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MAX1522EUT+T ,Simple SOT23 Boost Controllersapplications where♦ Low Quiescent Current (25µA typ)extremely low cost and small size are top prior ..
MAX1522EUT-T ,Simple SOT23 Boost Controllersapplications.

MAX1522EUT+T-MAX1523EUT-MAX1523EUT+T
Simple SOT23 Boost Controllers
General Description
The MAX1522/MAX1523/MAX1524 are simple, compact
boost controllers designed for a wide range of DC-DC
conversion topologies, including step-up, SEPIC, and
flyback applications. They are for applications where
extremely low cost and small size are top priorities.
These devices are designed specifically to provide a
simple application circuit and minimize the size and
number of external components, making them ideal for
PDAs, digital cameras, and other low-cost consumer
electronics applications.
These devices use a unique fixed on-time, minimum off-
time architecture, which provides excellent efficiency
over a wide-range of input/output voltage combinations
and load currents. The fixed on-time is pin selectable to
either 0.5µs (50% max duty cycle) or 3µs (85% max
duty cycle), permitting optimization of external compo-
nent size and ease of design for a wide range of output
voltages.
The MAX1522/MAX1523 operate from a +2.5V to +5.5V
input voltage range and are capable of generating a
wide range of outputs. The MAX1524 is intended for
bootstrapped operation, permitting startup with lower
input voltage. All devices have internal soft-start and
short-circuit protection to prevent excessive switching
current during startup and under output fault condi-
tions. The MAX1522/MAX1524 have a latched fault
mode, which shuts down the controller when a short-
circuit event occurs, whereas the MAX1523 reenters
soft-start mode during output fault conditions. The
MAX1522/MAX1523/MAX1524 are available in a space-
saving 6-pin SOT23 package.
________________________Applications
____________________________FeaturesSimple, Flexible Application Circuit2-Cell NiMH or Alkaline Operation (MAX1524)Low Quiescent Current (25µA typ)Output Fault Protection and Soft-StartHigh Efficiency Over 1000:1 IOUTRangePin-Selectable Maximum Duty FactorMicropower Shutdown ModeSmall 6-Pin SOT23 PackageNo Current-Sense Resistor
MAX1522/MAX1523/MAX1524
Simple SOT23 Boost Controllers
__________Typical Operating Circuit
19-1926; Rev 1; 8/10
EVALUATION KIT
AVAILABLE
PARTTEMP. RANGEPIN-
PACKAGE
TOP
MARK
MAX1522EUT-T-40°C to +85°C6 SOT23AAOX
MAX1523EUT-T-40°C to +85°C6 SOT23AAOY
MAX1524EUT-T-40°C to +85°C6 SOT23AAOZ
MAX1522EUT+T-40°C to +85°C6 SOT23+AAOX
MAX1523EUT+T-40°C to +85°C6 SOT23+AAOY
MAX1524EUT+T-40°C to +85°C6 SOT23+AAOZ
Ordering Information
Pin Configuration
SHDNSETVCCEXT
GND
MAX1522
MAX1523
MAX1524
TOP VIEW
MAX1522
MAX1523
MAX1524
INPUT
OFFON
VCCEXT
SETFB
SHDNGND
OUTPUT
VCC
50%85%
Low-Cost, High-Current,
or High-Voltage Boost
Conversion
LCD Bias Supplies
Industrial +24V and +28V
Power Supplies
Low-Cost, Multi-Output
Flyback Converters
SEPIC Converters
Low-Cost Battery-
Powered Applications
+Denotes a lead(Pb)-free/RoHS-compliant package.
-Denotes a package containing lead(Pb).
T = Tape and reel.
Simple SOT23 Boost Controllers
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC= SHDN= 3.3V, SET = GND , TA= -40°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.
Note 1:Actual startup voltage is dependent on the external MOSFET’s VGS(TH).
Note 2:Specification applies after soft-start mode is completed.
