19-2761; Rev 0; 1/03 KIT ATION EVALU E L B A AVAIL Ultra-High-Efficiency White LED Drivers Features ♦ Synchronous Step-Up Regulator Achieves >95% Efficiency Internal Switch and Synchronous Rectifier Eliminates External MOSFETs and Diodes 1MHz Fixed Frequency Minimizes Component Sizes The brightness can be easily adjusted using a multimode dimming interface, which allows brightness control through a DPWM signal, a 2- or 3-bit parallel control interface, or an analog signal. The DPWM signal can be connected directly to the control pin without the need for an external RC filter if its frequency is 10kHz or above. The MAX1984 drives up to eight LEDs, the MAX1985 drives up to six LEDs, and the MAX1986 drives up to four LEDs. Each device has an LED select pin (SEL) that allows one subset, the other subset, or all LEDs to be illuminated. All three devices are available in a 4mm ✕ 4mm thin QFN package. ♦ Open-LED Detection ♦ ♦ ♦ ♦ Up to 90% Total LED Efficiency Accurate LED Current Matching (8% max) Adjustable Maximum LED Current Multimode Dimming Control Digital Pulse-Width Modulation Control 2-Bit Parallel Control 3-Bit Parallel Control Analog Control ♦ Selectively Enable LEDs ♦ Unique 0.5mA LED Test Mode ♦ 2.7V to 5.5V Input Supply Range ♦ Small 4mm x 4mm 20-Pin Thin QFN Package Ordering Information PART Applications PDAs and Hand-Held PCs TEMP RANGE PIN-PACKAGE NO. OF LEDs MAX1984ETP -40°C to +85°C 20 Thin QFN 8 MAX1985ETP -40°C to +85°C 20 Thin QFN 6 MAX1986ETE -40°C to +85°C 16 Thin QFN 4 Cellular Phones Digital Cameras 15 BITB LX 2 14 REF LX 2 14 REF 13 SETI GND 3 12 LD8 N.C. 4 8 9 10 6 LD6 LD2 4mm x 4mm THIN QFN BITC 12 BITA LX 2 11 BITB MAX1986 GND 3 10 REF LD1 4 9 SETI 7 8 9 10 5 LD2 7 LD5 11 LD6 LDG LD3 6 LD1 5 LD4 11 LD7 OUT 1 LD5 LD2 5 12 N.C. 13 LD4 LD1 4 13 SETI MAX1985 14 LD3 MAX1984 15 LDG GND 3 16 4mm x 4mm THIN QFN 6 7 8 LD4 16 IN 17 LD3 18 OUT 1 MODE 19 15 BITB SEL 20 OUT 1 LDG 16 BITA 17 BITC BITA 18 IN BITC 19 MODE IN 20 SEL MODE TOP VIEW SEL Pin Configurations 4mm x 4mm THIN QFN ________________________________________________________________ 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 MAX1984/MAX1985/MAX1986 General Description The MAX1984/MAX1985/MAX1986 are white light-emitting diode (LED) drivers that use individual regulators to control the current of up to eight LEDs. A high-efficiency step-up regulator generates just enough voltage to keep all the current regulators in regulation. A versatile dimming interface accommodates analog, digitally adjusted pulse-width modulation (DPWM), or parallel control. The individual current regulators allow good current matching between LEDs. Open or shorted LEDs cannot affect the performance of other LEDs. The step-up regulator achieves high efficiency by using synchronous rectification. The internal N-channel switch and P-channel synchronous rectifier eliminate the need for external MOSFETs and diodes. The 1MHz switching frequency allows the use of low-profile inductors and ceramic capacitors. MAX1984/MAX1985/MAX1986 Ultra-High-Efficiency White LED Drivers ABSOLUTE MAXIMUM RATINGS OUT, IN, BITA, BITB, BITC, LD1, LD2, LD3, LD4, LD5, LD6, LD7, LD8 to GND ................................-0.3V to +6V LDG to GND........................................................................±0.3V LX to GND ................................................-0.3V to (VOUT + 0.3V) SETI, REF, MODE, SEL to GND ...................-0.3V to (VIN + 0.3V) Continuous Power Dissipation (TA = +70°C) 16-Pin Thin QFN (derate 16.9mW/°C above +70°C) ...1349mW 20-Pin Thin QFN (derate 16.9mW/°C above +70°C) ...1349mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°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 (Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7µF, CREF = 0.22µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS IN Supply Range MIN TYP 2.7 UNITS 5.5 V IN Undervoltage Lockout Threshold 50mV typical hysteresis 2.4 2.6 V IN Quiescent Current BITA = BITB = BITC = IN, LD1 to LD8 = GND 400 600 µA IN Shutdown Current BITA = BITB = BITC = GND 0.1 1 µA 1.250 1.270 V 0.2 5 mV REF Output Voltage IREF = 0 REF Line Regulation 2.7V < VIN < 5.5V REF Load Regulation -1µA < IREF < +50µA Oscillator Frequency 2.2 MAX 1.230 0.8 Oscillator Maximum Duty Cycle OUT Overvoltage Protection (OVP) Threshold 5 15 mV 1 1.2 MHz 85 VLD1 to VLD8 = 50mV, OUT