Summary of questions from the "Huaxinbang" Cup Mobile Power Design Competition - Technical Edition

The "Huaxinbang" Cup Mobile Power Design Competition, hosted by Electronics Fans Network, sponsored by Shenzhen Huaxinbang Technology Co., Ltd., and supported by Huaqiang PCB, began registration on May 24. In order to facilitate the majority of contestants to better understand and participate in the competition, Electronics Fans Network summarized some frequently asked specification and process questions in the previous article. Now we summarize the competition questions - technical article, hoping to help everyone's design.

1. The external charging current should be realized by adding an external MOS or transistor. The corresponding current should be set by R1, but the corresponding setting voltage cannot be found in the data sheet. Please help explain!

Answer: The external charging current is achieved by adding an external MOS or transistor. The corresponding current is set by R1. The voltage of IC's EXT_CH is: when 5V is connected and the lithium battery is not connected, Vext-ch=5V; when 5V is connected and the lithium battery is connected, Vext-ch=0V

2. "Boost maximum output current, 1A/2A": requires the same output port to achieve 2A and 1A optional, or to have two output ports to achieve 1A and 2A output respectively;

A: "Boost maximum output current, 1A/2A": 1A, 2A are optional, and you can also have 2 output ports at the same time, one 1A and one 2A;

3. “Boost has CC function, CC value/maximum output current”: Does it require that the output current changes with the output voltage? Like the Nokia charger, the no-load voltage is 5.4V, and the output voltage is only 4.5V when fully loaded?

Answer: "Boost has CC function, CC value/maximum output current": the output current is constant. When the input lithium battery voltage decreases, the current remains constant.

3. Can the work be returned after it is submitted?

A: In principle, we hope to keep your work for our analysis. If you wish to return it, we can study the return method later. Please join the QQ group: 240833263. Our customer service staff will reply in time when there is a result.

4. (1) Does the boost circuit directly increase the voltage of the lithium battery to 5V? If I press the button on the key pin to enter the boost mode, will the level of pin 2 EXT_CH change?

Answer: 1. The feedback voltage of the boost circuit = 1.25V, so theoretically the external feedback resistor can be adjusted to change the output voltage; but the LX withstand voltage of the IC is 6V, so it is generally recommended to output 5V; if a high-voltage tube is used for isolation between LX and the inductor, the output can be 9V/12V;

2 EXT_CH is valid only when the battery is being charged, that is, it is 0; at other times, including boost mode and standby mode, the level of EXT_CH is 1;

(2) Is the power supply in the boost mode a lithium battery? If I want to charge my mobile phone, is it powered directly by the lithium battery? I thought the USB port at the back of the application diagram you provided was the charging port for the mobile phone.

A: The power supply in boost mode is a lithium battery. If you charge your phone, the power supply is directly from the lithium battery.

5. When Boost is working, the LED power display is constant? Isn't this directly output by the IC? Do I need to write a program to control it?

A: When boost is working, the LED part controlled by IC is not always on; press the button briefly, the LED will light up for 5 seconds and then go out; so if you want the LED to be always on, you need to add a peripheral circuit!

6. How can we achieve Boost full load efficiency > 92% without synchronous rectification?

Answer: 1. How much difference can there be between synchronous rectification and Schottky efficiency? 2. Try to make the efficiency as high as possible. If you can't achieve 92%, what is the highest you can achieve?

7. Does the output voltage of 5V mean that the output of the rechargeable battery is also a stable 5V after the voltage is boosted? In other words, does it mean that the rechargeable battery cannot be higher than 5V after it is fully charged?

Answer: Generally, a fully charged lithium battery has a voltage of 4.2-4.3V.

8. (1) Do I need to add the PCB routing to the designed circuit diagram?

A: Yes

(2) Are there any guidance materials?

A: Yes, please log in to the 4901 application guide in the technical support section of Hotchip's official website www.hotchip.com.cn, but the score of the works following the guide will be lower.

9.1) Do you design the circuit yourself, or draw it according to the downloaded materials, or can you modify the drawings in the reference materials?

2) What is the input voltage? Can anyone provide it? Is it a battery or a voltage regulator module?

3) How stable is the output voltage required to be?

4) Does the overall meaning mean designing a charger?

Answer: 1 Design it yourself;

2 The input voltage is provided by an external 5V, such as USB or charger; Pin 15 of the chip is connected to the battery;

3. Boost output = 5V, because the withstand voltage of IC is 5V, so if LX does not isolate GND from high voltage, the output can only be 5V, otherwise the chip will burn out; if it does, the output can be 12V or even higher

4 Not so limited; it has many uses because it integrates linear charging part, boost part, button control part, LED indicator part, LED flashlight, etc.

