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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 (UCSPTM) 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 0.01A (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
-40C to +85C 12 Thin QFN-EP*
MAX1582EBE-T -40C to +85C 16 UCSP-16
*EP = Exposed paddle.
Typical Application Circuit
INPUT 2.6V TO 5.5V 2.2F 22H
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
0.1F 2 TO 4 LEDS MAIN DISPLAY
11
ANALOG OR DIRECT PWM DIMMING
CTRL PGND EN1 EN2 COMP CS GND OUT2
MAX1582
2 TO 3 LEDS
SUBDISPLAY
0.022F 7.5
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 = +70C) 12-Pin Thin QFN (derate 16.9mW/C above +70C) ....1349mW 16-Pin UCSP (derate 6.5mW/C above +70C)..............518mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C 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
(VV+ = +3.0V, VOUT1 = 20V, L1 = 22H, COUT = 0.1F, CCOMP = 0.022F, RSENSE = 7.5, VCTRL = +1.5V, EN1 = EN2 = V+, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (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 = +25C TA = +85C (VV+ VDIODE) 0.095 TA = +25C TA = +85C 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 = +25C TA = +85C 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 A 29 0.56 1 TYP MAX 5.5 2.55 UNITS V V mV mA A 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 A k S MHz % %
2
_______________________________________________________________________________________
High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting
ELECTRICAL CHARACTERISTICS (continued)
(VV+ = +3.0V, VOUT1 = 20V, L1 = 22H, COUT = 0.1F, CCOMP = 0.022F, RSENSE = 7.5, VCTRL = +1.5V, EN1 = EN2 = V+, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (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 = +85C EN1 = EN2 = V+, VOUT2 = 12V, VCS = 0, TA = +85C +2.6V < VV+ < +5.5V +2.6V < VV+ < +5.5V VV+ = VEN1 = VEN2 = +5.5V TA = +25C TA = +85C 0.02 0.1 1.6 0.6 1 TA = +25C TA = +85C 450 1.50 0.01 0.02 650 2.5 2.5 0.05 0.05 950 2.25 5 A mA A A V V A CONDITIONS MIN TYP MAX UNITS
MAX1582
MAIN AND SUBDISPLAY ON/OFF SWITCHES
ELECTRICAL CHARACTERISTICS
(VV+ = +3.0V, VOUT1 = +20V, L1 = 22H, COUT = 0.1F, CCOMP = 0.022F, RSENSE = 7.5, VCTRL = +1.5V, EN1 = EN2 = V+, TA = -40C to +85C, 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 k S 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 A V
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3
High-Efficiency, 26V Step-Up Converter for White LED Main and Subdisplay Backlighting MAX1582
ELECTRICAL CHARACTERISTICS (continued)
(VV+ = +3.0V, VOUT1 = +20V, L1 = 22H, COUT = 0.1F, CCOMP = 0.022F, RSENSE = 7.5, VCTRL = +1.5V, EN1 = EN2 = V+, TA = -40C to +85C, 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 mA CONDITIONS CTRL = V+, CS = GND MIN 91 MAX UNITS %
Note 1: Limits are 100% production tested at TA = +25C 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 -40C are guaranteed by design and not production tested.
Typical Operating Characteristics
(See the Typical Applications Circuit, VV+ = VVP = 3.6V, ILED = 15mA, L1 = 22H, COUT1 = 0.1F, CCOMP = 0.022F, RSENSE = 7.5, VCTRL = 1.5V, 4 LEDs, TA = +25C, 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 10H EFFICIENCY (%) 80 70 60 50 40 47H 4.7H 22H
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 (H)
4
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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 = 22H, COUT1 = 0.1F, CCOMP = 0.022F, RSENSE = 7.5, VCTRL = 1.5V, 4 LEDs, TA = +25C, 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
50s/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 2.2F 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 0.022F 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 0.1F 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 2.2F L1 22F LX PWM CONTROL PGND D1 COUT1 0.1F
V+
VP
fOSC 1.0MHz
SLOPE COMP. CURRENT SENSE
OVERVOLTAGE PROTECTION
OUT1
UP TO 27V
DAC OR PWM
CTRL
114k
336k gm COMP
2 TO 4 LEDS
50k CCOMP 0.022F
MAIN DISPLAY
1.25V CLAMP
EN1 ENABLE INPUTS EN2 OUT2 UP TO 13V
2 TO 3 LEDS
CS
SUBDISPLAY
MAX1582
SHUTDOWN GND
RSENSE 7.5
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 0.01A (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 1A.
Capacitor Selection
The exact values of input and output capacitors are not critical. The typical value for the input capacitor is 2.2F, and the typical value for the output capacitor is 0.1F. 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 0.022F 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 x 5A
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 10H to 47H. A 22H 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 ) x ILED(MAX ) VIN(MIN) x 0.8s + 0.8 x VIN(MIN) 2xL
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 x 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 x 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 x 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 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
16L,UCSP.EPS

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