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19-2296; Rev 3; 8/05
Low-Voltage, 400mA Step-Down
DC-DC Converters in SOT23
General Description
The MAX1920/MAX1921 step-down converters deliver
over 400mA to outputs as low as 1.25V. These convert-
ers use a unique proprietary current-limited control
scheme that achieves over 90% efficiency. These
devices maintain extremely low quiescent supply current
(50µA), and their high 1.2MHz (max) operating frequency
permits small, low-cost external components. This combi-
nation makes the MAX1920/MAX1921 excellent high-
efficiency alternatives to linear regulators in space-
constrained applications.
Internal synchronous rectification greatly improves effi-
ciency and eliminates the external Schottky diode
required in conventional step-down converters. Both
devices also include internal digital soft-start to limit
input current upon startup and reduce input capacitor
requirements.
The MAX1920 provides an adjustable output voltage
(1.25V to 4V). The MAX1921 provides factory-preset
output voltages (see the
Selector Guide).
Both are
available in space-saving 6-pin SOT23 packages. The
MAX1920 is also available in a 6-pin TDFN package.
♦
400mA Guaranteed Output Current
♦
Internal Synchronous Rectifier for >90% Efficiency
♦
Tiny 6-Pin SOT23 Package
♦
Available in 6-Pin TDFN Package (MAX1920)
♦
Up to 1.2MHz Switching Frequency for Small
External Components
♦
50µA Quiescent Supply Current
♦
0.1µA Logic-Controlled Shutdown
♦
2V to 5.5V Input Range
♦
Fixed 1.5V, 1.8V, 2.5V, 3V, and 3.3V Output
Voltages (MAX1921)
♦
Adjustable Output Voltage (MAX1920)
♦
±1.5% Initial Accuracy
♦
Soft-Start Limits Startup Current
Features
MAX1920/MAX1921
Ordering Information
PART
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
-40°C to +85°C
PIN-PACKAGE
6 SOT23-6
6 SOT23-6
6 TDFN
6 TDFN
6 SOT23-6
6 SOT23-6
MAX1920EUT-T
MAX1920EUT+T
MAX1920ETT-T
MAX1920ETT+T
MAX1921EUT_ _-T
MAX1921EUT_ _+T
Applications
Next-Generation Wireless Handsets
PDAs, Palmtops, and Handy-Terminals
Battery-Powered Equipment
CDMA Power Amplifier Supply
Note:
The MAX1921 offers five preset output voltage options.
See the Selector Guide, and then insert the proper designator
into the blanks above to complete the part number.
+Denotes
lead-free package.
Typical Operating Circuit
INPUT
2V TO 5.5V
IN
C
IN
LX
4.75kΩ
5600pF
4.7µF
4.7µH
OUTPUT
1.5V UP TO 400mA
Pin Configuration
FB
5
LX
4
3
PGND
TOP VIEW
IN
1
6
LX
MAX1921
AGND
PGND
AGND
2
MAX1920
MAX1921
5
PGND
AGND
6
4
OUT (FB)
1
MAX1920
ON
SHDN
OFF
OUT
SHDN
3
2
IN
SOT23-6
SHDN
TDFN
( ) ARE FOR MAX1920 ONLY
A "+" sign will replace the first pin indicator on lead-free packages.
________________________________________________________________
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.
