With the popularization of intelligent terminals, the application of the rich scene. People's dependence on intelligent terminal is also more and more serious. One of the key points that consumers are currently focusing on is standby time and charging speed. So the current manufacturers of intelligent terminals are generally equipped with quick charging function. In the process of research and development, the problem of fast charging is also emerging in an endless stream. In this paper, a solution to the problem of abnormal fast charging is proposed by combining signal timing and signal voltage.

1. Development status of intelligent terminal rapid charging

The development trend of intelligent terminal is large screen, high frequency and fast operation. In addition, third-party applications have increasingly high requirements on hardware (CPU/GPU processing speed is getting higher and higher), so the power consumption of intelligent terminals is also increasing and the battery charging time is getting longer and longer, which has exceeded the limit of people's patience. Therefore, more and more mobile phone manufacturers are equipped with quick charging function. In engineering practice, engineers are also encountering more and more problems about fast charging. Combined with signal timing and signal voltage, this paper proposes a solution to the problem of abnormal quick charging in engineering practice, which can help engineers locate and solve the problem quickly.

2 failure phenomena and problem analysis

2.1 failure phenomenon

Qualcomm 8994 platform supports the quick charging function, supports the charger whose input and output is 5v / 9v1.5a, and identifies the charger as A pure hardware process. When the Micro USB interface of the data line is inserted into the mobile phone slowly, the charger will occasionally detect the action as USB data communication due to the time sequence cannot meet the platform requirements, so it only provides 5 V 500 mA of input power, thus failing to realize the quick charging function. In the process of system test and simulated user test, it was found that many cases could not enter the fast charging phenomenon, which affected the consumer experience. When the mobile phone enters the quick charging state, the UI will display "quick charging" at the bottom of the lock screen, and the battery status will display "charging through ac power supply" in the battery information. However, when this failure occurs, the UI will display "charging in progress" at the bottom of the lock screen, and the battery status will display "charging through USB" in the battery information. Since the charging current is only 500 mA charging in USB mode, charging under this power will lead to charging time 4 to 5 times that of quick charging time, which will seriously affect the user experience.

2.2 failure cause analysis

2.2.1 charging identification principle

When the charger is plugged in, first the VBUS is connected to the sub-board of the USB channel on the side of the phone. According to the USB BC1.2(Battery Charge) protocol, within 300-900 ms after the VBUS is electrified (600 ms is set on the 8994 platform), if no D+ or d-short connection is detected, it will be judged as USB communication. If the D + and D - short answer the PMIC up D +, because the D + and D - short answer the phones side D + and D - and charger side D + and D - form A loop, so D - in the first high level at the same time, the high voltage charger will keep the D + the high level 1 s, 1 s D + and D - will be disconnected after, D - become low, identified as DCP (Dedicated Charging Port, the Port can provide more than 1.5 A current) after the D + and D - with A different level, communicate with PMIC, To confirm the support of several volts quick charging (the charger output VBUS voltage of 9 V in this project).

2.2 abnormal recognition waveform

When the charger is inserted into the phone, if only the first D+ is high level, then the D+, D- on the phone side and the circuit on the charger side are not connected, so the D- does not become high level, thus an exception occurs.

The 8994 platform thinks that the abnormal process is that the USB interface is inserted slowly, or the USB connector is not connected instantly (this connection may be on the side of the phone or on the side of the charger).

Therefore, in view of the two possible causes, we made the following analysis:

(1) in order to eliminate the problem caused by the connection of the connector, disassembly was carried out specifically for the insertion process to measure the conduction of the signal. Meanwhile, the test signal was connected to the oscilloscope and did not reproduce.

(2) if the insertion is slow, manually reproduce first. After many times of verification is indeed detected as USB communication failure phenomenon.

The following is the experimental analysis method of positioning problem and the solution:

2.3 problem verification method

A special experiment was carried out to see whether the problem was caused by slow insertion (since BC1.2 detection time was set at 600 ms, which was set by hardware and could not be modified by software. In fact, the value of 8994 platform was 680 ms, and if the detection value was exceeded, it would be recognized as USB). Detailed test methods are as follows:

(1) verify the relationship between the USB cable and the main board USB socket short connection and the D+ first detection

The D+ on the USB line was extracted, and the waveform was compared and analyzed with the D+ on the main board at the same time to confirm the short connection between the USB cable pin and the main board pin and the time sequence of the first D+ detection. The purpose of this experiment was to exclude the delay of the main board D+ signal and data line D+, and to eliminate the fault of the channel itself.

Waveform measured: D+ on the main board and D+ on the USB data line were triggered at the same time at 540 ms, excluding the abnormal D+ channel of the main board and data line.

(2) add the reference voltage on D- to detect the time interval between D+ and VBUS on the motherboard

USB d-plus 100k resistance to 0.35v (supplied by dc source), measure VBUS and D+ waveform, determine whether D+ d-short connection time exceeds the detection time (680 ms), if D+ d-short connection time is greater than 680 ms, the positioning problem. This experiment can rule out whether the problem is caused by abnormal D+ and d-channel (0.35v voltage also appeared in D+ at 330 ms in the test, indicating that D+ and d-channel are normal).

The above experimental process, connected to the oscilloscope to reproduce a week. According to the comparison of the pressure test of the USB cable plugged into the side of the phone and the charger, the results show that the average time of the VBUS plugged into the side of the charger D+ d-delayed is shorter than that of the one plugged into the side of the phone, but both meet the qualcomm detection time within 600 ms. Thus, it excluded the case that the path exception resulted in the failure to be pulled up according to the protocol D+/D-.

(3) waveform of abnormal state

As the data line of MicroUSB is longer than D+ and D- at pin pin, the signals of VBUS and D+D- will have a time difference when they reach the charging head due to this physical characteristic, but under normal circumstances they will not exceed the value specified in the protocol.

When the plug and pull speed is slowed down, the charging into the abnormal because the requirements of the protocol are not followed.

3 problem improvement methods

After repeated tests, the conclusion proves that the insertion process is slow and does not meet the time sequence. The waveform will show the abnormal waveform mentioned above, and then the high-voltage charger cannot be recognized.

The problem is solved by software UI prompt and background current lifting mechanism.

3.1 the UI prompt

When the insertion is slow and the user cannot enter the quick charging, the UI interface will prompt the user to "re-plug and unplug the USB data cable to enter the quick charging". After testing, the user can enter the quick charging.

3.2 background current lifting mechanism

When the user did not see the UI interface prompt to plug and unplug, we added the background current lifting mechanism on the BSP side. That is to say, if the user does not re-plug within 30 s and the background detects that the charging current is too small, the charging current will slowly increase to 1.5a required for quick charging. In this way, mobile phone charging can enter into quick charging and avoid affecting user experience.

4 conclusion

This paper introduces a method to judge the abnormality of quick charging. The method of solving the problem by software is given through experiment test and problem improvement. It provides a faster and more economical solution for the analysis and solution of such problems in the future.