19-2067; Rev 0; 7/01 Low-Dropout, Constant-Current Triple White LED Bias Supply 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 40µA of supply current when enabled and 0.05µA 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. Features ♦ Low 200mV Dropout at 9mA ♦ Up to 60mA/LED Bias Current ♦ 0.3% LED Current Matching ♦ Simple LED Brightness Control ♦ Low 40µA Supply Current ♦ Low 0.05µA Shutdown Current ♦ 2.5V to 5.5V Supply Voltage Range ♦ Thermal Shutdown Protection ♦ Tiny 6-Pin Thin SOT23 Package (1mm High) The MAX1916 is available in a space-saving 6-pin Thin SOT23 package. Applications Ordering Information Next-Generation Wireless Handsets PDAs, Palmtops, and Handy Terminals Digital Cameras, Camcorders PART TEMP. RANGE PINPACKAGE TOP MARK MAX1916EZT -40°C to +85°C 6 Thin SOT23 AAAG Battery-Powered Equipment Pin Configuration Typical Operating Circuit VCTRL TOP VIEW V+ EN 1 SET LED1 LED2 LED3 GND 2 MAX1916 6 LED1 5 LED2 4 LED3 ON OFF EN MAX1916 SET 3 GND THIN SOT23-6 ________________________________________________________________ Maxim Integrated Products 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. 1 MAX1916 General Description MAX1916 Low-Dropout, Constant-Current Triple White LED Bias Supply ABSOLUTE MAXIMUM RATINGS EN, SET, LED1, LED2, LED3 to GND ..................... -0.3V to +6V Continuous Power Dissipation (TA = +70°C) 6-Pin Thin SOT23 (derate 9.1mW/°C above +70°C) ... 727mW Operating Temperature Range ......................... -40°C to +85°C Storage Temperature Range ........................... -65°C to +150°C Lead Temperature (soldering, 10s)................................... 300°C 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 = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER Operating Voltage Range Undervoltage Lockout Threshold SET Input Current Range SYMBOL VEN VUVLO VEN rising 2.2 Hysteresis VSET ISET = 42µA LED_ Dropout Voltage 260 µA 253 A/A 1.154 1.215 1.276 V 0.01 1 µA 0.3 5 5 TA = -40°C to +85°C 60 100 180 ISET = 42µA (Note 3) 200 360 ISET = 84µA (Note 3) 230 410 0.01 1 TA = +25°C Input High Voltage VIH VEN > VIH for enable Input Low Voltage VIL VEN < VIL for disable EN Input Bias Current IEN VEN = 2.5V to 5.5V, EN is the power-supply input VEN = 0.4V % mA ISET = 22µA (Note 2) VLED1 = VLED2 = VLED3 = 5.5V, EN = GND, each LED_ LED_ Leakage Current in Shutdown V mV 230 TA = -40°C to +25°C Each LED_ UNITS V 207 ISET = 42µA ILED_ MAX 5.5 2.47 5 EN = GND, VSET = 3.3V LED_-to-LED_ Current Matching TYP 85 ILED/ISET, ISET = 42µA SET Leakage Current in Shutdown Maximum LED_ Sink Current MIN 2.5 ISET SET to LED_ Current Ratio SET Bias Voltage CONDITIONS EN is the power-supply input mV µA 2.5 V 2.2 TA = +25°C 40 100 0.05 1 µA Thermal Shutdown Temperature 170 °C Thermal Shutdown Hysteresis 10 °C Note 1: Limits are 100% production tested at TA = +25°C. 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 _______________________________________________________________________________________ Low-Dropout, Constant-Current Triple White LED Bias Supply OUTPUT CURRENT vs. VEN SUPPLY VOLTAGE LED3 LED2 10 LED1 20.0 19.9 LED CURRENT (mA) 15 OUTPUT CURRENT (mA) LED CURRENT (mA) 20 20 15 10 5 5 MAX1916 toc03 MAX1916 toc01 25 LED CURRENT vs. TEMPERATURE MAX1916 toc02 LED CURRENT vs. V+ BIAS VOLTAGE 19.8 19.7 19.6 UNMATCHED LEDS 0 0 3 4 5 19.