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19-2526; Rev 0; 7/02
White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump
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). o 30mA/LED Drive Capability o Proprietary 1x/1.5x Modes for Ultra-High Efficiency o Low Input Ripple and EMI o Eliminates Ballast Resistors o Digital or PWM LED Dimming Control o 0.1A Shutdown Current o 2.7V to 5.5V Supply Voltage Range o Soft-Start Limits Inrush Current o Thermal-Shutdown Protection o No External Inductor, Schottky, or Zener Diode Required o Tiny 16-Pin 4mm 4mm Thin QFN Package
Features
o Excellent 0.3% LED-to-LED Current Matching
MAX1570
Applications
White LED Backlighting Cell Phones and Smart Phones PDA and Palmtop Computers Portable MP3 Players Digital Cameras and Camcorders
Ordering Information
PART MAX1570ETE TEMP RANGE -40C to +85C PIN-PACKAGE 16 Thin QFN
Pin Configuration
C2N OUT C2P IN 16 C1P EN2 GND LED5 1 2 3 4 5 6 7 8 15 14 13 12 11 C1N PGND EN1 SET
ON/OFF AND DIMMING EN1 EN2 SET 2.7V TO 5.5V IN 1F
Typical Operating Circuit
1F C1P 1F C1N C2P C2N OUT 4.7F
1x/1.5x REGULATING CHARGE PUMP
MAX1570
10 9
MAX1570
LED1 REFERENCE AND CONTROL LED2 LOW-DROPOUT CURRENT REGULATORS LED3 LED4 LED5 RSET GND PGND
LED4 LED3 LED2 LED1
THIN QFN (4mm x 4mm)
________________________________________________________________ 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.
White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump MAX1570
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 = +70C) 16-Pin Thin QFN (derate 16.9 mW/C) .......................1349mW 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
(VIN = 3.6V, GND = PGND = 0, EN1 = EN2 = IN, CIN = C1 = C2 = 1F, COUT = 4.7F, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER IN Operating Voltage Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis Supply Current Shutdown Supply Current Soft-Start Done Time EN1 = GND, EN2 = IN, ISET = 33A SET Bias Voltage SET Leakage in Shutdown SET Current Range SET to LED_ Current Ratio LED_ to LED_ Current Matching Maximum LED_ Sink Current LED_ Dropout Voltage ILED/ISET, ISET = 67A, VLED_= 1V ISET = 67A, VLED_= 1V ISET = 130A, VLED_= 1V ISET = 33A (Note 1) ISET = 67A (Note 2) ISET = 100A (Note 2) LED1 Regulation Voltage (1.5x Mode) LED Leakage in Shutdown Maximum OUT Current Open-Loop OUT Resistance Switching Frequency EN1, EN2 High Voltage EN1, EN2 Low Voltage EN1, EN2 Input Current IN = 2.7V to 5.5V IN = 2.7V to 5.5V EN_ = GND or 5.5V 0.01 1.6 0.4 1.00 EN1 = GND, EN2 = IN, ISET = 33A EN1 = IN, EN2 = GND, ISET = 67A EN1 = IN, EN2 = IN, ISET = 100A EN1 = GND, EN2 = GND, VLED_= 5.5V IN 3.4V, OUT 3.9V 1x mode (VIN - VOUT)/IOUT 1.5x mode (1.5VIN - VOUT)/IOUT 1 150 1.00 1.75 8 185 277 360 EN1 = IN, EN2 = GND, ISET = 67A EN1 = IN, EN2 = IN, ISET = 100A EN1 = EN2 = GND, VIN = 5.5V, VSET = 0 or 5.5V 20 215 -3 28 230 0.3 30 100 200 230 200 300 400 0.01 180 360 410 215 323 440 1.00 A mA MHz V V A mV mV 0.190 0.380 0.570 1MHz switching, no load EN1 = EN2 = GND VIN rising or falling CONDITIONS MIN 2.7 2.25 2.45 35 2.0 0.1 2.1 0.200 0.400 0.600 0.01 0.210 0.420 0.630 1.00 130 245 +3 A A A/A % mA V 3.5 5 TYP MAX 5.5 2.60 UNITS V V mV mA A ms
2
_______________________________________________________________________________________
White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 3.6V, GND = PGND = 0, EN1 = EN2 = IN, CIN = C1 = C2 = 1F, COUT = 4.7F, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER LED1 Dual ModeTM Threshold Thermal-Shutdown Threshold Thermal-Shutdown Hysteresis CONDITIONS MIN 50 TYP 75 160 20 MAX 100 UNITS mV C C
MAX1570
