19-2526; Rev 0; 7/02 White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump Applications Features ♦ Excellent 0.3% LED-to-LED Current Matching ♦ 30mA/LED Drive Capability ♦ Proprietary 1x/1.5x Modes for Ultra-High Efficiency ♦ Low Input Ripple and EMI ♦ Eliminates Ballast Resistors ♦ Digital or PWM LED Dimming Control ♦ 0.1µA Shutdown Current ♦ 2.7V to 5.5V Supply Voltage Range ♦ Soft-Start Limits Inrush Current ♦ Thermal-Shutdown Protection ♦ No External Inductor, Schottky, or Zener Diode Required ♦ Tiny 16-Pin 4mm ✕ 4mm Thin QFN Package White LED Backlighting Cell Phones and Smart Phones Ordering Information PDA and Palmtop Computers Portable MP3 Players Digital Cameras and Camcorders PART TEMP RANGE PIN-PACKAGE MAX1570ETE -40°C to +85°C 16 Thin QFN Typical Operating Circuit Pin Configuration C2N OUT C2P IN 16 15 14 1µF C1P 1 12 C1N EN2 2 11 PGND GND 3 10 EN1 LED5 4 9 SET MAX1570 5 6 7 1µF 13 8 LED4 LED3 LED2 LED1 THIN QFN (4mm x 4mm) C1P 2.7V TO 5.5V IN C1N C2P C2N 1x/1.5x REGULATING CHARGE PUMP OUT 4.7µF 1µF MAX1570 ON/OFF AND DIMMING LED1 EN1 EN2 SET REFERENCE AND CONTROL LED2 LOW-DROPOUT CURRENT REGULATORS LED3 LED4 LED5 RSET GND PGND ________________________________________________________________ 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 MAX1570 General Description The MAX1570 fractional charge pump drives up to five white LEDs with regulated constant current for uniform intensity. The MAX1570 maintains the highest possible efficiency over the full 1-cell lithium-ion (Li+) battery input voltage range by utilizing a 1x/1.5x fractional charge pump and very-low-dropout current regulators. The MAX1570 operates with 1MHz fixed-frequency switching, allowing for tiny external components. The regulation scheme is optimized to ensure low EMI and low input ripple. An external resistor sets the full-scale LED current, while two digital inputs control on/off and select between three levels of brightness. A pulse-width modulation (PWM) signal can also be used to modulate LED brightness. The MAX1570 is available in 16-pin 4mm ✕ 4mm Thin QFN packaging (0.8mm max height). MAX1570 White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump ABSOLUTE MAXIMUM RATINGS IN, OUT, EN1, EN2 to GND ......................................-0.3V to +6V SET, LED1, LED2, LED3, LED4, LED5 to GND ...........................................-0.3V to (VIN + 0.3V) PGND to GND..........................................................-0.3 to +0.3V C1N, C2N to GND ..........................................-0.3V to (VIN + 1V) C1P, C2P to GND ..........................................-0.3V to the greater (VOUT + 1V) or (VIN + 1V) OUT Short Circuit to GND..............................................Indefinite Continuous Power Dissipation (TA = +70°C) 16-Pin Thin QFN (derate 16.9 mW/°C) .......................1349mW 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 (VIN = 3.6V, GND = PGND = 0, EN1 = EN2 = IN, CIN = C1 = C2 = 1µF, COUT = 4.7µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS IN Operating Voltage Undervoltage Lockout Threshold MIN TYP MAX UNITS 5.5 V 2.45 2.60 2.7 VIN rising or falling 2.25 Undervoltage Lockout Hysteresis 35 Supply Current 1MHz switching, no load 2.0 3.5 Shutdown Supply Current EN1 = EN2 = GND 0.1 5 Soft-Start Done Time 2.1 EN1 = GND, EN2 = IN, ISET = 33µA SET Bias Voltage SET Leakage in Shutdown 0.380 0.400 0.420 0.570 0.600 0.630 0.01 1.00 EN1 = EN2 = GND, VIN = 5.5V, VSET = 0 or 5.5V 20 µA 130 µA 230 245 A/A ISET = 67µA, VLED_= 1V -3 0.3 +3 % ISET = 130µA, VLED_= 1V 28 LED_ to LED_ Current Matching Maximum LED_ Sink Current 30 