“LM5036 is a highly integrated half-bridge PWM controller that integrates auxiliary bias power supplies to provide high power density solutions for telecommunications, data communications, and industrial power converters. LM5036 contains all the functions required to implement a half-bridge topology power converter using voltage mode control. This device is suitable for the primary side of isolated DC-DC converters with input voltages up to 100V.
LM5036 is a highly integrated half-bridge PWM controller that integrates auxiliary bias power supplies to provide high power density solutions for telecommunications, data communications, and industrial power converters. LM5036 contains all the functions required to implement a half-bridge topology power converter using voltage mode control. This device is suitable for the primary side of isolated DC-DC converters with input voltages up to 100V. Compared with traditional half-bridge and full-bridge controllers, LM5036 has its own irreplaceable advantages:
The integrated auxiliary bias power supply supplies power to the LM5036 and the primary and secondary side components without the need for external auxiliary power supplies, reducing the size and cost of the circuit board, and helping to achieve high power density and good thermal reliability.
The enhanced pre-bias startup performance can realize the monotonic increase of the output voltage and avoid backflow current when the load is started under voltage.
The cycle-by-cycle current limit is improved by pulse matching, resulting in a uniform output current limit level within the input voltage range, and it can also prevent transformer saturation.
For this reason, starting from the controller application point of view, we design a typical application circuit based on the LM5036 controller. The evaluation board LM5036EVM-264 uses the following design indicators. In the design example part of the LM5036 data sheet, the same design circuit is also used for illustration.
The following figure shows the design schematic diagram and function description of the LM5036 evaluation version.
The upper part of the schematic diagram is the half-bridge isolation circuit and the secondary side synchronous rectification circuit. The middle part is the auxiliary power part of the Fly-buck structure.
The power (1) generated by Fly-buck on the primary side is used to supply power to the LM5036. The power Vaux2 (2) generated on the secondary side supplies power to the components on the secondary side, such as operational amplifiers, optocouplers, and isolation drivers. As mentioned earlier in the pre-bias startup section, Vaux2 participates in the pre-bias startup process at the same time as an enable signal to communicate between the primary side and the secondary side.
LM5036 REF pin (4) is a 5V voltage output with 39mA drive capability. In the design of the LM5036 evaluation board, the REF output is used to power the isolated drive UCC21225A and the optocoupler on the primary side. In other designs, REF can also be used to power other ICs or devices on the board.
The dual PWM (5) output of LM5036 has a 2A drive capability. In the evaluation board design, it directly drives the power tube of the half bridge without the need for additional drive circuits.
The dual synchronous rectifier SR output of LM5036 drives the synchronous rectifier tube on the secondary side through isolation drive. In applications with lower input voltage, synchronous rectification can improve efficiency.
The input pin VIN of LM5036 can be directly connected to the maximum voltage input of 100V (6). In applications that require an input greater than 100V, the LM5036 can also support application scenarios greater than 100V through the configuration of the connection circuit.
The mark (7) part of the schematic diagram is equipped with jumpers to select the peripheral circuit of the ON/OFF pin of the LM5036, so as to configure the LM5036 to work in a locked or auto-start state when the error is cleared.
The EVM board-level distribution of LM5036 is also relatively clear, as shown in the figure below, including the input filter part, the half-bridge topology and the secondary side rectification part, the integrated auxiliary source part, and the feedback loop part of the secondary side feedback. The overall design has an input voltage of 48V, an output voltage of 12V, and a full load current of 8A; in the entire EVM design document, there are detailed design procedures and related test waveforms. This article focuses on introducing some typical test waveforms and some calculation documents in the design to improve design calculation efficiency.
The figure below is the efficiency curve of the LM5036 evaluation board. It can be seen that even in the light load range, the evaluation board can achieve higher efficiency and a smoother efficiency curve. When the input voltage is low, a higher duty cycle can be achieved, which helps to improve efficiency.
For the pre-bias start function of LM5036:
The following figure is the test waveform of pre-bias startup. The test condition is that the input is 48V, and the output has a voltage of 2V (4-channel waveform) when starting. The blue waveform is the primary switching waveform, the green is the output voltage, and the yellow is the output Inductor current. It can be seen that when the output voltage is pre-biased with 2V, it can achieve a monotonous rise after startup, without falling or overshooting output.
LM5036EVM pre-bias startup test
In the entire LM5036EVM-264 evaluation board design process, in addition, there are many test waveforms, such as output voltage ripple, load dynamic test, static voltage and current, switch node test and many other test items. Generally speaking, as a DC/DC isolated power supply controller, LM5036 has unique advantages in half-bridge design, full-bridge application and other fields. With the development of power supply products in the market, the power density becomes higher and higher. Under reliability requirements, LM5036 is a very good choice for isolated power applications. Using the typical LM5036 design application skills mentioned in this article can greatly save research and development time and improve design efficiency. In the follow-up blog, we will focus on the major advantages of LM5036.