Is it sensible to have overvoltage protection on USB VBUS? - Page 1
Forum section: electronics / projects

author: Day101
author_rank: Contributor
timestamp: November 27, 2023, 10:24:12 am
content: When designing a product which recharges a battery from USB VBUS, is it a good idea to have overvoltage protection on the VBUS going into the charger IC?I found a combined "USB over voltage and surge protection" IC from TI but it's a bit expensive and I'm not sure if it's necessaryhttps://www.ti.com/product/TPD1S514

author: Berni
author_rank: Super Contributor
timestamp: November 27, 2023, 10:34:36 am
content: Products usually don't have much in the way of protection for USB power. They assume the input power is going to be within reason.When it comes to ESD the power rails are reasonably safe since there is a lot of capacitors on it, and if you get a case of a USB charger going haywire and mistakenly outputting 12V (perfectly possible with USB-PD fast chargers when malfunctioning) you would likely blow up the commonly used protection devices like TVS diodes.But it is a good idea to have ESD protection on the data lines. It is quite common to get 5V into the data lines due to a damaged cable and that can often kill the USB pins on chips.

author: MathWizard
author_rank: Super Contributor
timestamp: November 27, 2023, 05:08:05 pm
content: So do you mean from a PC motgherboard/ATX PSU, or just any 5V USB source ? Motherboards usually have the 5V USB behind a series mosfet. And if either the PSU or mobo see's too much voltage or current, they should do something about it. I think the mobo might have some reverse polarity protection, with diodes. IDK if they add OV protection like TVR diodes, or what ever they are, or mov's. They might have some zener's, at least they probably would for low current OV protection.Most anything I make these days, I'll add a reverse polarity diode across the power rail, anmd trust the PSU for it's own OV protection.

author: Day101
author_rank: Contributor
timestamp: November 27, 2023, 07:11:17 pm
content: Just from a 5v USB source. To charge a small consumer electronic device.I've noticed that a lot of the TI battery charger ICs have built in over-voltage protection up to around 30v and I also noticed they sell a TPD1S514 "USB overvoltage and surge protection" IC. which also offers protection up to 30v. So I assume they've added this for a reason. I guess there's a lot of faulty power adaptors out there that supply more than 5vI'm just not sure if these chargers are 1 in 100, or 1 in a million.

author: jbb
author_rank: Super Contributor
timestamp: November 28, 2023, 12:09:08 am
content: It’s a sample of 1 product, but I beat my head against this a few years ago. Here’s what I got out the end:There are two sorts of cases: Adaptor Behaving Badly and transients.Let’s discuss the sensible case first. I found 2 basic classes of transients:1. The USB cable is plugged in at both ends, and then the AC power to the adaptor is connected. The adaptor has some internal start-up transient, which is generally not so bad. I think I measured a peak of 5.7 V or so, so a 5.5 V rated device isn’t looking good here2. The USB cable is unplugged and the adaptor is powered on. When the USB cable is plugged in, you get an inrush of current.Case 2 was the most difficult for my design. When I plugged it in, the cable inductance L resonated with the VBus input capacitor C. Under theoretical conditions, this could get you a peak of twice the USB supply voltage. I managed to provoke a 12 V peak in one condition (X7R capacitors are non-linear, which can cause unexpected extra voltage gain :-| )To address Case 2, a TVS clamp diode can work well. However, you get a bit of a tolerance problem; to reliably cope with 5.25 V on VBus you need around a 6V TVS (preferably a little more, check your tolerances and temperature coefficients). But you can only count on that TVS really conducting once you hit about 1.7 times the rating (rough rule of thumb from LittleFuse SMD series), ie 10.2 V. So it’s good if you canIf the wall adaptor is Behaving Badly and throws many volts DC at you, it’s painful. Theoretically, USB C sources should never go above 5V without negotiating first, but there are non-compliant devices which just chuck out 20 V immediately. Do you want to protect against this unlikely case? Given that USB C is now going (or planning?) up to 48 V @ 5 A, a nervous designer could really overdo it.