rising, 100mV typical hysteresis 5.1 % 5.3 5.5 V INTERNAL MOSFET SWITCHES N-Channel MOSFET On-Resistance ILX = 200mA 0.4 0.8 Ω N-Channel MOSFET Leakage Current VLX = 5.5V, BITA = BITB = BITC = GND 0.1 1 µA P-Channel MOSFET On-Resistance ILX = 200mA 0.5 1 Ω P-Channel MOSFET Leakage Current LX = GND, VOUT = 5.5V, BITA = BITB = BITC = GND 0.1 1 µA 0.65 0.81 MAX1984 N-Channel MOSFET Current Limit 0.50 MAX1985 0.40 0.52 0.65 MAX1986 0.30 0.39 0.52 A CONTROL INPUTS BITA, BITB, BITC Input Logic Low Level 2.7V < VIN < 5.5V BITA, BITB, BITC Input Logic High Level 2.7V < VIN < 5.5V MODE Input Logic Low Level 2.7V < VIN < 5.5V MODE Input Logic High Level 2.7V < VIN < 5.5V MODE, BITA, BITB, BITC Input Bias Current 2.7V < VIN < 5.5V 2 0.4 1.6 V V 0.4 VIN - 0.4 V V 0.01 _______________________________________________________________________________________ 1 µA Ultra-High-Efficiency White LED Drivers (Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7µF, CREF = 0.22µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN SEL Input Logic Low Level 2.7V < VIN < 5.5V SEL Input Logic Midlevel 2.7V < VIN < 5.5V 0.50 SEL Input Logic High Level 2.7V < VIN < 5.5V 2.05 SEL Input Bias Current TYP MAX UNITS 0.4 V 1.85 V V SEL = GND, current out of the pin 5 SEL = IN, current into the pin 10 µA FULL-SCALE LED CURRENT ADJUSTMENT LD1 to LD8 Output Current VLD_ = 80mV, SETI = BITA = BITB = BITC = IN 16.5 18 19.5 VLD_ = 80mV, RSETI = 278kΩ ±0.1%, BITA = BITB = BITC = IN 22.5 25 27.5 VLD_ = 80mV, RSETI = 1.8MΩ ±0.1%, BITA = BITB = BITC = IN 12.5 14 15.5 VLD_ = 80mV, RSETI = 597kΩ ±0.1%, BITA = BITB = BITC = IN 16.5 18 19.5 0.42 0.50 0.60 80 100 120 VLD1 = 1V, RSETI = 10kΩ, BITA = BITB = BITC = IN SETI = GND mA 26 LD1 to LD8 Regulation Voltage SETI = IN, ILX = 120mA (MAX1984), 110mA (MAX1985), 98mA (MAX1986) SETI High-Level Threshold (18mA LED Default Current) 2.7V < VIN < 5.5V VIN - 0.4 SETI Low-Level Threshold (0.5mA LED Default Current) 2.7V < VIN < 5.5V 50 SETI Output Current SETI = GND 40 mV V 125 mV 70 100 µA 3 4 Ω OUTPUT CURRENT SOURCE LD1 to LD8 On-Resistance VLD_ = 50mV, VOUT = 3.5V LD1 to LD8 Current-Source Compliance BITA = BITB = BITC = IN, 80mV < VLD_ < 1V (Note 1) 0.3 5 % LD1 to LD8 Leakage Current BITA = BITB = BITC = GND 0.01 1 µA DIGITAL BRIGHTNESS CONTROL 2-Bit Control DAC LSB MODE = SETI = BITB = IN, BITA = BITC = GND (Note 2) 26 33 39 % 3-Bit Control DAC LSB SETI = BITC = IN, MODE = BITA = BITB = GND (Note 2) 7 14 21 % 5.5 V 7 % DPWM BRIGHTNESS CONTROL DPWM Input Supply Range MODE = BITC = IN DPWM Shutdown Duty Cycle BITC = GND 2.3 3 5 _______________________________________________________________________________________ 3 MAX1984/MAX1985/MAX1986 ELECTRICAL CHARACTERISTICS (continued) MAX1984/MAX1985/MAX1986 Ultra-High-Efficiency White LED Drivers ELECTRICAL CHARACTERISTICS (Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7µF, CREF = 0.22µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 3) PARAMETER CONDITIONS IN Supply Range IN Undervoltage Lockout Threshold 50mV typical hysteresis IN Quiescent Current BITA = BITB = BITC = IN, LD1 to LD8 = GND REF Output Voltage IREF = 0 REF Line Regulation 2.7V < VIN < 5.5V REF Load Regulation -1µA < IREF < +50µA Oscillator Frequency MIN MAX UNITS 2.7 TYP 5.5 V 2.2 2.6 V 600 µA 1.230 1.270 V 5 mV 15 mV 0.8 1.2 MHz 5.1 5.5 V OUT Overvoltage Protection Threshold VLD1 to VLD8 = 50mV, OUT rising, 100mV typical hysteresis INTERNAL MOSFET SWITCHES N-Channel MOSFET On-Resistance ILX = 200mA 0.8 Ω P-Channel MOSFET On-Resistance ILX = 200mA 1.0 Ω N-Channel MOSFET Current Limit MAX1984 0.50 MAX1985 0.40 0.81 0.65 MAX1986 0.30 0.52 A CONTROL INPUTS BITA, BITB, BITC Input Logic Low Level 2.7V < VIN < 5.5V BITA, BITB, BITC Input Logic High Level 2.7V < VIN < 5.5V MODE Input Logic Low Level 2.7V < VIN < 5.5V MODE Input Logic High Level 2.7V < VIN < 5.5V SEL Input Logic Low Level 2.7V < VIN < 5.5V SEL Input Logic Midlevel 2.7V < VIN < 5.5V SEL Input Logic High Level 2.7V < VIN < 5.5V FULL-SCALE LED CURRENT ADJUSTMENT VLD_ = 80mV, SETI = BITA = BITB = BITC = IN LD1 to LD8 Output Current 4 0.4 1.6 V 0.4 VIN - 0.4 0.50 V V 0.4 V 1.85 V 2.05 V 16 20 VLD_ = 80mV, RSETI = 278kΩ ±1%, BITA = BITB = BITC = IN 22 28 VLD_ = 80mV, RSETI = 1.8MΩ ±1%, BITA = BITB = BITC = IN 11.5 16.0 VLD_ = 80mV, RSETI = 697kΩ ±1%, BITA = BITB = BITC = IN 15.5 20.0 SETI = GND 0.42 0.60 _______________________________________________________________________________________ V mA Ultra-High-Efficiency White LED Drivers (Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7µF, CREF = 0.22µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 3) PARAMETER CONDITIONS MIN TYP MAX UNITS 120 mV LD1 to LD8 Regulation Voltage SETI = IN, ILX = 120mA (MAX1984), 110mA (MAX1985), 98mA (MAX1986) SETI High-Level Threshold (18mA LED Default Current) 2.7V < VIN < 5.5V VIN - 0.4 SETI Low-Level Threshold (0.5mA LED Default Current) 2.7V < VIN < 5.5V 50 125 mV SETI Output Current SETI = GND 40 100 µA 80 V OUTPUT CURRENT SOURCE LD1 to LD8 On-Resistance LD1 to LD8 Current-Source Compliance DIGITAL BRIGHTNESS CONTROL ILD_ = 25mA, VOUT = 3.5V 4 Ω BITA = BITB = BITC = IN, 80mV < VLD_ < 1V (Note 1) 8 % 2-Bit Control DAC LSB MODE = SETI = BITB = IN, BITA = BITC = GND 26 39 % 3-Bit Control DAC LSB SETI = BITC = IN, MODE = BITA = BITB = GND (Note 2) 7 21 % 2.3 5.5 V 3 7 % DPWM BRIGHTNESS CONTROL DPWM Input Supply Range MODE = BITC = IN DPWM Shutdown Duty Cycle BITC = GND Note 1: Current variation is caused by the current source voltage changes. Note 2: Measurement is with respect to 100% of the programmed LED output current. Note 3: Specifications to -40°C are guaranteed by design, not production tested. _______________________________________________________________________________________ 5 MAX1984/MAX1985/MAX1986 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (Circuit of Figure 1; VIN = 3.3V, SETI = IN, MODE = IN, TA = +25°C, unless otherwise noted.) VIN = 4.2V VIN = 3.0V 70 60 VIN = 4.2V VIN = 3.0V 80 90 VIN = 3.6V 70 5 10 15 20 25 VIN = 4.2V VIN = 3.0V 70 50 50 0 80 60 60 50 0 5 10 15 20 0 25 5 10 20 LED CURRENT (mA) LED CURRENT (mA) STEP-UP REGULATOR EFFICIENCY vs. INPUT VOLTAGE (25mA LED CURRENT) STEP-UP REGULATOR EFFICIENCY vs. INPUT VOLTAGE (4mA LED CURRENT) TOTAL EFFICIENCY vs. LED CURRENT (8 LEDs) 90 8 LEDs 8 LEDs 80 6 LEDs 70 MAX1984/85/86 toc06 90 EFFICIENCY (%) EFFICIENCY (%) 90 80 70 6 LEDs 85 4 LEDs VIN = 3.0V 4 LEDs 60 60 η Σ VLEDi x ILEDi VIN = 3.6V ηTOTAL = VIN = 4.2V 80 3.0 3.5 4.0 4.5 5.0 2.5 3.0 3.5 4.0 4.5 5.0 5 10 15 20 25 INPUT VOLTAGE (V) LED CURRENT (mA) TOTAL EFFICIENCY vs. LED CURRENT (6 LEDs) TOTAL EFFICIENCY vs. LED CURRENT (4 LEDs) TOTAL EFFICIENCY vs. INPUT VOLTAGE (25mA LED CURRENT) 70 VIN = 4.2V 60 Σ VLEDi x ILEDi VIN = 4.2V 80 70 i =1 ηTOTAL = INPUT_POWER 15 LED CURRENT (mA) 20 8 LEDs 70 6 LEDs 60 i =1 INPUT_POWER 50 50 10 80 4 LEDs Σ VLEDi x ILEDi 60 50 5 90 η η ηTOTAL = MAX1984/85/86 toc09 VIN = 3.6V EFFICIENCY (%) 80 VIN = 3.0V 90 EFFICIENCY (%) VIN = 3.0V 100 MAX1984/85/86 toc08 100 MAX1984/85/86 toc07 VIN = 3.6V 0 0 5.5 INPUT VOLTAGE (V) 100 90 5.5 i =1 INPUT_POWER 50 50 2.5 25 100 MAX1984/85/86 toc05 100 MAX1984/85/86 toc04 95 6 15 LED CURRENT (mA) 100 EFFICIENCY (%) VIN = 3.6V EFFICIENCY (%) 80 90 100 MAX1984/85/86 toc02 VIN = 3.6V EFFICIENCY (%) EFFICIENCY (%) 90 100 MAX1984/85/86 toc01 100 STEP-UP REGULATOR EFFICIENCY vs. LED CURRENT (4 LEDs) STEP-UP REGULATOR EFFICIENCY vs. LED CURRENT (6 LEDs) MAX1984/85/86 toc03 STEP-UP REGULATOR EFFICIENCY vs. LED CURRENT (8 LEDs) EFFICIENCY (%) MAX1984/MAX1985/MAX1986 Ultra-High-Efficiency White LED Drivers 25 0 5 10 15 LED CURRENT (mA) 20 25 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) _______________________________________________________________________________________ 5.0 5.5 Ultra-High-Efficiency White LED Drivers TOTAL EFFICIENCY vs. INPUT VOLTAGE (4mA LED CURRENT ) 60 8 LEDs MAX9184/85/86 toc12 MAX9184/85/86 toc11 25.0 26 25 LED CURRENT (mA) 70 25.5 LED CURRENT (mA) 80 26.0 24 LD1 TO LD8 23 24.5 6 LEDs 50 4 LEDs RSETI = 278kΩ RSETI = 278kΩ 22 24.0 40 3.0 3.5 4.0 4.5 5.0 2.5 5.5 3.0 3.5 4.0 4.5 5.0 0 5.5 50 100 150 200 INPUT VOLTAGE (V) LD_VOLTAGE (mV) STARTUP WAVEFORMS LED CURRENT vs. DPWM DUTY MAXIMUM LED CURRENT vs. SETI RESISTANCE 0 20 4V B 2V 0 100mA 0 C THEORETICAL 15 ACTUAL 10 50kHz DPWM FREQUENCY 5 30 MAX9184/85/86 toc15 25 5V MAXIMUM LED CURRENT (mA) MAX1984/85/86 toc13 A 300 250 INPUT VOLTAGE (V) MAX9184/85/86 toc14 2.5 LED CURRENT (mA) EFFICIENCY (%) 90 LED CURRENT MATCHING LED CURRENT vs. INPUT VOLTAGE MAX1984/85/86 toc10 100 THEORETICAL 25 20 ACTUAL 15 20mA D 0 100µs/div A: BITA VOLTAGE, 5V/div B: OUT VOLTAGE, 2V/div C: INDUCTOR CURRENT, 100mA/div D: LD_ CURRENT, 20mA/div RSETI = 278kΩ 0 10 0 20 40 60 DPWM DUTY (%) 80 100 0 500 1000 1500 2000 SETI RESISTANCE (kΩ) _______________________________________________________________________________________ 7 MAX1984/MAX1985/MAX1986 Typical Operating Characteristics (continued) (Circuit of Figure 1; VIN = 3.3V, SETI = IN, MODE = IN, TA = +25°C, unless otherwise noted.) MAX1984/MAX1985/MAX1986 Ultra-High-Efficiency White LED Drivers Pin Description PIN NAME MAX1984 MAX1985 MAX1986 1 1 1 OUT 2 2 2 LX Step-Up Regulator Output. Bypass OUT to GND with a 4.7µF capacitor. Inductor Connection. LX is connected to the drains of the internal N-channel and P-channel MOSFETs. 