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 unregu-
lated 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
1µA Shutdown Current
o
Small 10-Pin µMAX 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
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
10 µMAX
10 µMAX
*Future
product—contact factory for availability.
Selector Guide
MODE
1.5x
1.5x
V
SET
200mV
1.25V
V
OUT
Adjustable Current
5.0V or Adjustable
Typical Operating Circuit
*Future
product—contact factory for availability.
Pin Configuration
V
IN
IN1
C1+
C1
C
IN
C1-
C2+
C2
C2-
GND
IN2
SHDN
OUT
TOP VIEW
C
OUT
MAX1912
SET
GND
1
IN1
C2-
C1+
OUT
2
3
4
5
10
SET
9
C1-
IN2
C2+
SHDN
MAX1912/
MAX1913
8
7
6
10-PIN
µMAX
________________________________________________________________
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.
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, V
IN
+ 1V
C1+, C2+ to GND..........-0.3V, greater of V
OUT
+ 1V or V
IN
+ 1V
OUT Short-Circuit to GND ..........................................Continuous
Continuous Power Dissipation
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
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
(V
IN
= 3.6V, GND = 0,
SHDN
= SET = IN, C
IN
= 2.2µF, C1 = C2 = 0.47µF, C
OUT
= 2.2µF,
T
A
= 0°C to +85°C.
Typical values are at
T
A
= +25°C, 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 < V
IN
< 5.3V
2.7V < V
IN
< 5.3V
Rising temperature, 15°C hysteresis typical
1.6
160
V
IN
= 3.6V
V
IN
= 5.3V, V
OUT
= 0,
SHDN
= 0
V
IN
= 3.6V,
SHDN
= 0
V
IN
= 3.6V
f = 750kHz
625
0 < I
LOAD
< 60mA
Output current change for 3V < V
OUT
< 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
µA
µA
kHz
ppm/°C
nA
µA
V
V
°C
ELECTRICAL CHARACTERISTICS
(V
IN
= 3.6V, GND = 0,
SHDN
= SET = IN, C
IN
= 2.2µF, C1 = C2 = 0.47µF, C
OUT
= 2.2µF,
T
A
= -40°C to +85°C,
unless otherwise
noted.) (Note 1)
PARAMETER
Input Voltage Operating Range
Undervoltage Lockout Threshold
Maximum Output Current
Supply Current in Shutdown
V
IN
= 5.3V, V
OUT
= 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
µA
2
_______________________________________________________________________________________
60mA 1.5x High-Efficiency White LED
Charge Pumps
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 3.6V, GND = 0,
SHDN
= SET = IN, C
IN
= 2.2µF, C1 = C2 = 0.47µF, C
OUT
= 2.2µF,
T
A
= -40°C to +85°C,
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 < V
IN
< 5.3V
2.7V < V
IN
< 5.3V
1.6
CONDITIONS
V
IN
= 3.6V,
SHDN
= 0
0 < I
LOAD
< 60mA
0.19
MIN
MAX
10
0.21
100
1
0.4
UNITS
µA
V
nA
µA
V
V
MAX1912/MAX1913
Note 1:
Limits to -40°C are guaranteed by design, not production tested.
Typical Operating Characteristics
(T
A
= +25°C, 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
I
IN
(mA)
V
IN1
20mV/div
V
OUT
V
IN
20mV/div
2
V
OUT
1
1µs/div
C
IN
= 10µF, C
OUT
= 4.7µF
MAX1912 DRIVING 4 LEDS (60mA)
V
IN
= 3.3V
1µs.div
MAX1912 DRIVING 4 LEDS (60mA)
10µF - 1Ω - 10µF INPUT FILTER, C
OUT
= 4.7µF
V
IN
= 3.3V
0
0
1
2
3
V
IN
(V)
4
5
6
STARTUP INPUT CURRENT AND
OUTPUT VOLTAGE
MAX1912/13 toc04
INTENSITY CHANGE STEP RESPONSE
MAX1912/13 toc05
V
SHDN
5V/div
V
LOGIC
2V/div
V
OUT
1V/div
V
SET
100mV/div
45mA
I
IN
1ms/div
CIRCUIT OF FIGURE 2
R1 = R2 = R3 = 15Ω
C
IN
= 10µF, C
OUT
= 2.2µF
V
IN
= 3.3V
50mA/div
I
LED
50µs/div
CIRCUIT OF FIGURE 10
R
A
= 22kΩ, R
B
= 1.5kΩ, R
L
= 4.7Ω
C
IN
= 10µF, C
OUT
= 4.7µF
V
LOGIC(HIGH)
= 2V
15mA
_______________________________________________________________________________________
3
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
C2-
C1+
OUT
SHDN
C2+
IN2
C1-
SET
Ground
Supply Voltage Input. Connect to IN2. Bypass to GND with a 2.2µF ceramic capacitor.
Transfer Capacitor 2 Connection, Negative Side
Transfer Capacitor 1 Connection, Positive Side
Output. Bypass to GND with a 2.2µF 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,
V
OUT
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 phas-
es (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 C
OUT
. 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 volt-
age, 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 nor-
mal 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
0.1µA. 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 out-
put 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 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.
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 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.
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:
I
LED
= 0.2/R
If additional matching LEDs with ballast resistors are
connected to the output as in Figure 2, the current
4
_______________________________________________________________________________________
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 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 V
SET
. The
increased ballast resistance tolerates wider LED mis-
match 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 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. R
L
may be initially estimated from the
maximum load current:
R
L
≈
0.2/I
L(MAX)
Use this as a starting point to calculate R
A
and R
B
from
the formula below. The total load current at different
DAC output voltages is determined by:
I
L
=
0.2 (V
DAC
−
0.2)
×
R
B
−
R
L
R
L
×
R
A
Setting Output Voltage (MAX1913)
The MAX1913 has a SET voltage threshold of 1.25V.
The output voltage is set by connecting a resistor volt-
age 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 50kΩ, 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
(V
LOGIC
= 0) is applied, and dimmed with a logic high
input. The total LED current is determined by:
I
L
=
0.2 (V
LOGIC
−
0.2)
×
R
B
−
R
L
R
L
×
R
A
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 1Ω 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 switched-
capacitor voltage regulators. For best circuit perfor-
mance, use a ground plane and keep C
IN
, C
OUT
, 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
_______________________________________________________________________________________
5
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