TCA9548A: Operation at 1.65V on both sides

Selim Ozdogan

Part Number: TCA9548A

Hello,

I am planning to use TCA9548APW in one of our design as following:

There are 8 identical slave devices that has following specifications for min/typ/max values for I2C:

Since the datasheet of TCA9548APW states 'In the event where the master device and all slave devices operate at the same voltage, then VDPUM = VDPUX = VCC.' and TCA9548APW is able to operate between 1.65V to 5.5V, I will set V_I2C to 1.65V which is not the typical value for slave device but within the limit. Can you comment that this configuration would work with 1.65V ( I concern because it is at the minimum value). As an information, The longest SCL SDA line on the PCB is around 20cm and I2C will operate at standard mode. 4.7k pull-up allows up to 250pF. Value of pull-ups can be lowered to 2.2k if require due to bus capacitance.

For the VOL of TCA9548A, followings makes me a bit of confused:

Is there a maximum value of VOL for TCA9548A like 0.4V or can it go up to 0.7V for 1.65V as indicated in the graph?

Regards,

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 317320 points

1.65 V is the worst case of a 1.8 V ±0.15 V supply. Just use 1.8 V.

The TCA9548A is a passive switch. A closed switch behaves like a resistor; the output voltage is the input voltage plus the voltage drop over the switch.

To avoid V_OL increasing by too much, minimize the current, i.e., use weak pull-up resistors. In your curcuit, the current through the switch will be about 0.4 mA.

0 Selim Ozdogan over 1 year ago in reply to Clemens Ladisch

Prodigy 80 points

The reason I go with 1.65V is thet it is in the limit of TCA9548A and it is in the limit of slave device. Slave device communicates at 1.5V but 1.65 is acceptable. If I go for 1.8V on the pull-ups, it will not be able to communicate with the slave.

If my supply is able to provide exactly 1.65V to VCC=VDPUM = VDPUX, it should work as expected right, even it is the worst case?

Do you mean in the that 0.4mA is the case when using 4.7k pull-up with 1.65V?

Regards,

0 Clemens Ladisch over 1 year ago in reply to Selim Ozdogan

Guru 317320 points

1.65 V is allowed; 1.649 V is not.

Yes, when a device on one side pulls the line low, the current through the pull-up resistor on the other side also flows through the switch.

0 Alex Vish over 1 year ago

TI__Genius 10552 points

Hi Selim,

Looks like Clemens already provided a solution here and this thread is marked as resolved. Is there anything else you need help with here?

Regards,

Alex

0 Selim Ozdogan over 1 year ago in reply to Clemens Ladisch

Prodigy 80 points

Would you think that providing 1.8V to VCC and pulling up VDPUM and VDPUX to 1.65V or to 1.5V would work in a more reliable way?

0 Clemens Ladisch over 1 year ago in reply to Selim Ozdogan

Guru 317320 points

With a pull-up voltage of 1.5 V, you can use any V_CC up to 2.5 V (see figure 14).

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TCA9548A: Operation at 1.65V on both sides