10.1. You all say this is a mobile power source. When I design the finished product, should I add a battery? If so, what kind of battery should I use? A general rechargeable battery or a mobile phone battery?

2. I saw the picture of your sample: the charging part and the discharging part are separated, each of which belongs to a circuit board. Considering the product's visibility, it is good to divide them into two circuit boards, but if I design them into one circuit board, will it affect your rating of me?

Answer: 1. The selection of battery is definitely up to you.

2. The sample board picture is the work of other engineers. It is for reference only. No matter it is one board or two boards or any other style, you can give full play to your imagination. It will not affect the score. What we want is your creativity. 11. Does your chip output support synchronous rectification?

Answer: No.

12. Can it be simulated? Otherwise, how can we make sure the circuit is correct before making the finished product?

A: No! There is no model of 4901.

13. Are there any requirements for the structure of PCB design? After designing, do I need to add a shell, or can I just fix it on a board?

Answer: There are no specific requirements for the shape of the shell and PCB, but it will affect the score of structural creativity.

14. I don’t know how the chip performs? The data given is: High efficiency of boost circuit: 90% Requirement: Boost full load efficiency> 92% It is quite difficult

A: The built-in boost is actually a controller. The full-load efficiency mainly depends on the peripheral power devices: inductor, MOS, Schottky, etc.

15. What is the input voltage range of this mobile power supply? What is the output voltage range? I hope you can be more specific.

Answer: Hello, the input voltage range of the mobile power supply is: 4.5V-6V, but it is recommended that you define the input voltage as 5V, so that it is more compatible.

16. Does the circuit schematic need to be redesigned? Or should the PCB be designed according to the external expansion circuit provided?

A: Hello, designers can add peripheral functional circuits and then design; the external expansion circuits we provide are for designers to use as reference for design.

17. When will the chip be delivered?

A: The chip will be sent together with your PCB sample. The PCB sample is 40% off, sponsored by Huaqiang PCB. The chip is completely free, sponsored by Huaxinbang. If you make the board yourself, you need to submit the design plan to the competition organizing committee, and the chip will be issued after the review.

18. Can the charging current be adjusted? Will it be automatically cut off after charging for too long?

Answer: The charging current can be adjusted and increased; it will automatically cut off when charging to 4.25V.

19. If the battery cannot reach 4.25V, should it be charged continuously?

A: It will automatically cut off when charging reaches 4.25V. This means that lithium batteries can be used directly without the need for additional circuit components.

20. Looking at this battery charging diagram, is the battery voltage 3.7v lithium battery selected?

What do the values ​​of R1 and R5 in the external expansion application diagram depend on? Is it related to the charging current of the internal battery?

The function and selection of MOS tubes, N-channel depletion type, what are the requirements for selection...? Are all MOS tubes P-channel enhancement type? Is P-channel certain? Is the MOS tube in the instructions wrong?

Answer: 1. The battery is a 3.7V lithium battery with a full voltage of 4.25V. 2. The resistance of the two resistors in the external expansion application diagram is to adjust the external expansion current. Its value is related to the threshold voltage of the selected MOS tube and has nothing to do with the internal charging current. 3. The MOS tube is to generate a large charging current. Choose a P-channel enhancement type. The selection mainly depends on how much current you want to expand. The MOS tube can generate the current you need. The description says P tube. MOS tubes include P-channel enhancement type, P-channel depletion type, N-channel enhancement type, and N-channel depletion type.

21. Why do we need to use the external current expansion function, and 2A? Do general digital devices need such a high current? What does the selection of MOS tubes depend on?

A: There is no rule that external expansion is required. External expansion is reserved for customers with demand. Nowadays, large-screen mobile phones or IPADs all require 2A. The MOS tube is mainly related to the current you need to expand externally.

22. What is the function of the PNP transistor? Why is a 0.5R resistor added to the recommended circuit for charging expansion? Will it affect the voltage detection inside the chip?

Answer: The function of PNP is to generate a large charging current, which is mainly used for current limiting.

23. In standby mode, what is the KEY pin level?

A: In standby mode, the voltage level of the key pin is the battery voltage minus a diode drop.

24. When charging a lithium battery, if an external 2A charge is used, is the charging mode linear or PWM? Can the charging be current limited?

Answer: The charging mode for lithium battery is linear mode, and the charging mode for external mobile phone is PWM mode. The charging current can be adjusted. The key is the power consumption of 2A. Can you provide a better solution? Thank you!!