[Wuhan University of Technology School Competition] LM5122 boost module

Xiao Zhuohua, member of the first prize team of the 13th Wuhan University of Technology Electronic Design Competition, Gao Pengfei, Wang Biao, instructor Zhang Jialiang

• This part of the circuit is built with the LM5122 chip as the core. The LM5122 is a synchronous boost controller with polyphase functionality, primarily intended for high-efficiency synchronous boost regulator applications. This control method is based on peak current mode control. Current mode control provides inherent line feedforward, cycle-by-cycle current limiting, and simplifies loop compensation. Switching frequency is programmable to 1 MHz. Two rugged N-channel MOSFET gate drivers with adaptive dead-time control allow for higher efficiency.
• The LM5122 package is divided into 20-pin and 24-pin packages. This design uses a 20-pin package. Its chip pin distribution and functions are shown in the figure below.
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• Introduction to several main pins of the LM5122 chip: Pin 5 is the power input end of the VCC regulator. Use short, low-impedance paths to the input capacitor and source power connections. Pin 17 is the VCC bias supply pin and is decoupled locally to the PGND pin using a low ESR/ESL capacitor as close to the controller as possible. Pin 9 (AGND) is the analog ground terminal and returns the internal voltage reference and analog circuitry.
• Pin 11 (COMP) is the output of the internal error amplifier. Connect the loop compensation network between this pin and the FB pin. Pin No. 10 (FB) is the feedback terminal and is the reverse input of the internal error amplifier. A resistor divider from the output to the TO pin sets the output level voltage. The threshold on the FB pin is 1.2V. If the FB pin voltage is higher than 2.7V on initial power-up, the controller is assigned to slave mode.
• The input voltage in this design is 12V. The output terminal is designed as follows: a resistor and two capacitors are connected between the chip COMP pin and FB pin to form a loop compensation network. At the same time, the threshold on the FB pin is 1.2V, so the output voltage can be adjusted through resistor division. As shown in Figure 2, the FB terminal is connected to ground through a 6.8kΩ and adjustable potentiometer, and two series resistors are connected to the output terminal.
• When the potentiometer resistance is 0Ω, the output voltage is about 22V
• When the potentiometer resistance is 10kΩ, the output voltage is about 9.6V
• Therefore, the output voltage through the potentiometer R15 is about 10V-22V adjustable, which meets the 15V output voltage required by the question.
• The schematic diagram of the LM5122 boost circuit is shown below
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