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19-2847; Rev 0; 4/03
White LED 1x/1.5x Charge Pump in UCSP
General Description
The MAX1573 fractional charge pump drives up to four white LEDs with regulated constant current for uniform intensity. By utilizing proprietary adaptive 1x/1.5x modes and ultra-low-dropout current regulators, it maintains the highest possible efficiency over the full 1-cell Li+ battery input voltage range. The 1MHz fixedfrequency switching allows for tiny external components and 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 amongst three levels of brightness. A pulse-width modulation (PWM) signal can also be used to modulate LED brightness, requiring no additional components. The MAX1573 is available in the chip-scale package (UCSPTM) (4 x 4 grid) to minimize PC board area. o Proprietary Adaptive 1x/1.5x Modes o High Efficiency (PLEDs/PBATT), Up to 92% o 2% LED Current Matching and Accuracy o 28mA/LED Drive Capability o Low Input Ripple and EMI o Eliminates Ballast Resistors o Logic or PWM Dimming Control o Low 0.1A Shutdown Current o 2.7V to 5.5V Input Voltage Range o Soft-Start Limits Inrush Current o Output Overvoltage Protection o Thermal Shutdown Protection o No External Schottky Diode Required o Tiny 2.1mm x 2.1mm x 0.6mm UCSP Package
Features
MAX1573
Applications
Cell Phones, Smart Phones PDAs, Digital Cameras, Camcorders MP3 Players Other Handhelds with Color Displays
PART MAX1573EBE-T
Ordering Information
TEMP RANGE -40C to +85C PIN-PACKAGE 14 UCSP (4 x 4)
Typical Operating Circuit
1F 1F
Pin Configuration
TOP VIEW
1 2 3 4
VIN 2.7V TO 5.5V 1F ON/OFF AND DIMMING CONTROL
C1N IN
C1P
C2N
C2P OUT 1F
VOUT UP TO 4 LEDS
C1P A C2N B IN C C1N D
OUT
EN1
EN2
C2P
SET
EN1 EN2
MAX1573
LED1 LED2 LED3
LED4
LED2
SET GND RSET
LED4
GND
LED3
LED1
UCSP 4 4 UCSP is a trademark of Maxim Integrated Products, Inc. ________________________________________________________________ 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 1x/1.5x Charge Pump in UCSP MAX1573
ABSOLUTE MAXIMUM RATINGS
IN, OUT, EN1, EN2 to GND ...................................-0.3V to +6.0V SET, LED1, LED2, LED3, LED4 to GND ......-0.3V to (VIN + 0.3V) C1N, C2N to GND ..........................................-0.3V to (VIN + 1V) C1P, C2P to GND ............................................-0.3V to greater of .............................................................(VOUT + 1V) or (VIN + 1V) OUT Short Circuit to GND ..........................................Continuous Continuous Power Dissipation (TA = +70C) 14-Bump UCSP (derate 7.36mW/C above +70C) ....589mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C
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 = VEN1 = VEN2 = 3.6V, CIN = C1 = C2 = COUT = 1F, TA = -40C to +85C. Typical values are at TA = +25C, unless otherwise noted.) (Note 1)
