19-2290; Rev 2; 3/04 1.5x/2x High-Efficiency White LED Charge Pumps The MAX1910/MAX1912 power LEDs with a regulated output voltage or current (up to 120mA) from an unregulated input supply (2.7V to 5.3V). These are complete DC-DC converters requiring only four small ceramic capacitors and no inductors. Input ripple is minimized by a unique regulation scheme that maintains a fixed 750kHz switching frequency over a wide load range. Also included are logic-level shutdown and soft-start to reduce input current surges at startup. The MAX1910 has two automatically selected operating modes: 1.5x and 2x. 1.5x mode improves efficiency at higher input voltages, while 2x mode maintains regulation at lower input voltages. The MAX1912 operates only in 1.5x mode. The MAX1910 and the MAX1912 are available in a space-saving 10-pin µMAX package. Features ♦ High-Efficiency 1.5x/2x Charge Pumps ♦ Low Input Ripple with 750kHz Operation ♦ 200mV Current-Sense Threshold Reduces Power Loss ♦ Current- or Voltage-Regulated Charge Pump ♦ Up to 120mA Output Current ♦ No Inductors Required ♦ Small Ceramic Capacitors ♦ Regulated ±5% LED Current ♦ Load Disconnected in Shutdown ♦ 1µA Shutdown Current ♦ Small 10-Pin µMAX Package Ordering Information Applications White LED Backlighting TEMP RANGE PIN-PACKAGE Cellular Phones MAX1910EUB PART -40°C to +85°C 10 µMAX PDAs MAX1912EUB -40°C to +85°C 10 µMAX Digital Still Cameras MP3 Players Backup-Battery Boost Converters Typical Operating Circuit Pin Configuration TOP VIEW VIN IN1 IN2 GND 1 SHDN OUT IN1 C1+ C1 CIN C1C2+ SET C2 C2- COUT MAX1910 MAX1912 GND 10 SET 2 MAX1910 MAX1912 9 C1- C2- 3 8 IN2 C1+ 4 7 C2+ OUT 5 6 SHDN µMAX ________________________________________________________________ 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 MAX1910/MAX1912 General Description MAX1910/MAX1912 1.5x/2x High-Efficiency White LED Charge Pumps ABSOLUTE MAXIMUM RATINGS IN1, IN2, OUT, SHDN, SET to GND …………………-0.3V to +6V C1-, C2-, to GND..................................................-0.3V, VIN + 1V C1+, C2+ to GND..........-0.3V, greater of VOUT + 1V or VIN + 1V OUT Short-Circuit to GND ..........................................Continuous Continuous Power Dissipation (TA = +70°C) 10-Pin µMAX (derate 5.6 mW/°C above +70°C) ..........444mW Operating Temperature Range ...........................-40°C to +85°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 = 3.6V, GND = 0, SHDN = SET = IN, CIN = 2.2µF, C1 = C2 = 0.47µF, COUT = 2.2µF, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER CONDITIONS Input Voltage Operating Range Undervoltage Lockout Threshold Both rising and falling edges MIN TYP V 2.2 2.5 V 35 SET Regulation Point MAX1912 Current Regulation Maximum Output Current UNITS 5.3 Undervoltage Lockout Hysteresis MAX1910 Current Regulation MAX 2.7 0.19 0.2 Output current change for 2.7V < VOUT < 5V Output current change for 3V < VOUT < 5V MAX1910 VIN = 2.7V 80 MAX1912 VIN = 3.6V 120 mV 0.21 V 0.5 %/V 0.5 %/V mA No Load Input Current VIN = 3.6V 1.5 2.5 Supply Current in Shutdown VIN = 5.3V, VOUT = 0, SHDN = 0 0.1 10 µA Output Leakage Current in Shutdown Switching Frequency VIN = 3.6V, SHDN = 0 0.1 10 µA 750 875 kHz Switching Frequency Temperature Coefficient VIN = 3.6V 625 250 f = 750kHz SET Input Current 1 SHDN Input Current SHDN = 0 or 5.5V SHDN Input Voltage Low 2.7V < VIN < 5.3V SHDN Input Voltage High 2.7V < VIN < 5.3V Thermal-Shutdown Threshold Rising temperature, 15°C hysteresis typical mA ppm/°C 100 nA 1 µA 0.4 V 1.6 V 160 °C ELECTRICAL