Maxim MAX1913 60ma 1.5x high-efficiency white led charge pump Datasheet

19-2290; Rev 0; 1/02
60mA 1.5x High-Efficiency White LED
Charge Pumps
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
Features
♦ High-Efficiency 1.5x Charge Pumps
♦ Low Input Ripple with 750kHz Operation
♦ 200mV Current-Sense Threshold Reduces
Power Loss
♦ Current- or Voltage-Regulated Charge Pump
♦ 60mA Output Current
♦ No Inductors Required
♦ Small Ceramic Capacitors
♦ Regulated ±3% Output Voltage
♦ Load Disconnected in Shutdown
♦ 1µA Shutdown Current
♦ Small 10-Pin µMAX Package
Applications
Backlight White LED Biasing
Ordering Information
TEMP RANGE
PIN-PACKAGE
Cellular Phones
MAX1912EUB
-40°C to +85°C
10 µMAX
PDAs
MAX1913EUB50*
-40°C to +85°C
10 µMAX
Digital Still Cameras
PART
*Future product—contact factory for availability.
MP3 Players
Selector Guide
Backup-Battery Boost Converters
PART
Typical Operating Circuit
MODE
VSET
VOUT
MAX1912EUB
1.5x
200mV
Adjustable Current
MAX1913EUB50*
1.5x
1.25V
5.0V or Adjustable
*Future product—contact factory for availability.
Pin Configuration
VIN
IN1
IN2
SHDN
OUT
TOP VIEW
C1+
C1
CIN
C1-
GND 1
IN1
C2+
SET
C2
C2-
COUT
MAX1912
GND
10 SET
2
MAX1912/
MAX1913
9
C1-
C2-
3
8
IN2
C1+
4
7
C2+
OUT
5
6
SHDN
10-PIN µMAX
________________________________________________________________ Maxim Integrated Products
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
MAX1912/MAX1913
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.
MAX1912/MAX1913
60mA 1.5x High-Efficiency White LED
Charge Pumps
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 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
(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.)
PARAMETER
CONDITIONS
Input Voltage Operating Range
Undervoltage Lockout Threshold
Both rising and falling edges
MIN
TYP
MAX
5.3
V
2.2
2.5
V
Undervoltage Lockout Hysteresis
35
MAX1912
SET Regulation Point
0 < ILOAD < 60mA
MAX1912
Current Regulation
Output current change for 3V < VOUT < 5V
0.19
Maximum Output Current
UNITS
2.7
0.2
mV
0.21
0.5
V
%/V
60
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
750
875
kHz
Switching Frequency Temperature
Coefficient
f = 750kHz
625
250
SET Input Current
1
SHDN Input Current
SHDN = 0 or 5.5V
SHDN Input Voltage Low
2.7V < VIN < 5.3V
SHDN Input Voltage High
2.7V < VIN < 5.3V
Thermal-Shutdown Threshold
Rising temperature, 15°C hysteresis typical
ppm/°C
100
nA
1
µA
0.4
V
1.6
V
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
Input Voltage Operating Range
Undervoltage Lockout Threshold
Both rising and falling edges
Maximum Output Current
Supply Current in Shutdown
2
MIN
MAX
2.7
5.3
V
2.2
2.5
V
60
VIN = 5.3V, VOUT = 0, SHDN = 0
_______________________________________________________________________________________
UNITS
mA
10
µA
60mA 1.5x High-Efficiency White LED
Charge Pumps
(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
Output Leakage Current in Shutdown
VIN = 3.6V, SHDN = 0
MAX1912
SET Regulation Point
0 < ILOAD < 60mA
MIN
MAX
UNITS
10
µA
0.21
V
100
nA
µA
0.19
SET Input Current
SHDN Input Current
SHDN = 0 or 5.5V
1
SHDN Input Voltage Low
2.7V < VIN < 5.3V
0.4
SHDN Input Voltage High
2.7V < VIN < 5.3V
V
1.6
V
Note 1: Limits to -40°C are guaranteed by design, not production tested.
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
INPUT AND OUTPUT VOLTAGE RIPPLE
WITH ADDITIONAL INPUT FILTER
QUIESCENT CURRENT vs.
INPUT VOLTAGE
20mV/div
20mV/div
VOUT
VOUT
IIN (mA)
MAX1912/13 toc01
3
VIN
VIN1
MAX19112/13 toc03
4
MAX1912/13 toc02
INPUT AND OUTPUT VOLTAGE RIPPLE
2
1
0
1µs.div
1µs/div
0
1
MAX1912 DRIVING 4 LEDS (60mA)
10µF - 1Ω - 10µF INPUT FILTER, COUT = 4.7µF
VIN = 3.3V
CIN = 10µF, COUT = 4.7µF
MAX1912 DRIVING 4 LEDS (60mA)
VIN = 3.3V
STARTUP INPUT CURRENT AND
OUTPUT VOLTAGE
3
4
5
6
VIN (V)
INTENSITY CHANGE STEP RESPONSE
MAX1912/13 toc04
VSHDN
2
MAX1912/13 toc05
5V/div
VLOGIC
1V/div
VOUT
2V/div
100mV/div
VSET
45mA
50mA/div
IIN
1ms/div
CIRCUIT OF FIGURE 2
R1 = R2 = R3 = 15Ω
CIN = 10µF, COUT = 2.2µF
VIN = 3.3V
15mA
ILED
50µs/div
CIRCUIT OF FIGURE 10
RA = 22kΩ, RB = 1.5kΩ, RL = 4.7Ω
CIN = 10µF, COUT = 4.7µF
VLOGIC(HIGH) = 2V
_______________________________________________________________________________________
3
MAX1912/MAX1913
ELECTRICAL CHARACTERISTICS (continued)
60mA 1.5x High-Efficiency White LED
Charge Pumps
MAX1912/MAX1913
Pin Description
PIN
NAME
FUNCTION
1
GND
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
Ground
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.
