[Signal Conditioning] Rvo Pin of DS15BA101

Hi Chenglin,

The DS15BA101 Rvo pin resistor to GND will certainly lower the amplitude of the DS15BA101 output, but I do not think it will cause the DS15BA101 to shut off.

Can we have some more information about your application? How much cable or trace are you expecting to drive? I'm thinking if power is a concern, you may be able to take advantage of a passive equalizer like the DS38EP100, which does not require power or GND.

Thanks,

Michael

Hi, Michael

Currently we use HD3SS3411 as differential SW for bidirectional (TX/RX) bus turn around.

we use DS15BA101 for RX path re-driver, but while TX mode, the isolation of HD3SS3411

between B channel to C channel isn't sufficient.

There will be small magnitude of TX signal coupling to RX path , as well as the input of DS15BA101.

The DS15BA101 will boost the small signal leaks and output unwanted signals.

That's why we are thinking to pull down the RVO pin while TX mode to avoid unwanted interference.

Thanks

Chenglin WU

Hi Chenglin,

If you are using the DS15BA101 as an Rx path redriver, I'm wondering if it then makes more sense to use the DS15EA101. The DS15BA101 is intended for cable driving (that is, Tx path) applications, whereas it seems to be that you want to provide equalization for the receive path.

The DS15EA101 includes an "Enable" pin that will allow you to disable the device when no signal is present.

Thanks,

Michael

Hi, Michael

Thanks for your suggestion.

The reason we chose DS15BA101 instead of DS15EA101 is, the RX path signal swing is very small (less than 200mVpp differential)

Our idea is to boost up signal swing at TX point of RX path (which is device TX side).

So we didn't choose DS15EA101 since we had checked the signal swing with IBIS model , which was fine.

The problem we didn't expect is, while Host TX mode, the high speed multiplexor HD3SS3411 could leaks with small signal swing to RX path.

and even the leaking signal swing is 20~30mV pk-pk, it is still firing up the Buffer (DS15BA101).

(the leaking signal smaller than the minimum input requirement of DS15BA101)

We had tried to pull down the RVO pin to Gnd , which will make the Buffer (DS15BA101) keeping silence.

But one thing we have no idea is, will there be any side effect if we pulled down the RVO pin of Buffer (DS15BA101) while not in use?

Thanks

Hi Chenglin,

I will check on this RVO operation for you. Normally the RVO pin is only tied to VCC through a resistor, so I do not know the implications of shorting this pin to ground.

In the meantime, I've been re-reading your response about the choice of the DS15BA101, and I have a few questions for my own understanding.

1. It seems that in normal operation mode, the signal coming into the Rx path is less than 200 mVpp?

2. What is the signal amplitude of the source that is going into your Host in Rx mode? Is it also very small, or is it possible to make it 800 mVpp?

3. I'm also wondering if you simulated with the DS15EA101 in addition to the DS15BA101, or was it only the DS15BA101?

Thanks,

Michael

Hi Chenglin,

I just checked with our team about this operation, and I have determined the following:

The RVO pin determines the output voltage by measuring the input current, so the higher the resistance to VCC, the smaller the output voltage due to decreased input current. Since this is the case, then lowering the output voltage to minimum by tying RVO to GND when Rx mode is unused should not damage the device.

Thanks,

Michael

Hi, Michael

Thanks for your explain.

According to your questions:

The input signal for RX of DS15BA101 around 200mV pk to pk (normally).
In the case of TX, the leaking signal to input of DS15BA101 around 20mV pk to pk (or smaller) ,
which will trigger the Buffer to generate wanted output.
Since we put the DS15BA101 at device side, with 4inch of FR4 traces to Host,
we didn't put DS15EA101 because what we need is to boost-up the signal swing from device.

For the unwanted output of DS15BA101, I'd found relate thread for open state:
e2e.ti.com/.../540235

So we had tried to pull the IN+ and IN- pin with pull high/pull low resistors(7.68K)
to separate IN+/IN+ from common mode voltage a bit.

The solution works fine temporary. (the only side effect I think maybe
the duty cycle distortion for the output of DS15BA101)

About RVO pin you mention, since there will be no harm to the Buffer itself.
I still have one question about RVO pin, that is, if we connect and control the RVO pin
with ordinary NPN transistor (MMBT3904).

Will the parasitic capacitance of NPN (around 4pF ~ 10pF) affect the output performance of DS15BA101 ?


Thanks
Chenglin WU

Hi Chenglin,

I assume that your system will not need to switch quickly between Tx and Rx mode and that you will be able to connect RVO to GND with the NPN only in Tx mode. Since the RVO pin is only used for setting the output voltage and is not based on measured DC current as opposed to fast-switching current, I do not think this parasitic capacitance will be an issue regarding the output performance of the DS15BA101.

Thanks,

Michael