I. Design Flow of Power Management Circuit
The design flow of the power management circuit is as follows:
1. Analyze the power requirements and determine the main parameters of the power management circuit, including output voltage and current, input voltage, conversion efficiency, etc.
2. Select key components, including transformers, diodes, field-effect transistors, etc.
3. Design the circuit schematic and determine the circuit parameters and design scheme for each part.
4. Perform simulation analysis to ensure the reliability of the circuit operation and that its electrical performance meets the requirements.
5. Design and layout the circuit board, convert the schematic diagram into a circuit wiring diagram, and determine the placement and connection methods of the components.
6. Fabricate circuit boards, assemble components, and debug the circuit to ensure that the circuit achieves the design parameters and performance.
7. Conduct reliability testing to ensure the long-term stability and reliability of the power management circuit.
II. Common Problems and Solutions in Power Management Circuit Design
1. Electromagnetic compatibility issues
Electromagnetic compatibility (EMC) is a critical issue in power management circuit design, involving the selection of circuit boards and components, wiring design, and grounding. The solution involves minimizing loop area during the initial circuit board design phase, while employing various suppression measures such as filter capacitors and inductors.
2. Output voltage noise problem
Output voltage noise is a common problem in power management circuit design. We can reduce this noise by using filtering measures, such as adding capacitors or inductors.
3. Over-temperature protection issue
In power management circuits, issues such as overload and overcurrent can occur, causing the circuit temperature to rise and shortening its lifespan. Over-temperature protection circuits can address this; once the circuit temperature exceeds a certain level, protective measures are triggered, effectively protecting the circuit and related equipment.
In summary, power management circuit design is a crucial part of electronics technology, impacting the reliability and stability of electronic products. Power management circuit design requires detailed planning and execution based on specific power requirements and equipment specifications. It also necessitates considering common issues and implementing appropriate solutions. Continuous learning and exploration are essential in power management circuit design to improve design skills and contribute to the healthy development of electronic products.
III. Power Management Circuit Design Capabilities
(1) Charging current control
The charging current is controlled by R8P and R9P. The maximum charging current is 1200/R8P, and the maximum charging current is less than 6000/R9P, where 6000/R9P is the DC power supply current limit setting. When R8P=1.5 kΩ and R9P=3 kΩ, the DC power supply current limit is 6000/3000=2 A, and the charging current limit is 1200/1500=0.8 A. If R8P=1.2 kΩ and R9P=5 kΩ, the DC power supply current limit is 6000/5000=1.2 A, and the charging current limit is 1200/1200=1 A.
This system uses R8P=1.5 kΩ and R9P=3 kΩ.
(2) System voltage switching
When both DCIN and USB are connected to the system power input, DCIN input takes priority, and USB input is automatically turned off. DCIN simultaneously supplies battery charging and MBAT (system power supply), and the battery also helps reduce MBAT voltage fluctuations.
Once the battery is fully charged, the charging circuit is partially shut down, and DCIN supplies power to the MBAT system, with the MBAT voltage stabilizing at 4.4 V.
(3) Charging indicator
The MAX8903 pin DOK is a DC power connection indicator output, active low. The indicator light D2P is used to indicate the DC power connection status, and the signal is also connected to the CPU's GPIO pin for software detection of this status.
The CHG pin of the MAX8903 is the charging indicator output, which is active low. The D3P indicator is used to indicate the charging status, and the signal is also connected to the GPIO pin of the CPU for software detection of the charging status.
The FLT pin of the MAX8903 is the fault indication output, which is active low. The indicator light D1P is used to indicate the fault status, such as charging timeout.
(4) Battery temperature protection
The MAX8903 pin THM is connected to a 10 kΩ negative temperature coefficient thermistor to GND. This thermistor is used to detect the temperature change of the battery during charging. When the battery temperature exceeds the set limit temperature, charging is temporarily stopped until the battery temperature drops to a safe range.