mA ISET = 33µA (Note 1) 100 180 ISET = 67µA (Note 2) 200 360 ISET = 100µA (Note 2) 230 410 EN1 = GND, EN2 = IN, ISET = 33µA 185 200 215 EN1 = IN, EN2 = GND, ISET = 67µA 277 300 323 EN1 = IN, EN2 = IN, ISET = 100µA 360 LED Leakage in Shutdown EN1 = GND, EN2 = GND, VLED_= 5.5V Maximum OUT Current IN ≥ 3.4V, OUT ≥ 3.9V 400 440 0.01 1.00 150 1x mode (VIN - VOUT)/IOUT 1.00 1.75 8 1 EN1, EN2 High Voltage IN = 2.7V to 5.5V EN1, EN2 Low Voltage IN = 2.7V to 5.5V EN1, EN2 Input Current EN_ = GND or 5.5V mV mV µA mA 1.5x mode (1.5VIN - VOUT)/IOUT Switching Frequency 2 V 215 ILED/ISET, ISET = 67µA, VLED_= 1V Open-Loop OUT Resistance µA 0.210 EN1 = IN, EN2 = IN, ISET = 100µA SET to LED_ Current Ratio LED1 Regulation Voltage (1.5x Mode) 0.200 mA ms EN1 = IN, EN2 = GND, ISET = 67µA SET Current Range LED_ Dropout Voltage 0.190 V mV Ω MHz 1.6 V 0.01 _______________________________________________________________________________________ 0.4 V 1.00 µA White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump (VIN = 3.6V, GND = PGND = 0, EN1 = EN2 = IN, CIN = C1 = C2 = 1µF, COUT = 4.7µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS LED1 Dual Mode™ Threshold MIN TYP MAX UNITS 50 75 100 mV Thermal-Shutdown Threshold 160 °C Thermal-Shutdown Hysteresis 20 °C ELECTRICAL CHARACTERISTICS (VIN = 3.6V, GND = PGND = 0, EN1 = EN2 = IN, CIN = C1 = C2 = 1µF, COUT = 4.7µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 3) PARAMETER CONDITIONS IN Operating Voltage Undervoltage Lockout Threshold VIN rising or falling Supply Current 1MHz switching, no load Shutdown Supply Current EN1 = EN2 = GND SET Bias Voltage SET Leakage in Shutdown MAX UNITS 2.7 5.5 V 2.25 2.60 V 3.5 mA 5 µA EN1 = GND, EN2 = IN, ISET = 33µA 0.190 EN1 = IN, EN2 = GND, ISET = 67µA 0.380 0.420 EN1 = IN, EN2 = IN, ISET = 100µA 0.570 0.630 20 130 µA 215 250 A/A +3 EN1 = EN2 = GND, VIN = 5.5V, VSET = 0 or 5.5V SET Current Range SET to LED_ Current Ratio MIN ILED/ISET, ISET = 67µA, VLED_= 1V 1 LED_ to LED_ Current Matching ISET = 67µA, VLED_= 1V -3 Maximum LED_ Sink Current ISET = 130µA, VLED_= 1V 28 LED_ Dropout Voltage 180 ISET = 67µA (Note 2) 360 185 215 EN1 = IN, EN2 = GND, ISET = 67µA 277 323 EN1 = IN, EN2 = IN, ISET = 100µA 360 440 EN1 = GND, EN2 = GND, VLED_= 5.5V Maximum OUT Current IN ≥ 3.4V, OUT ≥ 3.9V Open-Loop OUT Resistance EN1, EN2 High Voltage 1 150 1x mode (VIN - VOUT)/IOUT EN1, EN2 Low Voltage IN = 2.7V to 5.5V EN1, EN2 Input Current EN_ = GND or 5.5V LED1 Dual Mode Threshold % mV 8 1.6 50 mV µA mA 1.75 1.5x mode (1.5VIN - VOUT)/IOUT IN = 2.7V to 5.5V µA 410 EN1 = GND, EN2 = IN, ISET = 33µA LED Leakage in Shutdown V mA ISET = 33µA (Note 1) ISET = 100µA (Note 2) LED1 Regulation Voltage (1.5x Mode) 0.210 Ω V 0.4 V 1 µA 100 mV Note 1: Dropout voltage is defined as the LED_ to GND voltage at which current sink into LED_ drops 20% from the value at LED_ = 1V. Note 2: Dropout voltage is defined as the LED_ to GND voltage at which current sink into LED_ drops 10% from the value at LED_ = 1V. Note 3: Specifications to -40°C are guaranteed by design and not production tested. Dual Mode is a trademark of Maxim Integrated Products, Inc. _______________________________________________________________________________________ 3 MAX1570 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (EN1 = EN2 = IN, CIN = 1µF, C1 = C2 = 1µF, COUT = 4.7µF, RSET = 9.09kΩ, TA = +25°C, unless otherwise noted.) 