3 3 3 GND Ground — 4, 12 — N.C. No Connection. Not internally connected. 4 5 4 LD1 LED1 Cathode Connection. LD1 is the open-drain output of an internal current regulator for controlling the current through LED1. It is able to sink up to 25mA. If not used, connect LD1 to GND. 5 6 5 LD2 LED2 Cathode Connection. LD2 is the open-drain output of an internal current regulator for controlling the current through LED2. It is able to sink up to 25mA. If not used, connect LD2 to GND. 6 7 7 LD3 LED3 Cathode Connection. LD3 is the open-drain output of an internal current regulator for controlling the current through LED3. It is able to sink up to 25mA. If not used, connect LD5 to GND. 7 9 8 LD4 LED4 Cathode Connection. LD4 is the open-drain output of an internal current regulator for controlling the current through LED4. It is able to sink up to 25mA. If not used, connect LD4 to GND. 8 8 6 LDG Common Ground Connection for Internal Current Regulators. Connect LDG to GND. 9 10 — LD5 LED5 Cathode Connection. LD5 is the open-drain output of an internal current regulator for controlling the current through LED5. It is able to sink up to 25mA. If not used, connect LD5 to GND. 10 11 — LD6 LED6 Cathode Connection. LD6 is the open-drain output of an internal current regulator for controlling the current through LED6. It is able to sink up to 25mA. If not used, connect LD6 to GND. 11 — — LD7 LED7 Cathode Connection. LD7 is the open-drain output of an internal current regulator for controlling the current through LED7. It is able to sink up to 25mA. If not used, connect LD7 to GND. 12 — — LD8 LED8 Cathode Connection. LD8 is the open-drain output of an internal current regulator for controlling the current through LED8. It is able to sink up to 25mA. If not used, connect LD8 to GND. 13 13 9 SETI Maximum LED Current Set Input. SETI sets the maximum current through each LED. Connect SETI to IN for a default maximum current of 18mA; connect SETI to GND for the 0.5mA LED test mode. Connect a resistor from SETI to GND to adjust the maximum current between 12mA to 25mA (see the Setting the Maximum LED Current section). 14 14 10 REF 1.25V Reference Output. Bypass REF to GND with a minimum 0.22µF ceramic capacitor. BITB Brightness Control Input (Multimode): DPWM Mode: Leave unconnected for greater than 50kHz operation. Add a capacitor from BITB to ground for lower frequency operation. Analog Mode: Analog control signal input. 2- or 3-Bit Parallel Mode: Digital input. Least significant bit (LSB) for 2-bit mode. 15 8 FUNCTION 15 11 _______________________________________________________________________________________ Ultra-High-Efficiency White LED Drivers PIN MAX1984 MAX1985 16 NAME MAX1986 16 12 BITA Brightness Control Input (Multimode): DPWM Mode: DPWM control signal input. Analog Mode: Connect to IN. 2- or 3-Bit Parallel Mode: Digital input. Most significant bit (MSB). Brightness Control Input: DPWM Mode: Connect to IN. Analog Mode: Connect to IN. 2-Bit Parallel Mode: Connect to GND. 3-Bit Parallel Mode: Digital input (LSB). 17 17 13 BITC 18 18 14 IN 19 19 20 15 20 16 FUNCTION Input Supply. IN provides power to the internal control circuitry and MOSFET drivers. Bypass IN to GND with a minimum 0.1µF ceramic capacitor. MODE Brightness Control Mode Selection Input. Connect MODE and BITC to IN for DPWM control. Connect MODE, BITA, and BITC to IN for analog control. For 2-bit parallel control, connect MODE to IN and BITC to ground. For 3-bit parallel control, connect MODE to GND. SEL LED Selection Input. Connect SEL to IN to turn on all LEDs. Connect SEL to ground to turn on only LED1–LED5 (MAX1984), LED1–LED4 (MAX1985), or LED1 to LED3 (MAX1986). Leave SEL unconnected or force to VIN/2 to turn