I would like to design a PCB in order to charge a smartphone (1.5 Amps) and in parallel pass through data to a smartphone from an external PCB. This is applied to CDP specifications. I think that the best way it's to provide the appropriate power in the USB port through the Vbus and the smartphone will take the power that it needs. Do I have to use the data buses also or can I charge the phone only through the Vbus in order not to interrupt the pass through mode?
Electronic – USB Charge and Data Transfer
chargeusb
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If I am not getting confused, this system of resistors is required by iPhones and other i-Devices to charge at different current levels. Otherwise an error message will pop up. If you don't have an iPhone you can quite safely remove these and replace them.
Apple stopped being as 'lax' with the charging interface and started being very picky about having the official chargers. We still doubted that there was an enumeration chip inside each charger - too expensive and complex. So there must be something else going on in those data lines. Time to sacrifice an official Apple iPhone 3Gs charger!
Taking it apart, desoldering the 4 data line resistors and measuring them on our multimeter, we found the following as shown in the schematic:
You can put a charge detector in parallel as long as you keep the stubs extremely short. I have done this before with a Fairchild charge detector. Don't remember the exact part number off the top of my head.
Or you could take a look at the BQ24392 from TI. It does its own enumeration (well, not enumeration... it does the charger detection upon initial connection, then connects the USB bus to the host), but it passes the detection results out, and it incorporates a USB bus switch so that the USB traces pass through it to the host. No stubs. It is specifically designed with USB 2.0 in mind. It correctly detects every type of charger in the known world, whether the charger is compliant with USB specifications or not.
But there may be a simpler option. How big is your battery? For smaller batteries (say less than 1 Ah) it may be easiest to simply always enable the 500 mA of current draw from USB. Of course, this means you will not comply strictly with the USB spec which dictates that until a profile is assigned, you have to stay under 100 mA. But in practice, it will work OK. It is rare, nowadays, to find a host which will object to the 500 mA being pulled from the USB port.
Best Answer
A direct answer to this question is yes, you must use data lines" upon first connect to the port. A "a smartphone" won't "take the power that it needs" unless it sees a "port charging signature" that it can (is designed to) recognize. Since we have no idea which signatures your phone does recognize, no practical answer can be given; some signatures are incompatible with USB signaling protocol. If no recognizable signature is detected by the phone, it will take only 500mA, or 900 mA if both ports are USB 3.0 capable. For more details, see references in the answer by Passerby.
As a side note, the concept of "CDP" is/was a part of so-called USB Battery Charging specifications, now BC1.2. These specifications were a flop, and only few manufacturer's made it to the market. Although the backward compatibility can be still traced across USB 3.0, 3.1, and USB Type-C specifications, you will be hard pressed to find a BC1.2 compliant device or host, maybe some DELL docking stations. Current mainstream is USB Power Delivery, and Type-C basic identification protocol, but most chargers have a simple "Chinese" signature with D+ and D- shorted.
ADDITION: If you want to convert a SDP (standard port on an ordinary PC) to CDP (charging data port), you can look at Maxim offerings (as well as Cypress, Microchip, Texas Instruments, NXP, etc), and add the necessary electronics to the port, and put all this stuff into an adapter. However, proper functionality might not be achievable without interaction of the host software with new charging electronics over some GPIO/I2C channel.
ADDITION2: No, USB 3.0 Rx and Tx pairs are not a part of any signature or BC1.2/QuickCharge/etc. negotiations. The USB 3.0 signals should be left alone.