USB upstream downstream

[Rajinder]

Hi,
I wonder if someone could please clear this up for me.
I have a set of electronics that will be powered from 5V USB. I need some USB ESD/EMI protection. I have seen quite a few solutions but some are upstream and others downstream. I have looked at various sites but am still confused. Which one do I need?
Thanks in advance.

 

[Harald Kapp]

I have seen quite a few solutions but some are upstream and others downstream.

More detail, please. What do you consider upstream and downstream? Usually these terms refer to the direction of data flow or a master /slave relationship (in communication terms ). upstream /downstream makes not much sense for power supply over USB as there can always be only one power supply but multiple loads.

 

[Rajinder]

We have a unit that is powered from DC or battery. This has USB connections both type A. They connect to a PC.
However we are looking to use one of these to power a set of electronics.
This electronics will have a micro
b connector. It will need USB/EMI protection and then some filtering (of the 5V from the type A) to a 3V LDO that will power up the electronics.

So I was not sure if I require a upstream ( I think I do) or downstream EMI/USD protection.

Hope that helps and is a bit clearer, thanks for your help.

 

[Harald Kapp]

We have a unit that is powered from DC or battery. This has USB connections both type A. They connect to a PC.
However we are looking to use one of these to power a set of electronics.

Do you mean the "unit" powers the PC? The common USB ports on a PC are USB masters and these supply power to attached slaves, not vice versa. But obviously your "units" deliver power via USB. This setup makes no sense to me.

I still do not understand how upstream / downstream plays a role here.
ESD protection is placed as near as possible to the port where the ESD may enter the device. In your case that would be after the micro USB connector. The components are the same ones whether on the master (host) side or on the slave side.

 

[Rajinder]

Do you mean the "unit" powers the PC? The common USB ports on a PC are USB masters and these supply power to attached slaves, not vice versa. But obviously your "units" deliver power via USB. This setup makes no sense to me.

I still do not understand how upstream / downstream plays a role here.
ESD protection is placed as near as possible to the port where the ESD may enter the device. In your case that would be after the micro USB connector. The components are the same ones whether on the master (host) side or on the slave side.

The unit we have connects to a PC for Comms.
The same unit when we are not talking to the PC will be connected to our electronics board to provide power. Yes we have a micro usb on our electronics board but for ESD/EMI protection, all I see when looking up suitable protection circuits is that the datasheet mention upstream or downstream protection.

 

[Harald Kapp]

The unit we have connects to a PC for Comms.

In that case the PC is master and supplies power. The "unit" will receive power from the PC.

The same unit when we are not talking to the PC will be connected to our electronics board to provide power.

How is that going to work? Is that a USB on the go (OTG) device? Otherwise I don't see how it can get power from the PC in one case and deliver power in another case? What is that "unit" you are talking about? Can you state a name and type?

the datasheet mention upstream or downstream protection

Can you link to such a datasheet so we can have a look at it? Maybe that will make matters more clear.

Why do you think you will need additional ESD protection at all? Usually each USB port should already provide internal ESD protection. I have a feeling there's something hidden in your question that I do not get.

 

[Rajinder]

In that case the PC is master and supplies power. The "unit" will receive power from the PC.

How is that going to work? Is that a USB on the go (OTG) device? Otherwise I don't see how it can get power from the PC in one case and deliver power in another case? What is that "unit" you are talking about? Can you state a name and type?

Can you link to such a datasheet so we can have a look at it? Maybe that will make matters more clear.

Why do you think you will need additional ESD protection at all? Usually each USB port should already provide internal ESD protection. I have a feeling there's something hidden in your question that I do not get.

I will post up a schematic later today, my description is probably not the best. Thanks

 

[Rajinder]

Hi
I have attached a schematic. The top schematic is a Stan alone unit that is sometimes connected to a PC.
I need to use this to power a circuit to be powered from 3V via the Type A USB.

My questions are as follows:
1. The additional circuit has a micro usb 5 pin connector, do I still need to use ESD/EMI protection for this?
2. The 5VUSB is noisy, typically 180mV of noise, I was thinking of using a LC or PI filter to smooth this before going into my 3V LDO. Does that seem ok?
3. Lastly, the micro usb has an additional pin called ID, do I just tie this to 5V via a pull up?
Thanks in advance.

 

[Harald Kapp]

do I still need to use ESD/EMI protection for this?

Each port should be protected.

I was thinking of using a LC or PI filter to smooth this before going into my 3V LDO. Does that seem ok?

You can do that, but a filter capacitor right next to input and output of the LDO as recommended by the manufacturer would typically suffice.

the micro usb has an additional pin called ID, do I just tie this to 5V via a pull up?

Read this info.

 

[Rajinder]

Each port should be protected.

You can do that, but a filter capacitor right next to input and output of the LDO as recommended by the manufacturer would typically suffice.

Read this info.

Thanks for your help.
I was looking at ESD/EMI protection for the additional circuit (all in one package to save PCB space). This is why I posted my earlier message, they give you either a downstream or upstream ESD/EMI protection. Based on my requirements, I believe that I need upstream ESD/EMI protection.

 

[Rajinder]

Hi,
I have attached a datasheet of a ESD/EMI protection IC. This mentions upstream? I have seen others that mention downstream?
This is what is confusing me.
Thanks in advance.

 

[Harald Kapp]

Your image is almost unreadable. I had to find the datasheet online
This is not a pureESD protection circuit but includes termination resistors and a filters. That is why it is dedicated to upstream ports: you don't want these resistors and filters on a downstream port.
A pure ESD protection chip (e.g. this one) doesn't contain termination resistors nor filters. It can therefore be used either upstream or downstream.

 

[bertus]

Hello,

Here is the complete datasheet of the chip that @Rajinder mentioned.
As @Harald Kapp said, the chip contains resistors and is asimetric:


Bertus

 

[Rajinder]

Thanks, I was looking for a chip that contained the EMI and series termination resistors too, to save PCB space. Guess I will have to add these and go for a similar ESD chip you mentioned.
Could I just not use a duplication of my original schematic i.e. RCLAMP0503F plus EMI cap/ resistor and the 10R resistors?