VCC, FB, SHDN, SET to GND...................................-0.3V to +6V
EXT to GND................................................-0.3V to (VCC+ 0.3V)
Continuous Power Dissipation (TA= +70°C)
6-Pin SOT23 (derate 8.7mW/°C above +70°C) ..........696mW
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
Soldering Temperature (reflow) ......................................+260°C
PARAMETERCONDITIONSMINTYPMAXUNITS
VCC Operating Voltage Range2.55.5V
MAX1522/MAX15232.5VCC Minimum Startup VoltagefEXT > 100kHz, MAX1524 (Note 1), bootstrap required1.5V
VCC rising2.372.47Undervoltage Lockout
ThresholdVCC falling2.202.30V
VCC Supply CurrentNo load, nonbootstrapped2550µA
VCC Shutdown CurrentSHDN = GND0.0011µA
SET = GND0.40.50.6Fixed tON TimeVFB =1.2VSET = VCC2.43.03.6µs
VFB > 0.675V0.5Minimum tOFF TimeVFB < 0.525V1.0µs
SET = GND455055Maximum Duty FactorSET = VCC808590%
FB Regulation Threshold
(Note 2)VCC = +2.5V to +5.5V1.231.251.27V
FB Undervoltage Fault
Threshold (Note 2)FB falling525575625mV
FB Input Bias CurrentVFB = 1.3V650nA
EXT high24EXT ResistanceIEXT = 20mA
EXT low1.53
Soft-Start Ramp Time2.23.24.2ms
Logic Input HighVCC = +2.5V to +5.5V, SET, SHDN1.6V
Logic Input LowVCC = +2.5V to +5.5V, SET, SHDN0.4V
Logic Input Leakage CurrentSET, SHDN = VCC or GND-1+1µA
MAX1522/MAX1523/MAX1524
MAX1522/MAX1523/MAX1524
Simple SOT23 Boost Controllers
EFFICIENCY vs. LOAD CURRENT
(DESIGN EXAMPLE 1)
MAX1522/3/4 toc01
LOAD CURRENT (mA)
EFFICIENCY (%)
VOUT = +5V
VIN = 3.3V
EFFICIENCY vs. LOAD CURRENT
(DESIGN EXAMPLE 2)
MAX1522/3/4 toc02
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = +4.2V
VIN = +3.6VVIN = +2.7V
VOUT = +12V
EFFICIENCY vs. LOAD CURRENT
(DESIGN EXAMPLE 3)
MAX1522/3/4 toc03
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = +2.4V
VIN = +1.8V
VIN = +3V
MAX1524
VOUT = +5V
EFFICIENCY vs. LOAD CURRENT
(DESIGN EXAMPLE 4)
MAX1522/3/4 toc04
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = +4.2V
VIN = +2.7V
VIN = +3.6V
VOUT = +24V
EFFICIENCY vs. LOAD CURRENT
(DESIGN EXAMPLE 5)
MAX1522/3/4 toc05
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = +3.0V
VIN = +2.4V
VIN = +1.8V
MAX1524
VOUT = +3.3V
STARTUP INPUT VOLTAGE
vs. OUTPUT CURRENT
MAX1522/3/4 toc06
LOAD CURRENT (mA)
STARTUP VOLTAGE (V)
VOUT = +3.3V
BOOTSTRAPPED
RESISTIVE LOADS
NO-LOAD INPUT CURRENT
vs. INPUT VOLTAGE
MAX1522/3/4 toc07
INPUT VOLTAGE (V)
INPUT CURRENT (mA)
NONBOOTSTRAPPED
BOOTSTRAPPED400ns/div
SWITCHING WAVEFORM
(CONTINUOUS CONDUCTION)
VIN = +3.3V, VOUT = +5V, IOUT = 350mA
A : VOUT, 200mV/div, AC-COUPLED
MAX1522/3/4 toc08
4μs/div
SWITCHING WAVEFORM
(DISCONTINUOUS CONDUCTION)
VIN = +3.3V, VOUT = +24V, IOUT = 10mA
A : VOUT, 200mV/div, AC-COUPLED
MAX1522/3/4 toc09
Typical Operating Characteristics
(TA= +25°C, unless otherwise noted.)
MAX1522/MAX1523/MAX1524
Simple SOT23 Boost Controllers
Typical Operating Characteristics (continued)
(TA= +25°C, unless otherwise noted.)
