USB ESD Protection Advice needed - Page 1
Forum section: electronics / beginners

author: luisr
author_rank: Contributor
timestamp: April 23, 2013, 02:44:21 pm
content: HiI've been looking for an off-the-shelf ESD protection for USB 2.0 OTG... I found a few nice devices like the TI TPD4S012/TPD4S014 but so far I was unable to find a hobbyist friendly device... all I have found comes in those nasty QFN or really tiny bga packages which I think (and according to some dave videos) will be a pain to solder... so far the only usable device I've found is the ST Micro ECMF02-4CMX8 which is available in a package with 0.5mm pin pitch, it would require to go down to 6mil traces when approaching the chip but that shouldn't be a problem since I'm planning to order the final board from OSHPark and 6mil is their minimum spec... BUT the aforementioned device is a "Common mode filter" and, according to the datasheet of the uC I'm planning to use, I shouldn't be using common mode chokes ont he USB...In case you where wondering, I'm "gluing" off-the-shelf components to create a small dev board for a 3.4" TFT with OTG capabilities for personal use; The TFT connector has an 0.5mm pin pitch so I will probably be using a reflow oven (DIY) to solder the hole board...I was wondering if somebody that knows or have experience with ESD Protection for USB 2.0 OTG and can recommend me a better way to do this.Thanks in advance

author: Hideki
author_rank: Frequent Contributor
timestamp: April 23, 2013, 05:07:16 pm
content: ECMF02-4CMX8 is QFN, but you can use 0.25 mm (~10 mil) traces, since there's no need to run them between the pins.Maybe take a look at the USBLC6-2 instead? 0.95 mm pitch in a SOT23-6L package.

author: free_electron
author_rank: Super Contributor
timestamp: April 23, 2013, 06:16:25 pm
content: usb6b. in sot23 package. very hobbyist friendly.

author: AlfBaz
author_rank: Super Contributor
timestamp: April 24, 2013, 12:25:06 am
content: Here's something simplehttp://www.digikey.com.au/product-detail/en/PRTR5V0U2X,215/568-4140-1-ND/1589981

author: luisr
author_rank: Contributor
timestamp: April 24, 2013, 08:12:43 pm
content: Quote from: Hideki on April 23, 2013, 05:07:16 pmYes, the ECMF02-4CMX8 would suit my needs if it wasn't by the common mode filter...Quote from: Hideki on April 23, 2013, 05:07:16 pmThanks, will do.Quote from: free_electron on April 23, 2013, 06:16:25 pmIs this the one you are suggesting?http://ve.mouser.com/ProductDetail/Bourns/CDNBS08-USB6B/?qs=sGAEpiMZZMvMnj9fkisOGKWwxokD3thDIf so, It has been flagged as obsolete by mouser...Quote from: AlfBaz on April 24, 2013, 12:25:06 amThanks, will do.

author: free_electron
author_rank: Super Contributor
timestamp: April 25, 2013, 03:54:56 am
content: No, 511-USB6B1. From st microelectronics. In mass production.

author: luisr
author_rank: Contributor
timestamp: April 25, 2013, 02:14:28 pm
content: Quote from: free_electron on April 25, 2013, 03:54:56 amThanks, it's "flow-through" design will sure easy things while laying out the board, but I'm concerned that the datasheet doesn't clearly say it can be used with HS USB 2.0! is it safe to use it with a HS USB controller?

author: codeboy2k
author_rank: Super Contributor
timestamp: April 26, 2013, 06:16:42 am
content: Quote from: AlfBaz on April 24, 2013, 12:25:06 amThese PRTR5V0U2X would appear to be much better than the 511-USB6B1. 1pF I/O to GND capacitance, vs 25pF for the USB6. If you had any doubts about the USB6 ability to do HS USB 2.0, then you need not worry with the PRTR5V0U2X.Also, half the cost.

