19-1926; Rev 1; 8/10
KIT
ATION
EVALU
BLE
AVAILA
Simple SOT23 Boost Controllers
____________________________Features
o
Simple, Flexible Application Circuit
o
2-Cell NiMH or Alkaline Operation (MAX1524)
o
Low Quiescent Current (25µA typ)
o
Output Fault Protection and Soft-Start
o
High Efficiency Over 1000:1 I
OUT
Range
o
Pin-Selectable Maximum Duty Factor
o
Micropower Shutdown Mode
o
Small 6-Pin SOT23 Package
o
No Current-Sense Resistor
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.
MAX1522/MAX1523/MAX1524
Ordering Information
PART
MAX1522EUT-T
MAX1523EUT-T
MAX1524EUT-T
MAX1522EUT+T
MAX1523EUT+T
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
6 SOT23
6 SOT23
6 SOT23
6 SOT23
6 SOT23
TOP
MARK
AAOX
AAOY
AAOZ
+AAOX
+AAOY
+AAOZ
MAX1524EUT+T
-40°C to +85°C
6 SOT23
+Denotes
a lead(Pb)-free/RoHS-compliant package.
-Denotes
a package containing lead(Pb).
T = Tape and reel.
________________________Applications
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
__________Typical Operating Circuit
INPUT
OUTPUT
Pin Configuration
TOP VIEW
GND
1
6
V
CC
V
CC
6 V
CC
MAX1522
SET
MAX1523
MAX1524
SHDN
EXT
5
N
50% 85%
FB
2
3
4
FB
GND
2
1
MAX1522
MAX1523
MAX1524
5
EXT
OFF ON
SET
3
4
SHDN
SOT23
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Simple SOT23 Boost Controllers
MAX1522/MAX1523/MAX1524
ABSOLUTE MAXIMUM RATINGS
V
CC
, FB,
SHDN,
SET to GND ...................................-0.3V to +6V
EXT to GND ................................................-0.3V to (V
CC
+ 0.3V)
Continuous Power Dissipation (T
A
= +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
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
(V
CC
=
SHDN
= 3.3V, SET = GND , T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
V
CC
Operating Voltage Range
V
CC
Minimum Startup Voltage
Undervoltage Lockout
Threshold
V
CC
Supply Current
V
CC
Shutdown Current
Fixed t
ON
Time
Minimum t
OFF
Time
Maximum Duty Factor
FB Regulation Threshold
(Note 2)
FB Undervoltage Fault
Threshold (Note 2)
FB Input Bias Current
EXT Resistance
Soft-Start Ramp Time
Logic Input High
Logic Input Low
Logic Input Leakage Current
V
CC
= +2.5V to +5.5V, SET,
SHDN
V
CC
= +2.5V to +5.5V, SET,
SHDN
SET,
SHDN
= V
CC
or GND
-1
MAX1522/MAX1523
f
EXT
> 100kHz, MAX1524 (Note 1), bootstrap required
V
CC
rising
V
CC
falling
No load, nonbootstrapped
SHDN
= GND
V
FB
=1.2V
V
FB
> 0.675V
V
FB
< 0.525V
SET = GND
SET = V
CC
V
CC
= +2.5V to +5.5V
FB falling
V
FB
= 1.3V
I
EXT
= 20mA
EXT high
EXT low
2.2
1.6
0.4
+1
45
80
1.23
525
SET = GND
SET = V
CC
0.4
2.4
2.20
2.37
2.30
25
0.001
0.5
3.0
0.5
1.0
50
85
1.25
575
6
2
1.5
3.2
55
90
1.27
625
50
4
3
4.2
50
1
0.6
3.6
CONDITIONS
MIN
2.5
TYP
MAX
5.5
2.5
1.5
2.47
UNITS
V
V
V
µA
µA
µs
µs
%
V
mV
nA
Ω
ms
V
V
µA
Note 1:
Actual startup voltage is dependent on the external MOSFET’s V
GS(TH)
.
Note 2:
Specification applies after soft-start mode is completed.
