TS5A23157-Q1: If the device is used as an I2C switch, do both NC (NO) and COM require pull-up resistors?

Lefeng Zhang

Part Number: TS5A23157-Q1

Tool/software:

Hi TI Members：

When the TS5A23157-Q1 is used as an I2C switch, do both NC (NO) and COM require pull-up resistors?

Because the datasheet does not describe the internal structure of the switch in detail, I wonder if the structure between (NCx and NOx) and (COMx) of this switch is similar to the CMOS shown in the screenshot below?

Thanks

Best Regards

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 316690 points

This device uses transmission gates; see [FAQ] What are the Types of Architectures TI Switches and Multiplexers Use and how do I know which one my device has internally?

In general, you need pull-up resistors on both sides to ensure that there is a valid voltage when the bus segment is disconnected. On the side where there is no I²C master, very weak pull-ups are enough.

0 Lefeng Zhang over 1 year ago in reply to Clemens Ladisch

Prodigy 10 points

Hi Clemens Ladisch，

Thank you for your reply. So the structure between COM and NC/NO of TS5A23157-Q1 is similar to the circuit shown in the figure below?

If TS5A23157-Q1 is used as the Switch of I2C, then my question is, is the resistor R2 on the “B" side of the figure below unnecessary?

In addition, if there is resistor R2, will the power(P3V3_S1) shown in the figure below leak to P3V3_S0 through the NMOS? We don't want P3V3_S1 to leak to P3V3_S0, but we don't care whether P3V3_S0 will leak to P3V3_S1.

Thanks

Best Regards

0 Clemens Ladisch over 1 year ago in reply to Lefeng Zhang

Guru 316690 points

The transistors in a transmission gate connect the body differently to prevent a current path through the body diode.

R2 is necessary if some I²C device on the B side can be powered while the switch is off. If you use the switch only to disconnect the devices when they are powered off anyway, R2 can be omitted.

0 Lefeng Zhang over 1 year ago in reply to Clemens Ladisch

Prodigy 10 points

Hi Clemens Ladisch，

Is the structure between COM and NC/NO of TS5A23157-Q1 similar to the circuit shown in the figure below?

Our application is shown in the figure below. The chip is used as an I2C switch. In some cases, COM and NC are connected, and in other cases, COM and NO are connected. Can you please help me see if a pull-up resistor is needed on the COM side?

Thanks

Best Regards

+1 Clemens Ladisch over 1 year ago in reply to Lefeng Zhang

Guru 316690 points

The structure is similar to the image, but without the body diodes.

In this circuit, the COM side is always connected to one of the NC/NO sides, so it is always pulled up by one of the other resistors, so it does not need its own pull-up.

0 Lefeng Zhang over 1 year ago in reply to Clemens Ladisch

Prodigy 10 points

Hi Clemens Ladisch，

Thanks

Best Regards

Switches & multiplexers

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TS5A23157-Q1: If the device is used as an I2C switch, do both NC (NO) and COM require pull-up resistors?