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MAX1556ETB ,16 mA IQ, 1.2 A PWM step-down DC-DC converterELECTRICAL CHARACTERISTICS(V = V = V = 3.6V, T = - 40°C to +85°C. Typical values are at T = +25°C, ..
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MAX4212EUK ,Miniature, 300MHz, Single-Supply, Rail-to-Rail Op Amps with Enableapplications.' Space-Saving SOT23-5, µMAX, or QSOP PackagesThe MAX4212 comes in a miniature 5-pin S ..
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MAX1553ETA+-MAX1553ETA+T-MAX1554ETA+-MAX1554ETA+T
High-Efficiency, 40V Step-Up Converters for 2 to 10 White LEDs
MAX1553/MAX1554High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDsEVALUATION KIT AVAILABLE
General DescriptionThe MAX1553/MAX1554 drive white LEDs in series with
a constant current to provide efficient display backlight-
ing in cellular phones, PDAs, and other hand-held
devices. The step-up converter includes an internal
40V, low RDSON, N-channel MOSFET switch for high
efficiency and maximum battery life. The MAX1553 has
a current limit of 480mA for driving two to six white
LEDs, while the MAX1554 has a current limit of 970mA
for driving up to 10 white LEDs.
A single analog/PWM Dual Mode™input provides two
simple means of brightness adjustment. A separate
enable input provides on/off control. Soft-start mini-
mizes inrush current during startup.
The MAX1553/MAX1554 are available in space-saving
8-pin TDFN 3mm x 3mm packages.
ApplicationsCellular Phones
PDA, Palmtop, and Wireless Handhelds
Color Display Backlight
Benefits and FeaturesHighly Integrated and Flexible Solution for Wide
Range of Backlighting ApplicationsConstant-Current Regulation for Even LED
IlluminationInternal 40V MOSFET Switch Capable of Driving
10 LEDs2.7V to 5.5V Input Voltage RangeAnalog or PWM Control of LED IntensityOptimized for Low Input Ripple
Soft-Start Minimizes Inrush Current
High Efficiency Improves Battery LifeUp to 88% Efficiency Driving 6 LEDsUp to 82% Efficiency Driving 9 LEDs (20mA,
VCC= 3.6V)
Tiny 8-Pin, 3mm x 3mm TDFN Package Saves SpaceSmall, Low-Profile External Components
TOP VIEW
BRT
VCC
GNDFB4
TDFN
3mm x 3mmMAX1553
MAX1554
Pin Configuration
Ordering InformationVCC
OFF
BRT
GND
2.7V TO 5.5V
INPUTEN
PWM
DC CONTROL
MAX1553
MAX1554
WHITE
LEDS
Typical Operating Circuit
PARTTEMP RANGEPIN-PACKAGETOP
MARKA X1 5 5 3 E TA-40°C to +85°C8 TD FN 3m m x 3m mAGX
A X1 5 5 4 E TA-40°C to +85°C8 TD FN 3m m x 3m mAGY
Dual Mode is a trademark of Maxim Integrated Products, Inc.
MAX1553/MAX1554High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDs
Absolute Maximum RatingsVCC, FB, OV to GND..............................................-0.3V to +6.0V
LX to GND..............................................................-0.3V to +45V
EN, BRT, SS to GND...................................-0.3V to (VCC+ 0.3V)
ILX...................................................................................0.9ARMS
Continuous Power Dissipation (TA= +70°C)
8-Pin 3mm x 3mm TDFN
(derate 24.4mW/°C above +70°C).............................1951mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
Electrical Characteristics(VCC= 3.3V, VOV= 0V, COUT= 1µF, RSENSE= 10Ω, 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.
