19-2221; Rev 1; 3/04
1.4MHz SOT23 Current-Mode
Step-Up DC-DC Converter
MAX1896
General Description
The MAX1896 step-up DC-DC converter incorporates
high-performance current-mode, fixed-frequency,
pulse-width modulation (PWM) circuitry and an internal
0.7Ω N-channel MOSFET to provide a highly efficient
regulator with fast response.
High switching frequency (1.4MHz) allows fast loop
response and easy filtering with small components. The
MAX1896 can produce an output voltage as high as
13V from an input as low as 2.6V. Soft-start is program-
mable with an external capacitor, which sets the input
current ramp rate. In shutdown mode, current con-
sumption is reduced to 0.01µA.
The MAX1896 is available in a space-saving 6-pin
SOT23 package. The ultra-small package and high
switching frequency allow cost and space-efficient
implementations.
♦
>90% Efficiency
♦
Adjustable Output Up to 13V
♦
Guaranteed 12V/120mA Output from 5V Input
♦
2.6V to 5.5V Input Range
♦
LT1613 Pin Compatible
♦
0.01µA Shutdown Current
♦
Programmable Soft-Start
♦
Space-Saving 6-Pin SOT23 Package
Features
Applications
Notebook Computers
LCD Displays
PCMCIA Cards
Portable Applications
Hand-Held Devices
PART
MAX1896EUT-T
Ordering Information
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
6 SOT23-6
Typical Operating Circuit
INPUT
2.6V TO 5.5V
Pin Configuration
TOP VIEW
OUTPUT
UP TO 13V
UP TO 600mA
IN
LX
LX
1
6
IN
GND
2
MAX1896
5
SS
MAX1896
R1
ON
OFF
SHDN
SS
FB
GND
R2
FB
3
4
SHDN
SOT23
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1.4MHz SOT23 Current-Mode
Step-Up DC-DC Converter
MAX1896
ABSOLUTE MAXIMUM RATINGS
LX to GND ..............................................................-0.3V to +14V
IN,
SHDN,
FB to GND...............................................-0.3V to +6V
SS to GND ...................................................-0.3V to (V
IN
+ 0.3V)
RMS LX Pin Current ..............................................................0.6A
Continuous Power Dissipation (T
A
= +70°C) (Note 1)
6-Pin SOT23 (derate 9.1mW/°C above +70°C)...........727mW
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
Note 1:
Thermal properties are specified with product mounted on PC board with one square-inch of copper area and still air.
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
IN
= V
SHDN
= 3V, FB = GND, SS = open,
T
A
= 0°C to +85°C,
unless otherwise noted.)
PARAMETER
Input Supply Range
Output Voltage Adjust Range
V
IN
Undervoltage Lockout
Quiescent Current
Shutdown Supply Current
ERROR AMPLIFIER
Feedback Regulation Set Point
FB Input Bias Current
Line Regulation
OSCILLATOR
Frequency
Maximum Duty Cycle
POWER SWITCH
Current Limit (Note 2)
On-Resistance
Leakage Current
SOFT-START
Reset Switch Resistance
Charge Current
CONTROL INPUT
Input Low Voltage
Input High Voltage
SHDN
Input Current
V
IL
V
IH
I
SHDN
V
SHDN,
V
IN
= 2.6V to 5.5V
V
SHDN,
V
IN
= 2.6V to 5.5V
V
SHDN
= 3V
V
SHDN
