19-2731; Rev 1; 10/03 KIT ATION EVALU E L B A AVAIL High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs Features ♦ Accurate Current Regulation for Uniform Illumination ♦ High Efficiency Up to 87% ♦ Flexible Analog or PWM Dimming Control ♦ Up to 900mW Output Power with Internal 30V MOSFET Switch ♦ Fast 1MHz (MAX1561) or 500kHz (MAX1599) PWM Operation ♦ Small, Low-Profile External Components ♦ 2.6V to 5.5V Input Range ♦ 26V (max) Output with Overvoltage Protection ♦ Optimized for Low 15mVP-P Input Ripple ♦ Soft-Start with Zero Inrush Current ♦ 0.3µA Shutdown Current ♦ Tiny 8-Pin 3mm x 3mm Thin DFN Package Ordering Information Applications TOP MARK PART TEMP RANGE PIN-PACKAGE PDAs, Palmtops, and Wireless Handhelds MAX1561ETA -40°C to +85°C 8 TDFN-EP* ACS e-Books and Subnotebooks MAX1599ETA -40°C to +85°C 8 TDFN-EP* AHG Cell Phones and Smart Phones White LED Display Backlighting *EP = Exposed paddle. Pin Configuration Typical Operating Circuit INPUT 2.6V TO 5.5V OUTPUT UP TO 6 LEDs TOP VIEW LX IN MAX1561 MAX1599 OUT OUT 1 PWM OR ANALOG DIMMING MAX1561 MAX1599 7 PGND 6 GND CTRL 3 CTRL PGND COMP CS GND 8 LX IN 2 5 COMP CS 4 3mm × 3mm THIN DFN Dual Mode is a trademark of Maxim Integrated Products, Inc. ________________________________________________________________ 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 MAX1561/MAX1599 General Description The MAX1561/MAX1599 step-up converters drive up to six white LEDs with a constant current to provide backlight in cell phones, PDAs, and other hand-held devices. The step-up converter topology allows series connection of the white LEDs so the LED currents are identical for uniform brightness. This configuration eliminates the need for ballast resistors and expensive factory calibration. The MAX1561/MAX1599 include an internal, high-voltage, low-RDS(ON) N-channel MOSFET switch for high efficiency and maximum battery life. A single Dual Mode™ input provides a simple means of brightness adjustment and on/off control. Fast 1MHz (500kHz for the MAX1599) current-mode, pulse-width modulated (PWM) operation allows for small input and output capacitors and a small inductor while minimizing ripple on the input supply/battery. Programmable soft-start eliminates inrush current during startup. Both devices are available in a space-saving, 8-pin 3mm x 3mm thin DFN package with exposed paddle (EP). MAX1561/MAX1599 High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs ABSOLUTE MAXIMUM RATINGS IN to GND .................................................................-0.3V to +6V PGND to GND .......................................................-0.3V to +0.3V LX, OUT to GND .....................................................-0.3V to +30V CTRL to GND...................-0.3V to the lower of +6V or (VIN + 2V) COMP, CS to GND.........................................-0.3 to (VIN + 0.3V) ILX.............................................................................................1A Continuous Power Dissipation (TA = +70°C) 3mm x 3mm 8-Pin TDFN (derate 24.4mW/°C above +70°C) .............................1950mW 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 (VIN = 3V, VOUT = 20V, COUT = 0.1µF, CCOMP = 0.15µF, RSENSE = 7.5Ω, VCTRL = 1.5V, Figure 1, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN Supply Voltage UVLO Threshold TYP 2.6 VIN rising or falling 2.10 UVLO Hysteresis 2.38 MAX UNITS 5.5 V 2.55 40 Quiescent Current No switching 0.38 0.55 Shutdown Supply Current CTRL = GND, VOUT = VIN TA = +25°C 0.3 2 TA = +85°C 1 OVLO Threshold VOUT rising 26 27 VOUT = 26V, VCTRL > 0.24V 10 20 30 0.01 1 OVLO Hysteresis