TXS0102: VoH/ViH/VoL/ViL Spec

Howard Chen

Part Number: TXS0102

Hi TI Team,

We use TI TXS0102DCUR to do MDC/MDIO voltage level translation between modem IC and ethernet switch IC based on SoC reference design. VCCA of TXS0102DCUR is connected to 1.8V and VCCB is connected to 3.3V. Attached is our schematic for your reference.

Minimum VoH of modem IC is 1.35V but minimum ViH of TI TXS0102DCUR is 1.6V. In the other side, minimum VoH of ethernet switch IC is 2.6V but minimum ViH of TI TXS0102DCUR is 2.9V;

Maximum VoL of modem IC is 0.45V but maximum ViL of TI TXS0102DCUR is 0.15V. In the other side, maximum VoL of ethernet switch IC is 0.4V but maximum ViL of TI TXS0102DCUR is 0.15V.

It seems that VoH/ViH/VoL/ViL don't match on our design. Is the ViH/ViL limit different for different cases? How to validate VIL/VIH in our design?

Thanks.

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 318700 points

The TXS does not really have strict V_IL/V_IH limits at its data I/Os; see [FAQ] Why are the TXS01xx VIH/VIL specifications so stringent?

The modem's output voltages are specified at a specific output current. For lower currents, the voltage drop from the rail will be lower.

The TXS has internal pull-up resistors; external ones should not be needed in most cases.

0 Howard Chen over 2 years ago in reply to Clemens Ladisch

Prodigy 60 points

Got it. We need to ask vendor to know the output current when they define output voltage and then we can calculate the ViL/ViH with output current, right?

0 Howard Chen over 2 years ago in reply to Clemens Ladisch

Prodigy 60 points

Vendor told us that default output current is 2mA. How to calculate ViH/ViL?

0 Clemens Ladisch over 2 years ago in reply to Howard Chen

Guru 318700 points

When the signal is high, no current flows. For an output current near zero, V_OH will be near 1.8 V or 3.3 V.

The V_OL depends on the actual current. If you're using only the internal pull-ups of the TXS, the current is 0.5 mA, so V_OL would be about 0.11 V. But with all those 1.5 kΩ resistors, any output must sink 3.9 mA, and V_OL cannot be estimated.

Please read the FAQ I linked to. The TXS is a passive switch; its V_IL does not matter. The V_OL and V_IL of the other devices must match.

0 Howard Chen over 2 years ago in reply to Clemens Ladisch

Prodigy 60 points

I read the FAQ you attached but I'm not sure whether my understanding is correct. My understanding is ViH/ViL are not critical parameter because they are defined by the corresponding VoH/VoL with voltage drop across internal FET. We only need to make sure VoH/VoL of TXS series can meet the requirement of other devices. Am I wrong?

+1 Clemens Ladisch over 2 years ago in reply to Howard Chen

Guru 318700 points

When you have devices A <-> TXS <-> B, then the V_OL of A plus the FET voltage drop must match the V_IL of B, and the V_OL of B plus the FET voltage drop must match the V_IL of A. For the voltage drop, see figure 2 of the Factors Affecting VOL for TXS and LSF Auto-bidirectional Translation Devices application note.

0 Howard Chen over 2 years ago in reply to Clemens Ladisch

Prodigy 60 points

Got it. Thank you for clear explanation.

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TXS0102: VoH/ViH/VoL/ViL Spec