA = 0 V and VCCB = 3.3 V, I will require pull ups still on the VCCB side of the translator?
2. Am I using the part correctly based on my description above for the partial powered down scenario and output enable?
Schematic Image:
