Abstract: This paper introduces the main characteristics and development status of digital power supply systems, briefly analyzes the performance characteristics and working principles of various chips that make up the system, and focuses on the circuit design of digital power supply systems. Specific solutions are provided for optimizing the design of digital power supply systems. Keywords: Digital power supply; Digital signal processor; Microcontroller; Fault management; Overcurrent protection; Digital control 0 Introduction Currently, switching power supplies are developing towards intelligence and digitalization. The recently launched intelligent digital power supply system, with its excellent characteristics and complete monitoring functions, is attracting attention. Digital power supplies provide intelligent adaptability and flexibility, possessing the ability to directly monitor, process, and adapt to system conditions, and can meet any complex power requirements. Furthermore, digital power supplies can ensure the long-term reliability of the system through remote diagnostics, including fault management, overcurrent protection, and preventing downtime. 1 Main Characteristics and Development Status of Digital Power Supply Systems 1.1 Main Characteristics of Digital Power Supply Systems Digital power supply systems have the following characteristics: 1) They are intelligent switching power supply systems with a digital signal processor (DSP) or microcontroller (MCU) as the core, and digital power drivers and PWM controllers as the controlled objects. Traditional switching power supplies controlled by microcontrollers (μP or μC) generally only control the power supply's startup and shutdown, and are not true digital power supplies. 2) Employing "Fusion Digital Power" technology, it achieves an optimized combination of analog and digital components in the switching power supply. For example, the analog component used in the power stage—the MOSFET driver—can be easily connected to the digital power controller to implement various protection and bias power management functions, while the PWM controller is also a digital-controlled analog chip. 3) High integration, achieving power system-on-chip integration, integrating a large number of discrete components into a single chip or a group of chips. 4) It can fully utilize the advantages of digital signal processors and microcontrollers, enabling the designed digital power supply to achieve high technical specifications. For example, its pulse width modulation (PWM) resolution can reach 150ps (10-12s), which is unattainable by traditional switching power supplies. Digital power supplies can also realize multi-phase control, nonlinear control, load current sharing, and fault prediction functions, providing convenient conditions for the development of green and energy-saving switching power supplies. 5) It facilitates the construction of distributed digital power supply systems. 1.2 Current Status of Digital Power Supply System Development With the development of modern science and technology and the demand from the switching power supply market, the international community began developing digital power supply systems in the early 21st century. In March 2005, Texas Instruments (TI) announced the launch of innovative digital power supply products that not only significantly improve the performance of power supply systems but also greatly extend their lifespan. The company also showcased the Fusjon Digital Power solution to demonstrate that digital power supply systems can achieve high performance and design flexibility at a highly competitive low cost. This solution includes the following three types of chips: 1) UCD7K series digital power drivers (including UCD7100 and UCD7201); 2) UCD8K series PWM controllers (including UCD8620 and UCD8220); 3) UCD9K series digital signal processors (UCD9110/9501). These chips have been serialized and officially launched in the fall of 2005. This product supports power systems from AC line to load and can be widely used in telecommunications facilities, computer servers, data center power systems, and uninterruptible power supplies (UPS). 2. Basic Structure of Digital Power Supply System 2.1 Digital Power Drivers Both the UCD7100 and UCD7201 are digital control power driver chips. The difference is that the UCD7100 is a single-ended output, while the UCD7201 is a double-ended output. Both have a rated output current of ±4A and can drive MOSFET switching power transistors. Both are compatible with the UCD9110/9501 digital controller. The main controller can monitor the output current, quickly detect overcurrent faults, and rapidly shut down the power supply with a detection cycle of only 25ns. Taking the UCD7100 as an example, its internal block diagram is shown in Figure 1. It mainly includes a 3.3V voltage regulator and reference voltage source, a trigger, a Schmitt trigger comparator, an undervoltage shutdown circuit, control gates, and a TrueDrive driver. "TrueDrive" is a proprietary technology of TI, and it is a hybrid output stage composed of parallel bipolar transistors and MOSFETs forming a