CH224K+SC8721 adjustable power supply verification board

1. Overall description of the verification board.
The verification board uses CH224K for PD deception. The voltage obtained by deception is used to achieve step-up and step-down output through the SC8721 chip, and the 3.3V voltage is output through the LDO or DC-DC module (choose one of the two) for use by the microcontroller.
(1) When CH224K chip deceives voltage, you can choose single resistor configuration or level configuration (controlled by microcontroller) to select a voltage range among 5V/9V/12V/15V/20V (the charger needs to support the corresponding protocol and voltage output).
(2) The SC8721 buck-boost chip can set the output voltage through external resistors or IIC communication (communication with the microcontroller). The external resistance of the verification board circuit is fixed. When the IIC control output voltage is not tested, the default output voltage is around 5V.
(3) The verification board provides three common LDO packages: SOT-23-5, SOT-223-4, and SOT-23-3. Just choose a suitable LDO with an output of 3.3V for welding.
(4) In view of the possible heating problems of LDO when the voltage difference is large, a DC-DC solution is also provided for the 3.3V output. In order to facilitate the direct use of the CN3903 buck module available on the market, the unit price is about 3 yuan. , link below.
[Taobao] https://m.tb.cn/h.UQAOlFA?tk=zUhYdeyPmy3 CZ3457 "DC-DC mini step-down power module 3A car power supply 5V-30V to 3.3V/5V/12V fixed output" Click the link to open it directly Or search on Taobao and open it directly
2. Description of each part of the verification board
2.1 CH224K voltage deception circuit
Type-C has a fuse at the bottom. You can replace the 0 ohm resistor in the 1812 package in the physical picture with a fuse.
The commonly used connections at ①, ②, and ③ are as shown in the figure above. If you need to change it to the circuit shown in the CH224K manual below, that is, when only using the PD protocol and E-Mark simulation function, you can adjust the jumper cap.
④ and ⑤ are frequently changed parts during verification.
When the jumper cap at ④ is connected to the second and third pin headers, you can configure the voltage range using a single resistor by selecting the jumper cap at ⑤ to connect.
When the jumper cap at ④ is connected to the first and second pin headers, the high and low levels of the CFG1, CFG2, and CFG3 pins can be controlled by the microcontroller to configure the voltage range.
2.2 3.3V output circuit The
jumper cap at ① selects whether to set VBUS as the LDO voltage input;
the jumper cap at ② selects whether to set VBUS as the DC-DC module input;
the jumper cap at ③ selects the 3.3V output from the LDO part;
④ For the jumper cap, select whether the 3.3V source is LDO or DC-DC module; (the picture shows the previous version, the pin size selection was wrong, so Dupont wire was used instead of the jumper cap, the new version has been corrected)
The verification board can also be welded accordingly The pin header of the output voltage is convenient for external power supply. The 3.3V voltage is mainly used to power the microcontroller. If the microcontroller is powered by other power sources, this part of the circuit can be ignored.
2.3 SC8721 buck-boost circuit
The jumper cap at ① selects whether to set VBUS as the input voltage of SC8721;
the jumper cap at ② selects whether to set 3.3V as the IIC communication pull-up voltage, usually the on state is selected;
C7 and C10 on the development board , C11, R10, R11 can be optionally welded.
The pin header on the right side of SC8721 leads to some control signal lines of the chip, as shown in the figure below.
Since the SC8721 is packaged in QFN, manual welding is very difficult. It is recommended to check it carefully after the welding is completed.
3. Microcontroller control demonstration.
I happen to have some ESP32C3 development boards on hand, which are used to simply demonstrate the control of decoy voltage file selection and voltage output control. The three buttons, from left to right, are:
Button 1: Decelive voltage gear cycle switching
Button 2: Reduce the output voltage
Button 3: Increase the output voltage
The demonstration can be seen in the video at the end of the article.
4. Follow-up (Dove)
(1) Test the output voltage performance parameters
(2) Make an adjustable power supply based on this solution.
 
If there is any unreasonableness in the design, friends are welcome to criticize and correct it in the comment area~