author: jbb
author_rank: Super Contributor
timestamp: November 28, 2023, 12:14:34 am
content: Sorry, realise that last post was way long…For charging:- suggest you consider, in the first instance, something like a 6.2V TVS diode to clamp transients- get a charger which has an absolute max VIN > 11 V so TVS has headroom to do its thing- if you’re aiming to charge at over a couple of hundred mA, recommend a buck converter type charger because a) they can charge faster from a given USB input and b) they generate less waste heat- highly recommend a charger with PowerPath or similar, i.e. a charger with a system power output pin that is separate to the battery connection. This way the charger can tell the difference between system load and battery charging

author: Day101
author_rank: Contributor
timestamp: November 28, 2023, 08:39:26 am
content: Thank you so much for taking the time to write this exceptionally helpful and welcome reply.I've been stressing about this for about 4 months and it's taken 3 board redesigns. I hadn't considered transients caused by plugging in cables etc.I erred on the side of caution and I hope the new design going to be robust enough. It's definitely not the cheapest option.I've used the TPD1S514-2 with the BQ24074. And I added a fuse on VBUS and on the battery, and an additional battery protection IC since I don't trust the ones that are on the batteries themselves. So it has overvoltage upto 28v on both the TPD1S514 and on the BQ24074, input current limiting, power path and a thermistor. My charging current is only 100mA for a 300mAh battery (it's only 6mm x 20 x 30mm) and I've never been able to detect any warming on the BQ24074 or on the battery.I think there's a lot of crazy power adaptors out there, I've become addicted to watching the teardowns from this guyI think a lot of the chargers out there could have really unpredictable voltagesThank you!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 28, 2023, 11:15:35 am
content: Maybe. Surge on short cables is unlikely to impossible; inrush might be worth a small TVS. For peripheral applications, the clamp diodes used for data lines often includes a TVS which can be biased from the supply, thus protecting it as well.Inrush in turn mainly matters due to ceramic capacitors, because you'd use ceramics for bypass, and the low ESR allows it to resonate with cable inductance. On top of which, the reduction in C under bias can cause peak voltage to be 3x or more the input voltage (the ideal linear lossless case is merely double: a sine wave peaking from 0 to 2*Vin), injecting whatever corresponding peak current into attached (presumably low voltage rated) devices.Lossy caps are good for this as well, but you might not have low enough ESR for the load, with a small enough cap that's compatible with USB (preferably 10uF or so), so a ceramic + TVS can be preferable.Tim

author: Berni
author_rank: Super Contributor
timestamp: November 28, 2023, 11:34:19 am
content: Having ferrite beads on the input can help with the ringing as it introduces a good deal of loss to only AC signals while letting your DC power trough.The ferrites are a good idea in general since it might help with a EMI issue of electrical noise radiating back out trough the cable from some internal switching converter.

author: Day101
author_rank: Contributor
timestamp: November 28, 2023, 12:44:37 pm
content: OK, maybe it's a good idea to let you see the power section in case there's anything obviously wrong.I've tried to annotate everything

