Talk about the backlight driver chip of the LCD on the mobile phone
LCD is one of the most important components on mobile phones. The effect of LCD display directly affects the user's intuitive experience. The LCD backlight driver chip is also one of the factors that have an impact. The LCD backlight driver chip with good performance can make the LCD display clear, uniform brightness, no flickering, etc., and the high-efficiency driver chip increases the standby time of the mobile phone, so choosing a suitable and excellent LCD backlight driver chip is very important.
The backlight driver chip to be selected is determined according to the LED connection method in the LCD screen. There are several commonly used backlight driver chips: boost DC/DC (inductor) type, charge pump (capacitor) type, and linear type. The following table is a comparison of these types:
Inductor boost DC/DC utilizes the energy storage characteristics of the inductive and capacitive components to boost the Vbat voltage to drive the LEDs for energy conversion from Vbat to the load LED. Inductor boost DC/DC is mainly used to drive the backlight LED is a series LCD screen. The advantage of the way of connecting LEDs in series is that the operating current of each LED is the same, so the illumination is basically the same and the brightness is uniform. The advantages are obvious in large-size screens and more applications. However, with Inductor boost DC/DC, due to the presence of inductance and the switching action of the internal switch, interference and noise may occur, which may interfere with other parts of the circuit, affecting the RF performance of the mobile phone, so when designing the circuit and PCB layout Pay special attention.
Fairchild offers a range of Inductor boost DC/DC backlight driver ICs, a synchronous boost boost DC/DC driver in the 53 series, with a maximum efficiency of 87%, a maximum Vout voltage of 16V, and the ability to drive 2~ 4 LED. Another feature is the integration of a P_MOSFET. In the case of the shutdown of the chip, the PMOSFET can be reliably turned off, thus cutting off the entire current path without any leakage current. This feature is used in PM_OLED drive. The most advantageous time is that some manufacturers' chips are turned off due to the existence of Diode on the current path, and current will flow from Vbat to form a large leakage current, which increases the power consumption of the system.
Figure 1 53 Series Block Diagram
Due to the backlight driver chip used as a parallel LED, the current match index has been significantly improved, and the cost is far lower than the Inductor boost DC/DC type, so the LCD screen with parallel LED lights is coming. The more mainstream. The backlight driving chips used for such LCD screens mainly include a capacitor charge pump type and a linear type. They have low electromagnetic interference, low noise, and cost advantages, so the application is more and more extensive.
The Fairchild 57 series is a charge pump type backlight driver. The current two products are all 6 channels and can work in 1x or 1.5x mode. One can divide 6 channels into 2 groups (4, 2), each group can be independently controlled by PWM signal. The advantage of this is that the design is flexible, and all 6 channels can be used for LCD backlight. Four channels are used for the backlight LED driving of the LCD, and two channels are used for the LED driving of the keyboard. Its efficiency can reach up to 92%, current matching is within 3%, and the typical value is 0.4%, which is leading in the industry. The other is to divide the 6 channels into 5 groups (2, 1, 1, 1, 1). Each group can be controlled independently through the I2C bus, and the design is more flexible.
Figure 2 57 Series 6-channel charge pump backlight driver
The Linear type backlight driver does not require an external inductor or capacitor for energy conversion. It uses a step-down method to set the current to drive the LED. Therefore, the Vf of the LED is not required to be too high. Due to the development of LED technology in recent years, the Vf of LEDs has become lower and lower, and has dropped to 3.2V or even lower. Therefore, the backlight type of the Linear type has become widespread, and the dropout of the Fairchild 56 series of the Linear backlight driver chip is 50mv. More advanced. In the mobile phone's main working battery voltage Vbat 3.6V-3.8V, the 56 series work efficiency can be maintained at 85% or higher.
The 56 Series linear backlight driver is available in 2, 4 and 6 channels. The backlight current is set by an external resistor, and the software 32-level dimming can be realized through the single wire interface.
Washing Machine Motor,Spin Motor Of Aluminium Wire,Washing Machine Motor Shaft,Automatic Washing Machine Spin Motor
WUJIANG JINLONG ELECTRIC APPLIANCE CO., LTD , https://www.jinlongmotor.com