ELECTRICAL CHARACTERISTICS
(VIN = 3.6V, GND = PGND = 0, EN1 = EN2 = IN, CIN = C1 = C2 = 1F, COUT = 4.7F, TA = -40C to +85C, unless otherwise noted.) (Note 3)
PARAMETER IN Operating Voltage Undervoltage Lockout Threshold Supply Current Shutdown Supply Current SET Bias Voltage SET Leakage in Shutdown SET Current Range SET to LED_ Current Ratio LED_ to LED_ Current Matching Maximum LED_ Sink Current LED_ Dropout Voltage ILED/ISET, ISET = 67A, VLED_= 1V ISET = 67A, VLED_= 1V ISET = 130A, VLED_= 1V ISET = 33A (Note 1) ISET = 67A (Note 2) ISET = 100A (Note 2) LED1 Regulation Voltage (1.5x Mode) LED Leakage in Shutdown Maximum OUT Current Open-Loop OUT Resistance EN1, EN2 High Voltage EN1, EN2 Low Voltage EN1, EN2 Input Current LED1 Dual Mode Threshold EN1 = GND, EN2 = IN, ISET = 33A EN1 = IN, EN2 = GND, ISET = 67A EN1 = IN, EN2 = IN, ISET = 100A EN1 = GND, EN2 = GND, VLED_= 5.5V IN 3.4V, OUT 3.9V 1x mode (VIN - VOUT)/IOUT 1.5x mode (1.5VIN - VOUT)/IOUT IN = 2.7V to 5.5V IN = 2.7V to 5.5V EN_ = GND or 5.5V 50 1.6 0.4 1 100 150 1.75 8 185 277 360 VIN rising or falling 1MHz switching, no load EN1 = EN2 = GND EN1 = GND, EN2 = IN, ISET = 33A EN1 = IN, EN2 = GND, ISET = 67A EN1 = IN, EN2 = IN, ISET = 100A EN1 = EN2 = GND, VIN = 5.5V, VSET = 0 or 5.5V 20 215 -3 28 180 360 410 215 323 440 1 A mA V V A mV mV mV 0.190 0.380 0.570 CONDITIONS MIN 2.7 2.25 MAX 5.5 2.60 3.5 5 0.210 0.420 0.630 1 130 250 +3 A A A/A % mA V UNITS V V mA A
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 -40C are guaranteed by design and not production tested.
Dual Mode is a trademark of Maxim Integrated Products, Inc. _______________________________________________________________________________________ 3
White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump MAX1570
Typical Operating Characteristics
(EN1 = EN2 = IN, CIN = 1F, C1 = C2 = 1F, COUT = 4.7F, RSET = 9.09k, TA = +25C, unless otherwise noted.)
LED EFFICIENCY vs. SUPPLY VOLTAGE (4 LEDs)
MAX1570 toc01
SUPPLY POWER vs. SUPPLY VOLTAGE (4 LEDs)
350 SUPPLY POWER (mW) 300 250 200 150 100 10mA/LED, EN1 = VIN, EN2 = GND 5mA/LED, EN1 = GND, EN2 = VIN 2.5 3.0 3.5 4.0 4.5 5.0 5.5 15mA/LED, EN1 = EN2 = VIN
MAX1570 toc02
SUPPLY CURRENT vs. SUPPLY VOLTAGE (4 LEDs)
90 80 SUPPLY CURRENT (mA) 70 60 50 40 30 20 15mA/LED, EN1 = EN2 = VIN
MAX1570 toc03
100 95 EFFICIENCY PLED/PSUPPLY (%) 90 85 80 75 70 65 60 55 50 5mA/LED, EN1 = GND, EN2 = VIN 3.0 3.2 3.4 3.6 15mA/LED, EN1 = EN2 = VIN 3.8 4.0 10mA/LED, EN1 = VIN, EN2 = GND
400
100
10mA/LED, EN1 = VIN, EN2 = GND 5mA/LED, EN1 = GND, EN2 = VIN
50 0
10 0 2.5 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 5.0
4.2
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
LED EFFICIENCY vs. SUPPLY VOLTAGE (5 LEDs)
MAX1570 toc04
SUPPLY POWER vs. SUPPLY VOLTAGE (5 LEDs)
MAX1570 toc05
SUPPLY CURRENT vs. SUPPLY VOLTAGE (5 LEDs)
MAX1570 toc06
100 95 EFFICIENCY PLED/PSUPPLY (%) 90 85 80 75 70 65 60 55 50 5mA/LED, EN1 = GND, EN2 = VIN 3.0 3.2 3.4 3.6 15mA/LED, EN1 = EN2 = VIN 3.8 4.0 10mA/LED, EN1 = VIN, EN2 = GND
500 450 400 SUPPLY POWER (mW) 350 300 250 200 150 100 50 0 2.5 3.0 5mA/LED, EN1 = GND, EN2 = VIN 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 10mA/LED, EN1 = VIN, EN2 = GND 15mA/LED, EN1 = EN2 = VIN
120 100 SUPPLY CURRENT (mA) 80 60 40 20 0 10mA/LED, EN1 = VIN, EN2 = GND 5mA/LED, EN1 = GND, EN2 = VIN 15mA/LED, EN1 = EN2 = VIN
4.2
5.0
2.5
3.0
SUPPLY VOLTAGE (V)
3.5 4.0 4.5 SUPPLY VOLTAGE (V)
5.0
EFFICIENCY vs. LED CURRENT (4 LEDs, EN1 = PWM AT 1kHz)
MAX1570 toc07
LED CURRENT vs. PWM DIMMING DUTY CYCLE INTO EN1 (5 LEDs)
MAX1570 toc08
SUPPLY CURRENT vs. SUPPLY VOLTAGE (4 LEDs, LED1 OPEN FOR 1.5X ONLY MODE)