= 0
1.0
25
0.01
50
0.1
0.3
V
V
µA
V
SS
= 1.2V
1.5
4
100
7.0
Ω
µA
I
LIM
R
ON
I
LXOFF
V
LX
= 12V, T
A
= +25°C
V
LX
= 12V
V
FB
= 1V, duty cycle = 50%
0.55
0.8
0.7
0.1
1
1
10
A
Ω
µA
f
OSC
DC
1000
82
1400
86
1800
kHz
%
V
FB
I
FB
V
FB
= 1.24V
2.6V < V
IN
< 5.5V
1.2
1.24
21
0.05
1.25
80
0.20
V
nA
%/V
SYMBOL
V
IN
V
OUT
UVLO
I
IN
Circuit of Figure 1
V
IN
rising, 50mV hysteresis
V
FB
= 1.3V, not switching
V
FB
= 1.0V, switching
V
SHDN
= 0, T
A
= +25°C
V
SHDN
= 0
2.25
2.4
0.2
1
0.01
0.01
CONDITIONS
MIN
2.6
TYP
MAX
5.5
13
2.55
0.4
5
0.5
10
UNITS
V
V
V
mA
µA
2
_______________________________________________________________________________________
1.4MHz SOT23 Current-Mode
Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS
(V
IN
= V
SHDN
= 3V, FB = GND, SS = open,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 3)
PARAMETER
Input Supply Range
Output Voltage Adjust Range
V
IN
Undervoltage Lockout
Quiescent Current
Shutdown Supply Current
ERROR AMPLIFIER
Feedback Regulation Set Point
FB Input Bias Current
Line Regulation
OSCILLATOR
Frequency
Maximum Duty Cycle
POWER SWITCH
Current Limit (Note 2)
On-Resistance
Leakage Current
SOFT-START
Reset Switch Resistance
Charge Current
CONTROL INPUT
Input Low Voltage
Input High Voltage
SHDN
Input Current
V
IL
V
IH
I
SHDN
V
SS
= 1.2V
V
SHDN
= V
IN
= 2.6V to 5.5V
V
SHDN
= V
IN
= 2.6V to 5.5V
V
SHDN
= 3V
V
SHDN
= 0
1.0
50
0.1
1.25
I
LIM
R
ON
I
LXOFF
V
LX
= 12V
V
FB
= 1V, duty cycle = 50%
0.55
1
10
100
7.50
0.3
A
Ω
µA
Ω
µA
V
V
µA
f
OSC
DC
1000
82
1800
kHz
%
V
FB
I
FB
V
FB
= 1.24V
2.6V < V
IN
< 5.5V
1.2
1.25
80
0.20
V
nA
%/V
SYMBOL
V
IN
V
OUT
UVLO
I
IN
Circuit of Figure 1
V
IN
rising, 50mV hysteresis.
V
FB
= 1.3V, not switching
V
FB
= 1.0V, switching
V
SHDN
= 0
2.25
CONDITIONS
MIN
2.6
TYP
MAX
5.5
13
2.55
0.4
5
10
UNITS
V
V
V
mA
µA
MAX1896
Note 2:
Current limit varies with duty cycle due to slope compensation. See the
Output Current Capability
section.
Note 3:
Specifications to -40°C are guaranteed by design and not production tested.
_______________________________________________________________________________________
3
1.4MHz SOT23 Current-Mode
Step-Up DC-DC Converter
MAX1896
Typical Operating Characteristics
(Circuit of Figure 1, V
IN
= 3.3V, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT
MAX1896 toc01
EFFICIENCY vs. OUTPUT CURRENT
MAX1896 toc02
EFFICIENCY vs. OUTPUT CURRENT
MAX1896 toc03
100
100
100
90
EFFICIENCY (%)
90
EFFICIENCY (%)
90
EFFICIENCY (%)
80
80
80
70
70
70
60
V
IN
= 3.3V,
V
OUT
= 5V,
CIRCUIT OF FIGURE 1
1
10
100
1000
60
V
IN
= 3.3V,
V
OUT
= 13V,
CIRCUIT OF FIGURE 3
1
10
100
1000
60
V
IN
= 5V,
V
OUT
= 13V,
CIRCUIT OF FIGURE 3
1
10
100
1000
50
OUTPUT CURRENT (mA)
50
OUTPUT CURRENT (mA)
50
OUTPUT CURRENT (mA)
NO LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX1896 toc04
OUTPUT VOLTAGE vs. OUTPUT CURRENT
CIRCUIT OF FIGURE 3
MAX1896 toc05
LOAD TRANSIENT (V
OUT
= 13V)
MAX1896 toc06
2.0