6
SHDN
7
C2+
Transfer Capacitor 2 Connection, Positive Side
8
IN2
Supply Voltage Input. Connect to IN1.
9
C1-
Transfer Capacitor 1 Connection, Negative Side
SET
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.
10
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.
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.
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.
4
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
0.1µA. The output is high impedance in shutdown.
Drive SHDN high or connect to IN for normal operation.
Thermal Shutdown
The MAX1912/MAX1913 shut down when their die temperature 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 (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
_______________________________________________________________________________________
60mA 1.5x High-Efficiency White LED
Charge Pumps
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 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.
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.
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) × RB
−
RL
RL × RA
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) × RB
−
RL
RL × RA
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 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 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 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
_______________________________________________________________________________________
5
MAX1912/MAX1913
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.
MAX1912/MAX1913
60mA 1.5x High-Efficiency White LED
Charge Pumps
IN
SW4
SW1
SW2
SW5
SW7
(REGULATING
SWITCH)
SW3
SW6
GND
OUT
C1-
C1+
C2-
MODE
PHASE
SW1
SW2
SW3
SW4
1.5x
Charging
OFF
ON
OFF
OFF
C2+
SW5
SW6
ON
OFF
ON
OFF
ON
OFF
1.5x
Transfer
ON
OFF
ON
ON
Figure 1. Functional Charge-Pump Switch Diagram (Switches Shown for Charging Phase)
1Ω
VIN
IN1
IN2
SW7
SHDN
OUT
C1+
0.47µF
2.2µF
C1C2+
SET
0.47µF
C2-
2.2µF
MAX1912
GND
10Ω
10Ω
Figure 2. LED Biasing with the MAX1912
6
_______________________________________________________________________________________
10Ω
60mA 1.5x High-Efficiency White LED
Charge Pumps
MAX1912/MAX1913
1Ω
VIN
IN2
IN1
SHDN
OUT
C1+
0.47µF
2.2 µF
C1-
2.2µF
MAX1912
C2+
1kΩ
0.47µF
SET
C2-
1kΩ
GND
1kΩ
10Ω
10Ω
10Ω
Figure 3. The MAX1912 Regulating Average Current Through LEDs
1Ω
VIN
IN1
IN2
SHDN
OUT
C1+
0.47µF
2.2µF
C1-
2.2µF
MAX1912
15Ω
25Ω
25Ω
C2+
0.47µF
SET
C2-
GND
10Ω
Figure 4. Alternate Method of Biasing to Improve LED-to-LED Matching
_______________________________________________________________________________________
7
MAX1912/MAX1913
60mA 1.5x High-Efficiency White LED
Charge Pumps
1Ω
VIN
IN1
IN2
SHDN
OUT
C1+
0.47µF
2.2µF
C1-
2.2µF
MAX1912
C2+
SET
0.47µF
C2-
2-PIN
CONNECTOR
GND
R4
3.3Ω
R1
10Ω
R2
10Ω
R3
10Ω
Figure 5. Alternate Method of Biasing LEDs Controls Total Current; Suitable When the LED Array Must Be Biased with Only Two
Connections
1Ω
VIN
IN1
IN2
SHDN
OUT
VOUT
C1+
0.47µF
2.2µF
C1C2+
R1
SET
0.47µF
C2-
2.2µF
MAX1913
GND
R2
Figure 6. Output Voltage Set with a Resistor-Divider
8
_______________________________________________________________________________________
60mA 1.5x High-Efficiency White LED
Charge Pumps
1Ω
IN1
IN2
SHDN
VIN
1Ω
IN1
VOUT
OUT
IN2
SHDN
2.2µF
C1+
C1-
2.2µF
MAX1913
10µF
10µF
0.47µF
C1-
C2+
SET
0.47µF
2.2µF
MAX1913
C2+
SET
0.47µF
C2-
GND
C2-
GND
Figure 8. C-R-C Filter Reduces Ripple On the Input
Figure 7. Output Voltage Internally Set to 5V
VIN
VOUT
OUT
C1+
0.47µF
1Ω
IN1
IN2
SHDN
OUT
C1+
0.47µF
2.2µF
C1-
2.2µF
MAX1912
10Ω
10Ω
10Ω
C2+
0.47µF
SET
C2-
GND
3.3V
MAX5380 (2-WIRE INPUT)
MAX5383 (3-WIRE INPUT)
RL
4.7Ω
RA
22.1kΩ
VDD
SERIAL
INPUT
RB
1.58kΩ
OUT
GND
HIGH DAC OUTPUT (2V) = 15mA LED CURRENT
LOW DAC OUTPUT (0V) = 45mA LED CURRENT
Figure 9. Circuit with SOT DAC for Intensity Control
_______________________________________________________________________________________
9
MAX1912/MAX1913
VIN
MAX1912/MAX1913
60mA 1.5x High-Efficiency White LED
Charge Pumps
VIN
1Ω
IN1
IN2
SHDN
OUT
C1+
0.47µF
2.2µF
C1-
2.2µF
MAX1912
C2+
0.47µF
SET
C2-
RB
GND
RL
RA
DIMMING INPUT
(0V OR VLOGIC)
Figure 10. Using Digital Logic Input for Intensity Control
10
______________________________________________________________________________________
60mA 1.5x High-Efficiency White LED
Charge Pumps
10LUMAX.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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX1912/MAX1913
Package Information
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