author: Day101
author_rank: Contributor
timestamp: November 28, 2023, 12:55:20 pm
content: 10uF is Samsung 16V 10uF X5R ±20% 0603 Multilayer Ceramic Capacitors MLCC - SMD/SMT ROHS (part number CL10A106MO8NQNC)100nF is Samsung 16V 100nF X7R ±10% 0402 Multilayer Ceramic Capacitors MLCC - SMD/SMT ROHS (part number CL05B104KO5NNNC)Ferrite is Murata BLM18PG121SN1D(https://datasheet.lcsc.com/lcsc/2304140030_Murata-Electronics-BLM18PG121SN1D_C14709.pdf)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 28, 2023, 01:53:25 pm
content: Mind that what you thought was 10uF, is only 3.04uF at 5V:https://product.samsungsem.com/mlcc/CL10A106MO8NQN.dofurther reduction in C as V goes up, is why inrush voltage can be so high, as mentioned.ESD12VD5 has a maximum clamping voltage of 23V at 5A:https://www.mccsemi.com/pdf/Products/ESD3V3D5~ESD12VD5(SOD-523).pdfMind this with respect to whatever is downstream.TPD1S514 is only available as a 2.0 x 1.3 mm 0.4mm pitch CSBGA, are you sure?https://www.ti.com/lit/ds/symlink/tpd1s514.pdfImpressive, rated for 100V 8/20µs surge. No need for input TVS -- this thing handles it ably!BQ thing -- handy features, maybe overkill, no idea; I wouldn't bother for something simple (light load device), but something you want to run that might draw more power than is available from the charger (cell phone, classic example), you need something to manage the current paths and this is good for that.Rated up to 28V, so the TVS alone (no need for the surge chip) would do; I would still choose a 5V TVS, though.Fuse may not be necessary, say if using a protected type cell/pack -- ditto undervoltage, of course you get the latter for free in the BQ which is nice. With these, a bare cell is also acceptable.Output reg -- maybe consider SEPIC or buck-boost ("flying inductor") regulator to improve efficiency and maintain Vout down to minimum Vbatt. Maybe add aux output (can do tricks with coupled inductors, at least for the SEPIC case) if you need a 4 or 5V supply for certain things, or, choose different parts to run them at 3.6 or whatever.Also if that's 3.6V chosen as a compromise between some 3.3V parts (which might be rated 3.0-3.6V recommended, 4.2V abs. max., or more) and some 3.6V (maybe 3.9, 4.2, etc. nominal-center), by extension you could consider splitting those into separate supplies; though it might not be worth the effort, or layout space, so like I said -- could consider, and maybe it's yes, maybe it's no, just something to think about.Note that you basically only want synchronous switching regs at this voltage; anything using diodes is going to cost, well, about 0.5V due to the diode, a pretty big penalty out of a 3.something V supply. Which limits how much cleverness you can employ with stuff like coupled inductors. It's still a good choice when little current is required for the aux suppl -- efficiency for the supply by itself might not be great, but for the system overall is still fine. A competing solution is using a charge pump, which can still have good efficiency if it's a sufficiently complex type (multilevel internal switching), and is a good way to make fractional, boosted, and inverted supplies at low currents.Tim

author: spostma
author_rank: Regular Contributor
timestamp: November 28, 2023, 08:35:51 pm
content: I would always add a 1Mohm resistor between GND and shield on the device side for ESD discharge.I would avoid magnetic USB couplers for USB Type-C laptop chargers (that charge at 12, 15, or 20V)because the sequence of un-mating of pins is uncertain, thus 30V transients on D+ and D- are to be expected.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 28, 2023, 09:36:37 pm
content: Quote from: spostma on November 28, 2023, 08:35:51 pmIf it's connected at all it should be hard grounded, through multiple points into the ground plane. Indeed USB... C, or 3?, stipulates shield is circuit ground.For purely power, no data connection at all, it doesn't really matter.Tim

author: thm_w
author_rank: Super Contributor
timestamp: November 28, 2023, 11:37:01 pm
content: What is the expected retail price of the product or BOM cost?Looks like TPD1S514 overkill to me unless its a high end or industrial product.Plug in 20V in to 90% of consumer 5V USB gadgets and I'm sure they will start smoking.

author: Day101
author_rank: Contributor
timestamp: November 29, 2023, 11:09:45 am
content: Thank you for all the helpful comments, sorry it's taken me a while to reply.I can definitely live with it being overkill. I chose not to use a 5v TVS because an overvoltage supply would kill the TVS and then a surge would brick the product. At least that's what I thought. And with the TPD1S514 I can keep going with upto 30v without bad stuff happening. The product will be around $150 so an extra 30c isn't going to make a difference and if it saves bad reviews caused by wacky power adaptors then that's great.I chose 3.6v recently instead of 3.3v in order to get more out of the 12 blue LEDs when they're flashed, and if it drops when the lipo discharges then that's OK, they just wont be quite as bright. My BLE module and accelerometer are ok from 1.7 to 3.6v. And the BLE uses less current when the voltage is higher, It has an internal DCDC regulator. (nrf52833)The product sleeps if the battery is below 3.3v and I think the dicsharge curve of the batteries suggest this is around 90% of the useable power.I was told by pcbway and JLC that CSBGA won't affect the cost. I'm not sure why they used the BGA package because all of the pins are exposed at the edges. it doesn't require via in pad