EVALUATION KIT AVAILABLE MAX1553/MAX1554 High-Efficiency, 40V Step-Up Converters for 2 to 10 White LEDs General Description Benefits and Features The MAX1553/MAX1554 drive white LEDs in series with a constant current to provide efficient display backlighting in cellular phones, PDAs, and other hand-held devices. The step-up converter includes an internal 40V, low RDSON, N-channel MOSFET switch for high efficiency and maximum battery life. The MAX1553 has a current limit of 480mA for driving two to six white LEDs, while the MAX1554 has a current limit of 970mA for driving up to 10 white LEDs. A single analog/PWM Dual Mode™ input provides two simple means of brightness adjustment. A separate enable input provides on/off control. Soft-start minimizes inrush current during startup. The MAX1553/MAX1554 are available in space-saving 8-pin TDFN 3mm x 3mm packages. • Highly Integrated and Flexible Solution for Wide Applications Range of Backlighting Applications • Constant-Current Regulation for Even LED Illumination • Internal 40V MOSFET Switch Capable of Driving 10 LEDs • 2.7V to 5.5V Input Voltage Range • Analog or PWM Control of LED Intensity • Optimized for Low Input Ripple • Soft-Start Minimizes Inrush Current • High Efficiency Improves Battery Life • Up to 88% Efficiency Driving 6 LEDs • Up to 82% Efficiency Driving 9 LEDs (20mA, VCC = 3.6V) • Tiny 8-Pin, 3mm x 3mm TDFN Package Saves Space • Small, Low-Profile External Components Cellular Phones PDA, Palmtop, and Wireless Handhelds Ordering Information Color Display Backlight PART TEMP RANGE PIN-PACKAGE MAX1553ETA -40°C to +85°C 8 TDFN 3mm x 3mm AGX MAX1554ETA -40°C to +85°C 8 TDFN 3mm x 3mm AGY Dual Mode is a trademark of Maxim Integrated Products, Inc. Pin Configuration Typical Operating Circuit TOP VIEW 2.7V TO 5.5V INPUT ON OFF VCC LX EN OV MAX1553 MAX1554 PWM OR DC CONTROL 19-2875; Rev 2; 5/15 BRT SS WHITE LEDS GND 1 8 LX VCC 2 7 0V EN 3 6 SS BRT 4 5 FB MAX1553 MAX1554 FB GND TOP MARK TDFN 3mm x 3mm High-Efficiency, 40V Step-Up Converters for 2 to 10 White LEDs MAX1553/MAX1554 Absolute Maximum Ratings VCC, FB, OV to GND..............................................-0.3V to +6.0V LX to GND ..............................................................-0.3V to +45V EN, BRT, SS to GND...................................-0.3V to (VCC + 0.3V) ILX ...................................................................................0.9ARMS Continuous Power Dissipation (TA = +70°C) 8-Pin 3mm x 3mm TDFN (derate 24.4mW/°C above +70°C) .............................1951mW 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 (VCC = 3.3V, VOV = 0V, COUT = 1µF, RSENSE = 10Ω, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Supply Voltage Undervoltage Lockout Threshold Quiescent Current CONDITIONS MIN TYP MAX MAX1553 2.7 5.5 MAX1554 3.15 5.50 VCC rising or falling, 35mV hysteresis typical 2.35 2.5 2.65 Not switching 0.33 0.65 Switching 0.44 0.9 TA = +25°C 0.1 1 TA = +85°C 1 Shutdown Supply Current VEN = 0V OV Threshold Rising edge 1.25 1.33 TA = +25°C 1.18 1 200 TA = +85°C 10 UNITS V V mA µA V OV Input Bias Current VOV = 1V BRT Input Resistance 0 < VBRT < 1.5V, EN = VCC 200 400 600 kΩ Maximum On-Time VCC = 3.3V 2.0 3.4 4.8 µs On-Time Constant (K) tON = K / VCC 150 250 350 192 203 212 nA TIMING CONTROL 6.3 Minimum Off-Time µs-V ns ERROR AMPLIFIER FB Threshold FB Input Bias Current VBRT = 1.25V VBRT = 3.3V VFB = 1.0V 280 TA = +25°C 15 TA = +85°C 100 200 mV nA N-CHANNEL SWITCH LX On-Resistance www.maximintegrated.com 0.8 1.4 Ω Maxim Integrated | 2 High-Efficiency, 40V Step-Up Converters for 2 to 10 White LEDs MAX1553/MAX1554 Electrical Characteristics (continued) (VCC = 