400μs/div
SOFT-START RESPONSE
200Ω RESISTIVE LOAD
A : VOUT, 5V/div
B : VSHDN, 5V/div
C : IL, 1A/div
MAX1522/3/4 toc10
400μs/div
FAULT-DETECTION RESPONSE
A : VOUT, 10V/div
B : VEXT, 5V/div
C : IL, 5A/div
MAX1522/3/4 toc11
MAX1522
40μs/div
LINE-TRANSIENT RESPONSE
VIN = +3.5V TO +4.0V, VOUT = +12V, IOUT = 60mA
A : VIN, 500mV/div, AC-COUPLED
B : VOUT, 10mV/div, AC-COUPLED
MAX1522/3/4 toc12
100μs/div
LOAD-TRANSIENT RESPONSE
VIN = +3.3V, VOUT = +12V, IOUT = 30mA TO 120mA
A : IOUT, 100mA/div
B : VOUT, 100mV/div, AC-COUPLED
MAX1522/3/4 toc13
Detailed Description
The MAX1522/MAX1523/MAX1524 are simple, com-
pact boost controllers designed for a wide range of
DC-DC conversion topologies including step-up,
SEPIC, and flyback applications. These devices are
designed specifically to provide a simple application
circuit with a minimum of external components and are
ideal for PDAs, digital cameras, and other low-cost
consumer electronics applications.
These devices use a unique fixed on-time, minimum
off-time architecture, which provides excellent efficien-
cy over a wide range of input/output voltage combina-
tions and load currents. The fixed on-time is pin
selectable to either 0.5µs or 3µs, permitting optimiza-
tion of external component size and ease of design for
a wide range of output voltages.
Control Scheme
The MAX1522/MAX1523/MAX1524 feature a unique
fixed on-time, minimum off-time architecture, which pro-
vides excellent efficiency over a wide range of
input/output voltage combinations. The fixed on-time is
pin selectable to either 0.5µs or 3µs for a maximum
duty factor of either 45% or 80%, respectively. An
inductor charging cycle is initiated by driving EXT high,
turning on the external MOSFET. The MOSFET remains
on for the fixed on-time, after which EXT turns off the
MOSFET. EXT stays low for at least the minimum off-
time, and another cycle begins when FB drops below
its 1.25V regulation point.
Bootstrapped vs. Nonbootstrapped
The VCCsupply voltage range of the MAX1522/
MAX1523/MAX1524 is +2.5V to +5.5V. The supply for
VCCcan come from the input voltage (nonboot-
strapped), the output voltage (bootstrapped), or an
independent regulator.
The MAX1522/MAX1523 are usually utilized in a non-
bootstrapped configuration, allowing for high or low
output voltage operation. However, when both the input
and output voltages fall within the +2.5V to +5.5V
range, the MAX1522/MAX1523 may be operated in
nonbootstrapped or bootstrapped mode. Bootstrapped
mode provides higher gate-drive voltage to the MOS-
FET switch, reducing I2R losses in the switch, but will
also increase the VCCsupply current to charge and
discharge the gate. Depending upon the MOSFET
selected, there may be minor variation in efficiency vs.
load vs. input voltage when comparing bootstrapped
and nonbootstrapped configurations.
The MAX1524 is always utilized in bootstrapped config-
uration for applications where the input voltage range
extends down below 2.5V and the output voltage is
between 2.5V and 5.5V. VCCis connected to the output
(through a 10Ωseries resistor) and receives startup
voltage through the DC current path from the input
through the inductor, diode, and 10Ωresistor. The
MAX1522/MAX1523/MAX1524
SimpleSOT23 Boost Controllers
Pin Description
PINNAMEFUNCTIONGNDGroundFBFeedback Input. Connect FB to external resistive voltage-divider. FB regulates to 1.25V.SET
On-Time Control. Connect SET to VCC to set the fixed 3μs on-time (85% duty cycle). Connect SET to
GND to set the fixed 0.5μs on-time (50% duty cycle). See On-Time SET Input section for more
information.SHDNShutdown Control Input. Drive SHDN high for normal operation. Drive SHDN low for low-power
shutdown mode. Driving SHDN low clears the fault latch of the MAX1522 and MAX1524.EXTExternal MOSFET Drive. EXT drives the gate of an external NMOS power FET and swings from VCC
to GND.
