For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim's website at www.maxim-ic.com.
General Description
The MAX1910/MAX1912 power LEDs with a regulated
output voltage or current (up to 120mA) from an unreg-
ulated 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 regula-
tion 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 µMAX package.
Applications
White LED Backlighting
Cellular Phones
PDAs
Digital Still Cameras
MP3 Players
Backup-Battery Boost Converters
Features
♦High-Efficiency 1.5x/2x Charge Pumps
♦Low Input Ripple with 750kHz Operation
♦200mV Current-Sense Threshold Reduces
Power Loss
♦Current- or Voltage-Regulated Charge Pump
♦Up to 120mA Output Current
♦No Inductors Required
♦Small Ceramic Capacitors
♦Regulated ±5% LED Current
♦Load Disconnected in Shutdown
♦1µA Shutdown Current
♦Small 10-Pin µMAX Package
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
1
2
3
4
5
10
9
8
7
6
SET
C1-
IN2
C2+C1+
C2-
IN1
GND
MAX1910
MAX1912
μMAX
TOP VIEW
OUT SHDN
Pin Configuration
19-2290; Rev 2; 3/04
PART TEMP RANGE PIN-PACKAGE
MAX1910EUB -40°C to +85°C 10 µMAX
MAX1912EUB -40°C to +85°C 10 µMAX
VIN
CIN
C1
C2
COUT
IN1 IN2
C1+
C1-
C2+
C2- GND
SET
OUT
SHDN
MAX1910
MAX1912
Typical Operating Circuit
EVALUATION KIT
AVAILABLE
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = 3.6V, GND = 0, SHDN = SET = IN, CIN = 2.2µF, C1 = C2 = 0.47µF, COUT = 2.2µF, TA= 0°C to +85°C. Typical values are at
TA= +25°C, unless otherwise noted.)
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.
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= +70°C)
10-Pin µMAX (derate 5.6 mW/°C above +70°C) ..........444mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) ................................ +300°C
PARAMETER CONDITIONS
MIN TYP MAX UNITS
Input Voltage Operating Range 2.7 5.3 V
Undervoltage Lockout Threshold Both rising and falling edges 2.2 2.5 V
Undervoltage Lockout Hysteresis 35 mV
SET Regulation Point
0.19
0.2
0.21
V
MAX1910 Current Regulation Output current change for 2.7V < VOUT < 5V 0.5
%/V
MAX1912 Current Regulation Output current change for 3V < VOUT < 5V 0.5
%/V
MAX1910 VIN = 2.7V 80
Maximum Output Current MAX1912 VIN = 3.6V
120
mA
No Load Input Current VIN = 3.6V 1.5 2.5 mA
Supply Current in Shutdown VIN = 5.3V, VOUT = 0, SHDN = 0 0.1 10 µA
Output Leakage Current in Shutdown
VIN = 3.6V, SHDN = 0 0.1 10 µA
Switching Frequency VIN = 3.6V
625 750 875
kHz
Switching Frequency Temperature
Coefficient f = 750kHz
250 ppm/°C
SET Input Current 1
100
nA
SHDN Input Current SHDN = 0 or 5.5V 1 µA
SHDN Input Voltage Low 2.7V < VIN < 5.3V 0.4 V
SHDN Input Voltage High 2.7V < VIN < 5.3V 1.6 V
Thermal-Shutdown Threshold Rising temperature, 15°C hysteresis typical
160
°C
ELECTRICAL CHARACTERISTICS
(VIN = 3.6V, GND = 0, SHDN = SET = IN, CIN = 2.2µF, C1 = C2 = 0.47µF, COUT = 2.2µF, TA= -40°C to +85°C, unless otherwise
noted.) (Note 1)
PARAMETER CONDITIONS MIN MAX
UNITS
Input Voltage Operating Range 2.7 5.3 V
Undervoltage Lockout Threshold Both rising and falling edges 2.2 2.5 V
MAX1910 VIN = 2.7V 80
Maximum Output Current MAX1910 VIN = 3.6V 120 mA
Supply Current in Shutdown VIN = 5.3V, VOUT = 0, SHDN = 0 10 µA
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 3.6V, GND = 0, SHDN = SET = IN, CIN = 2.2µF, C1 = C2 = 0.47µF, COUT = 2.2µF, TA= -40°C to +85°C, unless otherwise
noted.) (Note 1)
PARAMETER CONDITIONS MIN MAX
UNITS
Output Leakage Current in Shutdown VIN = 3.6V, SHDN = 0 10 µA
SET Regulation Point 0.19 0.21 V
SET Input Current 100 nA
SHDN Input Current SHDN = 0 or 5.5V 1 µA
SHDN Input Voltage Low 2.7V < VIN < 5.3V 0.4 V
SHDN Input Voltage High 2.7V < VIN < 5.3V 1.6 V
Note 1: Limits to -40°C are guaranteed by design, not production tested.