PARAMETER IN Operating Voltage Undervoltage Lockout Threshold Supply Current Shutdown Supply Current Soft-Start Completion Time SET Bias Voltage SET Leakage in Shutdown SET Current Range EN1 = EN2 = IN SET to LED_ Current Ratio (ILED/ISET) LED_ Current Accuracy LED_ Current Matching Maximum LED_ Sink Current LED_ Dropout Voltage LED_ Minimum Regulation Voltage (1.5x Mode) LED Leakage in Shutdown Maximum OUT Current Open-Loop OUT Resistance Switching Frequency EN1, EN2 Logic High Voltage EN1, EN2 Logic Low Voltage EN1, EN2 Input Current Thermal-Shutdown Threshold VIN = 2.7V to 5.5V VIN = 2.7V to 5.5V VEN_ = GND or 5.5V, TA = +25C 20C hysteresis 0.01 160 1.6 0.4 1 ISET = 60A EN1 = IN, EN2 = GND EN1 = GND, EN2 = IN EN1 = EN2 = IN, RSET = 10k, TA = 0C to +85C ISET = 60A, TA = 0C to +85C (Note 2) ISET = 130A, EN1 = EN2 = IN ISET = 87A (Note 3) EN1 = EN2 = IN, ISET = 87A EN1 = EN2 = GND, VLED = 5.5V, TA = +25C VIN 3.4V, VOUT 3.9V, EN1 = EN2 = IN 1x mode (1 x VIN - VOUT) / IOUT 1.5x mode (1.5 x VIN - VOUT) / IOUT 1 120 1.5 10 100 25.9 EN1 = EN2 = GND, TA = +25C 40 190 58 19.5 215 65 22 2.0 2.0 28 40 150 0.01 80 200 1 0.570 VIN rising or falling, 35mV hysteresis Switching, no load EN1 = EN2 = OUT = GND, TA = +25C CONDITIONS MIN 2.7 2.25 2.45 2 0.1 2.1 0.6 0.01 0.630 1 130 245 74 25.0 % % mA mV mV A mA MHz V V A C A/A TYP MAX 5.5 2.60 4 10 UNITS V V mA A ms V A A
Note 1: Specifications to -40C are guaranteed by design and not production tested. Note 2: LED_ current matching is defined as: (ILED - IAVG) / IAVG. Note 3: Dropout voltage is defined as the LED_ to GND voltage at which the LED_ current drops 10% from the value at VLED = 200mV.
2
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White LED 1x/1.5x Charge Pump in UCSP
Typical Operating Characteristics
(VIN = 3.6V, EN1 = EN2 = IN, CIN = C1 = C2 = COUT = 1F, RSET = 7.50k, TA = +25C, unless otherwise noted.)
EFFICIENCY (PLEDs/PBATT) vs. Li+ BATTERY DISCHARGE
MAX1573 toc01
MAX1573
EFFICIENCY (PLEDs/PBATT) vs. SUPPLY VOLTAGE
MAX1573 toc02
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1573 toc03
100
100 1/10 90 EFFICIENCY (%) 3/10 FULL
120 100 BATTERY CURRENT (mA) 80 60 40 3/10 20 0 1/10 3.0 3.2 3.4 3.6 3.8 4.0 FULL
90 EFFICIENCY (%)
FULL 3/10 1/10
80
80
70
70
60
60
50 4.2 3.9 3.8 3.7 3.6 3.5 3.4 3.0 Li+ BATTERY VOLTAGE, TIME-WEIGHTED (V)
50 3.0 3.2 3.4 3.6 3.8 4.0 4.2 SUPPLY VOLTAGE (V)
4.2
SUPPLY VOLTAGE (V)
INPUT RIPPLE vs. SUPPLY VOLTAGE
MAX1573 toc04
LED CURRENT vs. SUPPLY VOLTAGE
MAX1573 toc05
LED CURRENT vs. TEMPERATURE
17.4 17.3 LED CURRENT (mA) 17.2 17.1 17.0 16.9 16.8 16.7 16.6 16.5
MAX1573 toc06
9 8 INPUT RIPPLE (mVRMS) 7 6 5 4 3 2 1/10 1 0 3.0 3.2 3.4 3.6 3.8 4.0 3/10 FULL
20 19 18 LED CURRENT (mA) 17 16 15 14 13 12 11 10 LED3 LED1 LED4 LED2
17.5
4.2
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 TEMPERATURE (C)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
LED CURRENT vs. RSET
MAX1573 toc07
TYPICAL OPERATING WAVEFORMS IN 1x MODE
30 25 LED CURRENT (mA) 20 15 3/10 10 1/10 5 0 5 6 7 8 9 FULL
MAX1573 toc08
TYPICAL OPERATING WAVEFORMS IN 1.5x MODE
20mV/ div
MAX1573 toc09
3.6V Li+ BATTERY INPUT VIN
3.4V Li+ BATTERY INPUT VIN 20mV/ div
IIN
10mA/ div
IIN
10mA/ div
VOUT
20mV/ VOUT div
20mV/ div 500ns/div
10 11 12 13 14 15
500ns/div
RSET (k)
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3
White LED 1x/1.5x Charge Pump in UCSP MAX1573
Typical Operating Characteristics (continued)
(VIN = 3.6V, EN1 = EN2 = IN, CIN = C1 = C2 = COUT = 1F, RSET = 7.50k, TA = +25C, unless otherwise noted.)
