TS3L500AE: DC bias after AC coupling magnetics

Hi Itoh-san,

Just to clarify previous comments, the TS3L500E device will support voltages from 0V to VCC on the switch channels (Ax/Bx/LEDx pins). The allowed supply voltage for this device is 3V to 3.6V which means the device will support signals from 0V to 3V/3.6V. Any voltage outside this will result into damage to the device.

Most commonly used schematic is --> PHY - SWITCH - MAGNETICS/TRANSFORMER - RJ45 connector. 

Based on the block diagram you provided, I see that that there are two paths

1) RJ45/Remote to RJ45/?C --> Blue path through IC

2) RJ45/Remote to TRNS/PHY --> Through IC

It is not clear what the GREEN arrow means as based on the block diagram this will never connect. Could you help clarify.

Also, what is TRNS?

Thank you.

Hello Sandesh-san,

My apologies, you are correct.

Please find corrected schematic from this link. The common-side of the switch is connected to RJ45/Remote.

TRNS means pulse transformer. It should be same as AC coupling magnetics.

I think some people discussed similar use case in previous threads, and TI experts mentioned DC bias should be cared.
But I don't get what they are trying to say exactly. So could you please elaborate on that? 

Regards,

Itoh

Hi Itoh-San,

Adding a DC Bias is the idea of signal summation. A quick example can be shown below:

Signal S has a range of V- to V+; V- < 0V .

The DC Biased Signal S'  has a range of 0V to V+'. Where V+' = (V+) + | V- | 

To add a DC bias using a non-inverting summing amplifier can be used:

the DC bias should satisfy  the following equation, (V- = Signal S Minimum Voltage w.r.t. Ground  0V = DC_Bias + (V-).

That being said - This part can only accept voltages in-between 0V and VCC; Where VCC is between 3V and 3.6V.

If the signal with a DC bias goes beyond VCC then this part will not be the best solution.

If the signals do not go less than 0V and does not go above VCC then no DC bias is needed.

If you could - please confirm signal  Minimum Voltage and  Maximum Voltage so I can confirm if this part will work - or if a different IC or solution may be required. 

Please let me know!

Best,

Parker Dodson

Parker-san,

Thank you so much for your kind explanation!

Just a quick check, do you think the switch and DC-bias and amplifier power should be generated from isolated power supply in this system?

Regards,

Itoh