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Preliminary Product spec. T6311A
Low-Dropout, Constant-Current White LED Bias Supply
FEATURES
* Low 200mV Dropout at 9mA * Up to 150mA LED Bias Current * 0.3% LED Current Matching * Simple 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
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.
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
TM Technology Inc. reserves the right P. 1 to change products or specifications without notice.
Publication Date: JUN. 2005 Revision: C
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EN GND SET
TE CH
Preliminary Product spec. T6311A
PIN ARRANGEMENT(Top view) SOT23-6
LED1
SOP-8
1 2 3 4 8 7 6 5 EN GND SET NC
1 2 3
6 5 4
LED1 LED2 LED3
LED2 LED3 LED4
PIN DESCRIPTION
SYMBO L EN GND SET NC LED4 LED3 LED2 LED1 Pin no.
SOP-8 SOT23-6
DESCRIPTION
Enable Input/Power Input. Drive high (> 2.5V) to enable; drive low (< 2.2V) to disable. When disabled, SET, LED1, LED2, LED3 and LED4 are high impedance. When enabled, EN is the power input for the T6311A. Ground Bias Current Set Input. The current flowing into SET sets the bias current into each LED by ILED_= 240 x ISET. VSET is internally biased to 1.2V. SET is high impedance when EN is low. No connection. LED 4 Cathode Connection. Current flowing into LED4 is 240 times the current flowing into SET. LED4 is high impedance when EN is low. LED 3 Cathode Connection. Current flowing into LED3 is 240 times the current flowing into SET. LED3 is high impedance when EN is low. LED 2 Cathode Connection. Current flowing into LED2 is 240 times the current flowing into SET. LED2 is high impedance when EN is low. LED 1 Cathode Connection. Current flowing into LED1 is 240 times the current flowing into SET. LED1 is high impedance when EN is low.
8 7 6 5 4 3 2 1
1 2 3 4 5 6
TM Technology Inc. reserves the right P.2 to change products or specifications without notice.
Publication Date: JUN. 2005 Revision: C
tm
TE CH
Preliminary Product spec. T6311A
BLOCK DIAGRAM
V+ LED4
ON OFF EN
current controller
LED3
LED2
LED1
GND REF SET
+ -
RSET
VCTRL
Fig. 1
TM Technology Inc. reserves the right P.3 to change products or specifications without notice.
Publication Date: JUN. 2005 Revision: C
tm
Parameter
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Preliminary Product spec. T6311A
Symbol VIN TA TLEAD TS Value -0.3 to 6 -40 to +85 300 -65 to +150 1 Unit V C C C W
ABSOLUTE MAXIMUM RATINGS
Voltage on any pin relative to GND Operating Temperature Rang Maximum Soldering Temperature (at leads, 10 sec) Storage Temperature Rang Continuous Power Dissipation ( TA = +70C )
Electrical Characteristics
(TA = -40 to 85C unless otherwise noted. Typical values are at TA =25C, VEN =3.3V, VLED1 = VLED2= VLED3= VLED4= 1V) (Note 1)
Symbol VEN ISET VSET
Description Operating voltage range SET input current range SET to LED current ratio SET bias voltage SET leakage current in Shutdown
Conditions EN is power supply input ILED / ISET, ISET=42uA ISET=42uA EN=GND, VSET=3.3V Each LED ISET=20uA (Note 2) ISET=40uA (Note 3) ISET=80uA (Note 3) TA= -40 to +25C TA= -40 to +85C
Min. Typ. Max 2.5 5 220 1.08 240 1.2 0.01 0.3 100 100 200 230 0.01 150 180 360 410 1 5.5 260 260 1.32 1 5
Unit V uA A/A V uA uA % mA mV mV mV uA V
LED to LED current matching ISET=42uA ILED Maximum LED sink current LED dropout voltage LED leakage current in shutdown VIH VIL IEN Input high voltage Input low voltage EN intput bias current
VLED1=VLED2=VLED3=VLED4= 3.3V, EN=GND, TA=+25C, each LED VEN >VIH for enable 2.5 VEN 2.2 40 0.05 100 1
V uA uA
Note 1: Limits are 100% production tested at TA = +25C. Limits over the operating temperature range are guaranteed through correlation using statistical quality control (SQC) methods. Note 2: Dropout Voltage is defined as the LED to GND voltage at which current sink into LED drops 20% from the value at VLED = 1V. Note 3: Dropout Voltage is defined as the LED to GND voltage at which current sink into LED drops 10% from the value at VLED = 1V.
