LM2794 Datasheet, PDF (1/16 Pages) National Semiconductor (TI) – Current Regulated Switched Capacitor LED Supply with Analog and PWM Brightness Control

March 2004
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.
Features
n Regulated current sources with ±0.5% matching
between any two outputs
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
spectrum
n Standard Micro SMD-14 package: 2.08mm X 2.403mm
X 0.845mm High
n Thin Micro SMD-14 package: 2.08mm X 2.403mm X
0.600mm High
Applications
n White LED Display Backlights
n White LED Keypad Backlights
n 1-Cell Li-Ion battery-operated equipment including
PDAs, hand-held PCs, cellular phones
Basic Application Circuit
© 2004 National Semiconductor Corporation DS200285
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