NO LOAD SUPPLY CURRENT (mA)
13.10
1.5
OUTPUT VOLTAGE (V)
13.05
T
A
= +25°C
13.00
LOAD
CURRENT
100mA/div
OUTPUT
VOLTAGE
AC-COUPLED
200mV/div
1.0
0.5
V
OUT
= 13V,
CIRCUIT OF FIGURE 3
12.95
T
A
= -40°C
12.90
T
A
= +85°C
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
INDUCTOR
CURRENT
500mA/div
200
200µs/div
C
FF
= 100pF, C
OUT
= 0.1µF CERAMIC + 10µF CERAMIC
0
50
100
150
OUTPUT CURRENT (mA)
LOAD TRANSIENT (V
OUT
= 5V)
MAX1896 toc07
STARTUP WAVEFORM
WITHOUT SOFT-START
MAX1896 toc08
STARTUP WAVEFORM
WITH SOFT-START
I
OUT
= 10mA
SHDN
5V/div
OUTPUT
VOLTAGE
5V/div
MAX1896 toc09
LOAD
CURRENT
200mA/div
OUTPUT
VOLTAGE
AC-COUPLED
200mV/div
SHDN
5V/div
OUTPUT
VOLTAGE
5V/div
INDUCTOR
CURRENT
500mA/div
INDUCTOR
CURRENT
500mA/div
400µs/div
C
OUT
= 0.1µF CERAMIC + 22µF TANTALUM
INDUCTOR
CURRENT
500mA/div
100µs/div
V
IN
= 3.3V, C
OUT
= 0.1µF CERAMIC + 3.3µF TANTALUM
CIRCUIT OF FIGURE 3
2ms/div
V
IN
= 3.3V, C
SS
= 33nF,
C
OUT
= 3.3µF TANTALUM + 0.1µF CERAMIC
CIRCUIT OF FIGURE 3
4
_______________________________________________________________________________________
1.4MHz SOT23 Current-Mode
Step-Up DC-DC Converter
MAX1896
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
IN
= 3.3V, T
A
= +25°C, unless otherwise noted.)
STARTUP WAVEFORM
WITH SOFT-START
I
OUT
= 100mA
SHDN
5V/div
OUTPUT
VOLTAGE
5V/div
MAX1896 toc10
SWITCHING WAVEFORM
MAX1896 toc11
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
MAX1896 toc12
600
MAXIMUM OUTPUT CURRENT (mA)
500
400
300
200
100
0
MAXIMUM OUTPUT
CURRENT DEFINED AT
90% OF NO LOAD
OUTPUT VOLTAGE
2.5
3.0
3.5
4.0
4.5
5.0
V
OUT
= 5V
V
OUT
= 12V
LX VOLTAGE
5V/div
OUTPUT
VOLTAGE
AC-COUPLED
200mV/div
INDUCTOR
CURRENT
500mA/div
2ms/div
V
IN
= 3.3V, C
SS
= 33nF,
C
OUT
= 3.3µF TANTALUM + 0.1µF CERAMIC
CIRCUIT OF FIGURE 3
400ns/div
V
IN
= 5V,
C
OUT
= 0.1µF CERAMIC + 2.2µF CERAMIC
INDUCTOR
CURRENT
500mA/div
I
OUT
= 150mA
5.5
INPUT VOLTAGE (V)
Pin Description
PIN
1
2
3
NAME
LX
GND
FB
FUNCTION
Power Switching Connection. Connect LX to the inductor and output rectifier. Connect components
as close to LX as possible.
Ground
Feedback Input. Connect a resistive voltage-divider from the output to FB to set the output voltage.
See the
Setting the Output Voltage
section.
Shutdown Input. Drive
SHDN
low to turn off the converter. To automatically start the converter,
connect
SHDN
to IN. Drive
SHDN
with a slew rate of 0.1V/µs or greater. Do not leave
SHDN
unconnected.
SHDN
draws up to 50µA.
Soft-Start Input. Connect a soft-start capacitor from SS to GND to soft-start the converter. Leave SS
open to disable the soft-start function. See the
Soft-Start
section.
Internal Bias Voltage Input. Connect IN to the input voltage source. Bypass IN to GND with a
1µF or greater capacitor as close to IN as possible.
4
SHDN
5
6
SS
IN
_______________________________________________________________________________________
5
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