6VCC
Supply Voltage to the IC. Bypass VCC to GND with a 0.1μF capacitor. Connect VCC to a +2.5V to
+5.5V supply, which may come from VIN (nonbootstrapped) or VOUT (bootstrapped) or from the
output of another regulator. For bootstrapped operation, connect VCC to the output through a series
10Ω resistor.
MAX1522/MAX1523/MAX1524
Simple SOT23 Boost Controllers
guarantees startup with input voltages down to 1.5V at
VCC. The startup oscillator has a fixed 25% duty cycle
and will toggle the MOSFET gate and begin boosting
the output voltage. Once the output voltage exceeds
the UVLO threshold, the normal control circuitry is used
and the startup oscillator is disabled. However, N-chan-
nel MOSFETs are rarely specified for guaranteed
RDS(ON)with VGSbelow 2.5V; therefore, guaranteed
startup down to 1.5V input will be limited by the MOS-
FET specifications. Nevertheless, the MAX1524 boot-
strapped circuit on the MAX1524 EV kit typically starts
up with input voltage below 1V and no load.
The MAX1522/MAX1523 may also be utilized by con-
necting VCCto the output of an independent voltage
regulator between 2.5V and 5.5V to allow operation with
any combination of low or high input and output volt-
ages. In this case, the independent regulator must sup-
ply enough current to satisfy the IGATEcurrent as
calculated in the Power MOSFET Selectionsection
when considering the maximum switching frequency as
calculated in the CCM or DCM design procedure.
On-Time SET Input
The MAX1522/MAX1523/MAX1524 feature pin-selec-
table fixed on-time control, allowing their operation to
be optimized for various input/output voltage combina-
tions. Connect SET to VCCfor the 3µs fixed on-time.
Connect SET to GND for the 0.5µs fixed on-time.
The 3µs on-time setting (SET = VCC) permits higher
than 80% guaranteed maximum duty factor, providing
improved efficiency in applications with higher step-up
ratios (such as 3.3V boosting to 12V). This setting is
recommended for higher step-up ratio applications.
The 0.5µs on-time setting (SET = GND) permits higher
frequency operation, minimizing the size of the external
inductor and capacitors. The maximum duty factor is
limited to 45% guaranteed, making this setting suitable
for lower step-up ratios such as 3.3V to 5V converters.
Soft-Start
The MAX1522/MAX1523/MAX1524 have a unique soft-
start mode that reduces inductor current during startup,
reducing battery, input capacitor, MOSFET, and induc-
tor stresses. The soft-start period is fixed at 3.2ms and
requires no external components.
Fault Detection
Once the soft-start period has expired, if the output
voltage falls to, or is less than, 50% of its regulation
value, a fault is detected. Under this condition, the
MAX1522 disables the regulator until either SHDNis
toggled low or power is removed and reapplied, after
which it attempts to power up again in soft-start. For the
MAX1523, the fault condition is not latched, and soft-
start is repetitively reinitiated until a valid output voltage
is realized. The MAX1524 has a latched fault detection,
but when bootstrapped, the latch will be cleared when
VCC falls below 2.37V.
Shutdown Mode
DriveSHDNtoGNDtoplacethe MAX1522/MAX1523/
MAX1524 in shutdown mode. In shutdown, the internal
reference and control circuitry turn off, EXT is driven to
GND, the supply current is reduced to less than 1µA,
and the output drops to one diode drop below the input
voltage. Connect SHDNto VCCfor normal operation.
When exiting shutdown mode, the 3.2ms soft-start is
always initiated.
Undervoltage Lockout
The MAX1522/MAX1523 have undervoltage lockout
(UVLO) circuitry, which prevents circuit operation and
MOSFET switching when VCCis less than the UVLO
threshold (2.37V typ). The UVLO comparator has 70mV
of hysteresis to eliminate chatter due to VCCinput
impedance.