author: luisr
author_rank: Contributor
timestamp: April 26, 2013, 01:36:32 pm
content: Quote from: codeboy2k on April 26, 2013, 06:16:42 amyeah... the PRTR5V0U2X seens like a nice device, unfortunately it doesn't protect de ID pinThanks

author: AlfBaz
author_rank: Super Contributor
timestamp: April 26, 2013, 01:50:32 pm
content: Quote from: luisr on April 26, 2013, 01:36:32 pmAs far as I know the ID pin doesn't need protection. I forget why but its supposed to be able to detect a floating state as well as pulled low and high...Here's a cct that I have implemented. Its a rip from an NXP reference cct

author: luisr
author_rank: Contributor
timestamp: April 26, 2013, 02:51:47 pm
content: Quote from: AlfBaz on April 26, 2013, 01:50:32 pmI will search more info about this, so far I think that the ID pin should be protected but I can be wrong.BTW Thanks for the schematic...

author: AlfBaz
author_rank: Super Contributor
timestamp: April 26, 2013, 03:00:46 pm
content: If you find anything please post links to the info here, as I would like to be sure as well

author: codeboy2k
author_rank: Super Contributor
timestamp: April 27, 2013, 12:28:34 pm
content: I missed the fact that you were designing for OTG - in that case, yes, it is necessary and prudent to protect the ID pin as well.Here's some more ESD info, from my experience: I completely expect that any wire that leads from inside the device to outside the device will experience an ESD event at some point, and during the design stage all wires leading to outside the device should be assessed for their protection from these events, and if not able to withstand the event, should be remedied with protective devices.The schematic from AlfBaz is really good, but it should have the ID pin protected as well. If this device has a physical metal chassis I would only add that the shields (all shields) go to the chassis, which also should go to protective earth ground. PCB's in plastic or metal enclosures powered from wall plug packs don't really have a protective ground; in this case you add an earth ground terminal on the outside of the box for hookup to earth ground .This would be necessary for devices that are expected to live in a harsh environment, an also just prudent to provide a good path for the dissipation of ESD events.One good design practice (if you have the room for it) is to have a chassis ground ring around your pcb, on all layers, stitched top to bottom, every 15mm or so. All of the chassis connectors and the ESD protection diodes for incoming signals will ground to this chassis ground ring. Then, at just one point only, this is connected to your digital ground, usually at the power supply with a very wide trace. I've seen it done in the manner you've drawn it in your schematic, using a .01 or .1uF and a 1M bleeder, but this seems counter-productive to me. Why go to the trouble of isolating the grounds only to try to couple them together again with some form of RLC network. It seems far better, in my opinion, to maintain the separate islands (ground domains) and connect them together with a low impedance path at one point only. The goal is to keep ESD currents separate from signal currents and separate from low noise analog currents, etc. This shield ground around the board can also help reduce edge radiated EMI. However, in order to keep options open, you can provide unpopulated pads in a few places around the board to connect the chassis ground to the signal ground using ferrite beads, 0-ohms, or capacitors for high speed coupling. This may be necessary if you are doing EMC compliance testing, you might need to change the grounding scheme to meet compliance. It's somewhat of a black art, so good to keep options open.Regarding the MOV's to your digital ground, I've never done it like this, but my past work has always been industrial and I've always had a real earth ground to go to, so in my case I would send charge through MOVs to earth ground. In your case, I would just connect the USB diodes directly to chassis ground, I don't think the MOVs are necessary between chassis ground and signal ground. Also the PRTR5V0U2X has a zener from power to ground too, where you have put a MOV. It won't hurt, but it may not be necessary. The inclusion of the MOVs on your schematic has chassis ground basically floating, with the 1M bleeder to prevent any charge build up. Its not bad. It's one way of doing it too.Finally, I've not seen any 3-channel USB protection in other than BGA or CSP. There is a 4 channel device, PRTR5V0U4D, it comes in SC-74/TSOP6 which is not too bad. You can use a 4-channel device to protect D+, D-, ID, with one spare, and also the zener from VBUS to GNDIf you have 2 USB ports with ID, you can use (3) two channel devices, for a total of 6 channels, or a 4 channel and a 2 channel device.