USB phone charging ( specifically Sony Xperia Z2 - Page 1
Forum section: electronics / projects

author: trevwhite
author_rank: Frequent Contributor
timestamp: November 03, 2015, 01:36:56 pm
content: I have a Sony Z2 and its a nice phone but it does not charge properly. This seems to be a common fault but I can not figure out what is going on.I have a specific usb cable that seems to charge my phone okay but I measured it and it does not charge past 1A ever. Another cable I tried causes the phone to keep dropping out of charging 1 - 2 times per second continuously.I assumed the usb cable was really thin and voltage drops were causing the problem. So I chopped a cable up and connected it to my power supply. When I plugged the other end into my phone I ended up getting 733mA charge current. Adjusting the voltage over 4.8 - 5.25 volts made a bit of difference each way but not much. The crazy thing is that I tried this once yesterday and the phone started charging at 1.5A and I thought great, its just a voltage drop issue with some cables. Get the right cable and I should get fast charging.But today when I tried to charge the phone from my power supply again it was reading 700mA.Something isnt quite right. I tried shorting the D- and D+. This made no difference. I can not figure out how the phone is detecting what current it thinks the power supply cane handle.Any thoughts?Trev

author: DanielS
author_rank: Frequent Contributor
timestamp: November 03, 2015, 02:35:08 pm
content: I had a similar issue with my Nexus 7 where I hardly ever saw it pull more than 830mA or so from its 2A 5.1V original adapter. If I played games while "charging", the current pulled from the adapter was often not even enough to prevent the battery from draining.While the USB charging specification says to check for resistance across the data wires, many devices simply draw whatever current they can until the source voltage passes their threshold or reaches the current limit. Poor contact at the power adapter, micro-USB plug, internal ribbon cable to the motherboard, ringing from lead inductance and other stuff like that may limit current.When I was investigating why my N7 was charging so slowly, I found that power from the original adapter would sometimes get very noisy. I ended up modifying the N7's motherboard to add a 10µF MLCC across ground and Vusb to make the noise/ringing go away and that made charging more predictable regardless of what cable I used.

author: trevwhite
author_rank: Frequent Contributor
timestamp: November 03, 2015, 07:28:21 pm
content: Thanks that certainly made a difference. It seems the Z2 has a bit more complicated charging algorithm as well. If the voltage is too high with too much current available it just throws a wobbler. You have to ramp the current and voltage up but certainly not too much. I am guessing the cable that works is the one with rubbish thin power rails that limits the current through them. I can get it charging at 1500mAh now just by adding some capacitance but its twitchy. It throws itself out of charging mode if the noise gets too much or something.Least I have a bit more understanding of what is going on and the capacitor did make a big difference in that. Thanks