Part Number: TAS5825M
Subject: Clarification on minimum I2C rise/fall time requirement below 20 ns
Dear TI Support Team,
We would like to ask for a detailed clarification regarding the minimum I2C rise/fall time requirement for the TAS5825M / TAS5826M family.
In the datasheet timing table, the I2C rise time and fall time specification includes a minimum value of 20 ns.
Our I2C bus is operating in Standard-mode, below 100 kHz.
In some measurement conditions, the measured SCL/SDA rise or fall time is less than 20 ns.
However, the waveform looks clean, and we do not observe visible ringing, overshoot, undershoot, or I2C communication errors.
What we would like to understand is whether a rise/fall time faster than 20 ns can cause a real functional or reliability problem inside the IC, even when the waveform quality is clean.
Could you please clarify the following points?
- Is the 20 ns minimum rise/fall time an absolute requirement for correct internal I2C operation of the IC?
- If the measured rise/fall time is less than 20 ns, for example around 10 ns, but there is no ringing, overshoot, undershoot, or communication failure, can this still cause an internal malfunction of the I2C input circuit?
- Is the 20 ns minimum specification mainly intended to prevent external signal integrity issues such as ringing, EMI, or excessive edge rate?
- Or is the 20 ns minimum required because the IC input buffer, digital filter, spike filter, or internal I2C sampling circuit may not correctly recognize edges that are faster than 20 ns?
- If the edge is faster than 20 ns but all other I2C timing parameters are within specification, such as SCL high time, SCL low time, setup time, and hold time, should this condition be considered a real timing violation?
- In this case, should we intentionally add external RC components to slow down the I2C edge rate above 20 ns?
- If adding external capacitance improves the rise/fall time value but reduces the SCL high/low timing margin due to threshold-crossing delay, which parameter should be prioritized?
Our concern is that adding capacitance only to satisfy the 20 ns minimum rise/fall time may not be the best system-level solution if the original waveform is already clean and communication is stable.
Please let us know whether a rise/fall time below 20 ns is expected to create an actual IC operation risk, or whether it should mainly be treated as a signal integrity / EMI design guideline.
Best regards,