STARTUP AND SHUTDOWN RESPONSE
MAX1573 toc10
DIMMING RESPONSE
MAX1573 toc11
VEN_
5V/ div
VENI1
2V/ div
IIN
50mA/ div
VOUT LED_ = 4 17mA EN1 = EN2 500s/div
2V/ div
IOUT EN2 = IN 5s/div
50mA/ div
Pin Description
PIN A1 A2 A3 A4 B1 B2 B4 C1 C3 C4 D1 D2 D3 D4 NAME C1P OUT EN1 EN2 C2N C2P SET IN LED4 LED2 C1N GND LED3 LED1 FUNCTION Transfer Capacitor 1 Positive Connection. See the Component Selection section for capacitor value. Output. Bypass to GND with a 1F ceramic capacitor. Connect to the anodes of all the LEDs. OUT is high impedance during shutdown. Enable, Dimming Control Input 1. EN1 and EN2 control shutdown and the LED current. See Table 1. Enable, Dimming Control Input 2. EN1 and EN2 control shutdown and the LED current. See Table 1. Transfer Capacitor 2 Negative Connection. See the Component Selection section for capacitor value. Transfer Capacitor 2 Positive Connection. See the Component Selection section for capacitor value. Bias-Current Set Input. Connect a resistor from SET to GND to set the LED bias current (ISET). ISET = 600mV/RSET. Supply Voltage Input. IN supplies power for the IC. Bypass IN to GND with a 1F ceramic capacitor. LED4 Cathode Connection and Charge-Pump Feedback. The charge pump regulates to the lowest voltage on any of the LED_ inputs. Connect LED4 to the cathode of one output LED. Connect LED4 to IN if this LED is not populated. LED2 Cathode Connection and Charge-Pump Feedback. The charge pump regulates to the lowest voltage on any of the LED_ inputs. Connect LED2 to the cathode of one output LED. Connect LED2 to IN if this LED is not populated. Transfer Capacitor 1 Negative Connection. See the Component Selection section for capacitor value. Ground LED3 Cathode Connection and Charge-Pump Feedback. The charge pump regulates to the lowest voltage on any of the LED_ inputs. Connect LED3 to the cathode of one output LED. Connect LED3 to IN if this LED is not populated. LED1 Cathode Connection and Charge-Pump Feedback. The charge pump regulates to the lowest voltage on any of the LED_ inputs. Connect LED1 to the cathode of one output LED. Connect LED1 to IN if this LED is not populated.
4
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White LED 1x/1.5x Charge Pump in UCSP
Block Diagram
C1P C1N IN C2P C2N OUT
Output Regulation
The MAX1573 operates in 1x mode until just above dropout. Then the MAX1573 switches to 1.5x chargepump mode to regulate the lowest of LED1-LED4 to 150mV 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.
MAX1573
1x/1.5x REGULATED CHARGE PUMP
EN1
0.15V BRIGHTNESS CONTROL 0.6V MINIMUM SELECT P P
1.25V
EN2
Soft-Start
LDO CURRENT REGULATOR LED1
N LDO CURRENT REGULATOR LED2
SET
LDO CURRENT REGULATOR
LED3
MAX1573
LDO CURRENT REGULATOR LED4
The MAX1573 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 DACramped 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 the lowest of LED1-LED4 reaches regulation. If an overload condition occurs, soft-start repeats every 2.1ms. If the output is shorted to ground, the output current is limited by the MAX1573 fractional-switching technique.
GND
True Shutdown Mode
When EN1 and EN2 are grounded, the MAX1573 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.
Detailed Description
The MAX1573 is a complete charge-pump buck-boost converter requiring only four small ceramic capacitors. The MAX1573 utilizes a proprietary 1x/1.5x fractional charge-pump topology to drive up to four white LEDs with regulated constant current for uniform intensity. The MAX1573 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 MAX1573 includes a thermal-limit circuit that shuts down the IC at about +160C. Turn-on occurs after the IC cools by approximately 20C.