85 80 75 70 65 250 200 150 10mA/LED, EN1 = VIN, EN2 = GND 100 60 70 60 MAX1570 toc03 10mA/LED, EN1 = VIN, EN2 = GND 50 40 5mA/LED, EN1 = GND, EN2 = VIN 30 3.4 3.6 5mA/LED, EN1 = GND, EN2 = VIN 0 3.8 4.0 2.5 4.2 3.0 3.5 4.0 4.5 5.0 10 0 5.5 SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) LED EFFICIENCY vs. SUPPLY VOLTAGE (5 LEDs) SUPPLY POWER vs. SUPPLY VOLTAGE (5 LEDs) 85 80 75 70 65 15mA/LED, EN1 = EN2 = VIN 400 SUPPLY POWER (mW) 90 450 60 350 300 250 200 10mA/LED, EN1 = VIN, EN2 = GND 150 100 3.2 3.0 3.4 3.6 0 3.8 4.0 4.2 EFFICIENCY vs. LED CURRENT (4 LEDs, EN1 = PWM AT 1kHz) VIN = 3.9V 75 70 VIN = 3V 65 18 12 10 8 6 55 2 6 7 8 9 10 11 12 13 14 15 LED CURRENT (mA) 5mA/LED, EN1 = GND, EN2 = VIN 40 2.5 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 120 100 5.0 15mA/LED, EN1 = EN2 = VIN 80 60 10mA/LED, EN1 = VIN, EN2 = GND 40 5mA/LED, EN1 = GND, EN2 = VIN 20 0 5 10mA/LED, EN1 = VIN, EN2 = GND 60 SUPPLY CURRENT vs. SUPPLY VOLTAGE (4 LEDs, LED1 OPEN FOR 1.5X ONLY MODE) 14 4 50 fPWM = 1kHz VIN = 3.3V 16 60 80 5.0 SUPPLY CURRENT (mA) 85 80 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 20 LED CURRENT (mA) 90 3.0 LED CURRENT vs. PWM DIMMING DUTY CYCLE INTO EN1 (5 LEDs) MAX1570 toc07 95 15mA/LED, EN1 = EN2 = VIN 0 2.5 SUPPLY VOLTAGE (V) 100 5.0 20 5mA/LED, EN1 = GND, EN2 = VIN 50 MAX1570 toc08 50 15mA/LED, EN1 = EN2 = VIN 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 120 100 5mA/LED, EN1 = GND, EN2 = VIN 55 3.0 SUPPLY CURRENT vs. SUPPLY VOLTAGE (5 LEDs) MAX1570 toc05 10mA/LED, EN1 = VIN, EN2 = GND 95 500 MAX1570 toc04 100 2.5 MAX1570 toc06 3.2 50 MAX1570 toc09 3.0 15mA/LED, EN1 = EN2 = VIN SUPPLY CURRENT (mA) 50 4 15mA/LED, EN1 = EN2 = VIN 80 20 5mA/LED, EN1 = GND, EN2 = VIN 55 EFFICIENCY PLED/PSUPPLY (%) 300 90 SUPPLY CURRENT (mA) SUPPLY POWER (mW) EFFICIENCY PLED/PSUPPLY (%) 90 15mA/LED, EN1 = EN2 = VIN 350 100 MAX1570 toc02 10mA/LED, EN1 = VIN, EN2 = GND 95 400 MAX1570 toc01 100 SUPPLY CURRENT vs. SUPPLY VOLTAGE (4 LEDs) SUPPLY POWER vs. SUPPLY VOLTAGE (4 LEDs) LED EFFICIENCY vs. SUPPLY VOLTAGE (4 LEDs) EFFICIENCY PLED/PSUPPLY (%) MAX1570 White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump 0 0 10 20 30 40 50 60 70 80 90 100 PWM DUTY CYCLE (%) 2.5 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 5.0 White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump LED CURRENT vs. TEMPERATURE (VIN = 3.3V, RSET = 7.5kΩ) 11.9 11.8 EN1 = EN2 = VIN LED CURRENT (mA) 14 12 EN1 = VIN, EN2 = GND 10 8 EN1 = GND, EN2 = VIN 6 25 11.7 LED CURRENT (mA) 16 LED CURRENT vs. RSET 30 MAX1570 toc11 18 LED CURRENT (mA) 12.0 MAX1570 toc10 20 11.6 11.5 11.4 11.3 11.0 0 2.5 3.0 3.5 4.0 4.5 5.0 -15 SUPPLY VOLTAGE (V) 10 35 TEMPERATURE (°C) 60 10 85 5.0 = IN = EN , EN2 GN D, E N 2=I 2 = IN 7.5 10.0 MAX1570 toc15 IIN 50mA/div IIN AC-COUPLED 10mA/div IIN AC-COUPLED 10mA/div 15.0 12.5 STARTUP RESPONSE (VIN = 3.3V) (5 LEDs AT 15mA/LED) MAX1570 toc14 MAX1570 toc13 VIN AC-COUPLED 20mV/div VIN AC-COUPLED 1mV/div VOUT 2V/div VOUT AC-COUPLED 5mV/div VOUT AC-COUPLED 1mV/div 400ns/div 2µs/div DIMMING RESPONSE USING PWM INTO EN1 400µs/div LINE-TRANSIENT RESPONSE MAX1570 toc16 100µs/div N = GND RSET (kΩ) TYPICAL OPERATING WAVEFORM IN 1.5X MODE (ILOAD = 90mA, VIN = 3.6V) TYPICAL OPERATING WAVEFORM IN 1X MODE EN1 0 -40 5.5 E N1 15 5 EN1 = IN EN2 = GND 11.1 2 20 EN1 = 11.2 4 MAX1570 toc12 LED CURRENT vs. SUPPLY VOLTAGE MAX1570 toc17 ILED 15mA TO 5mA 5mA/div ILED 15mA 5mA/div VOUT AC-COUPLED 500mV/div VOUT AC-COUPLED 500mV/div EN1 0 TO 2V 2V/div VIN 4 TO 3.6V 500mV/div 100µs/div _______________________________________________________________________________________ 5 MAX1570 Typical Operating Characteristics (continued) (EN1 = EN2 = IN, CIN = 1µF, C1 = C2 = 1µF, COUT = 4.7µF, RSET = 9.09kΩ, TA = +25°C, unless otherwise noted.) White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump MAX1570 Pin Description 6 PIN NAME 1 C1P Transfer Capacitor 1 Positive Connection FUNCTION 2 EN2 Enable, Dimming Control Input 2. EN2 and EN1 control shutdown, 1/3 current, 2/3 current, and full current (see Table1). 