3.3V, VOV = 0V, COUT = 1µF, RSENSE = 10Ω, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER LX Current Limit LX Leakage Current MIN TYP MAX MAX1553 CONDITIONS 300 480 600 MAX1554, VCC = 4.2V 600 970 1200 TA = +25°C 0.1 5 TA = +85°C 1 VLX = 38V, VEN = 0V UNITS mA µA SHUTDOWN CONTROL EN Logic-Level High 1.8 V EN Logic-Level Low EN Input Current 0.4 VEN = 0V or 5.5V TA = +25°C 0.01 TA = +85°C 0.1 1 V µA Electrical Characteristics (VCC = 3.3V, VOV = 0V, COUT = 1µF, RSENSE = 10Ω, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER Supply Voltage Undervoltage Lockout Threshold Quiescent Current CONDITIONS MIN MAX MAX1553 2.7 5.5 MAX1554 3.15 5.50 VCC rising or falling, 35mV hysteresis typical 2.35 2.65 Not switching 0.65 Switching 0.9 UNITS V V mA OV Threshold Rising edge 1.18 1.33 V BRT Input Resistance 0 < VBRT < 1.5V, EN = VCC 200 600 kΩ TIMING CONTROL Maximum On-Time VCC = 3.3V Minimum Off-Time 2.0 4.8 µs 150 350 ns 192 217 mV 1.4 Ω ERROR AMPLIFIER FB Threshold VBRT = 1.25V N-CHANNEL SWITCH LX On-Resistance LX Current Limit MAX1553 300 600 MAX1554, VCC = 4.2V 600 1200 mA SHUTDOWN CONTROL EN Logic-Level High EN Logic-Level Low 1.8 V 0.4 V Note 1: Specifications to -40°C are guaranteed by design, not production tested. www.maximintegrated.com Maxim Integrated | 3 High-Efficiency, 40V Step-Up Converters for 2 to 10 White LEDs MAX1553/MAX1554 Typical Operating Characteristics (MAX1553 driving six white LEDs, VCC = VEN = 3.6V, Circuit of Figure 1, TA = +25°C, unless otherwise noted.) VCC = 3.6V 70 VCC = 3V 60 80 VCC = 3.6V VCC = 3V 70 10 15 20 5 EFFICIENCY vs. LOAD CURRENT WITH MAX1554 DRIVING 9 WHITE LEDS L1 = 47μH 4700pF ACROSS LEDs VCC = 4V 80 VCC = 3.6V 70 0 20 15 LED CURRENT vs. INPUT VOLTAGE 20 L1 = 47μH, 4700pF ACROSS LEDs 17 26 23 L1 = 22μH, NO CAPACITOR ACROSS LEDs 20 L1 = 47μH, 4700pF ACROSS LEDs 17 R1 = 14Ω, VBRT = 3.3V R1 = 10Ω, VBRT = 1.25V 11 11 5 10 15 2.5 20 3.0 3.5 4.0 4.5 5.0 2.5 5.5 3.0 3.5 4.0 4.5 LOAD CURRENT (mA) INPUT VOLTAGE (V) INPUT VOLTAGE (V) LED CURRENT vs. INPUT VOLTAGE WITH MAX1554 DRIVING 9 LEDS LED CURRENT vs. BRT VOLTAGE LED CURRENT vs. BRT DUTY CYCLE 17 25 25 LED CURRENT (mA) 20 20 15 5.5 MAX1553/54 toc09 30 LED CURRENT (mA) 23 5.0 30 MAX1553/54 toc08 35 MAX1553/54 toc07 26 LED CURRENT (mA) L1 = 33μH, 4700pF ACROSS LEDs 14 CIRCUIT OF FIGURE 3 0 20 15 LED CURRENT vs. INPUT VOLTAGE L1 = 33μH, 4700pF ACROSS LEDs 50 10 LOAD CURRENT (mA) 14 60 5 LOAD CURRENT (mA) L1 = 22μH, NO CAPACITOR ACROSS LEDs 23 LED CURRENT (mA) VCC = 5V 10 26 MAX1553/54 toc04 100 VCC = 3V 70 50 0 LOAD CURRENT (mA) 90 VCC = 3.6V 60 LED CURRENT (mA) 5 80 L1 = 33μH 4700pF ACROSS LEDs 50 0 EFFICIENCY (%) 90 60 L1 = 22μH NO CAPACITOR ACROSS LEDs 50 MAX1553/54 toc03 90 VCC = 5V VCC = 4V MAX1553/54 toc06 80 MAX1553/54 toc02 VCC = 4V 100 MAX1553/54 toc05 EFFICIENCY (%) 90 VCC = 5V VCC = 4V EFFICIENCY (%) VCC = 5V 100 MAX1553/54 toc01 100 EFFICIENCY vs. LOAD CURRENT DRIVING 6 WHITE LEDS EFFICIENCY vs. LOAD CURRENT DRIVING 6 WHITE LEDS EFFICIENCY (%) EFFICIENCY vs. LOAD CURRENT DRIVING 6 WHITE LEDS 20 15 10 10 14 5 5 CIRCUIT OF FIGURE 3 11 0 0 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) www.maximintegrated.com 5.0 5.5 0 0.6 1.2 1.8 2.4 BRT VOLTAGE (V) 3.0 3.6 0 20 40 60 80 100 BRT DUTY CYCLE (%) Maxim Integrated | 4 High-Efficiency, 40V Step-Up Converters for 2 to 10 White LEDs MAX1553/MAX1554 Typical Operating Characteristics (continued) (MAX1553 driving six white LEDs, VCC = VEN = 3.6V, Circuit of Figure 1, TA = +25°C, unless otherwise noted.) SWITCHING WAVEFORMS (DISCONTINUOUS OPERATION, 3.75V Li+ BATTERY, 10mA OUTPUT) SWITCHING WAVEFORMS (CONTINUOUS OPERATION, 3.75V Li+ BATTERY, 18mA OUTPUT) MAX1553/54 