PARAMETERCONDITIONSMINTYPMAXUNITSMAX15532.75.5Supply VoltageMAX15543.155.50V
Undervoltage Lockout ThresholdVCC rising or falling, 35mV hysteresis typical2.352.52.65V
Not switching0.330.65Quiescent CurrentSwitching0.440.9mA
TA = +25°C0.11Shutdown Supply CurrentVEN = 0VTA = +85°C1µA
OV ThresholdRising edge1.181.251.33V
TA = +25°C1200OV Input Bias CurrentVOV = 1VTA = +85°C10nA
BRT Input Resistance0 < VBRT < 1.5V, EN = VCC200400600kΩ
TIMING CONTROLMaximum On-TimeVCC = 3.3V2.03.44.8µs
On-Time Constant (K)tON = K / VCC6.3µs-V
Minimum Off-Time150250350ns
ERROR AMPLIFIERVBRT = 1.25V192203212FB ThresholdVBRT = 3.3V280mV
TA = +25°C15200FB Input Bias CurrentVFB = 1.0VTA = +85°C100nA
N-CHANNEL SWITCHLX On-Resistance0.81.4Ω
MAX1553/MAX1554High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDs
PARAMETERCONDITIONSMINMAXUNITSMAX15532.75.5Supply VoltageMAX15543.155.50V
Undervoltage Lockout ThresholdVCC rising or falling, 35mV hysteresis typical2.352.65V
Not switching0.65Quiescent CurrentSwitching0.9mA
OV ThresholdRising edge1.181.33V
BRT Input Resistance0 < VBRT < 1.5V, EN = VCC200600kΩ
TIMING CONTROLMaximum On-TimeVCC = 3.3V2.04.8µs
Minimum Off-Time150350ns
ERROR AMPLIFIERFB ThresholdVBRT = 1.25V192217mV
N-CHANNEL SWITCHLX On-Resistance1.4Ω
MAX1553300600LX Current LimitMAX1554, VCC = 4.2V6001200mA
SHUTDOWN CONTROLEN Logic-Level High1.8V
EN Logic-Level Low0.4V
Electrical Characteristics (continued)(VCC= 3.3V, VOV= 0V, COUT= 1µF, RSENSE= 10Ω, TA
= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERCONDITIONSMINTYPMAXUNITSMAX1553300480600LX Current LimitMAX1554, VCC = 4.2V6009701200mA
TA = +25°C0.15LX Leakage CurrentVLX = 38V,
VEN = 0VTA = +85°C1µA
SHUTDOWN CONTROLEN Logic-Level High1.8V
EN Logic-Level Low0.4V
TA = +25°C0.011EN Input CurrentVEN = 0V or 5.5VTA = +85°C0.1µA
Electrical Characteristics(VCC= 3.3V, VOV= 0V, COUT= 1µF, RSENSE= 10Ω, TA
= -40°C to +85°C, unless otherwise noted.) (Note 1)
Note 1:Specifications to -40°C are guaranteed by design, not production tested.
MAX1553/MAX1554High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDs
EFFICIENCY vs. LOAD CURRENT
DRIVING 6 WHITE LEDSMAX1553/54 toc01
LOAD CURRENT (mA)
EFFICIENCY (%)105
VCC = 5V
VCC = 4V
VCC = 3.6VVCC = 3V
L1 = 22μH
NO CAPACITOR ACROSS LEDs
EFFICIENCY vs. LOAD CURRENT
DRIVING 6 WHITE LEDSMAX1553/54 toc02
LOAD CURRENT (mA)
EFFICIENCY (%)105
VCC = 5VVCC = 4V
VCC = 3.6V
VCC = 3V
L1 = 33μH
4700pF ACROSS LEDs
EFFICIENCY vs. LOAD CURRENT
DRIVING 6 WHITE LEDSMAX1553/54 toc03
LOAD CURRENT (mA)
EFFICIENCY (%)105
VCC = 5VVCC = 4V
VCC = 3.6VVCC = 3V
L1 = 47μH
4700pF ACROSS LEDs
EFFICIENCY vs. LOAD CURRENT
WITH MAX1554 DRIVING 9 WHITE LEDSMAX1553/54 toc04
LOAD CURRENT (mA)
EFFICIENCY (%)105
VCC = 5VVCC = 4V
VCC = 3.6V
CIRCUIT OF FIGURE 3
LED CURRENT
vs. INPUT VOLTAGEMAX1553/54 toc05
INPUT VOLTAGE (V)
LED CURRENT (mA)
L1 = 22μH, NO CAPACITOR ACROSS LEDs
L1 = 47μH,
4700pF ACROSS LEDs
L1 = 33μH, 4700pF ACROSS LEDs
R1 = 10Ω, VBRT = 1.25V
LED CURRENT
vs. INPUT VOLTAGEMAX1553/54 toc06
INPUT VOLTAGE (V)
LED CURRENT (mA)
L1 = 22μH, NO CAPACITOR ACROSS LEDs
L1 = 47μH,
4700pF ACROSS LEDs
L1 = 33μH, 4700pF ACROSS LEDs
R1 = 14Ω, VBRT = 3.3V
LED CURRENT vs. INPUT VOLTAGE
WITH MAX1554 DRIVING 9 LEDSMAX1553/54 toc07
INPUT VOLTAGE (V)
LED CURRENT (mA)
CIRCUIT OF FIGURE 3
LED CURRENT
vs. BRT VOLTAGEMAX1553/54 toc08
BRT VOLTAGE (V)
LED CURRENT (mA)
LED CURRENT
vs. BRT DUTY CYCLE
MAX1553/54 toc09
BRT DUTY CYCLE (%)
LED CURRENT (mA)604020
Typical Operating Characteristics
(MAX1553 driving six white LEDs, VCC= VEN= 3.6V, Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
MAX1553/MAX1554High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDs
SWITCHING WAVEFORMS
(CONTINUOUS OPERATION,