3 GND Analog Ground. Connect directly to the exposed paddle underneath the IC. 4 LED5 LED5 Cathode Connection. Current flowing into LED5 is 230 times the current flowing out of SET. When using fewer than five LEDs, this pin can be left unconnected. LED5 is high impedance during shutdown. 5 LED4 LED4 Cathode Connection. Current flowing into LED4 is 230 times the current flowing out of SET. When using fewer than five LEDs, this pin can be left unconnected. LED4 is high impedance during shutdown. 6 LED3 LED3 Cathode Connection. Current flowing into LED3 is 230 times the current flowing out of SET. When using fewer than five LEDs, this pin can be left unconnected. LED3 is high impedance during shutdown. 7 LED2 LED2 Cathode Connection. Current flowing into LED2 is 230 times the current flowing out of SET. When using fewer than five LEDs, this pin can be left unconnected. LED2 is high impedance during shutdown. 8 LED1 LED1 Cathode Connection and Charge-Pump Feedback. Current flowing into LED1 is 230 times the current flowing out of SET. The charge pump regulates the voltage on LED1 to various voltages depending upon the status of EN1 and EN2 (see Table 1). Grounding LED1 forces OUT to operate at 5V while LED2–LED5 regulate the LED current to 230 x VSET/RSET. LED1 is high impedance during shutdown. 9 SET Bias Current Set Input. The current flowing out of SET programs the bias current into each LED by ILED_ = 230 x ISET. VSET is internally biased to various voltages (see Table 1). Connect a resistor to GND to set the bias current as VSET/RSET. SET is high impedance during shutdown. 10 EN1 Enable, Dimming Control Input 1. EN1 and EN2 control shutdown, 1/3 current, 2/3 current, and full current (see Table 1). 11 PGND 12 C1N Power Ground. Charge-pump switching current flows through this pin. Connect to GND and system ground as close to the MAX1570 and the input bypass capacitor as possible. Transfer Capacitor 1 Negative Connection Supply Voltage Input. Bypass IN to PGND with a 1µF ceramic capacitor. The input voltage range is 2.7V to 5.5V. IN is high impedance during shutdown. 13 IN 14 C2P Transfer Capacitor 2 Positive Connection 15 OUT Charge-Pump Output. Bypass to PGND with a 4.7µF ceramic capacitor as close to the IC as possible. Connect to the anodes of all the LEDs. OUT is high impedance during shutdown. 16 C2N Transfer Capacitor 2 Negative Connection — EP Exposed paddle. Connect to GND. _______________________________________________________________________________________ White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump The MAX1570 is a complete charge-pump buck/boost converter requiring only four small ceramic capacitors. The MAX1570 utilizes a proprietary 1x/1.5x fractional charge-pump topology to drive up to five white LEDs with regulated constant current for uniform intensity. The MAX1570 operates with a 1MHz fixed frequency. An external resistor (RSET) programs the full-scale LED current, while two digital inputs control on/off and provide brightness control. Output Regulation The MAX1570 operates in 1x charge-pump mode until just above dropout. Then the MAX1570 switches to 1.5x charge-pump mode to regulate the voltage at LED1 and maintain constant LED brightness even at very low battery voltages. Using this topology, there is no LED brightness change during the 1x/1.5x switchover, which guarantees no flicker