19-2290; Rev 0; 1/02 60mA 1.5x High-Efficiency White LED Charge Pumps The MAX1912 has a reduced feedback (SET) threshold of 200mV for minimum loss when operating as a current source. The MAX1913 has a 1.25V SET threshold for best accuracy in voltage-feedback applications. Connecting SET to IN on the MAX1913 selects a preset 5.0V output voltage. Contact factory for current-sense thresholds other than 200mV or preset output voltages other than 5.0V Features ♦ High-Efficiency 1.5x Charge Pumps ♦ Low Input Ripple with 750kHz Operation ♦ 200mV Current-Sense Threshold Reduces Power Loss ♦ Current- or Voltage-Regulated Charge Pump ♦ 60mA Output Current ♦ No Inductors Required ♦ Small Ceramic Capacitors ♦ Regulated ±3% Output Voltage ♦ Load Disconnected in Shutdown ♦ 1µA Shutdown Current ♦ Small 10-Pin µMAX Package Applications Backlight White LED Biasing Ordering Information TEMP RANGE PIN-PACKAGE Cellular Phones MAX1912EUB -40°C to +85°C 10 µMAX PDAs MAX1913EUB50* -40°C to +85°C 10 µMAX Digital Still Cameras PART *Future product—contact factory for availability. MP3 Players Selector Guide Backup-Battery Boost Converters PART Typical Operating Circuit MODE VSET VOUT MAX1912EUB 1.5x 200mV Adjustable Current MAX1913EUB50* 1.5x 1.25V 5.0V or Adjustable *Future product—contact factory for availability. Pin Configuration VIN IN1 IN2 SHDN OUT TOP VIEW C1+ C1 CIN C1- GND 1 IN1 C2+ SET C2 C2- COUT MAX1912 GND 10 SET 2 MAX1912/ MAX1913 9 C1- C2- 3 8 IN2 C1+ 4 7 C2+ OUT 5 6 SHDN 10-PIN 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 MAX1912/MAX1913 General Description The MAX1912/MAX1913* power LEDs with a regulated output voltage or current (up to 60mA) 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. MAX1912/MAX1913 60mA 1.5x High-Efficiency White LED Charge Pumps ABSOLUTE MAXIMUM RATINGS IN1, IN2, OUT, SHDN, SET to GND ...…………………-0.3V, +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 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 MAX 5.3 V 2.2 2.5 V Undervoltage Lockout Hysteresis 35 MAX1912 SET Regulation Point 0 < ILOAD < 60mA MAX1912 Current Regulation Output current change for 3V < VOUT < 5V 0.19 Maximum Output Current UNITS 2.7 0.2 mV 0.21 0.5 V %/V 60 mA No Load Input Current VIN = 3.6V 1.5 2.5 mA Supply Current in Shutdown VIN = 5.3V, VOUT = 0, SHDN = 0 0.1 10 µA Output Leakage Current in Shutdown VIN = 3.6V, SHDN = 0 0.1 10 µA Switching Frequency VIN = 3.6V 750 875 kHz Switching Frequency Temperature Coefficient f = 750kHz 625 250 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 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 Both rising and falling edges Maximum Output Current Supply Current in Shutdown 2 MIN MAX 2.7 5.3 V 2.2 2.5 V 60 VIN = 5.3V, VOUT = 0, SHDN = 0 _______________________________________________________________________________________ UNITS mA 10 µA 60mA 1.5x 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 Output Leakage Current in Shutdown VIN = 3.6V, SHDN = 0 MAX1912 SET Regulation Point 0 < ILOAD < 60mA MIN MAX UNITS 10 µA 0.21 V 100 nA µA 0.19 SET Input Current SHDN Input Current SHDN = 0 or 5.5V 1 SHDN Input Voltage Low 2.7V < VIN < 5.3V 0.4 SHDN Input Voltage High 2.7V < VIN < 5.3V V 1.6 V Note 1: Limits to -40°C are guaranteed by design, not production tested. Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) INPUT AND OUTPUT VOLTAGE RIPPLE WITH ADDITIONAL INPUT FILTER QUIESCENT CURRENT vs. INPUT VOLTAGE 20mV/div 20mV/div VOUT VOUT IIN (mA) MAX1912/13 toc01 3 VIN VIN1 MAX19112/13 toc03 4 MAX1912/13 toc02 INPUT AND OUTPUT VOLTAGE RIPPLE 2 1 0 1µs.div 1µs/div 0 1 MAX1912 DRIVING 4 LEDS (60mA) 10µF - 1Ω - 10µF INPUT FILTER, COUT = 4.7µF VIN = 3.3V CIN = 10µF, COUT = 4.7µF MAX1912 DRIVING 4 LEDS (60mA) VIN = 3.3V STARTUP INPUT CURRENT AND OUTPUT VOLTAGE 3 4 5 6 VIN (V) INTENSITY CHANGE STEP RESPONSE MAX1912/13 toc04 VSHDN 2 MAX1912/13 toc05 5V/div VLOGIC 1V/div VOUT 2V/div 100mV/div VSET 45mA 50mA/div IIN 1ms/div CIRCUIT OF FIGURE 2 R1 = R2 = R3 = 15Ω CIN = 10µF, COUT = 2.2µF VIN = 3.3V 15mA ILED 50µs/div CIRCUIT OF FIGURE 10 RA = 22kΩ, RB = 1.5kΩ, RL = 4.7Ω CIN = 10µF, COUT = 4.7µF VLOGIC(HIGH) = 2V _______________________________________________________________________________________ 3 MAX1912/MAX1913 ELECTRICAL CHARACTERISTICS (continued) 60mA 1.5x High-Efficiency White LED Charge Pumps MAX1912/MAX1913 Pin Description PIN NAME FUNCTION 1 GND 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 Ground Output. Bypass to GND with a 2.2µF ceramic capacitor. 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. 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 SET SET programs the output voltage with a resistive-divider from OUT (MAX1913), or programs output current with a resistor from SET to GND (MAX1912). For the MAX1913, when SET is connected to IN, VOUT is internally set to 5V. 10 Detailed Description The MAX1912/MAX1913 are complete charge-pump boost converters requiring only four small ceramic capacitors. They employ a 750kHz fixed-frequency 50% duty-cycle clock. The MAX1912/MAX1913 use a 1.5x charge- pump mode. This operation has two phases (see Figure 1), charge and transfer. In 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. Output Regulation The output voltage 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 charge-pump topologies because the charge transferred per cycle is only the amount required to supply the output load. Soft-Start The MAX1912/MAX1913 include soft-start circuitry to limit inrush current at turn-on. When starting up with the output voltage at zero, the output capacitor is charged 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. 4 Once the output capacitor is charged 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 soft-start sequence is repeated. The devices will 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 MAX1912/MAX1913 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 (MAX1912) The MAX1912 has 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/R If additional matching LEDs with ballast resistors are connected to the output as in Figure 2, the current _______________________________________________________________________________________ 60mA 1.5x High-Efficiency White LED Charge Pumps Setting Output Voltage (MAX1913) The MAX1913 has a SET voltage threshold of 1.25V. The output voltage is set by connecting a resistor voltage divider as shown in Figure 6. The output voltage is adjustable from 3V to 5V. To set the output voltage, select a value for R2 that is less than 50kΩ, then solve for R1 using the following equation: V R1 = R2 OUT − 1 1.25 If SET is connected to the input, the output voltage is 5V (Figure 7). Other parts with internally set voltages from 3V to 5V in 100mV steps are available by special order. bench power supplies. This resistor may 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 8 shows a C-R-C filter used to reduce input ripple to less than 1mV when driving a 60mA load. Applications Information Adjusting LED Intensity Figure 9 shows a circuit using a DAC to set the LED intensity. Maximum intensity occurs when the output of the DAC is zero. RL may 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 load current at different DAC output voltages is determined by: IL = 0.2 (VDAC − 0.2) × RB − RL RL × RA Figure 