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19-2290; Rev 1; 7/02
1.5x/2x High-Efficiency White LED Charge Pumps
General Description
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 MAX package.
Features
o High-Efficiency 1.5x/2x Charge Pumps o Low Input Ripple with 750kHz Operation o 200mV Current-Sense Threshold Reduces Power Loss o Current- or Voltage-Regulated Charge Pump o Up to 120mA Output Current o No Inductors Required o Small Ceramic Capacitors o Regulated 5% LED Current o Load Disconnected in Shutdown o 1A Shutdown Current o Small 10-Pin MAX Package
MAX1910/MAX1912
Applications
White LED Backlighting Cellular Phones PDAs Digital Still Cameras MP3 Players Backup-Battery Boost Converters
PART MAX1910EUB MAX1912EUB
Ordering Information
TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 10 MAX 10 MAX
Typical Operating Circuit
TOP VIEW
VIN IN1 C1+ C1 CIN C1C2+ C2 C2GND IN2 SHDN OUT
Pin Configuration
GND 1 IN1 C22 3 4 5
10 SET 9 C1IN2 C2+ SHDN
MAX1910 MAX1912
8 7 6
MAX1910 MAX1912
SET
COUT
C1+ OUT
MAX
________________________________________________________________ Maxim Integrated Products
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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.
1.5x/2x High-Efficiency White LED Charge Pumps MAX1910/MAX1912
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 = +70C) 10-Pin MAX (derate 5.6 mW/C above +70C) ..........444mW Operating Temperature Range ...........................-40C to +85C 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 = 0, SHDN = SET = IN, CIN = 2.2F, C1 = C2 = 0.47F, COUT = 2.2F, TA = 0C to +85C. Typical values are at TA = +25C, unless otherwise noted.)
PARAMETER Input Voltage Operating Range Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis SET Regulation Point MAX1910 Current Regulation MAX1912 Current Regulation Maximum Output Current No Load Input Current Supply Current in Shutdown Output Leakage Current in Shutdown Switching Frequency Switching Frequency Temperature Coefficient SET Input Current SHDN Input Current SHDN Input Voltage Low SHDN Input Voltage High Thermal-Shutdown Threshold SHDN = 0 or 5.5V 2.7V < VIN < 5.3V 2.7V < VIN < 5.3V Rising temperature, 15C hysteresis typical 1.6 160 Output current change for 2.7V < VOUT < 5V Output current change for 3V < VOUT < 5V MAX1910 VIN = 2.7V MAX1912 VIN = 3.6V VIN = 3.6V VIN = 5.3V, VOUT = 0, SHDN = 0 VIN = 3.6V, SHDN = 0 VIN = 3.6V f = 750kHz 625 80 120 1.5 0.1 0.1 750 250 1 100 1 0.4 2.5 10 10 875 0.19 Both rising and falling edges CONDITIONS MIN 2.7 2.2 35 0.2 0.5 0.5 0.21 TYP MAX 5.3 2.5 UNITS V V mV V %/V %/V mA mA A A kHz ppm/C nA A V V C
ELECTRICAL CHARACTERISTICS
(VIN = 3.6V, GND = 0, SHDN = SET = IN, CIN = 2.2F, C1 = C2 = 0.47F, COUT = 2.2F, TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER Input Voltage Operating Range Undervoltage Lockout Threshold Maximum Output Current Supply Current in Shutdown Both rising and falling edges MAX1910 VIN = 2.7V MAX1910 VIN = 3.6V VIN = 5.3V, VOUT = 0, SHDN = 0 CONDITIONS MIN 2.7 2.2 80 120 10 MAX 5.3 2.5 UNITS V V mA A
2
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1.5x/2x High-Efficiency White LED Charge Pumps
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 3.6V, GND = 0, SHDN = SET = IN, CIN = 2.2F, C1 = C2 = 0.47F, COUT = 2.2F, TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER Output Leakage Current in Shutdown SET Regulation Point SET Input Current SHDN Input Current SHDN Input Voltage Low SHDN Input Voltage High SHDN = 0 or 5.5V 2.7V < VIN < 5.3V 2.7V < VIN < 5.3V 1.6 CONDITIONS VIN = 3.6V, SHDN = 0 0.19 MIN MAX 10 0.21 100 1 0.4 UNITS A V nA A V V
MAX1910/MAX1912
Note 1: Limits to -40C are guaranteed by design, not production tested.