2
_______________________________________________________________________________________
Simple SOT23 Boost Controllers
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(DESIGN EXAMPLE 1)
MAX1522/3/4 toc01
MAX1522/MAX1523/MAX1524
EFFICIENCY vs. LOAD CURRENT
(DESIGN EXAMPLE 2)
V
IN
= +4.2V
90
EFFICIENCY (%)
MAX1522/3/4 toc02
EFFICIENCY vs. LOAD CURRENT
(DESIGN EXAMPLE 3)
MAX1522/3/4 toc03
100
100
100
V
IN
= +2.4V
V
IN
= +3V
90
EFFICIENCY (%)
90
EFFICIENCY (%)
80
70
80
V
IN
= +3.6V
70
V
IN
= +2.7V
80
V
IN
= +1.8V
70
60
V
OUT
= +5V
V
IN
= 3.3V
50
0.1
1
10
100
1000
LOAD CURRENT (mA)
60
V
OUT
= +12V
50
0.1
1
10
100
1000
LOAD CURRENT (mA)
60
MAX1524
V
OUT
= +5V
50
0.1
1
10
100
1000
LOAD CURRENT (mA)
EFFICIENCY vs. LOAD CURRENT
(DESIGN EXAMPLE 4)
MAX1522/3/4 toc04
EFFICIENCY vs. LOAD CURRENT
(DESIGN EXAMPLE 5)
MAX1522/3/4 toc05
STARTUP INPUT VOLTAGE
vs. OUTPUT CURRENT
MAX1522/3/4 toc06
100
100
1.75
90
EFFICIENCY (%)
80
70
80
70
V
IN
= +2.4V
60
V
IN
= +1.8V
MAX1524
V
OUT
= +3.3V
0.1
1
10
100
STARTUP VOLTAGE (V)
V
IN
= +4.2V
90
EFFICIENCY (%)
V
IN
= +3.0V
1.50
1.25
V
IN
= +3.6V
V
IN
= +2.7V
60
V
OUT
= +24V
50
0.1
1
10
100
LOAD CURRENT (mA)
1.00
V
OUT
= +3.3V
BOOTSTRAPPED
RESISTIVE LOADS
0
25
50
LOAD CURRENT (mA)
75
100
50
LOAD CURRENT (mA)
0.75
NO-LOAD INPUT CURRENT
vs. INPUT VOLTAGE
BOOTSTRAPPED
1
INPUT CURRENT (mA)
MAX1522/3/4 toc07
SWITCHING WAVEFORM
(CONTINUOUS CONDUCTION)
MAX1522/3/4 toc08
SWITCHING WAVEFORM
(DISCONTINUOUS CONDUCTION)
MAX1522/3/4 toc09
10
A
A
0.1
B
0.01
NONBOOTSTRAPPED
C
C
B
0.001
0.0001
0
1
2
3
4
5
INPUT VOLTAGE (V)
400ns/div
V
IN
= +3.3V, V
OUT
= +5V, I
OUT
= 350mA
A : V
OUT
, 200mV/div, AC-COUPLED
B : V
LX
, 5V/div
C : I
L
, 0.5A/div
4µs/div
V
IN
= +3.3V, V
OUT
= +24V, I
OUT
= 10mA
A : V
OUT
, 200mV/div, AC-COUPLED
B : V
LX
, 10V/div
C : I
L
, 0.5A/div
_______________________________________________________________________________________
3
Simple SOT23 Boost Controllers
MAX1522/MAX1523/MAX1524
Typical Operating Characteristics (continued)
(T
A
= +25°C, unless otherwise noted.)
SOFT-START RESPONSE
MAX1522/3/4 toc10
FAULT-DETECTION RESPONSE
MAX1522/3/4 toc11
A
A
B
B
C
400µs/div
200Ω RESISTIVE LOAD
A : V
OUT
, 5V/div
B : V
SHDN
, 5V/div
C : I
L
, 1A/div
C
400µs/div
A : V
OUT
, 10V/div
B : V
EXT
, 5V/div
C : I
L
, 5A/div
MAX1522
LINE-TRANSIENT RESPONSE
MAX1522/3/4 toc12
LOAD-TRANSIENT RESPONSE
MAX1522/3/4 toc13
A
A
B
B
40µs/div
V
IN
= +3.5V TO +4.0V, V
OUT
= +12V, I
OUT
= 60mA
A : V
IN,
500mV/div, AC-COUPLED
B : V
OUT,
10mV/div, AC-COUPLED
100µs/div
V
IN
= +3.3V, V
OUT
= +12V, I
OUT
= 30mA TO 120mA
A : I
OUT,
100mA/div
B : V
OUT,
100mV/div, AC-COUPLED
4
_______________________________________________________________________________________
Simple SOT23 Boost Controllers
Pin Description
PIN
1
2
3
NAME
GND
FB
SET
Ground
Feedback Input. Connect FB to external resistive voltage-divider. FB regulates to 1.25V.
On-Time Control. Connect SET to V
CC
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.
Shutdown 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.
External MOSFET Drive. EXT drives the gate of an external NMOS power FET and swings from V
CC
to GND.
Supply Voltage to the IC. Bypass V
CC
to GND with a 0.1µF capacitor. Connect V
CC
to a +2.5V to
+5.5V supply, which may come from V
IN
(nonbootstrapped) or V
OUT
(bootstrapped) or from the
output of another regulator. For bootstrapped operation, connect V
CC
to the output through a series
10Ω resistor.
FUNCTION
MAX1522/MAX1523/MAX1524
4
5
SHDN
EXT
6
V
CC
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.
time, and another cycle begins when FB drops below
its 1.25V regulation point.
Bootstrapped vs. Nonbootstrapped
The V
CC
supply voltage range of the MAX1522/
MAX1523/MAX1524 is +2.5V to +5.5V. The supply for
V
CC
can 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 I
2
R losses in the switch, but will
also increase the V
CC
supply 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. V
CC
is connected to the output
(through a 10Ω series resistor) and receives startup
voltage through the DC current path from the input
through the inductor, diode, and 10Ω resistor. The
MAX1524 features a low-voltage startup oscillator that
5
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-
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