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19-2290; Rev 0; 1/02
60mA 1.5x High-Efficiency White LED Charge Pumps
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. 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 o High-Efficiency 1.5x 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 60mA Output Current o No Inductors Required o Small Ceramic Capacitors o Regulated 3% Output Voltage o Load Disconnected in Shutdown o 1A Shutdown Current o Small 10-Pin MAX Package
Features
MAX1912/MAX1913
Applications
Backlight White LED Biasing Cellular Phones PDAs Digital Still Cameras MP3 Players Backup-Battery Boost Converters
PART MAX1912EUB MAX1913EUB50* PART MAX1912EUB MAX1913EUB50*
Ordering Information
TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 10 MAX 10 MAX
*Future product--contact factory for availability.
Selector Guide
MODE 1.5x 1.5x VSET 200mV 1.25V VOUT Adjustable Current 5.0V or Adjustable
Typical Operating Circuit
*Future product--contact factory for availability.
Pin Configuration
VIN IN1 C1+ C1 CIN C1C2+ C2 C2GND IN2 SHDN OUT
TOP VIEW
COUT
MAX1912
SET
GND 1 IN1 C2C1+ OUT 2 3 4 5
10 SET 9 C1IN2 C2+ SHDN
MAX1912/ MAX1913
8 7 6
10-PIN MAX
________________________________________________________________ Maxim Integrated Products
1
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60mA 1.5x High-Efficiency White LED Charge Pumps MAX1912/MAX1913
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 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 MAX1912 SET Regulation Point 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 VIN = 3.6V VIN = 5.3V, VOUT = 0, SHDN = 0 VIN = 3.6V, SHDN = 0 VIN = 3.6V f = 750kHz 625 0 < ILOAD < 60mA Output current change for 3V < VOUT < 5V 60 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 0.21 TYP MAX 5.3 2.5 UNITS V V mV 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 VIN = 5.3V, VOUT = 0, SHDN = 0 Both rising and falling edges CONDITIONS MIN 2.7 2.2 60 10 MAX 5.3 2.5 UNITS V V mA A
2
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60mA 1.5x 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 MAX1912 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 < ILOAD < 60mA 0.19 MIN MAX 10 0.21 100 1 0.4 UNITS A V nA A V V
MAX1912/MAX1913
Note 1: Limits to -40C are guaranteed by design, not production tested.
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
INPUT AND OUTPUT VOLTAGE RIPPLE
MAX1912/13 toc01
INPUT AND OUTPUT VOLTAGE RIPPLE WITH ADDITIONAL INPUT FILTER
MAX1912/13 toc02
QUIESCENT CURRENT vs. INPUT VOLTAGE
MAX19112/13 toc03
4
3 IIN (mA)
VIN1 20mV/div VOUT
VIN 20mV/div
2
VOUT
1
1s/div CIN = 10F, COUT = 4.7F MAX1912 DRIVING 4 LEDS (60mA) VIN = 3.3V
1s.div MAX1912 DRIVING 4 LEDS (60mA) 10F - 1 - 10F INPUT FILTER, COUT = 4.7F VIN = 3.3V
0 0 1 2 3 VIN (V) 4 5 6
STARTUP INPUT CURRENT AND OUTPUT VOLTAGE
MAX1912/13 toc04
INTENSITY CHANGE STEP RESPONSE
MAX1912/13 toc05
VSHDN
5V/div VLOGIC 2V/div
VOUT
1V/div
VSET
100mV/div 45mA
IIN 1ms/div CIRCUIT OF FIGURE 2 R1 = R2 = R3 = 15 CIN = 10F, COUT = 2.2F VIN = 3.3V
50mA/div
ILED 50s/div CIRCUIT OF FIGURE 10 RA = 22k, RB = 1.5k, RL = 4.7 CIN = 10F, COUT = 4.7F VLOGIC(HIGH) = 2V
15mA
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60mA 1.5x High-Efficiency White LED Charge Pumps MAX1912/MAX1913
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 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. FUNCTION
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.
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 0.1A. The output is high impedance in shutdown. Drive SHDN high or connect to IN for normal operation.
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.
Thermal Shutdown
The MAX1912/MAX1913 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.
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.
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
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60mA 1.5x High-Efficiency White LED Charge Pumps
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. 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.
MAX1912/MAX1913
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) x RB - RL RL x RA
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 50k, 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.
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) x RB - RL RL x RA
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 2-10) 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
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60mA 1.5x High-Efficiency White LED Charge Pumps MAX1912/MAX1913
IN
SW1
SW4
SW2
SW5
SW7 (REGULATING SWITCH)
SW6
SW3
GND
OUT
C1-
C1+
C2-
C2+
MODE 1.5x
PHASE Charging
SW1 OFF
SW2 ON
SW3 OFF
SW4 OFF
SW5 ON OFF
SW6 OFF ON
SW7 ON OFF
1.5x Transfer ON OFF ON ON Figure 1. Functional Charge-Pump Switch Diagram (Switches Shown for Charging Phase)
1 VIN IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2-
IN2
SHDN OUT
MAX1912
SET GND
2.2F
10
10
10
Figure 2. LED Biasing with the MAX1912
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60mA 1.5x High-Efficiency White LED Charge Pumps MAX1912/MAX1913
1 VIN IN1 C1+ 0.47F 2.2 F C1C2+ 0.47F C2GND SET 1k 1k IN2 SHDN OUT
MAX1912
2.2F
1k
10
10
10
Figure 3. The MAX1912 Regulating Average Current Through LEDs
1 VIN IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2-
IN2
SHDN OUT
MAX1912
2.2F 15 SET 25 25
GND
10
Figure 4. Alternate Method of Biasing to Improve LED-to-LED Matching
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60mA 1.5x High-Efficiency White LED Charge Pumps MAX1912/MAX1913
1 VIN IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2GND R4 3.3 IN2 SHDN OUT
MAX1912
SET
2.2F
2-PIN CONNECTOR R1 10 R2 10 R3 10
Figure 5. Alternate Method of Biasing LEDs Controls Total Current; Suitable When the LED Array Must Be Biased with Only Two Connections
1 VIN IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2-
IN2
SHDN OUT VOUT
MAX1913
SET GND
2.2F
R1
R2
Figure 6. Output Voltage Set with a Resistor-Divider
8
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60mA 1.5x High-Efficiency White LED Charge Pumps MAX1912/MAX1913
VIN
1 IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2-
IN2
SHDN VIN OUT VOUT
1 IN1 C1+
IN2
SHDN OUT VOUT
MAX1913
SET
2.2F
10F
10F
0.47F C1C2+ 0.47F C2-
MAX1913
SET GND
2.2F
GND
Figure 7. Output Voltage Internally Set to 5V
Figure 8. C-R-C Filter Reduces Ripple On the Input
VIN
1 IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2-
IN2
SHDN OUT
MAX1912
2.2F 10 SET 10 10
GND
RB 1.58k
RL 4.7
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 9. Circuit with SOT DAC for Intensity Control
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9
60mA 1.5x High-Efficiency White LED Charge Pumps MAX1912/MAX1913
VIN
1 IN1 C1+ 0.47F 2.2F C1C2+ 0.47F C2-
IN2
SHDN OUT
MAX1912
2.2F
SET GND RB RL
RA DIMMING INPUT (0V OR VLOGIC)
Figure 10. Using Digital Logic Input for Intensity Control
10
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60mA 1.5x High-Efficiency White LED Charge Pumps
Package Information
10LUMAX.EPS
MAX1912/MAX1913
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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