CHARACTERISTICS (VIN = 3.6V, GND = 0, SHDN = SET = IN, CIN = 2.2µF, C1 = C2 = 0.47µF, COUT = 2.2µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS Input Voltage Operating Range Undervoltage Lockout Threshold Maximum Output Current Supply Current in Shutdown 2 MIN MAX UNITS 2.7 5.3 V 2.5 V Both rising and falling edges 2.2 MAX1910 VIN = 2.7V 80 MAX1910 VIN = 3.6V 120 VIN = 5.3V, VOUT = 0, SHDN = 0 _______________________________________________________________________________________ mA 10 µA 1.5x/2x High-Efficiency White LED Charge Pumps (VIN = 3.6V, GND = 0, SHDN = SET = IN, CIN = 2.2µF, C1 = C2 = 0.47µF, COUT = 2.2µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS MIN VIN = 3.6V, SHDN = 0 Output Leakage Current in Shutdown SET Regulation Point 0.19 SET Input Current SHDN Input Current SHDN = 0 or 5.5V SHDN Input Voltage Low 2.7V < VIN < 5.3V SHDN Input Voltage High 2.7V < VIN < 5.3V MAX UNITS 10 µA 0.21 V 100 nA 1 µA 0.4 V 1.6 V Note 1: Limits to -40°C are guaranteed by design, not production tested. Typical Operating Characteristics (Circuit of Figure 2, VIN = 3.3V, TA = +25°C, unless otherwise noted.) START-UP INPUT CURRENT AND OUTPUT VOLTAGE INPUT AND OUTPUT VOLTAGE RIPPLE INPUT AND OUTPUT VOLTAGE RIPPLE MAX1910/12 toc02 MAX1910/12 toc01 MAX1910/12 toc03 VIN VIN 5V/div VSHDN CIRCUIT OF FIGURE 7 DRIVING 4 LEDS (60mA) 2V/div 20mV/div 20mV/div VOUT 50mA/div VOUT VOUT IIN IOUT = 60mA 1µs/div 1ms/div LED CURRENT vs. INPUT VOLTAGE INTENSITY CHANGE STEP RESPONSE 1µs/div QUIESCENT CURRENT vs. INPUT VOLTAGE 2.5 2.0 1.5 MAX1910/12 toc05 3.0 120 LED CURRENT (mA) QUIESCENT CURRENT (mA) 3.5 MAX1910/12 toc06 140 MAX1910/12 toc04 4.0 100 80 100mV/div VSET 60 40 1.0 2V/div VLOGIC CIRCUIT OF FIGURE 9 20 0.5 60mA 20mA IOUT 0 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 2.7 3.0 3.3 3.6 3.9 4.2 4.5 40µs/div INPUT VOLTAGE (V) _______________________________________________________________________________________ 3 MAX1910/MAX1912 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (Circuit of Figure 2, VIN = 3.3V, TA = +25°C, unless otherwise noted.) INPUT CURRENT vs. INPUT VOLTAGE DRIVING 4 LEDS EFFICIENCY vs. INPUT VOLTAGE 90 80 MAX1910/12 toc08 140 MAX1910/12 toc07 100 120 100 70 CURRENT (mA) EFFICIENCY (%) MAX1910/MAX1912 1.5x/2x High-Efficiency White LED Charge Pumps 60 50 40 30 80 60 40 20 CIRCUIT OF FIGURE 2 MAX1910 4 WHITE LEDs IOUT = 60mA 10 CIRCUIT OF FIGURE 2 MAX1910 ILOAD = 60mA 20 0 0 2.7 3.0 3.3 3.6 3.9 4.2 2.7 4.5 3.0 3.3 3.6 3.9 4.2 4.5 INPUT VOLTAGE (V) INPUT VOLTAGE (V) Pin Description PIN NAME 1 GND FUNCTION 2 IN1 Supply Voltage Input. Connect to IN2. Bypass to GND with a 2.2µF ceramic capacitor. 3 C2- Transfer Capacitor 2 Connection, Negative Side 4 C1+ Transfer Capacitor 1 Connection, Positive Side 5 OUT Output. Bypass to GND with a 2.2µF ceramic capacitor. 6 SHDN 7 C2+ Transfer Capacitor 2 Connection, Positive Side 8 IN2 Supply Voltage Input. Connect to IN1. 9 C1- Transfer Capacitor 1 Connection, Negative Side 10 SET SET programs the output current with a resistor from SET to GND. SET can also program the output voltage with a resistor-divider between OUT and GND. Ground Shutdown Input. Drive low to turn off the device and disconnect the load from the input. OUT is high impedance in shutdown. Drive high or connect to IN for normal operation. Detailed Description The MAX1910/MAX1912 are complete charge-pump boost converters requiring only four small ceramic capacitors. They employ a 750kHz fixed-frequency 50% duty-cycle clock. The