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19-2067; Rev 0; 7/01
Low-Dropout, Constant-Current Triple White LED Bias Supply
General Description
The MAX1916 low-dropout bias supply for white LEDs is a high-performance alternative to the simple ballast resistors used in conventional white LED designs. The MAX1916 uses a single resistor to set the bias current for three LEDs, which are matched to 0.3%. The MAX1916 consumes only 40A of supply current when enabled and 0.05A when disabled. The MAX1916's 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 MAX1916 requires a 200mV dropout at a 9mA load on each output to match the LED brightness. The MAX1916 is available in a space-saving 6-pin Thin SOT23 package. o Low 200mV Dropout at 9mA o Up to 60mA/LED Bias Current o 0.3% LED Current Matching o Simple LED Brightness Control o Low 40A Supply Current o Low 0.05A Shutdown Current o 2.5V to 5.5V Supply Voltage Range o Thermal Shutdown Protection o Tiny 6-Pin Thin SOT23 Package (1mm High)
Features
MAX1916
Applications
Next-Generation Wireless Handsets PDAs, Palmtops, and Handy Terminals Digital Cameras, Camcorders Battery-Powered Equipment
PART MAX1916EZT
Ordering Information
TEMP. RANGE -40C to +85C PINPACKAGE 6 Thin SOT23 TOP MARK AAAG
Typical Operating Circuit
VCTRL V+
Pin Configuration
TOP VIEW
EN 1 6 LED1
SET ON OFF EN
LED1 LED2
LED3
GND 2
MAX1916
5
LED2
MAX1916
GND
SET 3
4
LED3
THIN SOT23-6
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Low-Dropout, Constant-Current Triple White LED Bias Supply MAX1916
ABSOLUTE MAXIMUM RATINGS
EN, SET, LED1, LED2, LED3 to GND ..................... -0.3V to +6V Continuous Power Dissipation (TA = +70C) 6-Pin Thin SOT23 (derate 9.1mW/C above +70C) ... 727mW Operating Temperature Range ......................... -40C to +85C Storage Temperature Range ........................... -65C to +150C Lead Temperature (soldering, 10s)................................... 300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VEN = 3.3V, VLED1 = VLED2 = VLED3 = 1V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Operating Voltage Range Undervoltage Lockout Threshold SET Input Current Range SET to LED_ Current Ratio SET Bias Voltage SET Leakage Current in Shutdown LED_-to-LED_ Current Matching Maximum LED_ Sink Current LED_ Dropout Voltage ILED_ VSET SYMBOL VEN VUVLO ISET ILED/ISET, ISET = 42A ISET = 42A EN = GND, VSET = 3.3V ISET = 42A Each LED_ ISET = 22A (Note 2) ISET = 42A (Note 3) ISET = 84A (Note 3) LED_ Leakage Current in Shutdown Input High Voltage Input Low Voltage EN Input Bias Current Thermal Shutdown Temperature Thermal Shutdown Hysteresis VIH VIL IEN VLED1 = VLED2 = VLED3 = 5.5V, EN = GND, each LED_ VEN > VIH for enable VEN < VIL for disable VEN = 2.5V to 5.5V, EN is the power-supply input VEN = 0.4V TA = +25C 40 0.05 170 10 TA = +25C 2.5 2.2 100 1 C C 60 100 200 230 0.01 180 360 410 1 A mV TA = -40C to +25C TA = -40C to +85C 0.3 CONDITIONS EN is the power-supply input VEN rising Hysteresis 5 207 1.154 230 1.215 0.01 MIN 2.5 2.2 85 260 253 1.276 1 5 5 TYP MAX 5.5 2.47 UNITS V V mV A A/A V A % mA
V
A
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.
