LM3520 Datasheet | National Semiconductor

Description The LM3520 is a dual step-up DC/DC converter, designed to drive up to 5 white LEDs with a constant current and to power an organic LED display with a constant voltage. A single external resistor is used to set the maximum LED current. The LED current can be adjusted by applying a PWM signal to the EN pin. For higher efficiency the LM3520 operates with pulse frequency modulation (PFM) control scheme when the sub-display is enabled. When Main display is enabled, the device is operating in PWM mode. Overvoltage protection circuitry and a 1MHz switching frequency allow for the use of small, low cost external ponents. Additional features include a low-side NFET switch that can turn off the LED string with no DC current path to ground. The LM3520 is available in a small 14-pin thermallyenchanced LLP package. Features n Integrated OLED and white-LED driver n 80% efficiency n Drives up 5 LEDs at 20m A/3.6V and 4 LEDs at 30m A/3.6V for main-display n Up to 20V @ 50m A/3.6V for sub-display n True shutdown isolation n Small External ponents n 1 MHz Switching Frequency n 23V Over Voltage Protection n Wide Input Voltage Range: 2.7V to 5.5V n Cycle-By-Cycle Current Limit n PWM Dimming Control n Low Profile 14-Pin LLP(3mm x 4mm x 0.8mm) Applications n n n n n Flip-phones/Clam-shell Cellular Phones Handheld Devices High-fashion cellular phones White LED Backlighting Digital Cameras Typical Applications Main Display with OLED Sub Display © 2005 National Semiconductor Corporation DS201288 .national. Functional Block Diagram FIGURE 1. Functional Block Diagram .national. Pin Description Pin # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Pin Name VSW VIN AGND NC MAIN_EN SUB_EN PFM_EN SUB_FB VSUB VO_MAIN MAIN_FB MAIN_RTN DGND NC Switching Voltage Input Voltage Analog Ground No Connect Main Enable Sub Display Enable PFM mode: OLED sub-display, pin must be tied to SUB_EN Sub Display Feedback Sub Display Power Supply Voltage Main Output Voltage...