MAX1570 toc09
100 95 EFFICIENCY PLED/PSUPPLY (%) 90 85 80 75 70 65 60 55 50 5 6 7 8 9 VIN = 3V VIN = 3.9V
20 18 16 LED CURRENT (mA) 14 12 10 8 6 4 2 0 fPWM = 1kHz VIN = 3.3V
120 100 SUPPLY CURRENT (mA) 80 60 40 20 0 5mA/LED, EN1 = GND, EN2 = VIN 15mA/LED, EN1 = EN2 = VIN
10mA/LED, EN1 = VIN, EN2 = GND
10 11 12 13 14 15
0
10 20 30 40 50 60 70 80 90 100 PWM DUTY CYCLE (%)
2.5
3.0
LED CURRENT (mA)
3.5 4.0 4.5 SUPPLY VOLTAGE (V)
5.0
4
_______________________________________________________________________________________
White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump
Typical Operating Characteristics (continued)
(EN1 = EN2 = IN, CIN = 1F, C1 = C2 = 1F, COUT = 4.7F, RSET = 9.09k, TA = +25C, unless otherwise noted.)
LED CURRENT vs. TEMPERATURE (VIN = 3.3V, RSET = 7.5k)
MAX1570 toc11
MAX1570
LED CURRENT vs. SUPPLY VOLTAGE
MAX1570 toc10
LED CURRENT vs. RSET
MAX1570 toc12
20 18 16 LED CURRENT (mA) 14 12 10 8 6 4 2 0 2.5 3.0 3.5 4.0 4.5 5.0 EN1 = GND, EN2 = VIN EN1 = VIN, EN2 = GND EN1 = EN2 = VIN
12.0 11.9 11.8 LED CURRENT (mA) 11.7 11.6 11.5 11.4 11.3 11.2 11.1 11.0 EN1 = IN EN2 = GND -40 -15 10 35 TEMPERATURE (C) 60
30 25 LED CURRENT (mA) 20 15
EN1
E N1
= EN
10
EN1 =
= IN
2=I
N
, EN2
= GND
5 0 85 5.0 7.5
GN D, E N
2 = IN
5.5
10.0 RSET (k)
12.5
15.0
SUPPLY VOLTAGE (V)
TYPICAL OPERATING WAVEFORM IN 1X MODE
MAX1570 toc13
TYPICAL OPERATING WAVEFORM IN 1.5X MODE (ILOAD = 90mA, VIN = 3.6V)
MAX1570 toc14
STARTUP RESPONSE (VIN = 3.3V) (5 LEDs AT 15mA/LED)
MAX1570 toc15
IIN AC-COUPLED 10mA/div VIN AC-COUPLED 1mV/div VOUT AC-COUPLED 1mV/div
IIN AC-COUPLED 10mA/div VIN AC-COUPLED 20mV/div VOUT AC-COUPLED 5mV/div
IIN 50mA/div
VOUT 2V/div
2s/div
400ns/div
400s/div
DIMMING RESPONSE USING PWM INTO EN1
MAX1570 toc16
LINE-TRANSIENT RESPONSE
MAX1570 toc17
ILED 15mA TO 5mA 5mA/div
ILED 15mA 5mA/div
VOUT AC-COUPLED 500mV/div EN1 0 TO 2V 2V/div 100s/div 100s/div
VOUT AC-COUPLED 500mV/div VIN 4 TO 3.6V 500mV/div
_______________________________________________________________________________________
5
White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump MAX1570
Pin Description
PIN 1 2 3 4 NAME C1P EN2 GND LED5 Transfer Capacitor 1 Positive Connection Enable, Dimming Control Input 2. EN2 and EN1 control shutdown, 1/3 current, 2/3 current, and full current (see Table1). Analog Ground. Connect directly to the exposed paddle underneath the IC. 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. 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. 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. 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. 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. 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. Enable, Dimming Control Input 1. EN1 and EN2 control shutdown, 1/3 current, 2/3 current, and full current (see Table 1). 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 1F ceramic capacitor. The input voltage range is 2.7V to 5.5V. IN is high impedance during shutdown. Transfer Capacitor 2 Positive Connection Charge-Pump Output. Bypass to PGND with a 4.7F ceramic capacitor as close to the IC as possible. Connect to the anodes of all the LEDs. OUT is high impedance during shutdown. Transfer Capacitor 2 Negative Connection Exposed paddle. Connect to GND. FUNCTION
5
LED4
6
LED3
7
LED2
8
LED1
9
SET
10 11 12 13 14 15 16 --
EN1 PGND C1N IN C2P OUT C2N EP
6
_______________________________________________________________________________________
White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump
Detailed Description
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.