toc10 VLX MAX1553/54 toc11 10V/div VLX 10V/div VOUT 200mV/div VOUT 200mV/div IL 200mA/div IL 200mA/div 2μs/div 2μs/div L1 = 47μH, 4700pF CAPACITOR ACROSS LEDs L1 = 47μH, 4700pF CAPACITOR ACROSS LEDs STARTUP/SHUTDOWN WAVEFORMS BRT STEP RESPONSE MAX1553/54 toc12 VEN MAX1553/54 toc13 5V/div VFB 200mV/div VBRT 1V/div VFB 200mV/div VOUT VOUT 2V/div 10V/div 40ms/div L1 = 22μH www.maximintegrated.com 20ms/div L1 = 22μH, VBRT = 0.5V TO 1.25V TO O.5V Maxim Integrated | 5 MAX1553/MAX1554 High-Efficiency, 40V Step-Up Converters for 2 to 10 White LEDs Pin Description PIN NAME FUNCTION 1 GND Ground 2 VCC Voltage-Supply Input. 2.7V to 5.5V. The IC is powered from VCC. 3 EN Enable Input. Drive high or connect to VCC to enable the IC. Drive EN low for shutdown. 4 BRT Brightness-Control Input. Either an analog or PWM control signal can be used. The LED current can be controlled over a 10 to 1 range. The PWM signal must be between 100Hz and 10kHz, and must have an amplitude greater than 1.72V. 5 FB Feedback Input. Connect to the cathode of the LED string and connect a resistor from FB to GND to set the LED current. 6 SS Soft-Start Timing-Control Input. Connect a capacitor from SS to GND to control soft-start timing. See the SoftStart section for information on selecting the soft-start capacitor. SS is pulled to ground with an internal 200Ω switch when EN is low. 7 OV Overvoltage Sense. Connect to a resistor-divider from the anode of the LED string to set the overvoltage threshold. See Figures 1, 2, and 3. 8 LX Inductor Connection. Connect to the inductor and diode. LX is high impedance when EN is low. — EP Exposed Pad. Connect to GND. Detailed Description Control Scheme The MAX1553/MAX1554 utilize a minimum off-time, current-limited control scheme. If the voltage at FB drops below the regulation threshold, the internal low-side MOSFET turns on and the inductor current ramps up to the current limit. Once the current-limit comparator trips, the low-side MOSFET turns off for the minimum off-time (250ns). After 250ns, if the voltage at FB is above the regulation threshold, the low-side MOSFET stays off. If the voltage at FB is below the regulation point, the low-side MOSFET turns back on and the cycle repeats. By using a regulation control scheme that is not fixed frequency and that can skip pulses, the MAX1553/MAX1554 operate with very high efficiency. Soft-Start Soft-start is provided on the MAX1553/MAX1554 to minimize inrush current. The soft-start time is set with an external capacitor, C3 (Figures 1, 2, and 3). Use the following equation to solve for C3: C3 = tSS Shutdown The MAX1553/MAX1554 feature a low-current shutdown feature. When EN is low, the IC turns off, reducing its supply current to approximately 0.1µA. For normal operation, drive EN high or connect to VCC. Overvoltage Protection The MAX1553/MAX1554 have an adjustable overvoltage- protection circuit. When the voltage at OV reaches the overvoltage threshold (1.25V typ), the protection circuitry prevents the internal MOSFET from switching, allowing the output voltage to decay. The peak output voltage in an overvoltage-protection event is set with a resistor-divider from the output connected to OV (R2 and R3 in Figures 1, 2, and 3). Select a value for R3 (10kΩ is recommended), then solve for R2 using the following equation: ⎛V ⎞ R2 = R3 x ⎜ OUT(PEAK) − 1⎟ ⎝ ⎠ VOV where VOV is the overvoltage threshold (1.25V typ), and VOUT(PEAK) is the desired peak output voltage. 