on only LED6 to LED8 (MAX1984), LED3–LED6 (MAX1985), or LED4 (MAX1986). VIN 2.7V TO 5.5V C2 0.1µF C1 2 x 2.2µF 14 C3 0.22µF VIN 13 L1 10µH 3 GND 2 LX REF SETI 18 IN OUT MAX1984 LD1 LD2 16 15 BRIGHTNESS CONTROL 17 19 LED SELECT 20 8 BITA LD3 BITB LD4 BITC LD5 MODE LD6 SEL LD7 LDG LD8 1 4 D1 5 D2 6 D3 7 D4 9 D5 10 D6 11 D7 12 D8 C4 2 x 2.2µF Figure 1. Standard Application Circuit of the MAX1984 _______________________________________________________________________________________ 9 MAX1984/MAX1985/MAX1986 Pin Description (continued) MAX1984/MAX1985/MAX1986 Ultra-High-Efficiency White LED Drivers L VIN CIN IN LX OUT FB STEP-UP CONTROLLER MAX1984 MAX1985 MAX1986 GND CURRENT SENSE MIN UVLO COMP 2.4V CREF COUT REF AND BIAS BLOCK REF EN1 IREF LD1 LDG EN2 IREF LD2 LDG EN3 IREF LD3 LDG EN4 IREF LD4 LDG EN5 IREF LD5 LDG EN6 IREF LD6 LDG EN7 IREF LD7 LDG EN8 IREF LD8 LDG LD1 LD2 LD3 LD4 SHUTDOWN MODE DIMMING CONTROL BITA BITB DIMMING CONTROL BLOCK IREF BITC LD5* LD6* SETI RSETI LED SELECT SEL LOGIC EN [8:1] LD7** LD8** LDG *MAX1984 AND MAX1985 ONLY. **MAX1984 ONLY. Figure 2. System Functional Diagram 10 ______________________________________________________________________________________ Ultra-High-Efficiency White LED Drivers The standard application circuit of the MAX1984 drives eight white LEDs (Figure 1). The standard application circuit of the MAX1985 drives six white LEDs (Figure 6). The standard application circuit of the MAX1986 drives four white LEDs (Figure 7). The input voltage range is from 2.7V to 5.5V. Table 1 lists the recommended component options and Table 2 lists the component suppliers. Detailed Description The MAX1984/MAX1985/MAX1986 are white LED drivers that use individual regulators to control the current of up to eight LEDs. A high-efficiency step-up regulator generates just enough voltage to keep all the current regulators in regulation. A versatile dimming interface accommodates analog, DPWM, or parallel control. LED Current Regulators Good LED current matching is achieved using individual current regulators for each LED (Figure 3). The regulator is an analog gain block with an open-drain N-channel MOSFET output stage and can sink up to 25mA LED current. The LED current is sensed using an internal 1Ω resistor connected between the source of the MOSFET and ground. The regulator controls the output current by comparing the voltage across the current-sense resistor with a reference voltage (IREF) set by the dimming control circuitry. Startup and Feedback The step-up converter is regulated at a voltage just high enough to power the LEDs. Since the forward voltage is different for each LED, the LED with the largest forward voltage sets the regulation voltage. Each current regulator’s voltage drop (from LD_ to LDG) is monitored and the lowest voltage drop is used as the step-up regulator’s feedback. At startup, it is important to ensure the output voltage rises high enough to forward bias all LEDs and allow their current regulators to detect their presence. Therefore, before the current regulators are enabled the step-up regulator output is made to rise up to the OUT OVP threshold (5.3V, typ). Then, the step-up regulator stops switching and each current regulator output is tested Table 1. Component List DESCRIPTION DESIGNATION MAX1984 2 x 2.2µF, 6.3V X5R ceramic capacitors (0603) Taiyo Yuden JMK107BJ225MA TDK C1608X5ROJ225K C1, C4 D1–D4, D5*, D6*, D7**, D8** MAX1985 MAX1986 2 x 2.2µF, 6.3V X5R ceramic capacitors (0603) Taiyo Yuden JMK107BJ225MA TDK C1608X5ROJ225K 2.2µF, 6.3V X5R ceramic capacitors (0603) Taiyo Yuden JMK107BJ225MA TDK C1608X5ROJ225K 15µH, 0.85A inductor Sumida CLS5D11HP-150NC 22µH, 0.65A inductor Sumida CLS5D11HP-220NC Surface-mount white LEDs Nichia NSCW215T 10µH, 1A inductor Sumida CLS5D11HP-100NC L1 *MAX1984 and MAX1985 only. **MAX1984 only. Table 2. Component Suppliers PHONE FAX Nichia SUPPLIER 717-285-2323 717-285-9378 www.nichia.com WEBSITE Sumida 847-545-6700 847-545-6720 www.sumida.com Taiyo Yuden 800-348-2496 847-925-0899 www.t-yuden.com TDK 847-803-6100 847-390-4405 www.component.tdk.com ______________________________________________________________________________________ 11 MAX1984/MAX1985/MAX1986 Standard Application Circuits MAX1984/MAX1985/MAX1986 Ultra-High-Efficiency White LED Drivers THRESHOLD EN_ LD_ CURRENT SENSE IREF SLOPE COMP OC COMP