MAX158

19-2783; Rev 0; 4/03 High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting General Description The MAX1582 drives up to six white LEDs in series with a constant current to provide display backlighting for two (main and sub-) displays in cell phones and other hand-held devices. This configuration eliminates the need for ballast resistors and expensive factory calibration. The proprietary dual-output, step-up pulse-width modulation (PWM) converter includes a 30V, low RDSON N-channel MOSFET switch for high efficiency and maximum battery life. The MAX1582 utilizes 1MHz current-mode PWM control to allow small input and output capacitors and a small inductor, while minimizing ripple on the input supply and avoiding interference to sensitive circuitry in the equipment. Integrated overvoltage protection eliminates the need for an external zener diode to protect the IC from open circuit. Flexible dimming control utilizes either an analog control signal or direct digital PWM control without external RC filtering. This also increases dimming accuracy at low brightness levels. The PWM dimming signal can be any frequency from 200Hz to 200kHz. Soft-start eliminates inrush current during startup. The MAX1582 is available in tiny 4 ✕ 4 chip-scale (UCSP™) and 12-pin thin QFN packages. KIT ATION EVALU ABLE AVAIL Features o Accurate Current Regulation for Uniform Illumination o Lights Up Two LED Sections for Main and Subdisplays o Up to 84% Efficiency o Internal High-Power, 30V MOSFET o Low 15mVP-P Input Ripple o Flexible Dimming Control Analog DAC Controlled Direct-Digital PWM (No RC Required) from 200Hz to 200kHz o Overvoltage Protection to Eliminate Zener Diode o Constant 1MHz PWM Operation o Low-Profile Inductor and Capacitors o Soft-Start Eliminates Inrush Current o 2.6V to 5.5V Input o 0.01µA (typ) Shutdown Current o Tiny UCSP (2.1mm ✕ 2.1mm ✕ 0.61mm) and Thin QFN (4mm ✕ 4mm) Packages MAX1582 Applications Cell Phones with One or Two Displays Smart Phones, Palmtops, and Wireless Handhelds Other Hand-Held Devices with Dual Displays PART MAX1582ETC Ordering Information TEMP RANGE PIN-PACKAGE TOP MARK AACE 1582EBE -40°C to +85°C 12 Thin QFN-EP* MAX1582EBE-T -40°C to +85°C 16 UCSP-16 *EP = Exposed paddle. Typical Application Circuit INPUT 2.6V TO 5.5V 2.2µF 22µH UCSP is a trademark of Maxim Integrated Products, Inc. Pin Configurations OUT1 10 9 OUT2 CS EN2 8 7 4 COMP 5 GND 6 EN1 V+ VP LX PGND 12 V+ VP CTRL 1 2 3 TOP VIEW MAX1582 OUT1 ANALOG OR DIRECT PWM DIMMING 0.1µF 2 TO 4 LEDS MAIN DISPLAY 11 CTRL PGND EN1 EN2 COMP CS GND OUT2 MAX1582 2 TO 3 LEDS SUBDISPLAY 0.022µF 7.5Ω 4mm x 4mm THIN QFN Pin Configurations continued at end of data sheet. ________________________________________________________________ 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. LX High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting MAX1582 ABSOLUTE MAXIMUM RATINGS V+, VP, CTRL to GND............................................-0.3V to +6.0V PGND to GND .......................................................-0.3V to +0.3V LX, OUT1 to GND ...................................................-0.3V to +30V OUT2 to GND .........................................................-0.3V to +14V COMP, CS, EN1, EN2 to GND ....................