TCA6408A: Current of SDA

rock shen

Intellectual 585 points

Part Number: TCA6408A
Other Parts Discussed in Thread: TXS0102

Dear Sir:

From page6 of TCA6408A spec that as below,

How to understand the spec of IOL of SDA?

Is it means the TCA6408A's driver strength is 3mA minimum?

How to set the pull up of the TCA6408A's SDA & SCL pin to follow below spec?

Thanks!

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 316220 points

The I²C specification says that the driver must have an V_OL of at most 0.4 V when I_OL = 3 mA. This is the same as saying that I_OL is at least 3 mA when V_OL = 0.4 V.

You must size the pull-ups so that the current is at most 3 mA, i.e., R_PU ≥ V_CC / 3 mA. In practice, currents between 0.5 mA and 3 mA are used, depending on the speed and bus capacitance. Also see I²C Bus Pullup Resistor Calculation.

0 rock shen over 4 years ago in reply to Clemens Ladisch

Intellectual 585 points

Dear Sir:

To TCA6408A IC,because the voltage level issue,

we add TI's level shift txs0102,

both side A & side B need the driver strength same?

Or could be difference that follow the I2C spec?

Thanks!

0 Clemens Ladisch over 4 years ago in reply to rock shen

Guru 316220 points

The TXS is a passive switch; when it is closed, all pull-up resistors are in parallel.

The TXS has internal pull-up resistors; it should work fine without any external pull-up resistors.

0 rock shen over 4 years ago in reply to Clemens Ladisch

Intellectual 585 points

Hi,Sir:

Needn't check current of each level shift side?

Just follow the pull up resistor calculator rule,right?

Thanks!

0 Clemens Ladisch over 4 years ago in reply to rock shen

Guru 316220 points

When using the TXS, do not add any pull-up resistors.

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TCA6408A: Current of SDA