Typical Operating Characteristics
(Circuit of Figure 2, VIN = 3.3V, TA = +25°C, unless otherwise noted.)
INPUT AND OUTPUT VOLTAGE RIPPLE
MAX1910/12 toc01
1μs/div
VIN
VOUT
20mV/div
IOUT = 60mA
START-UP INPUT CURRENT AND
OUTPUT VOLTAGE
MAX1910/12 toc03
IIN
1ms/div
VOUT
2V/div
50mA/div
5V/div
VSHDN
QUIESCENT CURRENT vs. INPUT VOLTAGE
MAX1910/12 toc04
INPUT VOLTAGE (V)
QUIESCENT CURRENT (mA)
4.03.50.5 1.0 1.5 2.52.0 3.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
04.5
LED CURRENT vs. INPUT VOLTAGE
MAX1910/12 toc05
INPUT VOLTAGE (V)
LED CURRENT (mA)
4.23.93.63.33.0
20
40
60
80
100
120
140
0
2.7 4.5
INTENSITY CHANGE STEP RESPONSE
MAX1910/12 toc06
40μs/div
VLOGIC
IOUT
VSET
2V/div
100mV/div
60mA
20mA
CIRCUIT OF FIGURE 9
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
4 _______________________________________________________________________________________
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
“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 dou-
bler. C2 is not used in doubler mode. The device transi-
tions 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 charge-
pump mode.
Output Regulation
The output is regulated by controlling the rate at which
the transfer capacitors are charged. The switching fre-
quency 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
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN = 3.3V, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. INPUT VOLTAGE
MAX1910/12 toc07
INPUT VOLTAGE (V)
EFFICIENCY (%)
4.23.93.63.33.0
10
20
30
40
50
60
70
80
90
100
0
2.7 4.5
CIRCUIT OF FIGURE 2
MAX1910 4 WHITE LEDs
IOUT = 60mA
Pin Description
PIN NAME FUNCTION
1 GND Ground
2 IN1 Supply Voltage Input. Connect to IN2. Bypass to GND with a 2.2µF ceramic capacitor.
3 C2- Transfer Capacitor 2 Connection, Negative Side
4 C1+ Transfer Capacitor 1 Connection, Positive Side
5 OUT Output. Bypass to GND with a 2.2µF ceramic capacitor.
6SHDN 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.
7 C2+ Transfer Capacitor 2 Connection, Positive Side
8 IN2 Supply Voltage Input. Connect to IN1.
9 C1- Transfer Capacitor 1 Connection, Negative Side
10 SET 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.
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
_______________________________________________________________________________________ 5
charge-pump topologies because the charge trans-
ferred per cycle is only the amount required to supply
the output load.
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 volt-
age 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 cur-
rent 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 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
0.1µA. 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 tem-
perature reaches +160°C. Normal operation continues
after the die cools by 15°C. 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 regu-
lates 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 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 paral-
lel 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.
Setting Output Voltage
The MAX1910 has a SET voltage threshold of 0.2V.
Output voltage can be set by connecting a resistor volt-
age-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 20kΩ, then solve
for R1 using the following equation:
Capacitor Selection
Use low-ESR ceramic capacitors. Recommended values
are 0.47µF for the transfer capacitors, 2.2µF to 10µF for
the input capacitor, and 2.2µF to 4.7µF for the output
capacitor. To ensure stability over a wide temperature
range, ceramic capacitors with an X7R dielectric are rec-
ommended. 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 10µF input capacitor and a 4.7µF 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 1Ωresistor (as shown in
Figures 2–9) improves stability when operating from low-
impedance 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 fil-
ter to the input further reduces ripple. Figure 7 shows a C-
R-C filter used to reduce input ripple. With 10µF-1Ω-10µF,
input ripple is less than 1mV when driving a 60mA load.
RR VOUT
1202 1=⎛
⎝
⎜⎞
⎠
⎟
.-
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
6 _______________________________________________________________________________________
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. RLcan be initially estimated from the
maximum load current:
RL≈0.2/IL(MAX)
Use this as a starting point to calculate RAand RBfrom
the formula below. The total LED current, IL, at different
DAC output voltages is determined by:
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.
The total LED current is determined by:
PC Board Layout
The MAX1910/MAX1912 are high-frequency switched-
capacitor voltage regulators. For best circuit perfor-
mance, 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: 2497
PROCESS: BiCMOS
IR
VR
RR
LL
LOGIC B
LA
=×
×
02 02.( .)
--
IR
VR
RR
LL
DAC B
LA
=×
×
02 02.( .)