OSCILLATOR OSC SUMMING COMPARATOR LOGIC GATE DRIVERS FB 1Ω 100mV LDG OV COMP 5.3V OUT Figure 3. Current Regulator Functional Diagram Figure 4. Step-Up Regulator Functional Diagram for an LED’s presence. The current regulators are enabled and any regulator with an output voltage less than 45mV is detected and is ignored, preventing outputs left open or shorted to ground from dominating the step-up regulation loop. Outputs shorted to IN, OUT, or any voltage above 45mV resemble valid LEDs and are regulated at the current set point. MOSFET and turns on the P-channel MOSFET when one of the following three conditions occurs: the summing comparator output becomes high, the switch current exceeds the overcurrent threshold, or the falling edge of the oscillator occurs. As the LEDs draw current, the step-up regulator’s output voltage gradually falls and the voltage drop across each of the current regulators reduces. Eventually, the voltage drop across whichever current regulator drives the LED with the highest forward voltage reaches the step-up regulator’s threshold (100mV, typ) and step-up switching starts again (see the Startup Waveform in the Typical Operating Characteristics). Step-Up Regulator The step-up regulator employs a fixed-frequency current-mode control method to generate the bias voltage for the white LEDs. The regulator takes the minimum value of all the LD_ pin voltages as the feedback signal to ensure that the output voltage is high enough to drive all the LEDs. The heart of the controller is a multiinput, open-loop comparator that sums three signals: the feedback error signal with respect to the 100mV reference, the current-sense signal, and the slope compensation ramp (Figure 4). In normal operation, the controller starts a new cycle by turning on the N-channel MOSFET and turning off the P-channel MOSFET on the rising edge of the internal oscillator if all of the following three conditions are satisfied: the summing comparator output is low, the switch current does not exceed the overcurrent threshold, and the output voltage does not exceed the overvoltage threshold. The controller turns off the N-channel 12 Both the N-channel MOSFET and the P-channel MOSFET turn off if the output voltage exceeds the overvoltage rising threshold. Both switches stay off until all of the following three conditions are satisfied: the output voltage is below the overvoltage falling threshold, the summing comparator output is low, and the next rising edge of the oscillator occurs. Brightness Control Interface The light intensity of the white LEDs can be easily adjusted from 15% to 100% of the full-scale LED current chosen by SETI. The MAX1984/MAX1985/MAX1986 support DPWM control, analog control, and 2-bit or 3-bit parallel control. DPWM Control To use the DPWM control mode, connect MODE and BITC to IN, leave BITB unconnected, and connect the DPWM signal to BITA. The LED current is given by the following equation: ILED = D ✕ ILED(FS) where ILED(FS) is the full-scale LED current set by SETI, and D is the duty cycle of the DPWM signal. The average voltage of the DPWM signal is obtained through an internal RC filter (Figure 5). The 0.1ms filter time constant allows the use of DPWM frequencies from 10kHz to 2MHz. If lower frequencies are preferred, an external ______________________________________________________________________________________ Ultra-High-Efficiency White LED Drivers VBITB × ILED(FS) ILED = K1 + K2 × 0.75 × VREF τ = 0.2MΩ ✕ CEXT + 0.098ms where K1 = 0.0465, K2 = 0.953, VBITB is the voltage at the BITB pin, VREF is the 1.25V internal reference voltage, and ILED(FS) is the full-scale LED current set by SETI. In analog mode, the MAX1984/MAX1985/MAX1986 enter shutdown mode when both VBITA and VBITB are logic low. where CEXT is the external capacitance. The recommended DPWM duty-factor range is from 20% to 100% for DPWM frequencies between 20kHz and 2MHz, using the internal 0.1ms filter. For lower DPWM operating frequencies, use CEXT and ensure the voltage on C EXT (BITB), including ripple, remains above DFMIN ✕ 0.75 ✕ VREF, where DFMIN is the minimum reliable DPWM duty factor of 15%. Parallel Control The MAX1984/MAX1985/MAX1986 also support 2-bit or 3-bit parallel control. To use the 3-bit parallel control mode, connect MODE to ground. BITA is the most significant bit and BITC is the least