2 x 105 where tSS is the soft-start time. A value of 0.1µF provides a soft-start time of 20ms. www.maximintegrated.com Maxim Integrated | 6 High-Efficiency, 40V Step-Up Converters for 2 to 10 White LEDs MAX1553/MAX1554 Functional Diagram VCC LX ENABLE CONTROL CIRCUITRY EN CONTROL LOGIC DRIVER CURRENT LIMIT GND UVLO VLIM 1.25V BANDGAP REFERENCE REF MINIMUM tOFF ONE-SHOT MINIMUM tON ONE-SHOT BIAS GENERATOR ERROR COMPARATOR FB OV COMPARATOR OV 128kΩ 96kΩ 110kΩ BRT MAX1553 MAX1554 REF 1.25V 67kΩ SS L1 47μH TOKO A920CY-470M 2.7V TO 5.5V INPUT C1 4.7μF ON OFF VCC LX EN OV D1 CMDSH2-3 C2 0.47μF 25V PWM OR DC CONTROL BRT C3 0.1μF SS 2.7V TO 5.5V INPUT C1 10μF R2 200kΩ C4 4700pF R3 10kΩ MAX1553 FB GND R1 10Ω Figure 1. Circuit with the MAX1553 Driving Six White LEDs www.maximintegrated.com L1 4.7μH MURATA LQH32C ON OFF D2–D7 WHITE LEDs VCC LX EN OV D1 CMDSH1-60M C2 0.47μF 50V R2 330kΩ C4 3300pF R3 10kΩ MAX1553 PWM OR DC CONTROL BRT C3 0.1μF SS D2–D10 WHITE LEDs FB GND R1 10Ω Figure 2. Circuit with the MAX1553 Driving Nine White LEDs at Up to 15mA Maxim Integrated | 7 MAX1553/MAX1554 High-Efficiency, 40V Step-Up Converters for 2 to 10 White LEDs Adjusting the LED Current Adjusting the output current changes the brightness of the LEDs. The LED current is set by the voltage at BRT (VBRT) and the sense resistor (R1) at FB. The VBRT range for adjusting output current is 0 to 1.25V. Over this range, the LED current is found from the following equation: + 0.17 V ILED = BRT 6.67 x R1 BRT can be overdriven; however, applying a V BRT greater than 1.72V does not increase the output current above the level at 1.72V. See the LED Current vs. BRT Voltage graph in the Typical Operating Characteristics section. To set the maximum LED current, calculate R1 when VBRT is at its maximum, as follows: R1 = VBRT(MAX) + 0.17 6.67 x ILED(MAX) where VBRT(MAX) is 1.72V if BRT is connected to any value greater than 1.72V, such as V CC . Otherwise, VBRT(MAX) is the maximum applied BRT control voltage. Power dissipation in R1 is typically less than 5mW; therefore, power dissipation in a standard chip resistor is not a concern. PWM Dimming Control The BRT input is also used as a digital input allowing LED brightness control with a logic-level PWM signal applied directly to BRT. The frequency range is from 100Hz to 10kHz, and the duty cycle range is 0 to 100%. A 0% duty cycle corresponds to the minimum current, and a 100% duty cycle corresponds to full current. See the LED Current vs. BRT Duty Cycle graph in the Typical Operating Characteristics section. The BRT resistor and SS capacitor form a lowpass filter, so PWM dimming results in DC current to the LEDs without the need for additional RC filters. Capacitor Selection A 0.47µF ceramic output capacitor (C2) is recommended for most applications. For circuits driving six or fewer LEDs, use a 4.7µF ceramic input capacitor (C1). For circuits driving more than six LEDs, use a 10µF input capacitor (C1). For best stability over a wide temperature range, use capacitors with an X5R, X7R, or better dielectric. Inductor Selection The MAX1553 has a 480mA inductor current limit and can drive up to six LEDs at 20mA or nine LEDs at www.maximintegrated.com L1 22μH A915BY-220M 3.15V TO 5.5V INPUT C1 10μF ON OFF VCC LX EN OV D1 CMDSH1-60M C2 0.47μF 50V R2 330kΩ C4 3300pF R3 10kΩ MAX1554 PWM OR DC CONTROL BRT C3 0.1μF SS D2–D11 WHITE LEDs FB GND R1 10Ω Figure 3. Circuit with the MAX1554 Driving 10 White LEDs 15mA. Inductor values from 4.7µH to 47µH work satisfactorily. Larger values provide the best efficiency while small inductor values allow the smallest inductor size. A good choice for best efficiency is the TOKO D62 or D62L series at 47µH. For smallest size, the Murata LQH32C at 4.7µH works well. The MAX1554 has a 970mA inductor current limit and can drive up to 10 LEDs at 20mA. Inductor values from 4.7µH to 22µH work