# USB help

#### Rajinder1268

##### Member level 2
Hi all,
I have attached a copy of a schematic that I am working with. The schematic with the usb type A connector is connected only sometimes to a PC.
I need to use the type A usb to power a second set of electronics, which will be connected to a micro usb.
My questions:
1. Do I need to have ESD/EMI filtering for this extra circuit?
2. I have measured the noise from the USB5V, it is pk-pk 186mV, I was thinking of a LC or PI filter before it is connected to my 3V LDO.
3. Lastly the micro USB is 5 pin, it has an extra pin called ID, what do I need to do with this pin?

#### Attachments

• IMG_20210411_130700.jpg
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#### KlausST

##### Super Moderator
Staff member
Hi,

some things are not clear to me:
* Where is the PC at your drawing?
* is the PC used as USB_host for data transfer?
* "The second set of electronics".. is it Master, slave, OTG? Or just something that needs power without data communication?

1) if data lines are connected to any circuitry in "the second set of electronics" then you (most probably) need to protect this electronics against ESD.
Usually the datasheet and the application notes of the devices used in "the second set of electronics" tell you how to treat them.
The datasheets also tell you whether you need to install EMI filters or not.

2) undamped LC or PI filters may cause resonances. Maybe this makes pp-noise higher than before.
For a reliable device I recommend to follow datasheet recommendations, and at least install some protection against overvoltage spikes.

3) I dont memorize this. What about an internet search "USB ID function"?

Klaus

#### Rajinder1268

##### Member level 2
Hi,

some things are not clear to me:
* Where is the PC at your drawing?
* is the PC used as USB_host for data transfer?
* "The second set of electronics".. is it Master, slave, OTG? Or just something that needs power without data communication?

1) if data lines are connected to any circuitry in "the second set of electronics" then you (most probably) need to protect this electronics against ESD.
Usually the datasheet and the application notes of the devices used in "the second set of electronics" tell you how to treat them.
The datasheets also tell you whether you need to install EMI filters or not.

2) undamped LC or PI filters may cause resonances. Maybe this makes pp-noise higher than before.
For a reliable device I recommend to follow datasheet recommendations, and at least install some protection against overvoltage spikes.

3) I dont memorize this. What about an internet search "USB ID function"?

Klaus
Hi,
PC is not shown but is used for data transfer.
The second Electronics is used to obtain power 5VUSB, 0V and data lines, so I will probably need ESD protection. It is for a low power PIC microcontroller.

I am using a LDO 3V, what would you recommend for overvoltage protection?

#### KlausST

##### Super Moderator
Staff member
Hi,
It is for a low power PIC microcontroller.
If the data lines directly go to the PIC, then read PIC datasheet and other informations provided by the manufacurer.

I am using a LDO 3V, what would you recommend for overvoltage protection?
How can I say? ... without having any information about the LDO?

And if you give the exact type ... I´d need to read the datasheets and other informations provided by the manufacurer.
The same could (shold) you do. ;-)

*****
It´s not clear to me. Are you designing the top circuit of the schematic or the botom part "The second set of electronics".
If the bottom part: Then I recommend to focus on this. (We almost have no information about it)
(No need for reading a PC´s schematic or reading any other device´s schematic)
Focus on the circuit and the parts you use.

*****
Note:
We professionals don´t have every information in mind. The datasheets are our friends.

Klaus

#### Rajinder1268

##### Member level 2
Hi,

If the data lines directly go to the PIC, then read PIC datasheet and other informations provided by the manufacurer.

How can I say? ... without having any information about the LDO?

And if you give the exact type ... I´d need to read the datasheets and other informations provided by the manufacurer.
The same could (shold) you do. ;-)

*****
It´s not clear to me. Are you designing the top circuit of the schematic or the botom part "The second set of electronics".
If the bottom part: Then I recommend to focus on this. (We almost have no information about it)
(No need for reading a PC´s schematic or reading any other device´s schematic)
Focus on the circuit and the parts you use.

*****
Note:
We professionals don´t have every information in mind. The datasheets are our friends.

Klaus
No problem. It is the second Electronics that I am doing, the top design
Hi,

If the data lines directly go to the PIC, then read PIC datasheet and other informations provided by the manufacurer.

How can I say? ... without having any information about the LDO?

And if you give the exact type ... I´d need to read the datasheets and other informations provided by the manufacurer.
The same could (shold) you do. ;-)

*****
It´s not clear to me. Are you designing the top circuit of the schematic or the botom part "The second set of electronics".
If the bottom part: Then I recommend to focus on this. (We almost have no information about it)
(No need for reading a PC´s schematic or reading any other device´s schematic)
Focus on the circuit and the parts you use.

*****
Note:
We professionals don´t have every information in mind. The datasheets are our friends.

Klaus
The LDO is MIC5501-3.0YM5-TR
I am doing the second Electronics circuit, the top schematic has already been done.
If you could just point out some guidelines, then I can have a look myself.
Thanks

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