Rainbow Electronics MAX1524 User Manual

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 off­time 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 compo­nent 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 condi­tions. The MAX1522/MAX1524 have a latched fault
mode, which shuts down the controller when a short­circuit event occurs, whereas the MAX1523 reenters
soft-start mode during output fault conditions. The
MAX1522/MAX1523/MAX1524 are available in a space­saving 6-pin SOT23 package.

________________________Applications

____________________________Features

♦ Simple, Flexible Application Circuit
♦ 2-Cell NiMH or Alkaline Operation (MAX1524)
♦ Low Quiescent Current (25µA typ)
♦ Output Fault Protection and Soft-Start
♦ High Efficiency Over 1000:1 I

OUT

Range

♦ Pin-Selectable Maximum Duty Factor
♦ Micropower Shutdown Mode
♦ Small 6-Pin SOT23 Package
♦ No Current-Sense Resistor

MAX1522/MAX1523/MAX1524

Simple SOT23 Boost Controllers

________________________________________________________________ Maxim Integrated Products 1

__________Typical Operating Circuit

19-1926; Rev 0; 2/01

For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

PART

TEMP. RANGE

PIN­PACKAGE

TOP

MARK

MAX1522EUT-T

6 SOT23-6

AAOX

MAX1523EUT-T

6 SOT23-6

AAOY

MAX1524EUT-T

6 SOT23-6

AAOZ

Ordering Information

Pin Configurations

FB

SHDNSET

16V

CC

5 EXT

GND

MAX1522
MAX1523
MAX1524

SOT23-6

TOP VIEW

2

34

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

-40°C to +85°C

-40°C to +85°C

-40°C to +85°C

INPUT

OUTPUT

V

CC

6

V

CC

EXT

5

N

MAX1522

3

MAX1523

4

SET

SHDN

MAX1524

50% 85%

OFF ON

GND

2

FB

1

Simple SOT23 Boost Controllers

2 _______________________________________________________________________________________

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 V

GS(TH)

.

Note 2: Specification applies after soft-start mode is completed.

V

CC

, FB, SHDN, SET to GND...................................-0.3V to +6V

EXT to GND................................................-0.3V to (V

CC

+ 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

PARAMETER CONDITIONS

MIN

TYP

MAX

UNITS

VCC Operating Voltage Range 2.5 5.5 V

MAX1522/MAX1523 2.5

V

CC

Minimum Startup Voltage

f

EXT

> 100kHz, MAX1524 (Note 1), bootstrap required 1.5

V

VCC rising

Undervoltage Lockout
Threshold

V

CC

falling

V

V

CC

Supply Current No load, nonbootstrapped 25 50 µA

V

CC

Shutdown Current SHDN = GND

1µA

SET = GND 0.4 0.5 0.6

Fixed tON Time VFB =1.2V

SET = V

CC

2.4 3.0 3.6

µs

VFB > 0.675V 0.5

Minimum t

OFF

Time

V

FB

< 0.525V 1.0

µs

SET = GND 45 50 55

Maximum Duty Factor

SET = V

CC

80 85 90

%

FB Regulation Threshold
(Note 2)

V

CC

= +2.5V to +5.5V

V

FB Undervoltage Fault
Threshold (Note 2)

FB falling

575 625 mV

FB Input Bias Current VFB = 1.3V 6 50 nA

EXT high 2 4

EXT Resistance I

EXT

= 20mA

EXT low 1.5 3

Ω

Soft-Start Ramp Time 2.2 3.2 4.2 ms
Logic Input High VCC = +2.5V to +5.5V, SET, SHDN 1.6 V
Logic Input Low VCC = +2.5V to +5.5V, SET, SHDN 0.4 V
Logic Input Leakage Current SET, SHDN = VCC or GND -1 +1 µA

MAX1522/MAX1523/MAX1524

2.37 2.47

2.20 2.30

0.001

1.23 1.25 1.27

525

MAX1522/MAX1523/MAX1524

Simple SOT23 Boost Controllers

_______________________________________________________________________________________ 3

100

50

0.1 1 100 1000

EFFICIENCY vs. LOAD CURRENT

(DESIGN EXAMPLE 1)

70

80

90

MAX1522/3/4 toc01

LOAD CURRENT (mA)

EFFICIENCY (%)

10

60

V

OUT

= +5V

V

IN

= 3.3V

100

50

0.1 1 100 1000

EFFICIENCY vs. LOAD CURRENT

(DESIGN EXAMPLE 2)

