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Switched-Capacitor Boost Backlight LED Drivers Overview

The presence of an inductor often contributes to the problem instead of the solution, especially in space-constrained, low- noise applications. National’s switched-capacitor LED drivers provide a small, inductor-less solution for both parallel and series LED confi gurations. In this topology, the input voltage connects to a multiple-gain switched capacitor that produces a regulated output. The switched capacitor remains in the most effi cient gain over the widest input voltage consumingthe least amount of energy through gain transitions that maintain regulation based on LED forward voltage and load requirements. Multiple-gain boost modes allow for the highest possible effi ciency over a wide input voltage range resulting in longer battery life. Following, you’ll fi nd switched-capacitor drivers, including some that feature low noise, making them ideal for EMI-sensitive applications.

LM2756 – Multiple-Display LED Driver with I

2

C-Compatible Brightness Control

A highly integrated switched-capacitor multi-display LED driver that can drive up to 8 LEDs in parallel with a total output current of 180 mA. Regulated internal current sources deliver excellent current and bright- ness matching in all LEDs. Eight LED driver current sinks are split into three independently controlled groups for multiple lighting features. The LM2756 has 32 exponen- tial dimming steps with an 800:1 dimming ratio digitally controlled by an I LM2756 Typical Application Circuit

Group AGroup BGroup C

D1AD2AD3AD4AD53D62D1BD1CV IN OUT - 1 µF

LM2756

1 µF

2

C-compatible interface. Package: Low profi le 20-bump micro SMD (1.615 mm x 2.015 mm x 0.6 mm)

1 µF1 µF+ GNDHWENSDIOSCLC1+C1-C2+C2-I

LM2757 Typical Application Circuit

I SET 2 C ControlSignals V

LM2757 – Switched-Capacitor Boost Regulator with High Impedance Output in Shutdown

A constant frequency, pre-regulated, switched-capacitor regulator operates at 1.25 MHz to produce a low-noise regulated output voltage. The device can be confi gured to provide up to 100 mA at 4.1V, 110 mA at 4.5V, or 180 mA at 5V. Excellent effi ciency is achieved without the use of an inductor by operating the charge pump in a gain of either 3/2 or 2 according to the input voltage and output voltage option selection. The LM2757 presents a high impedance at the V

V
OUT = 4.1V (100mA), 4.5V (110mA)5.0V (180mA) M0D3
IN = 3.0V - 5.5VB2,B3A3B1A1C3C1,C2 A2 GND V
IN V
OUT C
1 +C C
IN 1µF 0.47µF 1.0µF C
OUT C
1 0.47µF

OUT

pin when shut down, which allows for application use requiring the regulated output bus to be driven by another supply while the LM2757 is shut down.A perfect fi t for space-constrained, battery-operated applica-tions, the LM2757 requires only four small, inexpensive ceramic capacitors. Built in soft-start, over-current protection, and thermal shutdown features are also included.

1 -

LM2757

C
2 +C

Package: Tiny 12-bump micro SMD (1.2 mm x 1.6 mm x 0.4 mm)

C
2 M1D2
2 - *Bump D1 is (NC) No Connect V

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