Thermal Shutdown
The MAX1570 includes a thermal-limit circuit that shuts down the IC at about 160C. Turn-on occurs after the IC cools by approximately 20C.
MAX1570
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 x 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).
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.
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.
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 -160C.
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).
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.
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
White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump MAX1570
Table 1. Enable Input Modes
EN_ INPUT LOGIC LEVELS EN1 = 0, EN2 = 0 EN1 = 0, EN2 = 1 EN1 = 1, EN2 = 0 EN1 = 1, EN2 = 1 Shutdown mode On, VSET = 200mV, LED1 threshold = 200mV On, VSET = 400mV, LED1 threshold = 300mV On, VSET = 600mV, LED1 threshold = 400mV MODE LED CURRENT 0 1/3 2/3 Full
Table 2. Capacitor Selection
OUTPUT (mA) 40 80 150 CIN (F) 1 1 1 C1 (F) 0.22 0.47 1.0 C2 (F) 0.22 0.47 1.0 COUT (F) 4.7 4.7 4.7
Table 3. Capacitor Manufacturers
COMPONENT NAME CIN COUT C1 and C2 VALUE (F) 1 4.7 1 0.47 0.22 MANUFACTURER Taiyo Yuden Taiyo Yuden Taiyo Yuden Taiyo Yuden Taiyo Yuden PART NO. JMK107BJ105MA JMK212BJ475MG JMK107BJ105MA LMK107BJ474MA LMK107BJ224KA DESCRIPTION 1F 20%, 6.3V X5R ceramic capacitor (0603) 4.7F 20%, 6.3V X5R ceramic capacitor (0805) 1F 20%, 6.3V X5R ceramic capacitor (0603) 0.47F 20%, 10V X5R ceramic capacitor (0603) 0.22F 10%, 10V X7R ceramic capacitor (0603)
8
_______________________________________________________________________________________
White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump
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 2.2F or 4.7F 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.
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. PD =
MAX1570
[((1.5 x V
IN
)
- VOUT + 0.4 V x 120mA = 324mW
)
]
PC Board Layout and Routing
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.
At higher IN voltages this device switches to 1x mode and power dissipation is lowered.
1F 1F
C1P VIN 1F IN
C1N
C2P
C2N OUT 4.7F 0 TO 20mA/LED
EN1 EN2 R1 14.3k PWM INPUT 0 TO 25V R2 14.3k
MAX1570
LED1 LED2 LED3
SET
LED4 LED5
1F
1F
C3 1F
RSET 9.09k
GND
PGND
C1P VIN 1F IN
C1N
C2P
C2N OUT 4.7F
Figure 2. Dimming Using Filtered-PWM Signal
1F 1F
C1P
C1N
C2P
C2N OUT 4.7F
EN2 PWM INPUT EN1
MAX1570
LED1 LED2 LED3
VIN
1
IN
SET LED4 LED5 RSET GND PGND
2.2F
2.2F LED1 LED2 EN2 LED3 SET LED4 LED5
EN1
MAX1570
Figure 1. Dimming Using PWM Signal into EN1
RSET GND PGND
Figure 3. C-R-C Filter Reduces Input Ripple
Chip Information
TRANSISTOR COUNT: 3187
_______________________________________________________________________________________
9
White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump MAX1570
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
A
10
______________________________________________________________________________________
White LED Current Regulator with 1x/1.5x High-Efficiency Charge Pump
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.)
MAX1570
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 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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