on the display. The switchover scheme has low hysteresis, minimizing operation in the less efficient 1.5x mode. The 1x mode produces almost no ripple, while the 1.5x mode regulates the output voltage by controlling the rate at which the transfer capacitors are charged. In this way, the switching frequency remains constant for reduced input ripple and stable noise spectrum. Soft-Start The MAX1570 includes soft-start circuitry to limit inrush current at turn-on. When starting up with an output voltage that is not near the input voltage, the output capacitor is charged directly from the input with a DAC ramped current source (with no charge-pump action) until the output voltage is near the input voltage. Once this occurs, the charge pump determines if 1x or 1.5x mode is required. In the case of 1x mode, the soft-start is terminated and normal operation begins. In the case of 1.5x mode, soft-start operates until LED1 reaches regulation. In case of an overload condition, soft-start repeats every 2.1ms. If the output is shorted to ground, the output current is limited by the MAX1570 fractionalswitching technique and then the device hits thermal shutdown once the die temperature reaches -160°C. True Shutdown Mode When EN1 and EN2 are grounded, the MAX1570 is in shutdown, and the charge pump examines whether the input voltage is greater than or less than the output voltage and shorts the transfer capacitor nodes to either IN or OUT as necessary. The output is high impedance in either case. Thermal Shutdown The MAX1570 includes a thermal-limit circuit that shuts down the IC at about 160°C. Turn-on occurs after the IC cools by approximately 20°C. Setting the Output Current SET controls the LED bias current. Current flowing into LED1, LED2, LED3, LED4, and LED5 is 230 times greater than the current flowing out of SET. Set the output current as follows: V ILED _ = 230 × SET RSET where VSET = 0.2V, 0.4V, or 0.6V (depending upon EN1 and EN2, see Table 1), and RSET is the resistor connected between SET and GND (see the Typical Operating Circuit). Applications Information Dimming Using EN1 and EN2 Use EN1 and EN2 inputs as a digital 2-bit number to control on/off, 1/3, 2/3, and full current (see Table 1). EN1 and EN2 control the voltage at SET (V SET ). Adjusting the SET voltage controls the current (ISET) through the SET resistor (RSET). Increasing VSET or reducing RSET increases ISET, which then increases the LED current (ILED_). The charge-pump feedback threshold at LED1 is increased as the current is increased to prevent dropout in the current regulators while improving efficiency at lower current settings. LED1 is regulated at 0.2V, 0.3V, or 0.4V when EN1 and EN2 are adjusted for 1/3, 2/3, or full current, respectively (see Table 1). A higher threshold improves LED-to-LED current matching, while a lower threshold improves efficiency by allowing the 1x mode at lower input voltages. Dimming Using PWM into EN1 Use EN2 for shutdown and drive EN1 with a PWM signal. Current can be varied from 1/3 to full. The waveforms in the Typical Operating Characteristics show the response time of dimming. EN2 keeps the part on, eliminating any soft-start delay that would impede PWM control, allowing a PWM frequency up to 5kHz (Figure 1). Dimming Using a Filtered-PWM Signal Use a high-frequency PWM signal to drive an R-C-R filter on the SET pin (Figure 2). A 0% PWM duty cycle corresponds to 20mA/LED, while a 100% PWM duty cycle corresponds to 0mA/LED. At PWM frequencies above 5kHz, C3 may be reduced. _______________________________________________________________________________________ 