SN74CB3Q3253: Hot-swap function check & external protection recommendation

Matt Qi

Part Number: SN74CB3Q3253

Hi,

My customer wants to know if SN74CB3Q3253 can support the hot-swap function.

And in this e2e SN74CB3Q3253: Whether it supports Hotswap and how to know it from datasheet - Switches & multiplexers forum - Switches & multiplexers - TI E2E support forums

I know that it can only support hot-insertion (level-2 isolation).

Thus, my questions are:

1. What's the difference between the hot-insertion and hot-swap? Because in the technical document, the hot-insertion is described as "during card insertion and removal".

2. Can we add the external surge-protection circuit (resistor, TVS)? Do you have any recommendation for the external protection circuit?

6 months ago

0 Matt Qi 6 months ago

TI__Intellectual 1400 points

Add some information:

The hot-swap is on the A side, and the protection will be set on the A side.

0 Clemens Ladisch 6 months ago

Guru 244370 points

The main question is what happens when only some devices are powered down.

Which devices are hot-swapped, i.e., powered down? Those on the left side, on the right side, and/or the switch itself?

0 Nir Gilgur 6 months ago

TI__Expert 3285 points

Hello Matt,

Hot-insertion is when you place a device while the system is on, and hot-swap is removing a device and placing a new one while the system is on.

Regarding the external surge-protection circuit question I am moving this E2E thread to a different section to answer it.

Thanks,

Nir

0 Josh Prushing 6 months ago in reply to Nir Gilgur

TI__Expert 3100 points

Hi Matt,

Adding an external ESD/TVS diode should be no problem here as long as we choose a diode with a working voltage above the operating voltage of the line being connected with the hot swap. Could you please provide this information?

Best Regards,

Josh Prushing

0 Matt Qi 6 months ago in reply to Clemens Ladisch

TI__Intellectual 1400 points

Hi Clemens,

The hot-swap is on the left side.

0 Matt Qi 6 months ago in reply to Josh Prushing

TI__Intellectual 1400 points

Hi Josh,

Do you mean the operating voltage?

The signal is the UART signal, I think it is a 3.3V system.

0 Clemens Ladisch 6 months ago in reply to Matt Qi

Guru 244370 points

The capabilities of the SN74CB3Q3253 do not matter, because it is never powered down.

A possible problem is that the TX signal is output on the 1A pin, and that the powered-down device on the left side might not be able to handle it. So if your left-side device does not have overvoltage-tolerant inputs, you must disable the switch (pull /OE high) when the left-side device is about to be pulled out.

0 Josh Prushing 6 months ago in reply to Clemens Ladisch

TI__Expert 3100 points

Hi Matt and Clemens,

TPD1E1B04 would be a good option for the TX/RX lines as long as the voltage on these lines never reaches 6.4V during the hot swap event. Unfortunately, this is a 1 channel device, so 2 devices would be needed. If there is confirmation that during the hot swap event the voltage on these lines will not be negative nor >4.5V, ESDS302 would be a good 2 channel option.

Just to clarify, ESD protection is only desired on the left TX/RX pins, correct? Or is ESD protection desired on every pin?

Best Regards,

Josh Prushing