significant bit. To use the 2-bit parallel control, connect MODE to IN and BITC to ground. BITA is the most significant bit and BITB is the least significant bit. In parallel mode, the MAX1984/MAX1985/MAX1986 enter shutdown mode when BITA, BITB, and BITC are logic low. Tables 3 and 4 are the truth tables. In DPWM mode, the MAX1984/MAX1985/MAX1986 enter shutdown mode when the DPWM duty cycle is below 5% (typ) and BITC is a logical low level. Analog Control To use the analog control mode, connect MODE, BITA, and BITC to IN. Connect BITB to a DC voltage that sets the LED current. The operational range for the analog SHUTDOWN THRESHOLD SHUTDOWN VIN MODE 0.75 x VREF BITA 1 DECODER BITB 100 DAC 3-BIT BITC IREF 0.75 x VREF LEVEL SHIFT 200kΩ 9.8MΩ TO CURRENT REGULATORS 38Ω 10pF SETI 18mA DEFAULT RSETI 0.5mA TEST SETI SETI VIN - 0.7V 0.045V 300kΩ 200kΩ 7.2MΩ Figure 5. Brightness Control Equivalent Functional Diagram ______________________________________________________________________________________ 13 MAX1984/MAX1985/MAX1986 control is from 140mV (15%) to 0.75 ✕ VREF (100%). The LED current is given by the following equation: capacitor can be connected from BITB to ground to increase the total time constant. Use the following equation to calculate the total time constant: MAX1984/MAX1985/MAX1986 Ultra-High-Efficiency White LED Drivers LED Selection Shutdown The MAX1984/MAX1985/MAX1986 provide a control input (SEL) to selectively turn on one subset, the other subset, or all of the LEDs. SEL is a three-level logic input that can be connected to logic low, logic high, or left unconnected. Table 5 is the truth table. As soon as the input voltage rises above the UVLO threshold and the internal reference is ready, the stepup regulator starts unless the device is in shutdown. If a 2-bit or 3-bit parallel control is used, the MAX1984/ MAX1985/MAX1986 enter shutdown mode when BITA, BITB, and BITC are logic low. The parts come out of shutdown if at least 1 bit is logic high. If DPWM control is used, the parts enter shutdown mode when the duty cycle of BITA is less than 5% (typ) and BITC is logic low. If analog control is used, the parts enter shutdown when the voltages on both BITA and BITB are logic low. LED Test Mode Connecting SETI to ground enables the LED test mode. In this mode, the LED current is set to 0.5mA and DC-to-DC switching is inhibited. OUT is powered from IN through an internal silicon diode. Forcing 0.5mA through the LED is a simple way to determine whether the diode has suffered any ESD damage. LEDs that do not light in this mode usually have suffered ESD or other damage. The dimming control inputs are ignored in the test mode. Table 3. 3-Bit Parallel Control Truth Table BITA BITB BITC BRIGHTNESS (%) COMMENTS 0 0 0 0 Shutdown 0 0 1 14.3 Minimum current 0 1 0 26.6 — 0 1 1 42.9 — 1 0 0 57.1 — 1 0 1 71.4 — 1 1 0 85.7 — 1 1 1 100 Full-scale current set by SETI Table 4. 2-Bit Parallel Control Truth Table BITA BITB BITC BRIGHTNESS (%) COMMENTS 0 0 0 0 Shutdown 0 1 0 33.3 Minimum current 1 0 0 66.7 — 1 1 0 100 Full-scale current set by SETI Overvoltage Protection Output OVP prevents the internal switches from being damaged if all LEDs are open. If the output voltage rises above OUT OVP rising threshold, the MAX1984/MAX1985/MAX1986 turn off the step-up regulator. Once the output voltage falls below OVP falling threshold, the step-up regulator turns on again. Applications Information Inductor Selection The MAX1984/MAX1985/MAX1986’s 1MHz switching frequency allows the use of low-profile surface-mount inductors. The MAX1984 works well with a 10µH inductor, the MAX1985 works well with a 15µH inductor, and the MAX1986 works well with a 22µH inductor. The inductor saturation current rating should be higher than the N-channel switch current limit. For high efficiency, choose an inductor made of high-frequency core material to reduce core losses. Using a shielded inductor reduces radiated EMI. Output Capacitor Selection The output capacitor affects the circuit’s stability and output-voltage ripple. The MAX1984 works well with a 4.7µF ceramic output capacitor, the MAX1985 works well with a 3.3µF ceramic output capacitor, and the MAX1986 works well with a 2.2µF ceramic output capacitor. Always use capacitors with working voltage ratings higher than the output OVP rising threshold (5.5V max). Table 