-0.3V to (VV+ + 0.3V) ILX ....................................................................................................1ARMS Continuous Power Dissipation (TA = +70°C) 12-Pin Thin QFN (derate 16.9mW/°C above +70°C) ....1349mW 16-Pin UCSP (derate 6.5mW/°C above +70°C)..............518mW 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 (VV+ = +3.0V, VOUT1 = 20V, L1 = 22µH, COUT = 0.1µF, CCOMP = 0.022µF, RSENSE = 7.5Ω, VCTRL = +1.5V, EN1 = EN2 = V+, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER Supply Voltage Undervoltage Lockout (UVLO) Threshold UVLO Hysteresis Quiescent Current Shutdown Supply Current Overvoltage Lockout (OVLO) Threshold OVLO Hysteresis VOUT1 = +26V, EN1 = EN2 = V+ OUT1 Input Bias Current OUT1 = V+, EN1 = EN2 = GND (Note 2) TA = +25°C TA = +85°C (VV+ VDIODE) 0.095 TA = +25°C TA = +85°C 290 32 0.80 PWM mode Pulse skipping CTRL = V+, CS = GND 91 0.100 0.01 1 500 50 1.0 12 0 94 780 82 1.25 20 No switching, VCTRL = VCS = +0.25V EN1 = EN2 = GND, OUT1 = V+ TA = +25°C TA = +85°C 26 V+ rising or falling CONDITIONS MIN 2.6 2.10 2.38 40 0.40 0.01 0.1 27 2 40 0.01 0.05 25.5 V 65 1 µA 29 0.56 1 TYP MAX 5.5 2.55 UNITS V V mV mA µA V V Output Voltage Range ERROR AMPLIFIER CTRL to CS Regulation CS Input Bias Current CTRL Input Resistance CS to COMP Transconductance OSCILLATOR Operating Frequency Minimum Duty Cycle Maximum Duty Cycle VCTRL = +1.0V, VV+ = +2.6V to +5.5V VCS = VCTRL / 10 0 < VCTRL < +1V VCOMP = +1.0V 0.106 1 V µA kΩ µS MHz % % 2 _______________________________________________________________________________________ High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting ELECTRICAL CHARACTERISTICS (continued) (VV+ = +3.0V, VOUT1 = 20V, L1 = 22µH, COUT = 0.1µF, CCOMP = 0.022µF, RSENSE = 7.5Ω, VCTRL = +1.5V, EN1 = EN2 = V+, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER N-CHANNEL SWITCH LX On-Resistance LX Leakage Current LX Current Limit OUT1 to OUT2 On-Resistance OUT2 to CS On-Resistance OUT1 to OUT2 Leakage Current OUT2 to CS Leakage Current EN1 and EN2 Logic Input Voltage High EN1 and EN2 Logic Input Voltage Low EN1 and EN2 Input Leakage VLX = +28V Duty cycle = 90% EN1 = GND, EN2 = V+ EN1 = V+, EN2 = GND EN1 = EN2 = V+, VOUT1 = 25V, VOUT2 = +9V, TA = +85°C EN1 = EN2 = V+, VOUT2 = 12V, VCS = 0, TA = +85°C +2.6V < VV+ < +5.5V +2.6V < VV+ < +5.5V VV+ = VEN1 = VEN2 = +5.5V TA = +25°C TA = +85°C 0.02 0.1 1.6 0.6 1 TA = +25°C TA = +85°C 450 1.50 0.01 0.02 650 2.5 2.5 0.05 0.05 950 2.25 5 Ω µA mA Ω Ω µA µA V V µA CONDITIONS MIN TYP MAX UNITS MAX1582 MAIN AND SUBDISPLAY ON/OFF SWITCHES ELECTRICAL CHARACTERISTICS (VV+ = +3.0V, VOUT1 = +20V, L1 = 22µH, COUT = 0.1µF, CCOMP = 0.022µF, RSENSE = 7.5Ω, VCTRL = +1.5V, EN1 = EN2 = V+, TA = -40°C to +85°C, unless otherwise noted.) (Notes 1, 3) PARAMETER Supply Voltage Undervoltage Lockout (UVLO) Threshold Quiescent Current Overvoltage Lockout (OVLO) Threshold OUT1 Input Bias Current Output Voltage Range ERROR AMPLIFIER CTRL to CS Regulation CTRL Input Resistance CS to COMP Transconductance OSCILLATOR Operating Frequency 0.75 1.30 MHz VCTRL = +1.0V, VV+ = +2.6V to +5.5V 0 < VCTRL < +1.0V VCOMP = 1.0V 0.093 290 32 0.107 780 85 V kΩ µS V+ rising or falling No switching, VC = +0.25V Rising VOUT1 = +26V, EN1 = EN2 = V+ (Note 2) 26 20 (VV+ VDIODE) CONDITIONS MIN 2.6 2.10 MAX 5.5 2.55 0.56 29 65 25.5 UNITS V V mA V µA V _______________________________________________________________________________________ 3 High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting MAX1582 ELECTRICAL CHARACTERISTICS (continued) (VV+ = +3.0V, VOUT1 = +20V, L1 = 22µH, COUT = 0.1µF, CCOMP = 0.022µF, RSENSE = 7.5Ω, VCTRL = +1.5V, EN1 = EN2 = V+, TA = -40°C to +85°C, unless otherwise noted.) (Notes 1, 3) PARAMETER Maximum Duty Cycle N-CHANNEL SWITCH LX On-Resistance LX Current Limit Duty cycle = 90% 450 2.25 950 Ω mA CONDITIONS CTRL = V+, CS = GND MIN 91 MAX UNITS % Note 1: Limits are 100% production tested at TA = +25°C for UCSP parts. Limits over the entire operating temperature range are guaranteed by design and characterization but are not production tested. Note 2: The minimum output voltage is the input voltage minus the forward voltage drop of the Schottky diode: VOUT(MIN) = VV+ - VDIODE Note 3: Specifications to -40°C are guaranteed by design and not production tested. Typical Operating Characteristics (See the Typical Applications Circuit, VV+ = VVP = 3.6V, ILED = 15mA, L1 = 22µH, COUT1 = 0.1µF, CCOMP = 0.022µF, RSENSE = 7.5Ω, VCTRL = 1.5V, 4 LEDs, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. LED CURRENT (vs. NUMBER of LEDs) MAX1582 toc01 EFFICIENCY vs. LED CURRENT (vs. INPUT VOLTAGE) MAX1582 toc02 EFFICIENCY vs. LED CURRENT (vs. INDUCTANCE) MAX1582 toc03 100 90 6 LEDs EFFICIENCY (%) 80 70 4 LEDs 60 50 40 0 5 10 LED CURRENT (mA) 15 2 LEDs 100 90 EFFICIENCY (%) 80 70 60 50 40 4.2 VIN 3.6 VIN 100 90 10µH EFFICIENCY (%) 80 70 60 50 40 47µH 4.7µH 22µH 2.7 VIN 20 0 5 10 LED CURRENT (mA) 15 20 0 5 10 LED CURRENT (mA) 15 20 INPUT RIPPLE vs. INDUCTANCE MAX1582 toc04 INPUT RIPPLE SPECTRUM MAX1582 toc05 LED CURRENT vs. DIRECT-PWM DIMMING DUTY CYCLE MAX1582 toc06 40 35 INPUT RIPPLE (mVP-P) 30 25 20 15 10 5 0 0 5 6 5 INPUT RIPPLE (mVRMS) 4 3 2 1 0 25 20 LED CURRENT (mA) 15 10 5 VCTRL = SQUARE WAVE 200Hz < FREQ < 200kHz 0 0 1 2 3 4 5 6 7 8 9 10 0 10 20 30 40 50 60 70 80 90 100 DIRECT-PWM DIMMING DUTY CYCLE (%) FREQUENCY (MHz) 10 15 20 25 30 35 40 45 50 INDUCTANCE (µH) 4 _______________________________________________________________________________________ High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting Typical Operating Characteristics (continued) (See the Typical Applications Circuit, VV+ = VVP = 3.6V, ILED = 15mA, L1 = 22µH, COUT1 = 0.1µF, CCOMP = 0.022µF, RSENSE = 7.5Ω, VCTRL = 1.5V, 4 LEDs, TA = +25°C, unless otherwise noted.) SWITCHING WAVEFORMS MAX1582 toc07 MAX1582 DIRECT-PWM DIMMING MAX1582 toc08 VIN 10mV/div VCTRL 32kHz 1V/div 0V VIN 50mV/div IIN 50mA/div 0mA VOUT 100mV/div VLX 10V/div VIN = 3.8V Li+ BATTERY VOUT 5V/div 0V 500ns/div 50µs/div Pin Description PIN QFN 1 2 3 UCSP A1 A2 A3 NAME V+ VP CTRL FUNCTION Input Voltage Supply. Input voltage range is 2.6V to 5.5V. Connect a 2.2µF capacitor from V+ to PGND. High-Current Input Supply. Connect to V+. Brightness Control Input. LED brightness is controlled by the voltage applied to CTRL. Varying the voltage from 0 to +1.62V adjusts the brightness from dim to bright, respectively. Any voltage above +1.62V does not increase brightness. Compensation Input. Connect a 0.022µF capacitor (CCOMP) from COMP to GND. CCOMP stabilizes the converter and controls soft-start. CCOMP discharges to GND when in shutdown. Ground. Connect to PGND at a single point near the IC. Enable 1 Input. Drive EN1 high to enable the main-display LEDs. Pull EN1 low to turn off the maindisplay LEDs. Pull both EN1 and EN2 low to place the IC in low-current shutdown mode. Enable 2. Drive EN2 high to enable the subdisplay LEDs. Pull