AA rechargeable battery

　　Analysis of driver technology solutions for LED backlights

　　Various vehicle-mounted displays such as car dashboards, car navigation, audio displays, and rear-seat entertainment are developing in a diversified and large-scale direction. Under this trend, the requirements for increasing the number of LED lights as well as high brightness and high dimming rate are increasing day by day. In order to meet the development trend of increasing the number of LED lamps, ROHM has built-in a buck-boost DC/DC converter with high withstand voltage and a current driver circuit that can drive low-power LEDs with multiple lamps and achieve high dimming rate. This chip expands the LED driver. Next, we introduce the LED driver BD81A34EFV-M for backlights developed by ROHM.

　　BD81A34EFV-M is roughly composed of three functional blocks: DC/DC converter section, current driver section, and protection circuit section.

　　As a backlight driver, a certain voltage is first generated by a DC/DC converter. Connect the output of the DC/DC converter to the LED anode side of the panel, and pour a constant current from the cathode side of the LED into the LED driver to make the LED light up. In order to support low-power multi-lamp LED driving, the number of LED channels (number of connectable columns) is designed to be 4.

　　By controlling the switching duty cycle of the DC/DC converter, the output reaches a level higher than the LED anode pin, which includes the number of LED segments linked to the current driver, that is, the VF generated by the LED, through the LED driver The error amplifier performs feedback control so that the LED cathode pins (LED1~4 pins) connected to the IC are 1.0V. Through the above control, the current driver section can keep the LED current constant. For panel brightness adjustment, the output current has a PWM-dimming function. The duty cycle of the LED current can change synchronously with the external PWM signal input. Not only that, BD81A34EFV-M is also equipped with LED open circuit and short circuit fault protection, LED ground fault protection, DC/DC converter output overcurrent and overvoltage protection functions. The complete protection circuit is very helpful to improve the reliability of the panel.

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