70

80

90

MAX1522/3/4 toc02

LOAD CURRENT (mA)

EFFICIENCY (%)

10

60

VIN = +4.2V

VIN = +3.6V

VIN = +2.7V

V

OUT

= +12V

100

50

0.1 1 100 1000

EFFICIENCY vs. LOAD CURRENT

(DESIGN EXAMPLE 3)

70

80

90

MAX1522/3/4 toc03

LOAD CURRENT (mA)

EFFICIENCY (%)

10

60

VIN = +2.4V

VIN = +1.8V

VIN = +3V

MAX1524
V

OUT

= +5V

100

50

0.1 1 100

EFFICIENCY vs. LOAD CURRENT

(DESIGN EXAMPLE 4)

70

80

90

MAX1522/3/4 toc04

LOAD CURRENT (mA)

EFFICIENCY (%)

10

60

VIN = +4.2V

VIN = +2.7V

VIN = +3.6V

V

OUT

= +24V

100

50

0.1 1 100

EFFICIENCY vs. LOAD CURRENT

(DESIGN EXAMPLE 5)

70

80

90

MAX1522/3/4 toc05

LOAD CURRENT (mA)

EFFICIENCY (%)

10

60

VIN = +3.0V

VIN = +2.4V

VIN = +1.8V

MAX1524
V

OUT

= +3.3V

1.75

1.50

1.25

1.00

0.75
05025 75 100

STARTUP INPUT VOLTAGE

vs. OUTPUT CURRENT

MAX1522/3/4 toc06

LOAD CURRENT (mA)

STARTUP VOLTAGE (V)

V

OUT

= +3.3V

BOOTSTRAPPED

RESISTIVE LOADS

10

0.0001
01 3 4

NO-LOAD INPUT CURRENT

vs. INPUT VOLTAGE

0.01

0.1

1

MAX1522/3/4 toc07

INPUT VOLTAGE (V)

INPUT CURRENT (mA)

2

0.001

NONBOOTSTRAPPED

BOOTSTRAPPED

5

400ns/div

SWITCHING WAVEFORM

(CONTINUOUS CONDUCTION)

VIN = +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

A

C

B

MAX1522/3/4 toc08

4µs/div

SWITCHING WAVEFORM

(DISCONTINUOUS CONDUCTION)

VIN = +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

A

C

B

MAX1522/3/4 toc09

Typical Operating Characteristics

(TA= +25°C, unless otherwise noted.)

MAX1522/MAX1523/MAX1524

Simple SOT23 Boost Controllers

4 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(TA= +25°C, unless otherwise noted.)

400µs/div

SOFT-START RESPONSE

200Ω RESISTIVE LOAD
A : V

OUT

, 5V/div

B : V

SHDN

, 5V/div

C : I

L

, 1A/div

A

C

B

MAX1522/3/4 toc10

400µs/div

FAULT-DETECTION RESPONSE

A : V

OUT

, 10V/div

B : V

EXT

, 5V/div

C : I

L

, 5A/div

A

C

B

MAX1522/3/4 toc11

MAX1522

40µs/div

LINE-TRANSIENT RESPONSE

VIN = +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

A

B

MAX1522/3/4 toc12

100µs/div

LOAD-TRANSIENT RESPONSE

VIN = +3.3V, V

OUT

= +12V, I

OUT

= 30mA TO 120mA

A : I

OUT,

100mA/div

B : V

OUT,

100mV/div, AC-COUPLED

A

B

MAX1522/3/4 toc13

Detailed 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. 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 efficien­cy over a wide range of input/output voltage combina­tions and load currents. The fixed on-time is pin
selectable to either 0.5µs or 3µs, permitting optimiza­tion 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 pro­vides 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
V

CC

can come from the input voltage (nonboot­strapped), the output voltage (bootstrapped), or an
independent regulator.

The MAX1522/MAX1523 are usually utilized in a non­bootstrapped 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 MOS­FET 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 config­uration 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 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

MAX1522/MAX1523/MAX1524

Simple SOT23 Boost Controllers

_______________________________________________________________________________________ 5

Pin Description

PIN NAME FUNCTION

1 GND Ground
2 FB Feedback Input. Connect FB to external resistive voltage-divider. FB regulates to 1.25V.

3 SET

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.

4 SHDN

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.

5 EXT

External MOSFET Drive. EXT drives the gate of an external NMOS power FET and swings from V

CC

to GND.

6V

CC

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 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.