Part Number: TCA9406
Other Parts Discussed in Thread: PCA9306, TCA9509, TCA9617B, TCA9517A, TCA9517, TCA9803
Hello,
I am using TCA9406 for I²C level translation between 1.8 V (VCCA) and 3.3 V (VCCB) systems.
Configuration details are as follows:
VCCA = 1.8 V
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VCCB = 3.3 V
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OE = 1.8 V (High)
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External pull-ups on both sides tried from 5 kohms to 20 kohms (to 1.8 V and 3.3 V respectively)
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Layout follows the typical application circuit in the datasheet.
However, on the oscilloscope we observe:
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3.3 V side: 0.7 V ~ 3.3 V swing
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1.8 V side: 1.0 V ~ 1.8 V swing
In other words, the “Low” level never reaches 0 V but stays around 0.7–1.0 V, so I²C communication fails.
Changing pull-up values does not improve the situation.
All supply rails (VCCA/VCCB/OE) are stable.
When the same MCU and I²C device are connected directly (without TCA9406), we get clean 0 V ↔ 3.3 V waveforms, confirming that the issue only occurs with the level shifter inserted.
Could this behavior be related to:
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Internal FET not fully turning off when OE = VCCA = 1.8 V?
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The pass-FET pre-charge or threshold characteristics holding the bus at mid-level for certain pull-up combinations?
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Excessive bus capacitance outside of the recommended C_bus range?
We are considering switching to PCA9306, but I would like to know if there are specific conditions (pull-up range, EN/OE timing, etc.) required to make TCA9406 operate correctly in this 1.8 V↔3.3 V configuration.
Thank you for your support.
