Samsung phone charging - low current - Page 1
Forum section: electronics / general

author: Lt_Flash
author_rank: Regular Contributor
timestamp: May 22, 2019, 11:30:40 am
content: Hi,I've got a 5V 3A power supply based on TPS62133 IC, I've tested it with load resistors and confirmed it can easily maintain 5.0V at 3A of current, no issues here. I'm trying to charge a Samsung phone from that board and got into a strange situation - phone draws no more than 1A when connected to this power supply. According to BC1.2 specification D+ and D- lines has to be shorted together with no more than 200Ohm to indicate that it's a Dedicated Charging Port (DCP) to connected device - which I did, but nothing changed. Ok, I googled (a lot) and found that Samsung devices require D+ and D- lines to be pulled up to 1.2V in order for Samsung devices to recognize charger as Samsung-compliant. No worries, I've placed a 30kOhm resistor from 5V pin to D+ and D-, that are already connected together, and a 10kOhm resistor from D- to GND. That gives me a clean 1.25V on both D+ and D- pins. Connected a phone - and still no luck, phone draws 0.96A.I've measured voltage on all pins of OEM Samsung 5V 2A charger and found out following:5V pin - 5.30V when no load, ramps up to exactly 5.50V when phone is connected and charging (very strange for USB charger!)D+ and D- pins - ~1.2V when no load, down to 0.7V when phone is charging (as expected)Phone charging current is ~1.8-1.9A @ 5.5V when Samsung phone is charging from original OEM charger.I've tested this with Galaxy S7, S8 and S10+, as well as with Samsung Galaxy S2 tablet - results are always the same, devices are refusing to switch to higher than 1A of current during charging and my power supply is providing exactly 5.0V of output, not 5.3 or 5.5V as Samsung charger does.Also, 5.5V are confusing a bit, I'm 100% sure that my charger is NOT a Fast Adaptive charger, it's just a 5.0V 2A Samsung OEM one, I can attach a photo of it if required. Why would Samsung charger do that, it's way too high for USB spec?Does anyone has any idea what might be wrong? Thanks!

author: D3f1ant
author_rank: Frequent Contributor
timestamp: May 29, 2019, 05:29:30 am
content: They jack up the voltage slightly to allow for the loss of the cable. Try adjusting up your supply, the internal charge controller may be limiting current draw when power drops below 5V.I thought their modern phones negotiate the charge rate and voltage, right up to 8 or 9V.

author: Lt_Flash
author_rank: Regular Contributor
timestamp: May 29, 2019, 06:14:30 am
content: Quote from: D3f1ant on May 29, 2019, 05:29:30 amThanks for your reply. Yes, phones are able to use adaptive fast charging technology, but they also should be able to use older 5V 2A power supplies or USB dedicated charging port. My charger is 100% not limiting current and keeping voltage at exactly 5.0V, I've tested that with currents up to 3A - everything was stable. When I connect the phone to this charger it only draws 0.96A max but when it's connected to Samsung OEM charger it immediately starts to draw 1.9A.

author: Halcyon
author_rank: Unknown
timestamp: May 29, 2019, 10:31:06 am
content: Quote from: Lt_Flash on May 29, 2019, 06:14:30 amAt what voltage though? Samsung's use their own "Adaptive Fast Charge" and Qualcomm Quick Charge I believe. Just looking at the output on my Samsung charger, it will do both 5v and 9v.

author: Lt_Flash
author_rank: Regular Contributor
timestamp: May 29, 2019, 10:59:19 am
content: Quote from: Halcyon on May 29, 2019, 10:31:06 amAs I said before - I'm NOT using Fast Adaptive Charger, I'm using 5.0V 2A Samsung OEM charger and it charges at 5.5V and ~1.9A without any issues. Yes, that's not a fast charging, that's normal charging and what I'm trying to figure out is why phone is not drawing more than ~1.0A from my charger. Hope this makes sense.

author: D3f1ant
author_rank: Frequent Contributor
timestamp: May 29, 2019, 11:19:01 am
content: What I think your forgetting is that Ohms law applies to the cable....5V at charger end will be well under 5V at the phone. Hence the OEM charger compensates by having a higher voltage at the charger end.Ballpark maths, 2M of 24AWG wire will have a resistance of about 0.15ohm, hence a 0.15V drop at 1A, and a 0.3V drop at 2A.Samsungs decision to set their charger at over 5V starts to make some sense if they need 5V at the phone end of the cable.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 29, 2019, 11:30:34 am
content: AFAIK almost all 5V USB chargers are designed to output somewhat higher than exact 5.0V and most include some kind of active wire resistance compensation (i.e., they automagically increase the output voltage with increasing measured current, giving an effective negative series resistance). Even though not officially specified, I wouldn't be surprised if the phone used a simple voltage-based logic to determine that your charger cannot supply enough current because of the low voltage, even when it's within official specification. Try modifying your output voltage.Note that USB has quite flexible voltage tolerance and you can easily design for, say, 5.2V, while still guaranteeing staying within tolerances, without resorting to expensive voltage references or 0.1% resistors. If you can't/don't want to implement output wire resistance compensation, the classical ways of using a 4-wire remote sense, or just using thicker cable, will work.

