MAX1910EUB ,1.5x/2x High-Efficiency White LED Charge PumpsELECTRICAL CHARACTERISTICS(V = 3.6V, GND = 0, SHDN = SET = IN, C = 2.2µF, C1 = C2 = 0.47µF, C = 2.2 ..
MAX1910EUB ,1.5x/2x High-Efficiency White LED Charge PumpsFeaturesThe MAX1910/MAX1912 power LEDs with a regulated♦ High-Efficiency 1.5x/2x Charge Pumpsoutput ..
MAX1910EUB ,1.5x/2x High-Efficiency White LED Charge PumpsApplications Ordering InformationWhite LED BacklightingPART TEMP RANGE PIN-PACKAGECellular PhonesMA ..
MAX1910EUB+ ,1.5x/2x High-Efficiency White LED Charge PumpsApplications Ordering InformationWhite LED BacklightingPART TEMP RANGE PIN-PACKAGECellular PhonesMA ..
MAX1910EUB+ ,1.5x/2x High-Efficiency White LED Charge PumpsFeaturesThe MAX1910/MAX1912 power LEDs with a regulated♦ High-Efficiency 1.5x/2x Charge Pumpsoutput ..
MAX1910EUB+T ,1.5x/2x High-Efficiency White LED Charge PumpsELECTRICAL CHARACTERISTICS(V = 3.6V, GND = 0, SHDN = SET = IN, C = 2.2µF, C1 = C2 = 0.47µF, C = 2.2 ..
MAX487ECPA ,15kV ESD-Protected / Slew-Rate-Limited / Low-Power / RS-485/RS-422 TransceiversGeneral Description ________
MAX487ECPA+ ,±15kV ESD-Protected, Slew-Rate-Limited, Low-Power, RS-485/RS-422 TransceiversApplicationsMAX481EESA -40°C to +85°C 8 SOIndustrial-Control Local Area Networks MAX483ECPA 0°C to ..
MAX487ECSA ,15kV ESD-Protected / Slew-Rate-Limited / Low-Power / RS-485/RS-422 TransceiversFeaturesThe MAX481E, MAX483E, MAX485E, MAX487E–MAX491E, ' ESD Protection: ±15kV—Human Body Modelan ..
MAX487ECSA ,15kV ESD-Protected / Slew-Rate-Limited / Low-Power / RS-485/RS-422 TransceiversApplicationsIndustrial-Control Local Area Networks__Selection TableRECEIVER/ QUIESCENT NUMBER OFPAR ..
MAX487ECSA ,15kV ESD-Protected / Slew-Rate-Limited / Low-Power / RS-485/RS-422 Transceiversapplications. For
MAX487ECSA ,15kV ESD-Protected / Slew-Rate-Limited / Low-Power / RS-485/RS-422 TransceiversELECTRICAL CHARACTERISTICS(V = 5V ±5%, T = T to T , unless otherwise noted.) (Notes 1, 2)CC A MIN M ..
MAX1910EUB
1.5x/2x High-Efficiency White LED Charge Pumps
General DescriptionThe 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.
ApplicationsWhite LED Backlighting
Cellular Phones
PDAs
Digital Still Cameras
MP3 Players
Backup-Battery Boost Converters
FeaturesHigh-Efficiency 1.5x/2x Charge PumpsLow Input Ripple with 750kHz Operation200mV Current-Sense Threshold Reduces
Power LossCurrent- or Voltage-Regulated Charge PumpUp to 120mA Output CurrentNo Inductors RequiredSmall Ceramic CapacitorsRegulated ±5% LED CurrentLoad Disconnected in Shutdown1µA Shutdown CurrentSmall 10-Pin µMAX Package
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
Ordering Information
Pin Configuration19-2290; Rev 2; 3/04
Typical Operating Circuit
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
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 atStresses 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
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 otherwisenoted.) (Note 1)
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
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
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.)
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
Detailed DescriptionThe 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
“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 VINis greater than
~75% of VOUTfor more than 32 clock cycles (at full
load). The MAX1912 operates only in 1.5x charge-
pump mode.
Output RegulationThe 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
ypical Operating Characteristics (continued)(Circuit of Figure 2, VIN= 3.3V, TA = +25°C, unless otherwise noted.)
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumpscharge-pump topologies because the charge trans-
ferred per cycle is only the amount required to supply
the output load.
Soft-StartThe 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 ModeWhen driven low, SHDNturns off the charge pump.
This reduces the quiescent current to approximately
0.1µA. The output is high impedance in shutdown.
Drive SHDNhigh or connect to IN for normal operation.
Thermal ShutdownThe 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 CurrentThe 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 VoltageThe 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 VINto 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 SelectionUse 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.
MAX1910/MAX1912
1.5x/2x High-Efficiency White LED
Charge Pumps
Applications Information
Adjusting LED IntensityFigure 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: ≈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 LayoutThe 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 InformationTRANSISTOR COUNT: 2497
PROCESS: BiCMOS
