[Text / "High-tech LED - Technology and Applications" September issue]
Since the advent of liquid crystal display technology in the 1960s, due to its convenience, LCD screens have become an indispensable highlight in a variety of human-machine interfaces. Ultra-thin, power-saving, flicker-free, low-radiation features open the door for LCD screens in a variety of portable terminal markets. With the advent of the intelligent era, without the LCD screen of more than 3 inches, your mobile phone has no way to enjoy the entertainment brought by the intelligent era. The liquid crystal display itself does not emit light, and there is a demand for backlight driving. In the era when LEDs were used as backlights for LCD screens, how to choose a suitable LED driver solution to meet this trend of pursuing energy-saving, safe and green has become a headache for engineers. Series or parallel? Low or high pressure? Efficiency or cost?
8LED parallel drive SGM3145 ignores the high-voltage processing problem of low-voltage system, without considering the size and EMI of power inductors, bringing a lot of convenience to smart terminal products with performance and cost balance.
Here we introduce the internal architecture of SGM3145, which supports 1x and 1.5x voltage double mode intelligent switching. It can automatically adjust the chip working mode according to the input voltage change, and automatically keep the back LED current constant. Figure 1 is the internal block diagram of the chip. :
SGM3145 is divided into several functional modules, low dropout constant current source and PWM dimming unit (Low Dropout Current Sense), 1x, 1.5 times charge pump doubler unit (1X/1.5X Charge Pump), soft start unit (Soft) Start), low voltage detection unit (UVLO), overvoltage protection unit (OVP), and oscillator operating at 0.93MHz (0.93MHz OSC). The function of the low-voltage drop constant current source and the PWM dimming unit is to maintain the current of the 8-channel LEDs relatively constant. The maximum current of the product design channel is 27mA. The user can adjust the LED light flow of each channel by using the PWM duty cycle according to the actual application requirements. The actual current, such as 19?20mA required for a normal LCD screen, or a 23mA high-brightness screen driver for improved display (designed on the market as an Iphone). 1 times, 1.5 times charge pump doubler unit for chip voltage doubler driving LED lamp, when the input voltage is higher than the switching point, SGM3145 works in 1x working mode, the efficiency is approximately equal to the ratio of output voltage to input voltage, if For lithium batteries, it can guarantee more than 80% efficiency above 3.7V (assuming the Vf of the LED lamp is 3.2V, the maximum energy voltage range of the battery is 3.7?4.2V); when the input voltage is lower than the switching point, the chip will The input voltage is raised to 1.5 times, and the efficiency is reduced. For example, when the 3.6V input voltage is doubled, the efficiency is only about 59%. The double voltage switching point of the SGM3145 is set at 3.45V. Taking into account the maximum energy portion of the battery energy curve, when the Vf voltage of the LED lamp is controlled below 3.2V, the working time of the high efficiency 1x voltage double mode can be fully extended. The soft start unit is mainly used to prevent large inrush current at the input end caused by the instant start, especially for the lithium battery low voltage mode to prevent the instantaneous high current from causing the system to shut down. The overvoltage protection unit can avoid chip overvoltage damage caused by open LED terminals, and the overvoltage point of SGM3145 is placed at 5.4V. The low-voltage detection is mainly used to prevent the system voltage from being unstable due to the input voltage being too low, and the chip is set at 2.15V. The oscillator is used to generate the switching action of the chip to complete the charging and discharging, to ensure the normal operation of the chip.
Unfinished
For more information, please refer to the September issue of "High-tech LED-Technology and Applications"
Since the advent of liquid crystal display technology in the 1960s, due to its convenience, LCD screens have become an indispensable highlight in a variety of human-machine interfaces. Ultra-thin, power-saving, flicker-free, low-radiation features open the door for LCD screens in a variety of portable terminal markets. With the advent of the intelligent era, without the LCD screen of more than 3 inches, your mobile phone has no way to enjoy the entertainment brought by the intelligent era. The liquid crystal display itself does not emit light, and there is a demand for backlight driving. In the era when LEDs were used as backlights for LCD screens, how to choose a suitable LED driver solution to meet this trend of pursuing energy-saving, safe and green has become a headache for engineers. Series or parallel? Low or high pressure? Efficiency or cost?
8LED parallel drive SGM3145 ignores the high-voltage processing problem of low-voltage system, without considering the size and EMI of power inductors, bringing a lot of convenience to smart terminal products with performance and cost balance.
Here we introduce the internal architecture of SGM3145, which supports 1x and 1.5x voltage double mode intelligent switching. It can automatically adjust the chip working mode according to the input voltage change, and automatically keep the back LED current constant. Figure 1 is the internal block diagram of the chip. :
SGM3145 is divided into several functional modules, low dropout constant current source and PWM dimming unit (Low Dropout Current Sense), 1x, 1.5 times charge pump doubler unit (1X/1.5X Charge Pump), soft start unit (Soft) Start), low voltage detection unit (UVLO), overvoltage protection unit (OVP), and oscillator operating at 0.93MHz (0.93MHz OSC). The function of the low-voltage drop constant current source and the PWM dimming unit is to maintain the current of the 8-channel LEDs relatively constant. The maximum current of the product design channel is 27mA. The user can adjust the LED light flow of each channel by using the PWM duty cycle according to the actual application requirements. The actual current, such as 19?20mA required for a normal LCD screen, or a 23mA high-brightness screen driver for improved display (designed on the market as an Iphone). 1 times, 1.5 times charge pump doubler unit for chip voltage doubler driving LED lamp, when the input voltage is higher than the switching point, SGM3145 works in 1x working mode, the efficiency is approximately equal to the ratio of output voltage to input voltage, if For lithium batteries, it can guarantee more than 80% efficiency above 3.7V (assuming the Vf of the LED lamp is 3.2V, the maximum energy voltage range of the battery is 3.7?4.2V); when the input voltage is lower than the switching point, the chip will The input voltage is raised to 1.5 times, and the efficiency is reduced. For example, when the 3.6V input voltage is doubled, the efficiency is only about 59%. The double voltage switching point of the SGM3145 is set at 3.45V. Taking into account the maximum energy portion of the battery energy curve, when the Vf voltage of the LED lamp is controlled below 3.2V, the working time of the high efficiency 1x voltage double mode can be fully extended. The soft start unit is mainly used to prevent large inrush current at the input end caused by the instant start, especially for the lithium battery low voltage mode to prevent the instantaneous high current from causing the system to shut down. The overvoltage protection unit can avoid chip overvoltage damage caused by open LED terminals, and the overvoltage point of SGM3145 is placed at 5.4V. The low-voltage detection is mainly used to prevent the system voltage from being unstable due to the input voltage being too low, and the chip is set at 2.15V. The oscillator is used to generate the switching action of the chip to complete the charging and discharging, to ensure the normal operation of the chip.
Unfinished
For more information, please refer to the September issue of "High-tech LED-Technology and Applications"
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