Applications Information
Setting the Output Voltage
The output voltage is set by connecting FB to a resis-
tive voltage-divider between the output and GND
(Figures 1 and 2). Select feedback resistor R2 in the
30kΩto 100kΩrange. R1 is then given by:
where VFB= 1.25V.
Design Procedure
Continuous vs. Discontinuous Conduction
A switching regulator is operating in continuous con-
duction mode (CCM) when the inductor current is not
allowed to decay to zero. This is accomplished by
selecting an inductor value large enough that the
inductor ripple current becomes less than one half of
the input current. The advantage of this mode is that
peak current is lower, reducing I2R losses and output
ripple.
In general, the best transient performance and most of
the ripple reduction and efficiency increase of CCM are
realized when the inductance is large enough to
reduce the ripple current to 30% of the input current at
maximum load. It is important to note that CCM circuits
operate in discontinuous conduction mode (DCM)V
OUT121=−⎛⎜⎞⎟
MAX1522/MAX1523/MAX1524
SimpleSOT23 Boost Controllers
under light loads. The selection of 30% ripple current
causes this to happen at loads less than approximately
1/6th of maximum load.
There are two common reasons not to run in CCM:
1) High output voltage.In this case, the output-to-
input voltage ratio exceeds the level obtainable
by the MAX1522/MAX1523/MAX1524s’ maximum duty
factor. Calculate the application’s maximum duty cycle
using the equation in the Calculate the Maximum Duty
Cyclesection. If this number exceeds 80%, you will
have to design for DCM.
2) Small output current.If the maximum output current
is very small, the inductor required for CCM may be
disproportionally large and expensive. Since I2R losses
are not a concern, it may make sense to use a smaller
inductor and run in DCM. This typically occurs when
the load current times the output-to-input voltage ratio
drops below a few hundred milliamps, although this
also depends on the external components.
Calculate the Maximum Duty Cycle
The maximum duty cycle of the application is given by:
where VDis the forward voltage drop of the Schottky
diode (about 0.5V).
Design Procedure for CCM
On-Time Selection
For CCM to occur, the MAX1522/MAX1523/MAX1524
must be able to exceed the application’s maximum
duty cycle. For applications up to 45% duty cycle, con-
nect SET to GND for 0.5µs on-time to get fast switching
and a smaller inductor. For applications up to 80% duty
cycle, it is necessary to connect SET to VCCfor 3.0µs
on-time. For applications greater than 80% duty cycle,
CCM operation is not guaranteed; see the Design
Procedure for DCM section.
Switching Frequency
A benefit of CCM is that the switching frequency
remains high as the load is reduced, whereas in DCM
the switching frequency varies directly with load. This is
important in applications where switching noise needs
to stay above the audio band. The medium- and heavy-
load switching frequency in CCM circuits is given by:
Note that fSWITCHINGis not a function of load and
varies primarily with input voltage. However, when the
load is reduced, a CCM circuit drops into DCM, and
the frequency becomes load dependent:
Calculate the Peak Inductor Current
For CCM, the peak inductor current is given by:VVIPEAKOUTDMIN
LOADMAX=×+×115.×−××SWITCHINGLIGHTLOADON
OUTDIN
OUTD
LOAD
LOADMAXV.
018×+−SWITCHINGON
OUTDIN
OUTDtV
DutyCycleVVVMAX
OUTDINMIN
OUTD()=+−×()%100
MAX1522
MAX1523
INPUT
2.7V TO 4.2V
0.1μF
OFFON
VCCEXT
SETFB
SHDNGND
10μF
6.3V
33μH
CDR74B-330MBR0530T3
FDC633NR1
130kΩ
OUTPUT
12V
33μF
TPSD336M020R0200
CFB
220pF
CFF
220pF
15.0kΩ
Figure 1. MAX1522/MAX1523 Standard Operating Circuit

Partno	Mfg	Dc	Qty	Available	Descript
MAX1523EUT	MAXIM	N/a	2500	avai	Simple SOT23 Boost Controllers
MAX1523EUT+T \|MAX1523EUTT	MAXIM	N/a	40	avai	Simple SOT23 Boost Controllers
MAX1522EUT+T	MAXIC	N/a	2500	avai	Simple SOT23 Boost Controllers