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T6311A Schematic ( PDF Datasheet ) - Taiwan Memory Technology

Teilenummer T6311A
Beschreibung Constant-Current White LED Bias Supply
Hersteller Taiwan Memory Technology
Logo Taiwan Memory Technology Logo 




Gesamt 9 Seiten
T6311A Datasheet, Funktion
tm TE
CH
FEATURES
• Low 200mV Dropout at 9mA
• Up to 150mA LED Bias Current
• 0.3% LED Current Matching
www.DataSheet4US.cimomple LED Brightness Control
• Low 40uA Supply Current
• Low 0.05uA Shutdown Current
• 2.5V to 5.5V Supply Voltage Range
• SOP-8 and SOT23-6 Package
• Output channel :
SOP-8 package for four channel
SOT23-6 package for three channel
Applications
• Cellular Phones
• Portable Communication Devices
• Handheld Electronics
• Digital Cameras
• PDAs
• LED/Display Back Light Driver
• LEDs for Camera Flash
PART NUMBER EXAMPLES
PART NO.
T6311A-D
T6311A-X
PACKAGE
SOP-8
SOT23-6
Preliminary Product spec. T6311A
Low-Dropout, Constant-Current
White LED Bias Supply
GRNERAL DESCRIPTION
The T6311A low-dropout bias supply for
white LEDs is a high-performance alternative
to the simple ballast resistors used in
conventional white LED designs. The T6311A
uses a single resistor to set the bias current for
four LEDs, which are matched to 0.3%. The
T6311A consumes only 40uA of supply
current when enabled and 0.05uA when
disabled. The T6311A advantages over ballast
resistors include significantly better LED to
LED bias matching, much lower bias variation
with supply voltage variation, significantly
lower dropout voltage, and in some
applications, significantly improved efficiency.
The T6311A requires a 200mV dropout at a
9mA load on each output to match the LED
brightness. The T6311A is available in SOP-8
and SOT23-6 package.
TM Technology Inc. reserves the right
P. 1
to change products or specifications without notice.
Publication Date: JUN. 2005
Revision: C






T6311A Datasheet, Funktion
tm TE
CH
Preliminary Product spec. T6311A
Functional Description
The T6311A provides constant current bias
supply for white LED designs. The T6311A
uses a single resistor to set the bias current for
up to three LEDs. LED bias currents are
matched to 0.3% by the T6311A current
matching architecture (Fig. 1). Supply current
(IEN) is a low 40uA in normal operation and
0.05uA when disabled. The T6311A offers
www.DataSheets4eUv.ceormal advantages over using ballast resistors,
such as improved LED to LED brightness
matching, lower bias variation with supply
voltage changes, significantly lower dropout
voltage, and in some applications,
significantly improved efficiency. The
T6311A achieves a 200mV dropout with a
9mA load on each output. For circuits
requiring only one or two LEDs, leave unused
LED outputs unconnected.
Enable Input
EN powers the input of the T6311A. Drive
EN high (> 2.5V) to enable the device; drive
EN low (< 2.2V) to disable the device. When
driven high, EN draws 40µA to power the IC.
Driving EN low forces LED1, LED2, LED3,
LED4 and SET into a high-impedance state.
Setting the Output Current
SET controls the LED bias current. Current
flowing into LED1, LED2, LED3 and LED4
is 240 times greater than the current flowing
into SET. Set the output current as follows:
ILED = 240 ( (VCTRL - VSET) / RSET )
Applications Information
Very Low-Cost, High-Efficiency Solution
(Fig. 2). A battery (single Li+ or three NiMH
cells) powers the LEDs directly. This is the
least expensive and most efficient architecture.
Due to the high forward voltage of white
LEDs (3.3V), the LED brightness may dim
slightly at the end of battery life. The T6311A
current regulating architecture and low
dropout greatly minimize this effect compared
to using simple ballast resistors. The enable
function of the T6311A turns on and off the
LEDs. An existing low-dropout regulator is
used as VCTRL.
Brightness Adjustment Using a DAC
(Fig. 3). A DAC is used as VCTRL such that
the LED brightness may be dynamically
adjusted to eliminate factory calibration. A
battery (single Li+ or three NiMH cells) or a
regulated power source drives the LEDs.
where VSET = 1.2V, VCTRL is an external
voltage between 1.8V and 5.5V, and RSET is
the resistor connected between VCTRL and
SET (Fig. 1).
TM Technology Inc. reserves the right
P.6
to change products or specifications without notice.
Publication Date: JUN. 2005
Revision: C

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