lm2791ldx-l National Semiconductor Corporation, lm2791ldx-l Datasheet

lm2791ldx-l

Manufacturer Part Number

lm2791ldx-l

Description

Current Regulated Switched Capacitor Led Driver With Analog Brightness Control

Manufacturer

National Semiconductor Corporation

Datasheet

1.LM2791LDX-L.pdf (11 pages)

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LM2791

Current Regulated Switched Capacitor LED Driver with

Analog Brightness Control

General Description

The LM2791 is a CMOS charge-pump voltage doubler and

regulator that provides two regulated current sources. The

LM2791 is designed to drive two white (or blue) LEDs with

matched currents (within

sources for display backlights. They accept an input voltage

range from 3V to 5.8V and maintain a constant current

determined by an external set resistor.

The LM2791 delivers up to 36mA of load current to accom-

modate two high forward voltage (typically white) LEDs. The

switching frequency is 450kHz (min.) to keep the conducted

noise spectrum away from sensitive frequencies within por-

table RF devices.

In the LM2791, brightness is controlled by applying a voltage

between GND and 3.0V to the BRGT pin. The LM2791 is

available in active high or low shutdown versions. The shut-

down pin reduces the operating current to 1µA (max.).

The LM2791 is available in a 10 pin leadless leadframe

(LLP) CSP package.

Basic Application Circuit

0.3%) to produce balanced light

DS200183

Features

n Output matching of

n Drives up to two LED’s

n 3V to 5.8V Input Voltage

n Up to 36mA output current

n Soft start limits inrush current

n Analog brightness control

n Separate shutdown input

n Very small solution size - no inductor

n 0.7mA typical operating current

n 1µA (max.) shutdown current

n 450kHz switching frequency (min.)

n Linear regulation generates predictable noise spectrum

n LLP-10 package: 3mm X 3mm X 0.8mm

Applications

n White LED Display Backlights

n White LED Keypad Backlights

n 1-Cell Li-Ion battery-operated equipment including

n Flat Panel Dispalys

PDAs, hand-held PCs, cellular phones

20018301

0.3%

www.national.com

July 2002

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lm2791ldx-l Summary of contents

Page 1

... The shut- down pin reduces the operating current to 1µA (max.). The LM2791 is available pin leadless leadframe (LLP) CSP package. Basic Application Circuit © 2002 National Semiconductor Corporation Features n Output matching of n Drives up to two LED’ 5.8V Input Voltage ...

Page 2

... Connection Diagram Ordering Information Order Number Shutdown Polarity LM2791LD-L Active Low LM2791LDX-L Active Low LM2791LD-H Active High LM2791LDX-H Active High www.national.com 20018303 Top View 10-Lead LLP NSC Package Package Drawing Marking LLP-10 SNB LLP-10 SNB LLP-10 SLB LLP-10 SLB 2 Supplied As 1000 Units, Tape and Reel ...

Page 3

Pin Description Pin Name 1 BRGT Variable voltage input controls output current Charge pump output. OUT 3 C1− Connect this pin to the negative terminal of C1. 4 C1+ Connect this pin to the positive terminal of C1. ...

Page 4

Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications BRGT, SD Power Dissipation(Note 2) T (Note 2) JMAX θ (Note 7) JA Storge Temperature Lead Temp. ...

Page 5

Typical Performance Characteristics V = 3.6V, BRGT pin =0V 330Ω DIODE SET Supply Current at No Load SD-Threshold Diode Current vs. Temperature Unless otherwise specified Supply Current vs Supply Voltage 20018305 20018308 20018320 5 , ...

Page 6

Typical Performance Characteristics V = 3.6V, BRGT pin =0V, R DIODE SET I vs BRGT DIODE Switching Frequency vs Supply Voltage Start Up Time @ www.national.com Unless otherwise specified 330Ω (Continued) 20018313 Switching Frequency vs. Temperature ...

Page 7

Typical Performance Characteristics V = 3.6V, BRGT pin =0V 330Ω (Continued) DIODE SET Start Up Time @ 4.2 V Unless otherwise specified 20018316 1uF 3.6V, IN HOLD IN ...

Page 8

Circuit Description The LM2791 provides two matched current sources for driv- ing high forward voltage drop LEDs from Li-Ion battery sources. The device has on-chip current regulators which are composed of current mirrors with ratio. The ...

Page 9

Application Information turning-on its own parasitic diode and potentially latching-up result important to select a schottky diode that will carry at least 200mA or higher current to charge the output capacitor during start-up. A schottky diode ...

Page 10

Application Information BRIGHTNESS CONTROL USING PWM Brigthness control can be implemented by pulsing a signal at the SD pin. The recommended signal should be between 100Hz to 1kHz. If the operating PWM frequency is much less than 100Hz, flicker may ...

Page 11

... NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant ...

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