pull-up/pull-down circuit. Its advantages include strong driving capability, normal output even at low voltages, and overvoltage and undervoltage protection for controlling external power MOSFETs with extremely low output impedance. The power MOSFETs do not require a Schottky clamping diode for protection. The UCD7100 can provide a high peak current to the gate of the MOSTFET within a few hundred ns, quickly turning on the driver. The high-impedance digital input (IN) of the UCD7100 can receive signals with a logic level of 3.3V and a maximum switching frequency of 2MHz. A Schmitt comparator isolates the internal circuitry from external noise. If the controller's PWM output remains high and an overcurrent fault occurs, the current detection circuit shuts off the driver's output, and the system enters retry mode. The chip can be restarted via the watchdog circuit inside the DSP or MCU. The UCD7100's internal 3.3V/10mA voltage regulator can be used as the power supply for the digital controller. 2.2 PWM Controller The UCD8220/8620 is a dual-ended push-pull PWM controller digitally controlled by a DSP or MCU. The difference between the two is that the UCD8220 can start using a low voltage of 48V, while the UCD8620 has an internal 110V high voltage start-up circuit. The internal block diagram of the UCD8220 is shown in Figure 2. It mainly includes a 3.3V voltage regulator and reference voltage source, a pulse width modulator (PWM), drive logic, a push-pull driver, an undervoltage shutdown circuit, a current limiting circuit, and a current detection circuit. The UCD8220/8620 can operate in peak current mode or voltage mode, and can not only program the limit current but also output a digital limit current flag that can be monitored by the main controller. The timing waveforms of the UCD8220/8620 are shown in Figure 3. 2.3 Digital Signal Processor (DSP) The UCD9501 is a digital signal processor from TI specifically designed for digital power systems. Similar products include the TMS320F2808 and TMS320F2806. Internally, these components mainly include a 100MHz 32-bit CPU, clock oscillator, three 32-bit timers, watchdog circuit, internal/external interrupt controller, SCI bus, SPI bus, CAN bus and IC bus interface, 12-channel PWM signal output, system controller, 16-channel 12-bit ADC, 16K×16 Flash, 6K×16 SARAM, and 1K×16 ROM. It adopts a standard 3.3V input/output interface and is fully compatible with the UCD8K series. It can be programmed using Power PAD™ HTSSOP and QFN software packages. 3. Circuit Design of the Intelligent Digital Power Supply System The intelligent digital power supply system consists of six parts: PWM, power driver, DSP, interface circuit, display, and keyboard. The system block diagram is shown in Figure 4. The digital signal processor UCD9501 in the figure is connected to the keyboard and display through an interface chip. Users can not only observe the current power parameters on the display but also modify the power parameters at any time via the keyboard. To simplify configuration, an intelligent digital power supply system can also be constructed using a digital signal processor (UCD9501) and a digital control power driver (UCD7100), as shown in Figure 5. The AC voltage, after rectification and filtering, yields a +36–72 V DC input voltage U1, which is connected to the primary winding of the high-frequency transformer. After being divided by resistors R1 and R2, it is connected to the analog input terminals AN1 and AN2 of the UCD9501, respectively. The other end of the primary winding is connected to a power MOSFET. R3 is a current-limiting resistor. R4 is a current-sensing resistor. The output voltage of the bias winding, after rectification and filtering by VD1 and C1, yields a +12 V DC bias voltage, which is connected to the power supply terminal (UDD) of the UCD7100. The 3.3 V output from the UCD7100 provides power to the UCD9501. The secondary rectification and filtering circuit consists of VD2, L, and C2, with VD3 being a freewheeling diode and UD being the DC output voltage. The pulse width modulation (PWMA) signal output from the UCD9501 is sent to the IN terminal of the UCD7100. The current limit flag (CLF) terminal of the UCD7100 is connected to the interrupt terminal (INT) of the UCD9501, and the current limit setting terminal (ILIM) is connected to the GMTR terminal of the UCD9501. An optocoupler isolation amplifier can be used to isolate the output stage from the input stage. When UDD=12V, the load capacitance CLOAD=10nF of the UCD7100, and the switching frequency f=300kHz, the bias power consumption is P=CLOADUDD2=10nF*(12V)2*300kHz=0.432W. The bias current I=P/UDD=0.432W/12V=0.036A. If the UCD7201 is used, two external power MOSFETs can be driven. Furthermore, a digital power supply system can be formed using the UCD9501 and UCD8620. 4. Conclusion Digital power supply systems possess significant advantages such as high integration, cost-effectiveness, comprehensive power management functions, simple peripheral circuits, and user-friendly design capabilities, creating favorable conditions for the optimized design of intelligent power supply systems.