OUT Input Bias Current Output Voltage Range 29 2 VOUT = VIN, CTRL = GND (Note 1) (VIN - VD1) V mV mA µA V V µA 25.5 V 0.100 0.105 V TA = +25°C 0.01 1 TA = +85°C 0.03 ERROR AMPLIFIER CTRL to CS Regulation VCTRL = 1V, VIN = 2.6V to 5.5V CS Input Bias Current VCS = VCTRL/10 CTRL Input Resistance VCTRL ≤ 1.0V 0.095 µA 290 500 780 kΩ 100 170 240 mV MAX1561 6.5 8.2 10.5 MAX1599 13.6 16.4 21.0 32 50 82 MAX1561 0.80 1.0 1.25 MAX1599 0.4 0.5 0.6 CTRL Dual-Mode Threshold CTRL Dual-Mode Hysteresis 5 CTRL Shutdown Enable Delay (Note 2) CS-to-COMP Transconductance VCOMP = 1.0V mV ms µS OSCILLATOR Operating Frequency Minimum Duty Cycle Maximum Duty Cycle 2 PWM mode 12 Pulse skipping 0 CTRL = IN, CS = GND 91 94 _______________________________________________________________________________________ MHz % % High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs (VIN = 3V, VOUT = 20V, COUT = 0.1µF, CCOMP = 0.15µF, RSENSE = 7.5Ω, VCTRL = 1.5V, Figure 1, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS Ω N-CHANNEL SWITCH LX On-Resistance ILX = 190mA LX Leakage Current VLX = 28V, CTRL = GND LX Current Limit Duty cycle = 90% 1.45 2.25 TA = +25°C 0.01 5 TA = +85°C 1 450 700 950 µA mA ELECTRICAL CHARACTERISTICS (VIN = 3V, VOUT = 20V, COUT = 0.1µF, CCOMP = 0.15µF, RSENSE = 7.5Ω, VCTRL = 1.5V, Figure 1, TA = -40°C to +85°C, unless otherwise noted.) (Note 3) PARAMETER CONDITIONS Supply Voltage MIN MAX UNITS 2.6 TYP 5.5 V 2.10 2.55 V 0.55 mA V UVLO Threshold VIN rising or falling Quiescent Current No switching OVLO Threshold VOUT rising 26 29 VOUT = 26V, VCTRL > 0.24V 10 30 OUT Input Bias Current Output Voltage Range VOUT = VIN, CTRL = GND 1 (Note 1) (VIN - VD1) 25.5 µA V ERROR AMPLIFIER CTRL to CS Regulation VCTRL = 1V, VIN = 2.6V to 5.5V CTRL Input Resistance VCTRL ≤ 1.0V 0.093 0.107 V 240 780 kΩ 100 240 mV MAX1561 6 11 MAX1599 13 22 32 85 MAX1561 0.75 1.25 MAX1599 0.37 0.63 CTRL Dual-Mode Threshold CTRL Shutdown Enable Delay (Note 2) CS-to-COMP Transconductance VCOMP = 1.0V ms µS OSCILLATOR Operating Frequency Maximum Duty Cycle CTRL = IN, CS = GND 91 MHz % N-CHANNEL SWITCH LX On-Resistance LX Current Limit Duty cycle = 90% 450 2.25 Ω 950 mA Note 1: VD1 is the diode forward-voltage drop of diode D1 in Figure 1. Note 2: Time from CTRL going below the dual-mode threshold to IC shutdown. Note 3: Specifications to -40°C are guaranteed by design and not production tested. _______________________________________________________________________________________ 3 MAX1561/MAX1599 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (Circuit of Figure 1, VIN = 3.6V, ILED = 15mA, L1 = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 7.5Ω, 4 LEDs, TA = +25°C, unless otherwise noted.) 90 2.7VIN 70 4 LEDs 2 LEDs 60 70 3.6VIN 4.2VIN 60 50 40 22µH 5 10 15 80 4.7µH 47µH 70 60 50 40 0 40 20 0 5 10 15 20 0 5 10 15 20 LED CURRENT (mA) LED CURRENT (mA) LED CURRENT (mA) MAX1599 EFFICIENCY vs. LED CURRENT (vs. NUMBER OF LEDs) MAX1599 EFFICIENCY vs. LED CURRENT (vs. INPUT VOLTAGE) MAX1599 EFFICIENCY vs. LED CURRENT (vs. INDUCTANCE) 2 LEDs 4 LEDs 60 70 4.2VIN 2.7VIN 60 47µH 90 3.6VIN 0 5 10 15 60 5 10 15 20 0 5 10 15 LED CURRENT (mA) LED CURRENT (mA) LED CURRENT (mA) INPUT RIPPLE vs. INDUCTANCE INPUT RIPPLE SPECTRUM LED CURRENT vs. DIRECT-PWM DIMMING DUTY CYCLE 25 20 15 4 3 2 10 5 10 15 20 25 30 35 40 45 50 INDUCTANCE (µH) 15 10 VCTRL = SQUARE WAVE 200Hz < FREQ < 200kHz 0 0 20 5 1 5 20 MAX1561 toc09 5 INPUT RIPPLE (mVRMS) 30 LED CURRENT (mA) 35 25 MAX1561 toc08 6 MAX1561 toc07 40 0 22µH 70 40 0 20 80 50 40 40 MAX1561 toc06 MAX1561 toc05 80 50 50 100 EFFICIENCY (%) 80 70 90 EFFICIENCY (%) 6 LEDs 