author: soldar
author_rank: Super Contributor
timestamp: May 29, 2019, 11:34:27 am
content: Searching I see it will charge faster with screen off, flight mode, powered down, etc.You might want to play around a bit with enabling fast charging, turning off screen, and different combinations to see if any of this has any effect.

author: Lt_Flash
author_rank: Regular Contributor
timestamp: May 29, 2019, 11:39:23 am
content: I tried it with 5.15v and no luck. Manuals in the Internet say that D+ and D- has to be pulled to 1.2v which I did, but still no luck. Of course I tried with screen off and so on. Tests are exactly the same, same phone connected to Samsung OEM charger draws 1.9A at 5.5V and only 1A from my charger at 5.15V.

author: Macbeth
author_rank: Super Contributor
timestamp: May 29, 2019, 12:43:44 pm
content: My crude PSU interface is a pair of wires running to a salvaged PCB mount double Type A socket with the 10k/30k resistors wired as yours are. I then use a standard Type A to Micro USB lead to the phone (Galaxy Notes 2 & 4).The quality of the lead makes a big difference. Some of my unbranded ones will only output around 1A, my Anker leads get 2A easily. I've even got one of those poundshop multi adaptors with Type A to Mini, Micro, 2mm barrel jack, etc. that will only deliver 0.5A. Obviously they haven't even wired the D+/D- lines in that piece of crap.Also the current level of battery charge and whether the phone is switched on will affect the charge rate. My switched off phone is 90% charged right now and only drawing 600mA - 800mA in pulses.

author: Lt_Flash
author_rank: Regular Contributor
timestamp: May 29, 2019, 12:59:22 pm
content: The lead is the same and the phone is the same and I'm switching it right from Samsung OEM charger into my charger and back - and it won't charge at more than 1A from my charger and immediately draws 1.9A from Samsung charger, hence the question - what I might be doing wrong. Also, one thing I've noticed - when no load connected Samsung charger stays at 5.3V and when phone first connects it starts to draw ~0.5A and then charger ramps up voltage to 5.5V and current to 2A. You can really see that delay. When connected to my charger phone draws same ~0.5A for a second or two and then start to draw only 1A and no more. I even tried that with bench power supply and didn't see any difference, unfortunately.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 29, 2019, 01:56:35 pm
content: Try ramping your voltage up to 5.5V?

author: soldar
author_rank: Super Contributor
timestamp: May 29, 2019, 03:11:07 pm
content: Some laptops have the PSU communicate with the computer usingSMBusand that way they both agree on amps, etc. I wonder if this phone is doing the same. You might want to connect a scope to the data lines and observe if there is any activity when you connect. I had a Dell laptop that did this. A few pulses at connection time and the laptop agreed the PSU was good. But a regular PSU with no data exchange would charge much slower.

author: Lt_Flash
author_rank: Regular Contributor
timestamp: May 30, 2019, 07:40:59 am
content: Quote from: soldar on May 29, 2019, 03:11:07 pmNo, I don't think it's my case as I'm not using even a Fast Adaptive Charging technology where you have to set appropriate voltages on D+ and D- lines to get 5V, 9V, 12V or even 20V. Or, with QualComm Fast Adaptive Charging 3.0 (if I remember correctly, may be 4.0) you can even adjust voltages in small steps as required. In my case I'd expect the phone just to work from a normal charger, which it does, but for some reason it doesn't want to use non-OEM charger. I'll try raising voltage levels to 5.3-5.5V and see what happens.

author: Lt_Flash
author_rank: Regular Contributor
timestamp: June 09, 2019, 05:19:44 am
content: Quote from: Siwastaja on May 29, 2019, 01:56:35 pmThanks, mate, that helped. I've replaced TPS62133 that keeps exactly 5.00V on the output (and does that very precisely at currents up to its spec, 3A) with adjustable TLV62130, ramped up output voltage of my TLV62130 to ~5.35V and the phone started to draw ~1.8A. Looks like the loss in the cable is quite significant so Samsung phone becomes really unhappy if input voltage drops below ~5.1V and restricts draw to ~1A. If output voltage from regulator stays at ~5.2V at ~1.8A - the phone is happy and takes that current. Should have measured voltage on the output of my cable but that's kinda tricky with USB-C connector unless you disassemble the phone, that's why I was measuring it at the output of my charger. Unfortunately, this means I can't use TPS62133 with its fixed 5.0V output for anything but powering ICs on the same board, instead a TLV/TPS62130 with adjustable output should be used. Anyway, thanks again for your help!P.S. And still the voltage divider has to be used to pull D+ and D- to ~1.2V, otherwise phone ignores shorted D+ and D- pins which is kinda strange as that's how it should be according to USB BC1.2 spec.