TM Technology Inc. reserves the right P.4 to change products or specifications without notice.
Publication Date: JUN. 2005 Revision: C
tm
TBD
TE CH
Preliminary Product spec. T6311A
Typical Operating Characteristics
(VEN=+3.3V, VCTRL= 3.3V, RSET=24.9k ohm, V+=3.3V, TA=+25 C, unless otherwise noted.)(circuit of Fig. 1)
TM Technology Inc. reserves the right P.5 to change products or specifications without notice.
Publication Date: JUN. 2005 Revision: C
tm
TE CH
Preliminary Product spec. T6311A
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.
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 several 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 40A 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 ) 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
tm
TE CH
Preliminary Product spec. T6311A
TYPICAL APPLICATION CIRCUITS
V+ V
E x is tin g LDO
CTRL
T o o th e r c irc u its SET ON OFF EN GND LED1 LED2 LED3 LED4
Fig. 2 Very low-cost, high-efficiency solution
V+ DAC V
CTRL
SET ON OFF EN
LED1
LED2
LED3
LED4
GND
Fig. 3 Brightness adjust using DAC
TM Technology Inc. reserves the right P.7 to change products or specifications without notice.
Publication Date: JUN. 2005 Revision: C
tm
TE CH
Preliminary Product spec. T6311A
PACKAGE DIMENSIONS 8-LEAD SOP
B
B1
A1
A
C1 C2
C F
D
H
E
Symbol A A1 B B1 C C1 C2 D E F H
Min. 5.70 3.75 1.35 0.10 0.31 0.30 0.10
Dimension in mm Typ. 6.00 3.95 1.27 1.55 0.41 0.50 0.15 0~8
Max. 6.30 4.10 5.13 1.80 1.75 0.25 0.51 0.70 0.25
Min. 0.224 0.148 0.052 0.001 0.012 0.012 0.004
Dimension in inch Typ. 0.236 0.156 0.050 0.061 0.016 0.020 0.006 0~8
Max. 0.248 0.164 0.202 0.071 0.069 0.004 0.020 0.028 0.010
TM Technology Inc. reserves the right P.8 to change products or specifications without notice.
Publication Date: JUN. 2005 Revision: C
tm
TE CH
Preliminary Product spec. T6311A
PACKAGE DIMENSIONS SOT23-6
B B1 B2
A1
A
C1 C2
C F
I
D
H
G
E
Symbol A A1 B B1 B2 C C1 C2 D E F G H I
Min. 2.60 1.40 2.70
0.95 0.90 0 0.30 0.08
Dimension in mm Typ. 2.80 1.575 2.85 1.90(BSC) 0.95(BSC) 1.20 1.10 0.075 0.40 0.45 0.15 0.60(REF) 0~8 5~15
Max. 3.00 1.60 3.00
Min. 0.102 0.055 0.106
1.45 1.30 0.150 0.60 0.22
0.037 0.035 0 0.012 0.003
Dimension in inch Typ. 0.110 0.062 0.112 0.075(BSC) 0.037(BSC) 0.047 0.043 0.003 0.015 0.018 0.006 0~8 5~15
Max. 0.118 0.063 0.118
0.057 0.051 0.06 0.023 0.009
TM Technology Inc. reserves the right P.9 to change products or specifications without notice.
Publication Date: JUN. 2005 Revision: C

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