Low-Voltage, 400mA Step-Down
DC-DC Converters in SOT23
MAX1920/MAX1921
ABSOLUTE MAXIMUM RATINGS
IN, FB,
SHDN
to AGND . . . . . . . . . . . . . . . . . . . . .-0.3V to +6V
OUT to AGND, LX to PGND . . . . . . . . . . . .-0.3V to (IN + 0.3V)
AGND to PGND . . . . . . . . . . . . . . . . . . . . . . . . . .-0.3V to +0.3V
OUT Short Circuit to GND . . . . . . . . . . . . . . . . . . . . . . . . . . .10s
Continuous Power Dissipation (TA = +70°C)
6-Pin SOT23-6 (derate 8.7mW/°C above +70°C) . . . .695mW
6-Pin TDFN (derate 18.2mW/°C above +70°C) . . .1454.5mW
Operating Temperature Range . . . . . . . . . . . . . .-40°C to +85°C
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . .+150°C
Storage Temperature . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Lead Temperature (soldering 10s) . . . . . . . . . . . . . . . . .+300°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
IN
= 3.6V,
SHDN
= IN, T
A
= 0°C to +85°C. Typical parameters are at T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
Input Voltage Range
Startup Voltage
UVLO Threshold
UVLO Hysteresis
Quiescent Supply Current
Quiescent Supply Current
Dropout
Shutdown Supply Current
Output Voltage Accuracy
(MAX1921)
I
OUT
I
IN
I
IN
I
SHDN
No switching, no load
SHDN
= IN, OUT/FB = 0
SHDN
= GND
I
OUT
= 0, T
A
= +25°C
I
OUT
= 0 to 400mA, T
A
= -40°C to +85°C
I
OUT
= 0 to 200mA, T
A
= -40°C to +85°C
OUT BIAS Current
Output Voltage Range (MAX1920)
FB Feedback Threshold
(MAX1920)
FB Feedback Hysteresis
(MAX1920)
FB Bias Current (MAX1920)
Load Regulation
Line Regulation
SHDN
Input Voltage High
SHDN
Input Voltage Low
SHDN
Leakage Current
High-Side Current Limit
V
IH
V
IL
I
SHDN
I
LIMP
SHDN
= GND or IN
525
0.001
730
SHDN
= 0
OUT at regulation voltage
Figure 4, IN = 4.5V
T
A
= 25°C
V
FB
T
A
= -40°C to +85°C
V
HYS
I
FB
FB = 1.5V
I
OUT
= 0 to 400mA
V
IN
= 2.5V to 5.5V
1.6
0.4
1.000
950
1.25
1.231
1.220
1.210
5
0.01
0.005
0.2
0.20
1.25
1.25
8
UVLO
V
IN
rising
V
IN
falling
1.50
1.85
1.65
200
50
220
0.1
-1.5
-3
-3
70
300
4.0
+1.5
+3
+3
1
16
4.00
1.269
1.280
1.280
mV
µA
%/mA
%/V
V
V
µA
mA
V
µA
V
%
SYMBOL
I(LX) < 400mA
V
IN
I(LX) < 200mA
(MAX1921EUT15, MAX1921EUT18)
CONDITIONS
MIN
2.5
2.0
TYP
MAX
5.5
2.5
2.0
1.95
V
V
V
mV
µA
µA
µA
UNITS
2
_______________________________________________________________________________________
Low-Voltage, 400mA Step-Down
DC-DC Converters in SOT23
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 3.6V,
SHDN
= IN, T
A
= 0°C to +85°C. Typical parameters are at T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
Low-Side Current Limit
High-Side On-Resistance
Rectifier On-Resistance
Rectifier Off-Current Threshold
LX Leakage Current
LX Reverse Leakage Current
Minimum On-Time
Minimum Off-Time
SYMBOL
I
LIMN
R
ONHS
R
ONSR
I
LXOFF
I
LXLEAK
I
LXLKR
t
ON(MIN)
t
OFF(MIN)
IN =
SHDN
= 5.5V, LX = 0 to IN
IN unconnected, V
LX
= 5.5V,
SHDN
= GND
0.28
0.28
I
LX
= -40mA, V
IN
= 3V
I
LX
= 40mA, V
IN
= 3V
CONDITIONS
MIN
350
TYP
550
0.6
0.5
60
0.1
0.1
0.4
0.4
5.0
5.0
0.5
0.5
MAX
800
1.1
0.9
UNITS
mA
Ω
Ω
mA
µA
µA
µs
µs
MAX1920/MAX1921
Note 1:
All devices are 100% production tested at T
A
= +25°C. Limits over the operating temperature range are guaranteed
by design.