90 100 MAX1561 toc04 100 EFFICIENCY (%) 80 EFFICIENCY (%) 80 50 4 90 10µH EFFICIENCY (%) EFFICIENCY (%) 6 LEDs 100 MAX1561 toc02 90 MAX1561 EFFICIENCY vs. LED CURRENT (vs. INDUCTANCE) 100 MAX1561 toc01 100 MAX1561 EFFICIENCY vs. LED CURRENT (vs. INPUT VOLTAGE) MAX1561 toc03 MAX1561 EFFICIENCY vs. LED CURRENT (vs. NUMBER of LEDs) INPUT RIPPLE (mVP-P) MAX1561/MAX1599 High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs 0 0 1 2 3 4 5 6 7 FREQUENCY (MHz) 8 9 10 0 10 20 30 40 50 60 70 80 90 100 DIRECT-PWM DIMMING DUTY CYCLE (%) _______________________________________________________________________________________ High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs SWITCHING WAVEFORMS SOFT-START AND SHUTDOWN MAX1561 toc10 CTRL STEP RESPONSE MAX1561 toc11 MAX1561 toc12 VCTRL 1V/div 0V VIN 50mV/div VCTRL 1V/div 0V VIN 50mV/div VOUT 100mV/div IIN 50mA/div 0mA IIN 50mA/div 0mA VLX 10V/div VOUT 5V/div VOUT 5V/div VIN 10mV/div VIN = 3.8V Li+ BATTERY VIN = 3.8V Li+ BATTERY 0V 500ns/div 20ms/div LINE-TRANSIENT RESPONSE DIRECT-PWM DIMMING MAX1561 toc14 MAX1561 toc13 VCTRL 32kHz 1V/div 0V 4V VIN 500mV/div 3.5V VIN 50mV/div IIN 50mA/div IIN 50mA/div 0mA 0mA VOUT 5V/div VCS 100mV/div VIN = 3.8V Li+ BATTERY 0V 0V 50µs/div 0V 20ms/div 50µs/div _______________________________________________________________________________________ 5 MAX1561/MAX1599 Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = 3.6V, ILED = 15mA, L1 = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 7.5Ω, 4 LEDs, TA = +25°C, unless otherwise noted.) High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs MAX1561/MAX1599 Pin Description PIN NAME FUNCTION 1 OUT Overvoltage Sense. When VOUT is greater than 27V, the internal N-channel MOSFET turns off until VOUT drops below 25V, then the IC reenters soft-start. Connect a 0.1µF capacitor from OUT to PGND. 2 IN Input Voltage Supply. Input voltage range is 2.6V to 5.5V. Connect a 2.2µF capacitor from IN to PGND. Brightness Control Input. LED brightness is controlled by the voltage applied to CTRL. Varying the voltage from 0.24V to 1.62V adjusts the brightness from dim to bright, respectively. Any voltage above 1.62V does not increase brightness. If CTRL is held below 100mV for more than 8.2ms (16.4ms for the MAX1599), the IC shuts down. 3 CTRL 4 CS Current-Sense Feedback Input. Connect a resistor from CS to GND to set the LED bias current. The voltage at CS regulates to VCTRL / 10 or 0.162V, whichever is lower. 5 COMP Compensation Input. Connect a 0.1µF capacitor (CCOMP) from COMP to GND. CCOMP stabilizes the converter and controls soft-start. CCOMP discharges to GND when in shutdown. 6 GND 7 PGND Ground. Connect to PGND and the exposed pad directly under the IC. 8 LX Inductor Connection. This pin is high impedance during shutdown. Exposed Pad EP Ground. Connect directly to GND and PGND under the IC. Power Ground. Connect to GND and the exposed pad directly under the IC. Detailed Description The MAX1561/MAX1599s’ high efficiency and small size make them ideally suited to drive up to six series-connected LEDs. The device operates as a boost DC-DC converter that regulates output current rather than voltage. The MAX1561/MAX1599 provide even illumination by sourcing the same output current through each LED, eliminating the need for expensive factory calibration. The fast 1MHz (500kHz for the MAX1599) internal oscillator allows for a small inductor and small input and output capacitors while minimizing input and output ripple. The single analog control input allows easy adjustment of LED brightness and on/off control. This allows either simple