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TCA9406: TCA9406 Alternate - VOL Issue

Part Number: TCA9406

Hello,

I have built a board with a TCA9406 I2C level shifter to change 3.3V I2C to 1.8V I2C. I'm having trouble with a device on the 1.8V side of the level shifter - it won't recognize a low value of 0.4V which is the max value of VOL of the TCA9406 (this device's VIL is close to 0.25V).

Can you recommend a pin-compatible part to the VFSOP package with a lower voltage VOL on the VCCA side?

Thanks,

Ben

  • Hey Benjamin,

    "it won't recognize a low value of 0.4V which is the max value of VOL of the TCA9406 (this device's VIL is close to 0.25V)."

    This device does not actually redrive the signal, it uses a pass FET architecture which will basically send the VoL of the device on B side plus an offset voltage due to the parasitic Rdson of the pass FET. The VoL you mentioned is based on if the IoL throguh the device is 1mA.

    "Can you recommend a pin-compatible part to the VFSOP package with a lower voltage VOL on the VCCA side?"

    This device has a unique pin out so I do not know a pin to pin solution. Could you tell me what pull up resistors you are using on both sides and the bus capacitance? I'm wondering if we can up the pull up resistors to we can lower the IoL and get a lower VoL for the device with the ViL of 0.25V. Our device (TCA9406) has an internal rise time accelerator which means we can use really weak pull up resistors (lets you get a lower VoL).

    Thanks,

    -Bobby

  • The TCA9406 has internal 10-kΩ pullup resistors, and in most cases, does not need any external pullups.

    Without external pullups, the low voltage at the 1.8 V side will be lower than 0.25 V as long as the output impedance of the 3.3 V device is less than about 450 Ω. (The I²C specification requires an output impedance of at most 130 Ω.)