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5
White LED 1x/1.5x Charge Pump in UCSP MAX1573
Setting the Output Current
SET controls the LED bias current. Current flowing into LED1, LED2, LED3, and LED4 is a multiple of the current flowing out of SET. Set the output current as follows: 0.6V ILED _ = K x RSET where K = 22, 65, or 215 (depending upon EN1 and EN2, see Table 1), and RSET is the resistor connected between SET and GND (see the Typical Operating Circuit). 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 50kHz (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 18.7mA/LED, while a 100% PWM duty cycle corresponds to 0mA/LED. At PWM frequencies above 5kHz, C3 may be reduced.
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 always has very low input ripple.
Applications Information
Dimming Using EN1 and EN2
Use EN1 and EN2 inputs as a digital 2-bit number to control on/off, 1/10, 3/10, and full current (see Table 1). RSET programs the full current level (see the Setting the Output Current section).
Dimming Using PWM into EN1
Use EN2 for shutdown and drive EN1 with a PWM signal. Current can be varied from 1/10 to full. The waveforms in the Typical Operating Characteristics show the
PC Board Layout and Routing
The MAX1573 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 MAX1573 as possible. Also, place their ground pads close together and as close as possible to GND. See the MAX1573 EV kit for an example.
Table 1. EN1/EN2 States
EN1/EN2 STATES EN1 = low, EN2 = low EN1 = low, EN2 = high EN1 = high, EN2 = low EN1 = high, EN2 = high BRIGHTNESS Shutdown 1/10 Brightness 3/10 Brightness Full Brightness LED CURRENT ILED = 0 ILED = 22 x ISET ILED = 65 x ISET ILED = 215 x ISET
Component Selection
Use ceramic capacitors with an X5R dielectric or better temperature coefficient. The transfer capacitors may be reduced in value if the input voltage does not fall below 3.4V, if only two or three LEDs are used, or if four LEDs
1F
1F
1F
1F
C1P C1N VIN 1F IN
C2P C2N OUT VIN 1F 1F IN
C1P C1N
C2P C2N OUT 1F 0 TO 18.7mA/LED
MAX1573
EN2 PWM INPUT EN1 SET RSET GND LED1 LED2 LED3 LED4 PWM INPUT 0 TO 2.5V R1 14.3k C3 1F R2 14.3k RSET 9.09k EN1 EN2 SET
MAX1573
LED1 LED2 LED3 LED4 GND
Figure 1. Dimming Using PWM Signal into EN1 6
Figure 2. Dimming Using Filtered PWM Signal
_______________________________________________________________________________________
White LED 1x/1.5x Charge Pump in UCSP
1F 1F
C1P C1N 1 VIN 2.2F IN
C2P C2N OUT 1F
2.2F
EN1 EN2 SET RSET
MAX1573
LED1 LED2 LED3 LED4
are used at 10mA or less. Some typical external component values are shown in Table 2. Under normal operating conditions, power dissipation is low. Maximum power dissipation occurs at an input voltage of 4.2V and all four LEDs (with VF = 4V) are driven with 30mA per LED. The power is calculated as: PD = [(1.5 x VIN) - VF] x 120mA = 276mW At higher input voltages, the MAX1573 switches to 1x mode and power dissipation decreases.
MAX1573
GND
Figure 3. C-R-C Filter Reduces Input Ripple
Table 2. Typical Component Values
COMPONENT Input/Output Capacitors Transfer Capacitors LED RSET VALUE (F) 1 1 0.47 0.22 -- As required MANUFACTURER Taiyo Yuden Taiyo Yuden Taiyo Yuden Taiyo Yuden Nichia Panasonic PART JMK107BJ105KA JMK107BJ105KA LMK107BJ474KA LMK107BJ224KA NSCW215T -- DESCRIPTION 1F 10%, 6.3V X5R ceramic capacitor (0603) 1F 10%, 6.3V X5R ceramic capacitor (0603) 0.47F 10%, 10V X5R ceramic capacitor (0603) 0.22F 10%, 10V X7R ceramic capacitor (0603) White LEDs 1% resistor (0603)
Chip Information
TRANSISTOR COUNT: 3655 PROCESS: BiCMOS
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7
White LED 1x/1.5x Charge Pump in UCSP MAX1573
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.
16L,UCSP.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.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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