10 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. The total LED current is determined by: IL = 0.2 (VLOGIC − 0.2) × RB − RL RL × RA 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 2–10) will improve stability when operating from low-impedance sources such as high-current laboratory PC Board Layout The MAX1912/MAX1913 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. Chip Information TRANSISTOR COUNT: 2500 PROCESS: BiCMOS _______________________________________________________________________________________ 5 MAX1912/MAX1913 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 V SET . 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 R4. R1, R2, and R3 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. MAX1912/MAX1913 60mA 1.5x High-Efficiency White LED Charge Pumps IN SW4 SW1 SW2 SW5 SW7 (REGULATING SWITCH) SW3 SW6 GND OUT C1- C1+ C2- MODE PHASE SW1 SW2 SW3 SW4 1.5x Charging OFF ON OFF OFF C2+ SW5 SW6 ON OFF ON OFF ON OFF 1.5x Transfer ON OFF ON ON Figure 1. Functional Charge-Pump Switch Diagram (Switches Shown for Charging Phase) 1Ω VIN IN1 IN2 SW7 SHDN OUT C1+ 0.47µF 2.2µF C1C2+ SET 0.47µF C2- 2.2µF MAX1912 GND 10Ω 10Ω Figure 2. LED Biasing with the MAX1912 6 _______________________________________________________________________________________ 10Ω 60mA 1.5x High-Efficiency White LED Charge Pumps MAX1912/MAX1913 1Ω VIN IN2 IN1 SHDN OUT C1+ 0.47µF 2.2 µF C1- 2.2µF MAX1912 C2+ 1kΩ 0.47µF SET C2- 1kΩ GND 1kΩ 10Ω 10Ω 10Ω Figure 3. The MAX1912 Regulating Average Current Through LEDs 1Ω VIN IN1 IN2 SHDN OUT C1+ 0.47µF 2.2µF C1- 2.2µF MAX1912 15Ω 25Ω 25Ω C2+ 0.47µF SET C2- GND 10Ω Figure 4. Alternate Method of Biasing to Improve LED-to-LED Matching _______________________________________________________________________________________ 7 MAX1912/MAX1913 60mA 1.5x High-Efficiency White LED Charge Pumps 1Ω VIN IN1 IN2 SHDN OUT C1+ 0.47µF 2.2µF C1- 2.2µF MAX1912 C2+ SET 0.47µF C2- 2-PIN CONNECTOR GND R4 3.3Ω R1 10Ω R2 10Ω R3 10Ω Figure 5. Alternate Method of Biasing LEDs Controls Total Current; Suitable When the LED Array Must Be Biased with Only Two Connections 1Ω VIN IN1 IN2 SHDN OUT VOUT C1+ 0.47µF 2.2µF C1C2+ R1 SET 0.47µF C2- 2.2µF MAX1913 GND R2 Figure 6. Output Voltage Set with a Resistor-Divider 8 _______________________________________________________________________________________ 60mA 1.5x High-Efficiency White LED Charge Pumps 1Ω IN1 IN2 SHDN VIN 1Ω IN1 VOUT OUT IN2 SHDN 2.2µF C1+ C1- 2.2µF MAX1913 10µF 10µF 0.47µF C1- C2+ SET 0.47µF 2.2µF MAX1913 C2+ SET 0.47µF C2- GND C2- GND Figure 8. C-R-C Filter Reduces Ripple On the Input Figure 7. Output Voltage Internally Set to 5V VIN VOUT OUT C1+ 0.47µF 1Ω IN1 IN2 SHDN OUT C1+ 0.47µF 2.2µF C1- 2.2µF MAX1912 10Ω 10Ω 10Ω C2+ 0.47µF SET C2- GND 3.3V MAX5380 (2-WIRE INPUT) MAX5383 (3-WIRE INPUT) RL 4.7Ω RA 22.1kΩ VDD SERIAL INPUT RB 1.58kΩ OUT GND HIGH DAC OUTPUT (2V) = 15mA LED CURRENT LOW DAC OUTPUT (0V) = 45mA LED CURRENT Figure 9. Circuit with SOT DAC for Intensity Control _______________________________________________________________________________________ 9 MAX1912/MAX1913 VIN MAX1912/MAX1913 60mA 1.5x High-Efficiency White LED Charge Pumps VIN 1Ω IN1 IN2 SHDN OUT C1+ 0.47µF 2.2µF C1- 2.2µF MAX1912 C2+ 0.47µF SET C2- RB GND RL RA DIMMING INPUT (0V OR VLOGIC) Figure 10. Using Digital Logic Input for Intensity Control 10 ______________________________________________________________________________________ 60mA 1.5x High-Efficiency White LED Charge Pumps 10LUMAX.EPS 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 © 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX1912/MAX1913 Package Information