2
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Low-Dropout, Constant-Current Triple White LED Bias Supply
Typical Operating Characteristics
(VEN = 3.3V, VCTRL = 3.3V, RSET = 24.9k, V+ = 5V, TA = +25C, unless otherwise noted.) (Circuit of Figure 1)
MAX1916
LED CURRENT vs. V+ BIAS VOLTAGE
MAX1916 toc01
OUTPUT CURRENT vs. VEN SUPPLY VOLTAGE
MAX1916 toc02
LED CURRENT vs. TEMPERATURE
MAX1916 toc03
25
20.0
20 OUTPUT CURRENT (mA)
20 LED CURRENT (mA)
19.9 LED CURRENT (mA)
15
15
LED3 LED2 LED1
19.8
10
10
19.7
5 UNMATCHED LEDS 0 2 3 4 V+ BIAS VOLTAGE (V) 5 6
5
19.6
0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 VEN SUPPLY VOLTAGE (V)
19.5 -40 -15 10 35 60 85 TEMPERATURE (C)
LED CURRENT vs. RSET
VCTRL = 5.0V
MAX1916 toc04
LED CURRENT (ILED) vs. VCTRL
MAX1916 toc05
LED DROPOUT VOLTAGE vs. CURRENT
MAX1916 toc06
100
60 A 50 LED CURRENT (mA) 40 C 30 D 20 10 E F G 0 B
300 250 200 150 100 50 0
LED CURRENT (mA)
VCTRL = 3.3V
10
VCTRL = 2.5V
VCTRL = 1.8V 1 10 RSET (k) A: RSET = 10k B: RSET = 15k C: RSET = 22k D: RSET = 33k E: RSET = 47k F: RSET = 68k G: RSET = 100k 100 1.5 2.0 2.5 3.0 3.5 4.0
4.5
5.0
5.5
LED DROPOUT VOLTAGE (mV)
0
5
10
15
20
25
30
35
40
VCTRL (V)
LED CURRENT (mA)
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3
Low-Dropout, Constant-Current Triple White LED Bias Supply MAX1916
Typical Operating Characteristics (continued)
(VEN = 3.3V, VCTRL = 3.3V, RSET = 24.9k, V+ = 5V, TA = +25C, unless otherwise noted.) (Circuit of Figure 1)
IEN SUPPLY CURRENT vs. VEN SUPPLY VOLTAGE
40 IEN SUPPLY CURRENT (A) 35 30 25 20 15 10 5 0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 20mA 0
MAX1916 toc07
ENABLE AND SHUTDOWN RESPONSE
MAX1916 toc08
45
0
VEN 2V/div
ILED 20mA/div
40s/div
VEN SUPPLY VOLTAGE (V)
VCTRL TRANSIENT RESPONSE
3V
V+ TRANSIENT RESPONSE
MAX1916 toc10
MAX1916 toc09
VCTRL 1V/div
4V
V+ 1V/div
20mA 10mA
ILED 10mA/div
20mA 10mA
ILED 10mA/div
10s/div
20s/div
4
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Low-Dropout, Constant-Current Triple White LED Bias Supply
Pin Description
PIN 1 2 3 4 5 6 NAME EN GND SET LED3 LED2 LED1 FUNCTION Enable Input/Power Input. Drive high (> 2.5V) to enable; drive low (< 2.2V) to disable. When disabled, SET, LED1, LED2, and LED3 are high impedance. When enabled, EN is the power input for the MAX1916. Ground Bias Current Set Input. The current flowing into SET sets the bias current into each LED by ILED_= 230 x ISET. VSET is internally biased to 1.215V. SET is high impedance when EN is low. LED 3 Cathode Connection. Current flowing into LED3 is 230 times the current flowing into SET. LED3 is high impedance when EN is low. LED 2 Cathode Connection. Current flowing into LED2 is 230 times the current flowing into SET. LED2 is high impedance when EN is low. LED 1 Cathode Connection. Current flowing into LED1 is 230 times the current flowing into SET. LED1 is high impedance when EN is low.
MAX1916
ON OFF
VCTRL RSET
V+
EN
SET
THERMAL SHUTDOWN
LED1
LED2
LED3
1X 1.215V
230X
230X
230X
UVLO
REF
MAX1916
GND
Figure 1. MAX1916 Simplified Functional Diagram
Detailed Description
The MAX1916 provides constant-current bias supply for white LED designs. The MAX1916 uses a single resistor to set the bias current for up to three LEDs. LED bias currents are matched to 0.3% by the MAX1916's unique current-matching architecture (Figure 1). Supply current (IEN) is a low 40A in normal operation and 0.05A when disabled. The MAX1916 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 MAX1916 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 MAX1916. 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, and SET into a high-impedance state.
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5
Low-Dropout, Constant-Current Triple White LED Bias Supply MAX1916
V+ TO OTHER CIRCUITS
Setting the Output Current
SET controls the LED bias current. Current flowing into LED1, LED2, and LED3 is 230 times greater than the current flowing into SET. Set the output current as follows: ILED _ = 230 (VCTRL - VSET ) RSET
EXISTING VCTRL LDO
SET ON OFF EN
LED1 LED2 LED3
MAX1916
GND
where V SET = 1.215V, V CTRL is an external voltage between 1.8V and 5.5V, and RSET is the resistor connected between VCTRL and SET (Figure 1).
Applications Information
Figure 2. Very Low-Cost, High-Efficiency Solution
V+ DAC VCTRL
SET ON OFF EN
LED1 LED2
LED3
1) Very Low-Cost, High-Efficiency Solution (Figure 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 MAX1916's current-regulating architecture and low dropout greatly minimize this effect compared to using simple ballast resistors. The enable function of the MAX1916 turns on and off the LEDs. An existing low-dropout regulator is used as VCTRL. 2) Brightness Adjustment Using a DAC (Figure 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. 3) Existing 5V Supply (Figure 4). Use an existing system regulator, such as the MAX684, to provide the required LED voltage and provide power to other circuits. Due to the high forward voltage of white LEDs (3.3V), use a 3.6V to 5.5V regulated supply to provide enough voltage headroom such that the LEDs will maintain constant brightness for any battery voltage. Use the existing regulated supply as VCTRL.
MAX1916
GND
Figure 3. Brightness Adjust Using DAC
VBATT EXISTING 5.0V REGULATOR V+ TO OTHER CIRCUITS
SET ON OFF EN
LED1 LED2
LED3
Chip Information
TRANSISTOR COUNT: 220 PROCESS: BiCMOS
MAX1916
GND
Figure 4. Existing 5V Supply Circuit
6
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Low-Dropout, Constant-Current Triple White LED Bias Supply
Package Information
MAX1916
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 7 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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