logic-level on/off control, analog voltage control, or PWM duty-cycle control of both brightness and shutdown. In shutdown, supply current is reduced to a low 0.3µA. A soft-start gradually illuminates the LEDs, eliminating the inrush current during startup. Soft-Start The MAX1561/MAX1599 attain soft-start by charging CCOMP gradually with a current source. When VCOMP rises above 1.25V, the internal MOSFET begins switching at a reduced duty cycle. When VCOMP rises above 2.25V, the duty cycle is at its maximum. See the Typical Operating Characteristics for an example of soft-start operation. 6 Shutdown The MAX1561/MAX1599 enter shutdown when VCTRL is less than 100mV for more than 8.2ms (16.4ms for the MAX1599). In shutdown, supply current is reduced to 0.3µA by powering down the entire IC except for the CTRL voltage-detection circuitry. CCOMP is discharged during shutdown, allowing the device to reinitiate softstart when it is enabled. Although the internal N-channel MOSFET does not switch in shutdown, there is still a DC current path between the input and the LEDs through the inductor and Schottky diode. The minimum forward voltage of the LED array must exceed the maximum input voltage to ensure that the LEDs remain off in shutdown. However, with two or more LEDs, the forward voltage is large enough to keep leakage current low, less than 1µA (typ). Typical shutdown timing characteristics are shown in the Typical Operating Characteristics. Overvoltage Protection Overvoltage lockout (OVLO) occurs when V OUT is above 27V. The protection circuitry stops the internal MOSFET from switching and causes VCOMP to decay to 0V. The device comes out of OVLO and into softstart when VOUT falls below 25V. _______________________________________________________________________________________ High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs MAX1561/MAX1599 INPUT 2.6V TO 5.5V 2.2µF L1 IN LX COUT 0.1µF PWM CONTROL PGND fOSC SLOPE COMP CURRENT SENSE UP TO 26V OUT OVERVOLTAGE PROTECTION 2 TO 6 LEDS PWM OR ANALOG DIMING CTRL MAX1561 MAX1599 450kΩ 50kΩ COMP gm CCOMP 0.1µF CS SHUTDOWN TIMER SHUTDOWN RSENSE 7.5Ω 170mV GND Figure 1. Functional Diagram Design Procedure Adjusting LED Current Adjusting the MAX1561/MAX1599s’ output current changes the brightness of the LEDs. An analog input (CTRL) and the sense-resistor value set the output current. Output current is given by: ILED = VCTRL 10 × RSENSE The VCTRL voltage range for adjusting output current is 0.24V to 1.62V. To set the maximum current, calculate RSENSE when VCTRL is at its maximum as follows: RSENSE = 1.62V 10 × ILED(MAX) Power dissipation in RSENSE is typically less than 5mW, making a standard chip resistor sufficient. PWM Dimming Control CTRL is also used as a digital input allowing LED brightness control with a logic-level PWM signal applied directly to CTRL. The frequency range is from 200Hz to 200kHz, while 0% duty cycle corresponds to zero current and 100% duty cycle corresponds to full current. The error amplifier and compensation capacitor form a lowpass filter so PWM dimming results in DC current to the LEDs without the need for any additional RC filters; see the Typical Operating Characteristics. Capacitor Selection The exact values of input and output capacitors are not critical. The typical value for the input capacitor is 2.2µF and the typical value for the output capacitor is 0.1µF. Larger value capacitors can be used to reduce _______________________________________________________________________________________ 7 MAX1561/MAX1599 High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs input and