MAX1910 has two modes of operation: 1.5x and 2x. Each mode has two phases: charge and transfer (see Figure 1). In 1.5x mode charge phase, transfer capacitors C1 and C2 charge in series from the input voltage. In transfer phase, C1 and C2 are configured in parallel and connected from OUT to IN, transferring charge to COUT. If this system were allowed to operate unregulated and unloaded, it would generate an output voltage 1.5 times the input voltage (hence the terms 4 “fractional charge pump” and “1.5x mode”). When the input voltage drops sufficiently, the operating mode shifts from a 1.5x fractional charge pump to a 2x doubler. C2 is not used in doubler mode. The device transitions out of doubler mode when VIN is greater than ~75% of VOUT for more than 32 clock cycles (at full load). The MAX1912 operates only in 1.5x chargepump mode. Output Regulation The output is regulated by controlling the rate at which the transfer capacitors are charged. The switching frequency and duty cycle are constant, so the output noise spectrum is predictable. Input and output ripple are much smaller in value than with other regulating _______________________________________________________________________________________ 1.5x/2x High-Efficiency White LED Charge Pumps Soft-Start The MAX1910/MAX1912 include soft-start circuitry to limit inrush current at turn-on. When starting up with the output voltage at zero, the output capacitor charges through a ramped current source, directly from the input with no charge-pump action until the output voltage is near the input voltage. If the output is shorted to ground, the part remains in this mode without damage until the short is removed. Once the output capacitor charges to the input voltage, the charge-pumping action begins. Startup surge current is minimized by ramping up charge on the transfer capacitors. As soon as regulation is reached, soft-start ends and the part operates normally. If the SET voltage reaches regulation within 2048 clock cycles (typically 2.7ms), the part begins to run in normal mode. If the SET voltage is not reached by 2048 cycles, the softstart sequence is repeated. The devices continue to repeat the soft-start sequence until the SET voltage reaches the regulation point. Shutdown Mode When driven low, SHDN turns off the charge pump. This reduces the quiescent current to approximately 0.1µA. The output is high impedance in shutdown. Drive SHDN high or connect to IN for normal operation. Thermal Shutdown The MAX1910/MAX1912 shut down when their die temperature reaches +160°C. Normal operation continues after the die cools by 15°C. This prevents damage if an excessive load is applied or the output is shorted to ground. Design Procedure Setting Output Current The MAX1910/MAX1912 have a SET voltage threshold of 0.2V, used for LED current regulation (Figure 2). The current through the resistor and LED is: ILED = 0.2/RSET If additional matching LEDs with ballast resistors are connected to the output as in Figure 2, the current through each additional LED is the same as that in the regulated LED. In Figure 2, total LED current depends somewhat on LED matching. Figure 3 shows a connection that regulates the average of all the LED currents to reduce the impact of mismatched LEDs. Figure 4’s circuit improves LED current matching by raising the ballast resistance while maintaining a 200mV VSET. The increased ballast resistance tolerates wider LED mismatch, but reduces efficiency and raises the minimum input voltage