7 MAX1570 Detailed Description MAX1570 White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump Table 1. Enable Input Modes EN_ INPUT LOGIC LEVELS MODE LED CURRENT EN1 = 0, EN2 = 0 Shutdown mode EN1 = 0, EN2 = 1 On, VSET = 200mV, LED1 threshold = 200mV 1/3 0 EN1 = 1, EN2 = 0 On, VSET = 400mV, LED1 threshold = 300mV 2/3 EN1 = 1, EN2 = 1 On, VSET = 600mV, LED1 threshold = 400mV Full Table 2. Capacitor Selection OUTPUT (mA) CIN (µF) C1 (µF) C2 (µF) COUT (µF) 40 1 0.22 0.22 4.7 80 1 0.47 0.47 4.7 150 1 1.0 1.0 4.7 Table 3. Capacitor Manufacturers COMPONENT NAME VALUE (µF) MANUFACTURER PART NO. CIN 1 Taiyo Yuden JMK107BJ105MA 1µF ±20%, 6.3V X5R ceramic capacitor (0603) COUT 4.7 Taiyo Yuden JMK212BJ475MG 4.7µF ±20%, 6.3V X5R ceramic capacitor (0805) 1 Taiyo Yuden JMK107BJ105MA 1µF ±20%, 6.3V X5R ceramic capacitor (0603) 0.47 Taiyo Yuden LMK107BJ474MA 0.47µF ±20%, 10V X5R ceramic capacitor (0603) 0.22 Taiyo Yuden LMK107BJ224KA 0.22µF ±10%, 10V X7R ceramic capacitor (0603) C1 and C2 8 DESCRIPTION _______________________________________________________________________________________ White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump Component Selection Typical external component values are shown in Table 2 and Table 3. Maximum power dissipation occurs around 4.2V on IN and 4.0V at OUT with maximum load current. PC Board Layout and Routing PD = [((1.5 × V ) IN At higher IN voltages this device switches to 1x mode and power dissipation is lowered. The MAX1570 is a high-frequency switched-capacitor voltage regulator. For best circuit performance, use a solid ground plane and place CIN and COUT as close to the MAX1570 as possible. Also, place their ground tails close together. Connect PGND and GND directly under the IC to the exposed paddle, and connect CIN and COUT as close as possible to PGND. The input supply connections should be short; if this is not possible, an additional input supply filter capacitor (tantalum or electrolytic) may be required. Refer to the MAX1570 EV kit for a good layout example. 1µF C1P C2P 0 TO 20mA/LED 4.7µF LED1 MAX1570 LED2 EN2 R1 14.3kΩ LED3 R2 14.3kΩ LED4 SET LED5 RSET 9.09kΩ GND PGND Figure 2. Dimming Using Filtered-PWM Signal 1µF C1P LED1 LED2 PWM INPUT OUT EN1 4.7µF MAX1570 C2N C2N 1µF EN2 C2P 1µF C3 1µF OUT IN VIN C1N IN VIN 1µF C1N 1µF C1P PWM INPUT 0 TO 25V 1µF ] ) − VOUT + 0.4 V × 120mA = 324mW 1Ω VIN 1µF C1N C2P C2N OUT IN EN1 LED3 SET 4.7µF 2.2µF 2.2µF LED4 LED5 EN1 RSET MAX1570 LED1 LED2 GND EN2 PGND LED3 SET LED4 Figure 1. Dimming Using PWM Signal into EN1 LED5 RSET GND PGND Figure 3. C-R-C Filter Reduces Input Ripple Chip Information TRANSISTOR COUNT: 3187 _______________________________________________________________________________________ 9 MAX1570 Input Ripple For LED drivers, 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 input ripple. Figure 3 shows a C-R-C filter used to reduce input ripple to less than 2mVP-P when driving a 75mA load. Alternately, increasing CIN to 2.2µF or 4.7µF yields input ripple of 17mVP-P or 9mVP-P, respectively, with only a small increase in footprint. The 1x mode has very low input ripple. MAX1570 White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump 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.) PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.8 mm 21-0139 10 ______________________________________________________________________________________ A White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.8 mm 21-0139 A 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. MAX1570 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.)