MAX1698EUB ,High-Efficiency Step-Up Current Regulator for LEDsFeaturesThe MAX1698 is the most efficient driver for white or Over 90% Efficiencycolor LEDs. The d ..
MAX1698EUB ,High-Efficiency Step-Up Current Regulator for LEDsELECTRICAL CHARACTERISTICS(V = +3.3V, T = 0°C to +85°C, unless otherwise noted. Typical values are ..
MAX1698EUB+ ,High-Efficiency Step-Up Current Regulator for LEDsFeaturesThe MAX1698 and MAX1698A are efficient drivers for♦ Over 90% Efficiencywhite or color LEDs. ..
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MAX4507EAP ,Fault-Protected, High-Voltage Signal-Line ProtectorsApplications MAX4506C/D 0°C to +70°C Dice*MAX4506ESA -40°C to +85°C 8 SOProcess-Control Systems MAX ..
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MAX1698EUB
High-Efficiency Step-Up Current Regulator for LEDs
General DescriptionThe MAX1698 is the most efficient driver for white or
color LEDs. The device is ideal for LED backlit displays
in PDAs and digital cameras, and can also be used for
larger displays like those in laptop computers. Its
numerous benefits include greater simplicity, lower
cost, higher efficiency, longer bulb life, and greater reli-
ability when compared to fluorescent (CCFL) and elec-
troluminescent (EL) lamps.
The MAX1698 is a switch-mode boost controller in
which LED current, rather than output voltage, provides
the feedback signal. It can operate with battery inputs
as low as 0.8V. The device drives series-connected
LEDs with a controlled current that is measured at a
sense resistor connected at the feedback pin. The
required sense resistor is typically 15Ω, not an expen-
sive fractional-ohm value. LED current control and dim-
ming are accomplished with an adjust input (ADJ), not
with lossy current-limiting resistors. For larger light out-
put, multiple LED banks can be connected in parallel
with up to 5W total output power.
The MAX1698 is supplied in a space-saving 10-pin
µMAX package that occupies half the space of an 8-pin
SO. An evaluation kit (MAX1698EVKIT) is available to
speed designs.
ApplicationsBattery-Powered Backlight Applications
Backlight for LCD Panels
Cell Phones
Handy Terminals
PDAs
FeaturesOver 90% EfficiencyLossless, Adjustable LED BrightnessSpace-Saving 10-Pin µMAX PackageSimpler, Lower Cost, More Reliable Compared
to CCFL or EL BacklightsUp to 5W Output Power
MAX1698
High-Efficiency Step-Up
Current Regulator for LEDs
Typical Operating Circuit19-1621; Rev 0; 1/00
Pin Configuration
Ordering Information
MAX1698
High-Efficiency Step-Up
Current Regulator for LEDs
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= +3.3V, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°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.
VCC, SHDNto GND..................................................-0.3V to +6V
EXT, FB, CS, ADJ, REF to GND..................-0.3V to (VCC+ 0.3V)
GND to PGND.....................................................................±0.3V
Continuous Power Dissipation (TA= +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C)............444mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature Range (soldering, 10s)......................+300°C
MAX1698
High-Efficiency Step-Up
Current Regulator for LEDs
ELECTRICAL CHARACTERISTICS(VCC= +3.3V, TA
= -40°C to +85°C, unless otherwise noted.) (Note 1)
Note 1:Specifications to -40°C are guaranteed by design, not production tested.
MAX1698
High-Efficiency Step-Up
Current Regulator for LEDs5231678910
MXA1698-01
VBATT, VCC (V)
OUTPUT CURRENT (mA)
OUTPUT CURRENT vs. VBATT AND VCCNORMALIZED OUTPUT CURRENT
vs. ADJ VOLTAGE
MXA1698-02
ADJ VOLTAGE (V)
NORMALIZED OUTPUT CURRENT
MXA1698-03
INPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
OUTPUT CURRENT
vs. INPUT VOLTAGEBATTERY CURRENT
vs. BATTERY VOLTAGE
MXA1698-04
VBATT (V)
IOUT,
IBATT
(mA)
EFFICIENCY vs. BATTERY VOLTAGE
MXA1698-06
BATTERY VOLTAGE (V)
EFFICIENCY (%)
MXA1698-07
OUTPUT CURRENT (mA)
EFFICIENCY (%)
EFFICIENCY vs. OUTPUT CURRENTMXA1698-08
IOUT
50mA/div
5ms/div
SHUTDOWN/SOFT-START TIMING SHDN
5V/div
IBATT
100mA/div
3.3V
MXA1698-09
LED AND INDUCTOR CURRENT
WAVEFORMS INDUCTOR
CURRENT
500mA/div
LED
CURRENT
50mA/div
1µs/div
Typical Operating Characteristics(Circuit of Figure 2, VCC= VBATT = 3.3V,VADJ= VREF, TA= +25°C, unless otherwise noted.)
MAX1698
High-Efficiency Step-Up
Current Regulator for LEDsFigure 1. Functional Diagram
MAX1698
High-Efficiency Step-Up
Current Regulator for LEDs
Detailed DescriptionThe MAX1698’s high efficiency and small size make it
ideally suited to drive LEDs. It operates as a boost DC-
DC converter that controls output current rather than
voltage. Losses are minimized by a low, 300mV cur-
rent-sense threshold. In the standard configuration, a
feedback resistor, RFB, sets the current through the pri-
mary chain of LEDs. Additional chains of matching
LEDs can be added with an equivalent resistor. In
matched LED arrays, the secondary chain currents
closely track the primary chain. An optional zener
diode, D2, prevents overvoltage in the event that one of
the LEDs in the primary chain becomes an open circuit.
The LED brightness can be adjusted dynamically by a
voltage input at ADJ.
ShutdownIn shutdown, the MAX1698’s supply current is reduced
below 1µA. EXT goes low in shutdown, shutting off the
external N-channel FET. This leaves a current path
between the input and the LEDs through the boost
inductor and catch diode. The minimum forward volt-
age of the LED array must exceed the maximum VBATT
to ensure that the LEDs remain off in shutdown. Typical
shutdown timing characteristics are shown in the
Typical Operating Characteristics.
Soft-StartThe MAX1698 includes a soft-start function that elimi-
nates input current surges at turn-on. It does this by
extending the external FET driver (EXT) minimum off-
time during start-up. During the first 512 switching
cycles, the minimum off-time is 5µs. It is then allowed to
drop to 2µs for the next 1500 switching cycles. After
that time, the minimum off-time falls to the 1µs value
used during normal operation. (See Shutdown/Soft-
Start Timing in the Typical Operating Characteristics
section.)
Design Procedure
Setting the Maximum LED CurrentResistor RFBsets the maximum current in the primary
chain of LEDs:
where ILEDMAXis the maximum LED current.
Adjusting LED CurrentRFBsets the maximum LED current. This current can
be reduced proportional to the voltage at the ADJ pin
(see Normalized Output Current vs. ADJ Voltage in the
Typical Operating Characteristicssection). Figure 3
