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I wanted to use LSF0102 translator IC to translate 5V to 3.3V with TWI/I2C but I noticed in datasheet it says it needs the low voltage/side's power source to be able to sink current (about 15mA of current sink): sink current sink current output

And I started searching for an alternative translator that does not need a power source that can also sink current.
I came across the NCA9306 IC, which internal circuitry is -I dear to say- same/identical to the LSF0102 as shown in the datasheet. but NCA9306 doesnt mention that it needs to sink current. And I wonder how both ICs are so similar but the NCA9306 doesnt mention current sink.

Question:

  1. Does NCA9306 translator IC need a current source that can also sink current?
  2. Where and how, in the datasheets of the ICs is the current sink value mentioned in the electrical characteristics table(s)? I can not spot it.

The current sink must be a capability of the power supply, not the IC so maybe this is why its not mentioned in NCA9306?

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    \$\begingroup\$ A suitable op-amp will work for the 1.8V source. \$\endgroup\$
    – user319836
    Commented Sep 5, 2023 at 12:09
  • \$\begingroup\$ @RussellH yeah I have read this answer on a similar question as well. But I wonder, do they mean using a op-amp as a power source only, or is there a configuration to use the op-amp on the already-existing 1.8V source? \$\endgroup\$
    – Christianidis Vasilis
    Commented Sep 5, 2023 at 13:02
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    \$\begingroup\$ An opamp needs a voltage reference to know what voltage to output. (But it could be a simple resistor divider.) Anyway, the LSF is usually used because it's cheap; it would be simpler to replace the LSF+opamp with an easier-to-use translator like the TCA9406 or PCA951x. \$\endgroup\$
    – CL.
    Commented Sep 5, 2023 at 13:48
  • \$\begingroup\$ @CL. love you man. I shorted the translators by price and sometimes I dont know how far I need to dig to find something easier to use. turns out your suggestions were in the second page! \$\endgroup\$
    – Christianidis Vasilis
    Commented Sep 5, 2023 at 14:02

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The text you have quoted does not apply to your problem; it describes the current that flows through the pull-up resistors and that must be sunk by the devices that drive the signals low.

The NCA9306/PCA9306/LSF0102 are identical.

The current that flows out of Vref_A is limited by the 200 kΩ resistor and depends mostly on the difference between the supplies, and often is so small that other devices connected to the 1.8 V supply use it up. This might be the reason that many datasheets do not mention it. But it exists, and if your power supply does not sink it, its voltage might float up.

The amount of current is affected by the LSF only with the variations in the MOSFET's gate-to-source threshold voltage; use 0.5 V as a safe estimate. You can calculate this current as:

    IVref_A ≤ (3.3 V − 1.8 V − 0.5 V) / 200 kΩ = 5 µA

and to get rid of it, use a resistor to ground:

    RpulldownA ≤ 1.8 V / 5 µA = 360 kΩ

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  • \$\begingroup\$ Oh you are right! this current flows through that 200Kohm resistor, it couldnt be 15mA under 3.3 or even 5V! \$\endgroup\$
    – Christianidis Vasilis
    Commented Sep 5, 2023 at 13:00

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