required for regulation. Yet another method of biasing LEDs is shown in Figure 5. In this case, the current through the complete parallel combination of LEDs is set by R5. R1–R4 are only used to compensate for LED variations. This method of biasing is useful for parallel LED arrays that do not allow connection to individual LEDs. Setting Output Voltage The MAX1910 has a SET voltage threshold of 0.2V. Output voltage can be set by connecting a resistor voltage-divider as shown in Figure 6. The output voltage is adjustable from VIN to 5V. To set the output voltage, select a value for R2 that is less than 20kΩ, then solve for R1 using the following equation: V R1 = R2 OUT - 1 0.2 Capacitor Selection Use low-ESR ceramic capacitors. Recommended values are 0.47µF for the transfer capacitors, 2.2µF to 10µF for the input capacitor, and 2.2µF to 4.7µF for the output capacitor. To ensure stability over a wide temperature range, ceramic capacitors with an X7R dielectric are recommended. Place these capacitors as close to the IC as possible. Increasing the value of the input and output capacitors further reduces input and output ripple. With a 10µF input capacitor and a 4.7µF output capacitor, input ripple is less than 5mV peak-to-peak and output ripple is less than 15mV peak-to-peak for 60mA of output current. A constant 750kHz switching frequency and fixed 50% duty cycle create input and output ripple with a predictable frequency spectrum. Decoupling the input with a 1Ω resistor (as shown in Figures 2–9) improves stability when operating from lowimpedance sources such as high-current laboratory bench power supplies. This resistor can be omitted when operating from higher impedance sources such as lithium or alkaline batteries. For some designs, such as an LED driver, input ripple is more important than output ripple. Input ripple depends on the source supply’s impedance. Adding a lowpass filter to the input further reduces ripple. Figure 7 shows a CR-C filter used to reduce input ripple. With 10µF-1Ω-10µF, input ripple is less than 1mV when driving a 60mA load. _______________________________________________________________________________________ 5 MAX1910/MAX1912 charge-pump topologies because the charge transferred per cycle is only the amount required to supply the output load. MAX1910/MAX1912 1.5x/2x High-Efficiency White LED Charge Pumps The total LED current is determined by: Applications Information Adjusting LED Intensity IL = Figure 8 shows a circuit using a DAC to set the LED intensity. Maximum intensity occurs when the output of the DAC is zero. RL can be initially estimated from the maximum load current: RL ≈ 0.2/IL(MAX) Use this as a starting point to calculate RA and RB from the formula below. The total LED current, IL, at different DAC output voltages is determined by: IL = 0.2 (VLOGIC - 0.2) × RB RL RL × RA PC Board Layout The MAX1910/MAX1912 are high-frequency switchedcapacitor voltage regulators. For best circuit performance, use a ground plane and keep CIN, COUT, C1, C2, and feedback resistors (if used) close to the device. If using external feedback, keep the feedback node as small as possible by positioning the feedback resistors very close to SET. 0.2 (VDAC - 0.2) × RB RL RL × RA Chip Information Figure 9 uses a digital input for two-level dimming control. The LEDs are brightest when a logic-low input (VLOGIC = 0) is applied, and dimmed with a logic-high input. TRANSISTOR COUNT: 2497 PROCESS: BiCMOS IN SW4 SW1 SW2 SW5 SW7 (REGULATING SWITCH) SW3 