Typical Operating Characteristics
(Circuit of Figure 2, VIN = 3.3V, TA = +25C, unless otherwise noted.)
INPUT AND OUTPUT VOLTAGE RIPPLE
MAX1910/12 toc01
INPUT AND OUTPUT VOLTAGE RIPPLE
MAX1910/12 toc02
START-UP INPUT CURRENT AND OUTPUT VOLTAGE
MAX1910/12 toc03
5V/div VSHDN 1V/div
VIN CIRCUIT OF FIGURE 7 DRIVING 4 LEDS (60mA)
VIN 20mV/div
20mV/div VOUT 50mA/div
VOUT
VOUT VIN IOUT = 60mA 1s/div 1s/div
QUIESCENT CURRENT vs. INPUT VOLTAGE
MAX1910/12 toc04
LED CURRENT vs. INPUT VOLTAGE
MAX1910/12 toc05
INTENSITY CHANGE STEP RESPONSE
MAX1910/12 toc06
4.0 3.5 QUIESCENT CURRENT (mA) 3.0 2.5 2.0 1.5 1.0 0.5 0 0
140 120 LED CURRENT (mA) 100 80
VLOGIC
2V/div
VSET 60 40 20 IOUT 0 CIRCUIT OF FIGURE 9
100mV/div
60mA 20mA 40s/div
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
INPUT VOLTAGE (V)
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1.5x/2x High-Efficiency White LED Charge Pumps MAX1910/MAX1912
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN = 3.3V, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. INPUT VOLTAGE
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 2.7 3.0 3.3 3.6 3.9 4.2 4.5 INPUT VOLTAGE (V) CIRCUIT OF FIGURE 2 MAX1910 4 WHITE LEDs IOUT = 60mA
MAX1910/12 toc07
INPUT CURRENT vs. INPUT VOLTAGE DRIVING 4 LEDS
MAX1910/12 toc08
100
140 120 100 CURRENT (mA) 80 60 40 20 0 2.7 3.0 3.3 3.6 3.9 4.2 CIRCUIT OF FIGURE 2 MAX1910 ILOAD = 60mA
4.5
INPUT VOLTAGE (V)
Pin Description
PIN 1 2 3 4 5 6 7 8 9 10 NAME GND IN1 C2C1+ OUT SHDN C2+ IN2 C1SET Ground Supply Voltage Input. Connect to IN2. Bypass to GND with a 2.2F ceramic capacitor. Transfer Capacitor 2 Connection, Negative Side Transfer Capacitor 1 Connection, Positive Side Output. Bypass to GND with a 2.2F 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. Transfer Capacitor 2 Connection, Positive Side Supply Voltage Input. Connect to IN1. Transfer Capacitor 1 Connection, Negative Side 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. FUNCTION
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
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"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
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1.5x/2x High-Efficiency White LED Charge Pumps
charge-pump topologies because the charge transferred per cycle is only the amount required to supply the output load. 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.
MAX1910/MAX1912
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.
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 20k, 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 0.47F for the transfer capacitors, 2.2F to 10F for the input capacitor, and 2.2F to 4.7F 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 10F input capacitor and a 4.7F 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 1 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 10F-1-10F, input ripple is less than 1mV when driving a 60mA load.
Shutdown Mode
When driven low, SHDN turns off the charge pump. This reduces the quiescent current to approximately 0.1A. 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 +160C. Normal operation continues after the die cools by 15C. 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
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1.5x/2x High-Efficiency White LED Charge Pumps MAX1910/MAX1912
Applications Information
Adjusting LED Intensity
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 (VDAC - 0.2) x RB RL RL x RA The total LED current is determined by: IL = 0.2 (VLOGIC - 0.2) x RB RL RL x 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.
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.
