TCA9517: star application

Zhicheng Wang

Part Number: TCA9517

The above picture is Typical Star Application of TCA9517，The Slave Devices connect Master with TCA9517s . My question is that all slave devices connect with one bus(VCCB side) through one TCA9517，is that ok!

3 年多前

0 Amy Luo 3 年多前

TI__Guru**** 185470 points

Hi Zhicheng,

Generally, communication is unlikely to work properly when the B sides are connected to one another. The device uses a "VOL" level on its B side that is higher than its "VIL" level. This means that it doesn't recognize its own low output level as a logic low. It is also described in detail in the datasheet as shown in the screenshot below

0 Zhicheng Wang 3 年多前

Vcca=Vccb=3.3V，Is this ok?

0 Amy Luo 3 年多前回复 Zhicheng Wang

TI__Guru**** 185470 points

Yes, This is okay.

0 Zhicheng Wang 3 年多前回复 Amy Luo

A terminal is connected with 3M wire, and B terminal is connected with two IIC slave devices，Vcca=Vccb=3.3V，Is this ok?

0 Amy Luo 3 年多前回复 Zhicheng Wang

TI__Guru**** 185470 points

As described in the datasheet “The TCA9517 cannot be connected B-side to B-side”. So we cannot guarantee that's will work normally.

0 Zhicheng Wang 3 年多前回复 Amy Luo

B terminal is connected with two IIC slave devices，A terminal connected master，Only one chip TCA9517

0 Amy Luo 3 年多前回复 Zhicheng Wang

TI__Guru**** 185470 points

Can you draw an architecture diagram? In this way, I can understand your application more clearly.

0 Zhicheng Wang 3 年多前回复 Amy Luo

0 Amy Luo 3 年多前回复 Zhicheng Wang

TI__Guru**** 185470 points

As long as you stay within the recommended bus capacitance for the I2C standard you should be fine having multiple slave devices on the A and B side.

0 Zhicheng Wang 3 年多前回复 Amy Luo

I2C communication line is relatively long. Can a resistor with rs = 100 Ω be connected in series? How should this resistor be placed? How should the pull-up resistor be placed?

0 Amy Luo 3 年多前回复 Zhicheng Wang

TI__Guru**** 185470 points

Yes, a small resistor can be connected in series on the bus to reduce overshoot. In my opinion, the series resistor should be placed at the signal output end, so as to form an RC filter circuit with the back-end bus capacitor to filter out high-frequency overshoot.

The pull-up resistor should be placed near the OD output end. If both ends are OD output, the resistor should be placed in the middle of the signal path.

For more information about I2C applications, see https://www.ti.com.cn/cn/lit/pdf/scpa054

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TCA9517: star application