output ripple, but at the expense of size and higher cost. CCOMP stabilizes the converter and controls soft-start. Connect a 0.1µF capacitor from COMP to GND. For stable operation, COUT must not exceed 10 times CCOMP. Inductor Selection Inductor values range from 10µH to 47µH. A 22µH (47µH for the MAX1599) inductor optimizes the efficiency for most applications while maintaining low 15mVP-P input ripple. With input voltages near 5V, a larger value of inductance can be more efficient. To prevent core saturation, ensure that the inductor-saturation current rating exceeds the peak inductor current for the application. Calculate the peak inductor current with the following formula: IPEAK = VOUT(MAX) × ILED(MAX) 0.8 × VIN(MIN) + VIN(MIN) × 0.8µs 2 ×L Schottky Diode Selection The MAX1561/MAX1599s’ high switching frequency demands a high-speed rectification diode (D1) for optimum efficiency. A Schottky diode is recommended due to its fast recovery time and low forward-voltage drop. Ensure that the diode’s average and peak current rating exceed the average output current and peak inductor current. In addition, the diode’s reverse breakdown voltage must exceed VOUT. The RMS diode current can be calculated from: Applications Information PC Board Layout Due to fast switching waveforms and high-current paths, careful PC board layout is required. An evaluation kit (MAX1561EVKIT) is available to speed design. Order MAX1599 samples separately. When laying out a board, minimize trace lengths between the IC and RSENSE, the inductor, the diode, the input capacitor, and the output capacitor. Keep traces short, direct, and wide. Keep noisy traces, such as the LX node trace, away from CS. The IN bypass capacitor (CIN) should be placed as close to the IC as possible. PGND and GND should be connected directly to the exposed paddle underneath the IC. The ground connections of CIN and COUT should be as close together as possible. The traces from IN to the inductor and from the Schottky diode to the LEDs may be longer. Chip Information TRANSISTOR COUNT: 2895 PROCESS: BiCMOS IDIODE(RMS) ≅ IOUT × IPEAK 8 _______________________________________________________________________________________ High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs 6, 8, &10L, DFN THIN.EPS L A D D2 A2 PIN 1 ID 1 N 1 C0.35 b E PIN 1 INDEX AREA [(N/2)-1] x e REF. E2 DETAIL A e k A1 CL CL L L e e A DALLAS SEMICONDUCTOR PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, 6, 8 & 10L, TDFN, EXPOSED PAD, 3x3x0.80 mm NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY APPROVAL DOCUMENT CONTROL NO. 21-0137 REV. D 1 2 _______________________________________________________________________________________ 9 MAX1561/MAX1599 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.) MAX1561/MAX1599 High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs Package Information (continued) (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.) COMMON DIMENSIONS SYMBOL A MIN. MAX. 0.70 0.80 D 2.90 3.10 E 2.90 3.10 A1 0.00 0.05 L k 0.20 0.40 0.25 MIN. A2 0.20 REF. PACKAGE VARIATIONS PKG. CODE N D2 E2 e JEDEC SPEC b T633-1 6 1.50–0.10 2.30–0.10 0.95 BSC MO229 / WEEA 0.40–0.05 1.90 REF T833-1 8 1.50–0.10 2.30–0.10 0.65 BSC MO229 / WEEC 0.30–0.05 1.95 REF T1033-1 10 1.50–0.10 2.30–0.10 0.50 BSC MO229 / WEED-3 0.25–0.05 2.00 REF [(N/2)-1] x e DALLAS SEMICONDUCTOR PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, 6, 8 & 10L, TDFN, EXPOSED PAD, 3x3x0.80 mm APPROVAL DOCUMENT CONTROL NO. 21-0137 REV. D 2 2 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. 10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.