3.75V Li+ BATTERY, 18mA OUTPUT)MAX1553/54 toc10
2μs/div
VLX
VOUT
10V/div
200mV/div
200mA/div
L1 = 47μH, 4700pF CAPACITOR ACROSS LEDs
SWITCHING WAVEFORMS
(DISCONTINUOUS OPERATION,
3.75V Li+ BATTERY, 10mA OUTPUT)MAX1553/54 toc11
2μs/div
VLX
VOUT
10V/div
200mV/div
200mA/div
L1 = 47μH, 4700pF CAPACITOR ACROSS LEDs
STARTUP/SHUTDOWN WAVEFORMSMAX1553/54 toc12
40ms/div
VEN
VFB
VOUT
5V/div
200mV/div
10V/div
L1 = 22μH
BRT STEP RESPONSEMAX1553/54 toc13
20ms/div
VBRT
VFB
VOUT
1V/div
200mV/div
2V/div
L1 = 22μH,
VBRT = 0.5V TO 1.25V TO O.5V
Typical Operating Characteristics (continued)(MAX1553 driving six white LEDs, VCC= VEN= 3.6V, Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
MAX1553/MAX1554High-Efficiency, 40V Step-Up
Converters for 2 to 10 White LEDs
PINNAMEFUNCTIONGNDGround
2VCCVoltage-Supply Input. 2.7V to 5.5V. The IC is powered from VCC.ENEnable Input. Drive high or connect to VCC to enable the IC. Drive EN low for shutdown.BRT
Brightness-Control Input. Either an analog or PWM control signal can be used. The LED current can be
controlled over a 10 to 1 range. The PWM signal must be between 100Hz and 10kHz, and must have an
amplitude greater than 1.72V.
5FBFeedback Input. Connect to the cathode of the LED string and connect a resistor from FB to GND to set the
LED current.
6SS
Soft-Start Timing-Control Input. Connect a capacitor from SS to GND to control soft-start timing. See the Soft-
Start section for information on selecting the soft-start capacitor. SS is pulled to ground with an internal 200Ω
switch when EN is low.
7OVOvervoltage Sense. Connect to a resistor-divider from the anode of the LED string to set the overvoltage
threshold. See Figures 1, 2, and 3.LXInductor Connection. Connect to the inductor and diode. LX is high impedance when EN is low.EPExposed Pad. Connect to GND.
Pin Description
Detailed Description
Control SchemeThe MAX1553/MAX1554 utilize a minimum off-time, cur-
rent-limited control scheme. If the voltage at FB drops
below the regulation threshold, the internal low-side
MOSFET turns on and the inductor current ramps up to
the current limit. Once the current-limit comparator
trips, the low-side MOSFET turns off for the minimum
off-time (250ns). After 250ns, if the voltage at FB is
above the regulation threshold, the low-side MOSFET
stays off. If the voltage at FB is below the regulation
point, the low-side MOSFET turns back on and the
cycle repeats. By using a regulation control scheme
that is not fixed frequency and that can skip pulses, the
MAX1553/MAX1554 operate with very high efficiency.
Soft-StartSoft-start is provided on the MAX1553/MAX1554 to min-
imize inrush current. The soft-start time is set with an
external capacitor, C3 (Figures 1, 2, and 3). Use the fol-
lowing equation to solve for C3:
where tSSis the soft-start time. A value of 0.1µF pro-
vides a soft-start time of 20ms.
ShutdownThe MAX1553/MAX1554 feature a low-current shut-
down feature. When EN is low, the IC turns off, reduc-
ing its supply current to approximately 0.1µA. For
normal operation, drive EN high or connect to VCC.
Overvoltage ProtectionThe MAX1553/MAX1554 have an adjustable overvolt-
age- protection circuit. When the voltage at OV reaches
the overvoltage threshold (1.25V typ), the protection cir-
cuitry prevents the internal MOSFET from switching,
allowing the output voltage to decay.
The peak output voltage in an overvoltage-protection
event is set with a resistor-divider from the output con-
nected to OV (R2 and R3 in Figures 1, 2, and 3). Select
a value for R3 (10kΩis recommended), then solve for
R2 using the following equation:
where VOVis the overvoltage threshold (1.25V typ), and
VOUT(PEAK)is the desired peak output voltage.xV
OUTPEAK231=−⎛⎜⎞⎟()x
tSS32105=