Chip Information
TRANSISTOR COUNT: 2497 PROCESS: BiCMOS
IN
SW1
SW4
SW2
SW5
SW7 (REGULATING SWITCH)
SW6
SW3
GND
OUT
C1-
C1+
C2-
C2+
MODE 1.5x 1.5x 2x 2x
PHASE Charging Transfer Charging Transfer
SW1 OFF ON OFF ON
SW2 ON OFF OFF OFF
SW3 OFF ON ON ON
SW4 OFF ON ON ON
SW5 ON OFF ON OFF
SW6 OFF ON OFF ON
SW7 ON OFF ON OFF
Figure 1. Functional Charge-Pump Switch Diagram (Switches Shown for 1.5x Charging Phase) 6 _______________________________________________________________________________________
1.5x/2x High-Efficiency White LED Charge Pumps MAX1910/MAX1912
1 VIN IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2GND 15 15 15 15 IN2 SHDN OUT
MAX1910 MAX1912
SET
2.2F
Figure 2. LED Biasing with the MAX1912
1 VIN IN1 C1+ 0.47F 2.2 F C1C2+ 0.47F C2GND SET 1k 1k IN2 SHDN OUT
MAX1910 MAX1912
2.2F
1k
10
10
10
Figure 3. The MAX1912 Regulating Average Current Through LEDs
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1.5x/2x High-Efficiency White LED Charge Pumps MAX1910/MAX1912
1 VIN IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2-
IN2
SHDN OUT
MAX1910 MAX1912
SET GND
2.2F 15 30 30 30
15
Figure 4. Alternate Method of Biasing to Improve LED-to-LED Matching
1 VIN IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2GND R5 3.3 IN2 SHDN OUT
MAX1910 MAX1912
SET
2.2F
2-PIN CONNECTOR R1 15 R2 15 R3 15 R4 15
Figure 5. Alternate Method of Biasing LEDs Controls Total Current; Suitable When the LED Array Must Be Biased with Only Two Connections
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1.5x/2x High-Efficiency White LED Charge Pumps MAX1910/MAX1912
1 VIN IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2GND R2
IN2
SHDN OUT VOUT
MAX1910 MAX1912
SET
2.2F
R1
Figure 6. Output Voltage Set with a Resistor-Divider
1 VIN IN1 C1+ 0.47F 2.2F 2.2F C1C2+ 0.47F C2-
IN2
SHDN OUT
MAX1910 MAX1912
SET GND
2.2F
10
10
10
Figure 7. C-R-C Filter Reduces Ripple On the Input
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1.5x/2x High-Efficiency White LED Charge Pumps MAX1910/MAX1912
1 IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2GND SET RB 1.58k RL 4.7
VIN
IN2
SHDN OUT
MAX1910 MAX1912
2.2F 15 15 15 15
3.3V MAX5380 (2-WIRE INPUT) MAX5383 (3-WIRE INPUT) VDD SERIAL INPUT GND OUT
RA 22.1k
HIGH DAC OUTPUT (2V) = 15mA LED CURRENT LOW DAC OUTPUT (0V) = 45mA LED CURRENT
Figure 8. Circuit with SOT DAC for Intensity Control
VIN
1 IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2-
IN2
SHDN OUT
MAX1910 MAX1912
SET GND
2.2F
RB RL
RA DIMMING INPUT (0V OR VLOGIC)
Figure 9. Using Digital Logic Input for Intensity Control
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1.5x/2x High-Efficiency White LED Charge Pumps
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.)
10LUMAX.EPS
MAX1910/MAX1912
e
10
4X S
10
INCHES MAX DIM MIN 0.043 A 0.006 A1 0.002 A2 0.030 0.037 0.120 D1 0.116 0.118 0.114 D2 0.116 0.120 E1 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 0 6
MILLIMETERS MAX MIN 1.10 0.15 0.05 0.75 0.95 3.05 2.95 3.00 2.89 3.05 2.95 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
H y 0.500.1 0.60.1
1
1
0.60.1
TOP VIEW
BOTTOM VIEW
D2 GAGE PLANE A2 A b D1 A1
E2 c E1 L1
L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, 10L uMAX/uSOP
APPROVAL DOCUMENT CONTROL NO. REV.
21-0061
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 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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