satisfactorily. A good choice for high efficiency and small size when driving 9 or 10 LEDs is the TOKO D62 series at 22µH. When large inductor values are used to optimize efficiency, the MAX1553/MAX1554 operate with continuous inductor current. With large inductor values (typically greater than 10µH), stability, input, and output ripple are improved by connecting a capacitor in parallel with the LEDs (C4 in Figures 1, 2, and 3). To prevent saturation, use an inductor with a current rating that matches the device’s LX current limit. However, if size is particularly important, it is sometimes acceptable to operate the inductor 10% into saturation. For best efficiency, the inductor’s DC resistance should also be as low as possible. Diode Selection The MAX1553/MAX1554s’ 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 the diode’s average and peak current ratings exceed the average output current and peak inductor current. In addition, the diode’s reverse breakdown voltage must exceed VOUT. Maxim Integrated | 8 High-Efficiency, 40V Step-Up Converters for 2 to 10 White LEDs MAX1553/MAX1554 Table 1. Component Suppliers SUPPLIER PHONE WEBSITE Central Semiconductor 631-435-1110 www.centralsemi.com Kamaya 260-489-1533 www.kamaya.com Murata 814-237-1431 www.murata.com Nichia 248-352-6575 www.nichia.com Panasonic 714-373-7939 www.panasonic.com Sumida 847-956-0666 www.sumida.com Taiyo Yuden 408-573-4150 www.t-yuden.com TDK 847-803-6100 www.component.tdk.com TOKO 847-297-0070 www.toko.com Applications Information Low Input-Voltage Applications The MAX1553/MAX1554 have minimum input voltages of 2.7V (MAX1553) and 3.15V (MAX1554). However, lower battery voltages can still be boosted for LED drive as long as V CC remains within the operating range. Since most systems have a 3.3V system supply active when the display is active and backlit, that logic supply can be used to supply VCC, while the battery power connects directly to the boost inductor. No battery current is drawn when EN is low (Figure 4). PC Board Layout Due to fast-switching waveforms and high-current paths, careful PC board layout is required. An evaluation kit (MAX1553EVKIT) is available as an example of a proper layout. When laying out a board, minimize trace lengths between the IC and the inductor, diode, input capacitor, output capacitor, and R1. Keep traces short, direct, and wide. Keep noisy traces, such as the LX node trace, away from FB. Place the VCC bypass capacitor (C1) as close to the IC as possible. The ground connections of C1 and C2 should be as close together as possible. Star connect the grounds for R1, R3, C3, and the BRT voltage supply as close to the IC as possible. The traces from VCC to C1, from C2 to the LEDs, and from the LEDs to R1 can be longer if required. www.maximintegrated.com BATTERY INPUT C1 4.7μF L1 3.3V LOGIC C4 0.1μF ON OFF D1 C2 0.47μF LX VCC EN R2 OV MAX1553 MAX1554 SS WHITE LEDs FB BRT C3 0.1μF R3 GND R1 Figure 4. The MAX1553/MAX1554 can drive LEDs from battery voltages that are lower than the device operating voltage range by powering VCC from a logic supply and connecting the boost inductor to the battery. Chip Information TRANSISTOR COUNT: 740 PROCESS: BiCMOS Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. TDFN-EP T833-2 21-0137 90-0059 Maxim Integrated | 9 High-Efficiency, 40V Step-Up Converters for 2 to 10 White LEDs MAX1553/MAX1554 Revision History REVISION NUMBER REVISION DATE 2 5/15 DESCRIPTION Revised Benefits and Features section PAGES CHANGED 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com. Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. 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