SW6 GND OUT C1- C1+ C2- C2+ MODE PHASE SW1 SW2 SW3 SW4 SW5 SW6 1.5x Charging OFF ON OFF OFF ON OFF ON 1.5x Transfer ON OFF ON ON OFF ON OFF 2x Charging OFF OFF ON ON ON OFF ON 2x Transfer ON OFF ON ON OFF ON OFF Figure 1. Functional Charge-Pump Switch Diagram (Switches Shown for 1.5x Charging Phase) 6 _______________________________________________________________________________________ SW7 1.5x/2x High-Efficiency White LED Charge Pumps IN1 MAX1910/MAX1912 1Ω VIN SHDN IN2 OUT C1+ 0.47µF 2.2µF C1- 2.2µF MAX1910 MAX1912 C2+ SET 0.47µF C2- GND 15Ω 15Ω 15Ω 15Ω Figure 2. LED Biasing with the MAX1912 1Ω VIN IN1 IN2 SHDN OUT C1+ 0.47µF 2.2 µF C1- 2.2µF MAX1910 MAX1912 C2+ 1kΩ 0.47µF SET C2- GND 1kΩ 1kΩ 10Ω 10Ω 10Ω Figure 3. The MAX1912 Regulating Average Current Through LEDs _______________________________________________________________________________________ 7 MAX1910/MAX1912 1.5x/2x High-Efficiency White LED Charge Pumps 1Ω VIN IN2 IN1 SHDN OUT C1+ 0.47µF 2.2µF C1- 2.2µF MAX1910 MAX1912 15Ω 30Ω 30Ω 30Ω C2+ 0.47µF SET C2- GND 15Ω Figure 4. Alternate Method of Biasing to Improve LED-to-LED Matching 1Ω VIN IN1 IN2 SHDN OUT C1+ 0.47µF 2.2µF C1C2+ SET 0.47µF C2- 2.2µF MAX1910 MAX1912 2-PIN CONNECTOR GND R5 3.3Ω R1 15Ω R2 15Ω R3 15Ω Figure 5. Alternate Method of Biasing LEDs Controls Total Current; Suitable When the LED Array Must Be Biased with Only Two Connections 8 _______________________________________________________________________________________ R4 15Ω 1.5x/2x High-Efficiency White LED Charge Pumps IN1 IN2 MAX1910/MAX1912 1Ω VIN SHDN OUT VOUT C1+ 0.47µF 2.2µF C1- 2.2µF MAX1910 MAX1912 C2+ R1 SET 0.47µF C2- GND R2 Figure 6. Output Voltage Set with a Resistor-Divider 1Ω VIN IN1 IN2 SHDN OUT C1+ 0.47µF 2.2µF 2.2µF C1C2+ SET 0.47µF C2- 2.2µF MAX1910 MAX1912 GND 10Ω 10Ω 10Ω Figure 7. C-R-C Filter Reduces Ripple On the Input _______________________________________________________________________________________ 9 MAX1910/MAX1912 1.5x/2x High-Efficiency White LED Charge Pumps 1Ω VIN IN2 IN1 SHDN OUT C1+ 0.47µF 2.2µF C1- 2.2µF MAX1910 MAX1912 15Ω 15Ω C2+ 0.47µF SET C2- RB 1.58kΩ GND 3.3V MAX5380 (2-WIRE INPUT) MAX5383 (3-WIRE INPUT) RA 22.1kΩ VDD SERIAL INPUT RL 4.7Ω OUT HIGH DAC OUTPUT (2V) = 15mA LED CURRENT LOW DAC OUTPUT (0V) = 45mA LED CURRENT GND Figure 8. Circuit with SOT DAC for Intensity Control VIN 1Ω IN1 IN2 SHDN OUT C1+ 0.47µF 2.2µF C1- 2.2µF MAX1910 MAX1912 C2+ 0.47µF SET C2- RB GND RL RA DIMMING INPUT (0V OR VLOGIC) Figure 9. Using Digital Logic Input for Intensity Control 10 ______________________________________________________________________________________ 15Ω 15Ω 1.5x/2x High-Efficiency White LED Charge Pumps 10LUMAX.EPS e 4X S 10 MAX DIM MIN 0.043 A 0.006 A1 0.002 A2 0.030 0.037 D1 0.120 0.116 0.118 D2 0.114 E1 0.116 0.120 0.118 0.114 E2 0.199 0.187 H 0.0157 0.0275 L L1 0.037 REF b 0.007 0.0106 e 0.0197 BSC c 0.0035 0.0078 0.0196 REF S α 0∞ 6∞ H ÿ 0.50±0.1 0.6±0.1 1 1 0.6±0.1 BOTTOM VIEW TOP VIEW D2 MILLIMETERS INCHES 10 MAX MIN 1.10 0.15 0.05 0.75 0.95 3.05 2.95 2.89 3.00 2.95 3.05 2.89 3.00 4.75 5.05 0.40 0.70 0.940 REF 0.270 0.177 0.500 BSC 0.200 0.090 0.498 REF 0∞ 6∞ E2 GAGE PLANE A2 c A b D1 A1 α E1 L L1 FRONT VIEW SIDE VIEW PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, 10L uMAX/uSOP APPROVAL DOCUMENT CONTROL NO. 21-0061 REV. I 1 1 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 ____________________ 11 © 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX1910/MAX1912 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.)