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 -40 -15 10 35 60 V+ BIAS VOLTAGE (V) VEN SUPPLY VOLTAGE (V) TEMPERATURE (°C) LED CURRENT vs. RSET LED CURRENT (ILED) vs. VCTRL LED DROPOUT VOLTAGE vs. CURRENT 50 LED CURRENT (mA) VCTRL = 3.3V A 10 VCTRL = 2.5V B 40 C 30 D 20 E F 10 300 250 200 150 100 50 G VCTRL = 1.8V 0 1 10 85 MAX1916 toc06 VCTRL = 5.0V LED DROPOUT VOLTAGE (mV) 60 MAX1916 toc04 100 LED CURRENT (mA) 6 MAX1916 toc05 2 100 0 1.5 2.0 2.5 3.0 3.5 4.0 VCTRL (V) RSET (kΩ) 4.5 5.0 5.5 0 5 10 15 20 25 30 35 40 LED CURRENT (mA) A: RSET = 10kΩ B: RSET = 15kΩ C: RSET = 22kΩ D: RSET = 33kΩ E: RSET = 47kΩ F: RSET = 68kΩ G: RSET = 100kΩ _______________________________________________________________________________________ 3 MAX1916 Typical Operating Characteristics (VEN = 3.3V, VCTRL = 3.3V, RSET = 24.9kΩ, V+ = 5V, TA = +25°C, unless otherwise noted.) (Circuit of Figure 1) Typical Operating Characteristics (continued) (VEN = 3.3V, VCTRL = 3.3V, RSET = 24.9kΩ, V+ = 5V, TA = +25°C, unless otherwise noted.) (Circuit of Figure 1) IEN SUPPLY CURRENT vs. VEN SUPPLY VOLTAGE ENABLE AND SHUTDOWN RESPONSE MAX1916 toc08 MAX1916 toc07 45 40 IEN SUPPLY CURRENT (µA) MAX1916 Low-Dropout, Constant-Current Triple White LED Bias Supply 35 VEN 2V/div 0 30 25 20 20mA 15 ILED 20mA/div 0 10 5 0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 40µs/div VEN SUPPLY VOLTAGE (V) VCTRL TRANSIENT RESPONSE V+ TRANSIENT RESPONSE MAX1916 toc09 3V VCTRL 1V/div 20mA ILED 10mA/div 10mA 4V V+ 1V/div 20mA ILED 10mA/div 10mA 10µs/div 4 MAX1916 toc10 20µs/div _______________________________________________________________________________________ Low-Dropout, Constant-Current Triple White LED Bias Supply PIN NAME FUNCTION 1 EN 2 GND Ground 3 SET 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. 4 LED3 LED 3 Cathode Connection. Current flowing into LED3 is 230 times the current flowing into SET. LED3 is high impedance when EN is low. 5 LED2 LED 2 Cathode Connection. Current flowing into LED2 is 230 times the current flowing into SET. LED2 is high impedance when EN is low. 6 LED1 LED 1 Cathode Connection. Current flowing into LED1 is 230 times the current flowing into SET. LED1 is high impedance when EN is low. 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. VCTRL ON V+ OFF RSET EN SET THERMAL SHUTDOWN 1X UVLO REF 1.215V LED1 230X LED2 230X LED3 230X 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 40µA in normal operation and 0.05µA 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 40µA to power the IC. Driving EN low forces LED1, LED2, LED3, and SET into a high-impedance state. _______________________________________________________________________________________ 5 MAX1916 Pin Description MAX1916 Low-Dropout, Constant-Current Triple White LED Bias Supply Setting the Output Current V+ 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: TO OTHER CIRCUITS EXISTING VCTRL LDO SET ILED _ = 230 LED1 LED2 LED3 ON EN OFF (VCTRL − VSET ) RSET 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). MAX1916 GND Applications Information 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. Figure 2. Very Low-Cost, High-Efficiency Solution V+ VCTRL DAC SET LED1 LED2 LED3 ON OFF EN MAX1916 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. GND Figure 3. Brightness Adjust Using DAC VBATT V+ EXISTING 5.0V REGULATOR SET LED1 LED2 TO OTHER CIRCUITS 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. LED3 Chip Information ON OFF EN MAX1916 GND TRANSISTOR COUNT: 220 PROCESS: BiCMOS Figure 4. Existing 5V Supply Circuit 6 _______________________________________________________________________________________ Low-Dropout, Constant-Current Triple White LED Bias Supply 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 © 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX1916 Package Information