EN2 low to turn off the subdisplay LEDs. Pull both EN1 and EN2 low to place the IC in low-current shutdown mode. Current-Sense Feedback Input. Connect a resistor (RSENSE) from CS to GND to set the LED bias current. The voltage at CS regulates to VCTRL / 10 or +0.162V, whichever is lower. Display Switch Output. OUT2 is internally connected to CS when only the main display is lit. OUT2 is internally connected to OUT1 when only the subdisplay is lit. OUT2 is high impedance when both displays are lit and when the IC is shut down. Overvoltage Sense. When VOUT1 is greater than 27V, the internal N-channel MOSFET turns off until VOUT1 drops below 25V, then the IC reenters soft-start. Connect a 0.1µF capacitor from OUT1 to PGND. Inductor Connection. During shutdown, this pin is high impedance. Power Ground. Connect to GND at a single point near the IC. Exposed Paddle. Connect directly to GND and PGND under the IC. 4 5 6 7 8 A4 B4 C4 D4 D3 COMP GND EN1 EN2 CS 9 D2 OUT2 10 11 12 EP D1 C1 B1 — OUT1 LX PGND EP _______________________________________________________________________________________ 5 High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting MAX1582 2.6V TO 5.5V CIN 2.2µF L1 22µF LX PWM CONTROL PGND D1 COUT1 0.1µF V+ VP fOSC 1.0MHz SLOPE COMP. CURRENT SENSE OVERVOLTAGE PROTECTION OUT1 UP TO 27V DAC OR PWM CTRL 114kΩ 336kΩ gm COMP 2 TO 4 LEDS 50kΩ CCOMP 0.022µF MAIN DISPLAY 1.25V CLAMP EN1 ENABLE INPUTS EN2 OUT2 UP TO 13V 2 TO 3 LEDS CS SUBDISPLAY MAX1582 SHUTDOWN GND RSENSE 7.5Ω Figure 1. Functional Diagram Detailed Description The MAX1582’s high efficiency and small size make it ideally suited to drive up to six series-connected LEDs. Separate enable inputs are provided to control the main and subdisplay backlighting. The MAX1582 operates as a boost DC-to-DC converter that regulates output current rather than voltage. It provides even illumination by sourcing the same output current through each LED, eliminating the need for expensive factory calibration. The fast 1MHz internal oscillator allows for a small inductor and small input and output capacitors while minimizing input and output ripple. 6 Shutdown for Main and Subdisplay The MAX1582 has two enable inputs (EN1 and EN2) used to enable or shutdown the main and subdisplay LEDs. When EN1 and EN2 are both high, all LEDs are lit. With EN1 high and EN2 low, the main-display LEDs are lit, and the subdisplay LEDs are shorted by the MAX1582. With EN1 low and EN2 high, the main-display LEDs are shorted and the subdisplay LEDs are lit. When both EN1 and EN2 are low, the MAX1582 enters shutdown, reducing supply current to 0.01µA (typ). Although the internal N-channel MOSFET does not switch in shutdown, there is still a DC-current path _______________________________________________________________________________________ High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting between the input and the LEDs through the inductor and Schottky diode. To ensure the LEDs remain off when the MAX1582 is in shutdown, the minimum input forward voltage of the LED array must exceed the maximum input voltage. Typically, the leakage current through the LEDs in shutdown is less than 1µA. 