lm2795tlx National Semiconductor Corporation, lm2795tlx Datasheet

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lm2795tlx

Manufacturer Part Number
lm2795tlx
Description
Current Regulated Switched Capacitor Led Supply With Analog And Pwm Brightness Control
Manufacturer
National Semiconductor Corporation
Datasheet

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© 2004 National Semiconductor Corporation
LM2794/LM2795
Current Regulated Switched Capacitor LED Supply with
Analog and PWM Brightness Control
General Description
The LM2794/95 is a fractional CMOS charge-pump that
provides four regulated current sources. It accepts an input
voltage range from 2.7V to 5.5V and maintains a constant
current determined by an external sense resistor.
The LM2794/5 delivers up to 80mA of load current to accom-
modate four White LEDs. The switching frequency is
325kHz. (min.) to keep the conducted noise spectrum away
from sensitive frequencies within portable RF devices.
Brightness can be controlled by both linear and PWM tech-
niques. A voltage between 0V and 3.0V may be applied to
the BRGT pin to linearly vary the LED current. Alternatively,
a PWM signal can be applied to the SD pin to vary the
perceived brightness of the LED. The SD pin reduces the
operating current to 2.3µA (typ.) The LM2794 is shut down
when the SD pin is low, and the LM2795 is shut down when
the SD pin is high.
The LM2794/95 is available in a micro SMD-14 CSP pack-
age.
Basic Application Circuit
DS200285
Features
n Regulated current sources with
n High efficiency 3/2 boost function
n Drives one, two, three or four white LEDs
n 2.7V to 5.5V Input Voltage
n Up to 80mA output current
n Analog brightness control
n Active-low or high shutdown input (’94/95)
n Very small solution size and no inductor
n 2.3µA (typ.) shutdown current
n 325kHz switching frequency (min.)
n Constant Frequency generates predictable noise
n Standard Micro SMD-14 package: 2.08mm X 2.403mm
n Thin Micro SMD-14 package: 2.08mm X 2.403mm X
Applications
n White LED Display Backlights
n White LED Keypad Backlights
n 1-Cell Li-Ion battery-operated equipment including
between any two outputs
spectrum
X 0.845mm High
0.600mm High
PDAs, hand-held PCs, cellular phones
±
0.5% matching
20028503
www.national.com
March 2004

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lm2795tlx Summary of contents

Page 1

... SD pin is low, and the LM2795 is shut down when the SD pin is high. The LM2794/95 is available in a micro SMD-14 CSP pack- age. Basic Application Circuit © 2004 National Semiconductor Corporation Features n Regulated current sources with between any two outputs n High efficiency 3/2 boost function n Drives one, two, three or four white LEDs n 2 ...

Page 2

... LM2794BLX Active Low LM2795BL Active High LM2795BLX Active High Thin Micro SMD Package: Order Number Shutdown Polarity LM2794TL Active Low LM2794TLX Active Low LM2795TL Active High LM2795TLX Active High Pin Description Pin(*) Name A1 C1+ B2 C1− GND E1 C2− ...

Page 3

Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications BRGT Continuous Power Dissipation (Note 2) T (Note 2) JMAX Electrical Characteristics Limits in standard typeface ...

Page 4

Electrical Characteristics Limits in standard typeface are for T Range (−30˚C ≤ T ≤ +100˚C). Unless otherwise specified =124Ω ; LM2794 (LM2795 Symbol Parameter f Switching Frequency (Note 6) ...

Page 5

Typical Performance Characteristics V = 3.6V, BRGT pin = 0V 124Ω. IN SET DIODE DIODE IN BRGT = DIODE SET BRGT Unless otherwise specified, ...

Page 6

Typical Performance Characteristics = 3.6V, BRGT pin = 0V 124Ω. (Continued) SET SET BRGT R = 1KΩ SET Supply Current 1-4 = 15mA DIODE Shutdown Supply Current vs V www.national.com Unless otherwise ...

Page 7

Typical Performance Characteristics = 3.6V, BRGT pin = 0V 124Ω. (Continued) SET Start-Up Response @ V = 2.7V (LM2794) IN Start-Up Response @ V = 3.6V (LM2794) IN Start-Up Response @ V = 4.2V (LM2794) IN Unless otherwise ...

Page 8

Typical Performance Characteristics = 3.6V, BRGT pin = 0V 124Ω. (Continued) SET Available Additional Current I 1− 15mA, R DIODE www.national.com Unless otherwise specified OUT = 124 Ω SET ...

Page 9

Functional Block Diagram Application Information CIRCUIT DESCRIPTION The LM2794 1.5x/1x CMOS charge pump with four matched constant current outputs, each capable of driving up to 20mA through White LEDs. This device operates over the extended Li-Ion battery range ...

Page 10

Application Information SHUTDOWN MODE The shutdown pin (SD) disables the part and reduces the quiescent current to 2.3µA (typ.). The LM2795 has an active-high shutdown pin (HIGH = shutdown, LOW = operating). An internal pull-up is con- nected between SD ...

Page 11

Application Information I CURRENT SELECTION PROCEDURES LED The following procedures illustrate how to set and adjust output current levels. For constant brightness or analog brightness control “Brightness control using BRGT”. Otherwise refer to “Brightness control using PWM”. Brightness ...

Page 12

Application Information Output resistance results in droop in the P portional to the amount of current delivered by the pump. The P voltage is an important factor in determining the OUT total output current capability of an application. Taking total ...

Page 13

Application Information OUTPUT CURRENT CAPABILITY The primary constraint on the total current capability is the headroom voltage requirement of the internal current sources. Combining the V and V POUT HR previous two sections yields the basic inequality for deter- mining ...

Page 14

Application Information ÷ P LED Efficiency, as defined here part dependent on LED voltage. Variation in LED voltage does not affect power consumed by the circuit and typically does not relate to the brightness of ...

Page 15

Physical Dimensions inches (millimeters) unless otherwise noted For Ordering, Refer to Ordering Information Table Standard Micro SMD Package NS Package Number BLP14EHB The dimensions for X1, X2, X3 are given as: ± 2.098mm 0.030mm ± 2.403mm ...

Page 16

... 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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