New system power chip to create large-screen LCD TV and monitor applications
For the large LCD screen, everyone is familiar with it. I want the TV at home to look at the picture and the movement is smooth. The system power chip plays a key role. Fujitsu Semiconductor recently introduced a new product, a 5-channel system power chip for large-screen LCD panels, named MB39A302. Its function is not small, it can provide five kinds of voltages required for large-screen LCD panels through a single chip. Thanks to the built-in VCOM power amplifier, gate voltage shaping circuit and high current drive switching FET, the MB39A302 is ideal for applications such as large-screen LCD TVs and monitors.
Figure 1: The appearance of the MB39A302.
5 channels are useful
The MB39A302 is a system Power Supply chip consisting of a 5-channel power control section, including a 1-channel buck converter, a 1-channel boost converter, a 2-channel charge pump, an LDO channel, and VCOM regulated power. Amplifier and gate voltage shaping circuit. The built-in switching FET's buck converter is a voltage mode non-synchronous converter; the built-in switching FET boost converter also uses a voltage control mode.
Rich features
The device has many rich features, such as a power supply voltage range of 8 to 14V; a DC/DC converter with a built-in switching FET is 2 channels; and an output voltage feedback mode charge pump is 2 channels; it can be implemented with feedforward control. Linear adjustment function (Vlogic, Vs); built-in phase compensation component; built-in gamma buffer high precision LDO (Vref_o), feedback voltage ± 0.5%, maximum 60mA; built-in power supply delay access adjustable function gate voltage shaping circuit Built-in soft-start circuit without load dependence; built-in external p-channel gate control function for Vs timing control; built-in rising edge timing control function; various protection functions including short circuit protection, over current protection, over voltage protection, low Voltage malfunction prevention and overheat protection; frequency switching function (500kHz/750kHz) can be realized by pin control.
Distinctive function
We can understand the function of the device through the functional block diagram of Figure 2. Here we mainly introduce the power supply voltage function of MB39A302.
Figure 2: Functional block diagram of the MB39A302.
The power supply voltage function of the MB39A302 is used to generate output voltages for microcontrollers (Vlogic), source drive (Vs), and gate drive (VGL, VGH) required for normal LCD panels.
First look at the buck converter that generates the Vlogic voltage. Its built-in overvoltage protection function can prevent the device from being damaged due to overvoltage caused by faults such as open FB2 terminals or short circuit to ground. The protection circuit monitors the output voltage of the buck converter through the OUT terminal. When the OUT terminal voltage exceeds 3.7V, the NMOS power FET connected to the LX2 terminal stops operating, and the inductor current decreases, thereby reducing the output of the buck converter. When the voltage drop at the OUT terminal is below the voltage protection threshold, the buck converter resumes normal operation.
Look at the boost converter that generates the Vs voltage, which uses a built-in N-channel switching FET and pulse width modulation (PWM), and uses an external freewheeling diode to form a non-synchronous boost converter. The boost converter obtains excellent input voltage regulation characteristics through the input voltage feedforward voltage mode, and can also set the phase compensation through an external component. The built-in P-channel switching FET (opening resistor 18Ω) connected between the SW port and the OS port is linked with an external freewheeling diode, and the boost converter can always operate in continuous mode without being affected by the load. Phase compensation can be easily implemented.
There is also a reverse charge pump that generates VGL, which operates at a fixed switching frequency; the output voltage can be set by a resistor connected to the FBN terminal. The adjustment of the regulator is achieved by controlling the pump current of the drive circuit.
Finally, a boost charge pump that generates VGH operates at a fixed switching frequency; the output voltage can be set by the output set resistor connected to the FBP terminal. The adjustment of the regulator is achieved by controlling the pump current of the drive circuit.
In addition, Vlogic, VGL, VGH, and Vs are all equipped with a soft-start function that prevents inrush current during startup. The soft start time Vlogic, VGL, VGH is about 3ms (fixed value), and Vs can be set by an external capacitor.
Design support and planning
In order to provide a low-cost system supporting a large-screen liquid crystal display panel and a high frame rate, Fujitsu Semiconductor has developed a system power chip by integrating DC/DC converters with the core of power chip simulation technology accumulated over many years.
Figure 3: MB39A302 Evaluation Board.
To help users evaluate and develop products as quickly as possible, the evaluation board Fujitsu Semiconductor has also introduced an evaluation board for the MB39A302. In the future, Fujitsu Semiconductor will further develop a liquid crystal display panel system power supply with programmable output voltage setting through an I2C interface for a variety of liquid crystal display panels with the goal of integrating and reducing peripheral components, helping customers to shorten product development. Cycles reduce development costs.
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