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 input and output ripple, but at the expense of size and higher cost. CCOMP stabilizes the converter and controls soft-start. Connect a 0.022µF capacitor from COMP to GND. The minimum value for CCOMP is COUT / 10. The soft-start time is found from:  1.25V  t SS = CCOMP ×    5µA  MAX1582 Soft-Start The MAX1582 attains soft-start by charging CCOMP gradually with a current source. When VCOMP rises above 1.25V, the internal MOSFET begins switching, but at a reduced duty cycle. When VCOMP rises above 2.25V, the duty cycle is at its maximum. Overvoltage Protection OVLO occurs when VOUT1 rises above 27V. The protection circuitry stops the internal MOSFET from switching and causes V COMP to decay to GND. The device comes out of OVLO and into soft-start when VOUT1 falls below 25V. Inductor Selection Recommended inductor values range from 10µH to 47µH. A 22µH inductor optimizes the efficiency for most applications, while maintaining a low 15mVP-P input ripple. With input voltages near 5V, a larger value of inductance may 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 ≅ VOUT1(MAX ) × ILED(MAX ) VIN(MIN) × 0.8µs + 0.8 × VIN(MIN) 2×L Design Procedure Adjusting LED Current Adjusting the MAX1582’s output current changes the brightness of the LEDs. The LED current is set by the voltage at CTRL (VCTRL) and the sense-resistor value (RSENSE): ILED = VCTRL 10 × RSENSE Schottky Diode Selection The MAX1582’s 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 exceeds the average output current and peak inductor current. In addition, the diode’s reverse breakdown voltage must exceed V OUT1 . The RMS diode current can be calculated from: IDIODE(RMS) ≅ IOUT1 × IPEAK The VCTRL voltage range for adjusting output current is 0 to +1.62V. To set the maximum current, calculate RSENSE when VCTRL is at its maximum as follows: RSENSE = 1.62 10 × ILED(MAX ) Power dissipation in RSENSE is typically less than 5mW; therefore, a standard chip resistor is 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 any additional RC filters required. Applications Information PC Board Layout Due to fast-switching waveforms and high-current paths, careful PC board layout is required. An evaluation kit (MAX1582EVKIT) is available to speed design. _______________________________________________________________________________________ 7 High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting 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 input bypass capacitor (CIN) should be placed as close to the IC as possible. For the thin QFN package, PGND and GND should be connected directly to the exposed paddle underneath the IC. The ground connections of CIN and COUT1 should be as close together as possible. The traces from IN to the inductor and from the Schottky diode to the LEDs can be longer. MAX1582 Pin Configurations (continued) TOP VIEW (BALLS SOLDERED DOWN) 1 A V+ 2 VP 3 CTRL 4 COMP B PGND GND MAX1582 C LX EN1 Chip Information TRANSISTOR COUNT: 2546 PROCESS: BiCMOS D OUT1 OUT2 CS EN2 UCSP 8 _______________________________________________________________________________________ High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting 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.) 24L QFN THIN.EPS MAX1582 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 _______________________________________________________________________________________ 9 High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting MAX1582 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.) 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. 16L,UCSP.EPS