--
IN
GND
SW1
SW7
(REGULATING
SWITCH)
SW6
SW5
SW4 SW2
SW3
OUT
C1- C1+ C2- C2+
MODE PHASE SW1 SW2 SW3 SW4 SW5 SW6 SW7
1.5x Charging OFF ON OFF OFF ON OFF ON
1.5x Transfer ON OFF ON ON OFF ON OFF
2x Charging OFF OFF ON ON ON OFF ON
2x Transfer ON OFF ON ON OFF ON OFF
Figure 1. Functional Charge-Pump Switch Diagram (Switches Shown for 1.5x Charging Phase)
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
_______________________________________________________________________________________ 7
1Ω
VIN
2.2 μF
0.47μF
0.47μF
2.2μF
IN1 IN2
C1+
C1-
C2+
C2- GND
SET
OUT
SHDN
MAX1910
MAX1912
10Ω10Ω10Ω
1kΩ
1kΩ
1kΩ
Figure 3. The MAX1912 Regulating Average Current Through LEDs
VIN
2.2μF
1Ω
0.47μF
0.47μF
2.2μF
IN1 IN2
C1+
C1-
C2+
C2- GND
SET
OUT
SHDN
MAX1910
MAX1912
15Ω15Ω15Ω15Ω
Figure 2. LED Biasing with the MAX1912
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
8 _______________________________________________________________________________________
1Ω
VIN
2.2μF
0.47μF
0.47μF
2.2μF
IN1 IN2
C1+
C1-
C2+
C2- GND
SET
2-PIN
CONNECTOR
OUT
SHDN
MAX1910
MAX1912
R1
15Ω
R5
3.3Ω
R2
15Ω
R3
15Ω
R4
15Ω
Figure 5. Alternate Method of Biasing LEDs Controls Total Current; Suitable When the LED Array Must Be Biased with Only Two
Connections
VIN
2.2μF
1Ω
0.47μF
0.47μF
2.2μF
IN1 IN2
C1+
C1-
C2+
C2- GND
SET
OUT
SHDN
MAX1910
MAX1912
15Ω
15Ω30Ω30Ω30Ω
Figure 4. Alternate Method of Biasing to Improve LED-to-LED Matching
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
_______________________________________________________________________________________ 9
VIN
2.2μF2.2μF
1Ω
0.47μF
0.47μF
2.2μF
IN1 IN2
C1+
C1-
C2+
C2- GND
SET
OUT
SHDN
MAX1910
MAX1912
10Ω10Ω10Ω
Figure 7. C-R-C Filter Reduces Ripple On the Input
VIN
1Ω
2.2μF
0.47μF
0.47μF
2.2μF
IN1 IN2
C1+
C1-
C2+
C2- GND
SET
OUT
SHDN
MAX1910
MAX1912
R2
R1
VOUT
Figure 6. Output Voltage Set with a Resistor-Divider
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
10 ______________________________________________________________________________________
VIN
2.2μF
0.47μF
0.47μF
2.2μF
IN1 IN2
C1+
C1-
C2+
C2- GND
SET
OUT
SHDN
MAX1910
MAX1912
RL
RB
RA
DIMMING INPUT
(0V OR VLOGIC)
1Ω
Figure 9. Using Digital Logic Input for Intensity Control
VIN
1Ω
2.2μF
0.47μF
0.47μF
2.2μF
15Ω15Ω15Ω15Ω
IN1 IN2
C1+
C1-
C2+
C2- GND
SET
OUT
SHDN
MAX1910
MAX1912
RL
4.7Ω
RB
1.58kΩ
RA
22.1kΩ
3.3V
VDD
GND
OUT
SERIAL
INPUT
MAX5380 (2-WIRE INPUT)
MAX5383 (3-WIRE INPUT)
HIGH DAC OUTPUT (2V) = 15mA LED CURRENT
LOW DAC OUTPUT (0V) = 45mA LED CURRENT
Figure 8. Circuit with SOT DAC for Intensity Control
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
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
© 2004 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
10LUMAX.EPS
PACKAGE OUTLINE, 10L uMAX/uSOP
1
1
21-0061
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
TOP VIEW
FRONT VIEW
1
0.498 REF
0.0196 REF
S
6°
SIDE VIEW
α
BOTTOM VIEW
0° 0° 6°
0.037 REF
0.0078
MAX
0.006
0.043
0.118
0.120
0.199
0.0275
0.118
0.0106
0.120
0.0197 BSC
INCHES
1
10
L1
0.0035
0.007
e
c
b
0.187
0.0157
0.114
H
L
E2
DIM
0.116
0.114
0.116
0.002
D2
E1
A1
D1
MIN
-A
0.940 REF
0.500 BSC
0.090
0.177
4.75
2.89
0.40
0.200
0.270
5.05
0.70
3.00
MILLIMETERS
0.05
2.89
2.95
2.95
-
MIN
3.00
3.05
0.15
3.05
MAX
1.10
10
0.6±0.1
0.6±0.1
Ø0.50±0.1
H
4X S
e
D2
D1
b
A2 A
E2
E1 L
L1
c
α
GAGE PLANE
A2 0.030 0.037 0.75 0.95
A1
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.)