5. SEL Control Truth Table SEL MAX1984 MAX1985 MAX1986 Low (VSEL < 0.4V) LED1 to LED5 ON LED1 to LED4 ON LED1 to LED3 ON Mid (SEL unconnected or 0.5V < VSEL < 1.8V) LED6 to LED8 ON LED5 to LED6 ON LED4 ON High (VSEL > 2.05V) 14 All LEDs ON ______________________________________________________________________________________ Ultra-High-Efficiency White LED Drivers PC Board Layout and Grounding Careful PC board layout is very important for proper operation. Use the following guidelines for good PC board layout: To prevent noise from coupling into the device, connect an additional 0.1µF ceramic capacitor from the IN pin to the GND pin. Place that capacitor within 5mm of the pins. Setting the Maximum LED Current The full-scale current through each LED can be set using SETI. When SETI is connected to IN, the full-scale LED current is set to the default value of 18mA. When SETI is connected to GND, the LED current is set to 0.5mA LED test mode. If SETI is connected with a resistor to GND, the full-scale LED current can be adjusted from 14mA to 25mA: ILED(FS) = 12mA + K × 0.75 × VREF RSETI where K = 3851, and VREF is the internal reference voltage. 1) Minimize the area of high-current loops by placing the input capacitors, inductor, and output capacitors less than 0.2in (5mm) from the LX and GND pins. Connect these components with wide traces. Avoid using vias in the high-current paths. If vias are unavoidable, use many vias in parallel to reduce resistance and inductance. 2) Create islands for the analog ground and power ground. The analog ground island includes the exposed backside pad of the device, the REF bypass capacitor ground, and the SETI resistor ground. The power ground island includes the GND pin, the common ground for the current regulators (LDG), and the step-up regulator’s input/output capacitor grounds. The analog ground and power ground islands are connected together at only one location using a short trace between the GND pin and the exposed backside pad underneath the device. 3) Maximize the width of the power ground traces to improve efficiency, and reduce output-voltage ripple and noise spikes. 4) Place the IN pin and REF pin bypass capacitors within 5mm to the device. 5) Minimize the size of LX node while keeping it wide and short to reduce radiated EMI. Refer to the MAX1985 evaluation kit for an example of proper board layout. Chip Information TRANSISTOR COUNT: 3016 ______________________________________________________________________________________ 15 MAX1984/MAX1985/MAX1986 Input Capacitor Selection The input capacitor reduces the current peaks drawn from the input supply and reduces noise injection into all devices running from that supply. The input voltage source impedance determines the required size of the input capacitor. The standard application circuits (Figures 1, 6, and 7) use an input capacitor equal to the output capacitor to accommodate the high impedance seen in a typical lab environment. Actual applications usually have much lower source impedance since the step-up regulator typically runs directly from a lowimpedance battery. Often, the input capacitor can be reduced by 50% or more of the output capacitor value. MAX1984/MAX1985/MAX1986 Ultra-High-Efficiency White LED Drivers VIN 2.7V TO 5.5V L1 15µH 3 GND 14 C3 0.22µF VIN 13 2 LX SETI MAX1985 BITA LD1 1 3 GND 5 D1 6 D2 10 LD3 7 C3 0.22µF BRIGHTNESS CONTROL BITB LD4 D4 10 D5 9 12 17 BITC LD5 11 19 LED SELECT 20 MODE SEL LD6 N.C. 11 4 D6 C4 2 x 2.2µF BRIGHTNESS CONTROL 13 15 8 LDG N.C. 14 IN OUT LD1 SETI LD2 BITA LD3 BITB LD4 BITC LDG MODE SEL 1 4 D1 5 D2 7 D3 8 D4 C4 2 x 2.2µF 6 16 LED SELECT 12 Figure 6. Standard Application Circuit of the MAX1985 16 REF D3 9 2 LX MAX1986 VIN 15 L1 22µH 18 IN OUT REF C2 0.1µF C1 2 x 2.2µF LD2 16 VIN 2.7V TO 5.5V C2 0.1µF C1 2 x 2.2µF Figure 7. Standard Application Circuit of the MAX1986 ______________________________________________________________________________________ Ultra-High-Efficiency White LED Drivers 24L QFN THIN.EPS PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.8 mm 21-0139 A PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.8 mm 21-0139 A 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 ____________________ 17 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX1984/MAX1985/MAX1986 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)