DS90LV028A: Boost Failsafe method

Hi Ryuuchi-san,

Is this for an unused channel? If so can't they just short RIN+/RIN- together? Assuming there's no common mode voltage input, this would make the receiver output always high.

Regards,

I.K.  

Hello,

>Is this for an unused channel?
Yes.

>If so can't they just short RIN+/RIN- together?
Do you mean user change resistor value from 100ohm to 0ohm ?
As I said previously, they can not change layout pattern.

Best Regards,

Hi Ryuuichi-san,

They wouldn't have to change the layout - just populate the placement with the same size 0 ohm resistor. This is essentially the same concept as changing the DS90LV028A to a different P2P part like you mentioned, right? 

Regards,

I.K.

Hello,

>They wouldn't have to change the layout - just populate the placement with the same size 0 ohm resistor.

Understood.

However, I did not understand difference b/w 0ohm resistor and 100 ohm resistor case.

In case of 100 ohm case, this case is applied to "2. Terminated Input" which is described section of failsafe feature in datasheet.

On the ohter hand, in case of 0 ohm case, this case is applied to "1. Open Input Pins" which is described section of failsafe feature in datasheet.

Both case will work internal failsafe function. And since both case connect input to connector, so both case are influenced by differential noise from connector.

So, I wonder why you proposed this. Could you please explain ?

Best Regards, 

Oh my mistake, you're right. I was only thinking of a way to implement a failsafe but if the noise is still there then they will still run into this issue if they simply short the inputs together.

If they don't want to change the PCB they can try the SN65LVDS048A, which implements the failsafe differently (reference the Fail Safe section of the datasheet). 

Regards,

I.K. 

Hello,

>If they don't want to change the PCB they can try the SN65LVDS048A, which implements the failsafe differently (reference the Fail Safe section of the datasheet). 

Actually, it seems SN65LVDS048A has different failsafe from DS90LV048A. However, it seems this has 4ch receiver.

DS90LV048A has 2 receiver so package is different. Do you have 2ch version of this device ?

Best Regards,

DS90LV048A is a 4ch receiver.

If you mean the DS90LV028A, unfortunately there are no P2P versions for this device with a different failsafe. 

Regards,

I.K. 

Hello,

I'm sorry, maybe you refered following sentence and figure.

>Here is current customer's input for DS90LV048A.

This was mistake. Correct number is DS90LV028A as shown title of this thread.

>If you mean the DS90LV028A, unfortunately there are no P2P versions for this device with a different failsafe. 

Understood.

BTW, can you comment about following my previous original question ?

--

Q1. According to datasheet, there is following description in Fail-safe feature.

* Do not tie unused receiver inputs to ground or any other voltages.

It seems that 0V common mode voltage is NOT allowed in this device.
However,on the other hand, there is following description.

"VID is not allowed to be greater than 100 mV when VCM = 0 V or 3 V."

According to above, if VID is less than 100mV, it seems that RIN+ and RIN- can connect GND.
Is there any condition which user can connect RIN1+/RIN- to GND when input is terminated to 100ohm ?

--

Best Regards,

Here is current customer's input for DS90LV048A.

Hi Ryuuichi-san,

No, unused receiver inputs should not be tied to ground or any other voltages as this would interfere with the internal failsafe circuitry. 

Regards,

I.K.

Hello,

>this would interfere with the internal failsafe circuitry.

Can you explain what phenomenon will be observed ?

(Please show one of example which you assume.)

Best Regards,

Hello I.K

I would like you to confirm following additional questions.

Q1. Is it possible to connect SN65LVDS1 as Driver(Supply voltage : 2.5V) and DS90LV028A as Receiver(Supply voltage 3.3V) ?

Q2. Is it possible to connect GND for input of SN65LVDS1 ?

Background of these questions :

We are talking about how to solve this noise issue. One of solution, user will generate small Driver board(Driver Input connect to GND).

Because we think that this issue is caused by "open" state for connector.

However, they can supply to this small driver board only 2.5V(not supply 3.3V). Therefore they can not use DS90LV027A as driver.

Alternately, I proposed SN65LVDS1 as alternate(This has only one channel, but this noise issue happen only one channel.)

However, I would like you to confirm above two just in case.

(As long as I confirmed both datasheet, it seems that there is no issue from viewpoint of AC/DC spec of this usecase.)

Best Regards,

Hi Ryuuichi,

Yes, both of those cases are okay.

Regards,

I.k.

Hello,

Thank you for your reply.

Understood for additional question.

Please continue to support for following question.

>this would interfere with the internal failsafe circuitry.

Can you explain what phenomenon will be observed ?

(Please show one of example which you assume.)

Best Regards,

Hi Ryuuichi,

Actually, based on the datasheet, this should be okay to do. The datasheet says to not tie open receiver inputs to ground or any other voltage. However, the customer's input is not open - it is terminated with 100ohm. I don't see any limitations on that.

Regards,

I.K. 

Hello I.K,

Let me confirm about below.

Q2. Is it possible to connect GND for input of SN65LVDS1 ?

Previously, you said that this case is OK, but let me confirm about detail.

* Can I connect input of SN65LVDS1(D+) to GND directly or should insert pull down resistor ?

Best Regards

Hi Ryuuichi,

Yes that should be fine.

Regards,

I.K.