Typical Operating Characteristics
(C
IN
= 2.2µF ceramic, Circuit of Figure 1, components of Table 1, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= 3.3V)
MAX1920 toc01
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= 2.5V)
MAX1920 toc02
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= 1.5V)
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
V
IN
= 5V
V
IN
= 3.3V
V
IN
= 2.5V
MAX1920 toc03
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
V
IN
= 3.6V
V
IN
= 5V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
V
IN
= 2.7V
100
V
IN
= 4.2V
V
IN
= 3.3V
V
IN
= 5V
1
10
100
1000
0.1
1
10
100
1000
0.1
1
10
100
1000
LOAD CURRENT ( mA)
LOAD CURRENT ( mA)
LOAD CURRENT ( mA)
OUTPUT VOLTAGE ACCURACY vs. LOAD
(V
OUT
= 3.3V)
MAX1920 toc04
OUTPUT VOLTAGE ACCURACY vs. LOAD
(V
OUT
= 2.5V)
MAX1920 toc05
OUTPUT VOLTAGE ACCURACY vs. LOAD
(V
OUT
= 1.5V)
MAX1920 toc06
3.399
3.366
OUTPUT VOLTAGE
3.333
3.300
V
IN
= 4.2V
3.267
V
IN
= 3.6V
3.234
3.201
0
50
2.575
2.550
OUTPUT VOLTAGE
2.525
2.500
V
IN
= 3V
2.475
2.450
2.425
1.545
1.530
OUTPUT VOLTAGE
1.515
1.500
1.485
1.470
1.455
V
IN
= 5V
V
IN
= 5V
V
IN
= 5V
V
IN
= 3.3V
V
IN
= 2.5V
100 150 200 250 300 350 400
LOAD (mA)
0
50
100 150 200 250 300 350 400
LOAD (mA)
0
50
100 150 200 250 300 350 400
LOAD (mA)
_______________________________________________________________________________________
3
Low-Voltage, 400mA Step-Down
DC-DC Converters in SOT23
MAX1920/MAX1921
Typical Operating Characteristics (continued)
(C
IN
= 2.2µF ceramic, Circuit of Figure 1, components of Table 1, unless otherwise noted.)
SWITCHING FREQUENCY vs. LOAD
(V
OUT
= 1.8V)
MAX1920 toc07
SWITCHING FREQUENCY vs. LOAD
(V
OUT
= 1.5V)
MAX1920 toc08
NO LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX1920 toc09
10,000
10,000
10,000
NO-LOAD SUPPLY CURRENT (µA)
V
OUT
= 2.5V
1000
V
OUT
= 3.3V
SWITCHING FREQUENCY (kHz)
1000
SWITCHING FREQUENCY (kHz)
1000
100
100
100
V
OUT
= 1.5V
10
10
V
IN
= 3.3
1
0.1
1
10
LOAD (mA)
100
1000
10
V
IN
= 3.3
1
0.1
1
10
LOAD (mA)
100
1000
1
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5..0
5.5
SUPPLY VOLTAGE (V)
LIGHT-LOAD SWITCHING WAVEFORM
MAX1920 toc10
MEDIUM-LOAD SWITCHING WAVEFORM
MAX1920 toc11
SOFT-START AND SHUTDOWN RESPONSE
MAX1920 toc12
V
OUT
AC-COUPLED
5mV/div
V
OUT
AC-COUPLED
5mV/div
V
OUT
1V/div
I
IN
100mA/div
V
LX
2V/div
V
LX
2V/div
V
SHDN
5V/div
V
IN
= 3.3V, V
OUT
= 1.5V,
I
LOAD
= 40mA
1µs/div
V
IN
= 3.3V, V
OUT
= 1.5V,
I
LOAD
= 250mA
1µs/div
V
IN
= 3.3V, V
OUT
= 1.5V,
R
LOAD
= 6Ω
200µs/div
MEDIUM-LOAD
LINE-TRANSIENT RESPONSE
MAX1920 toc13
LIGHT-LOAD
LINE-TRANSIENT RESPONSE
MAX1920 toc14
LOAD-TRANSIENT RESPONSE
MAX1920 toc15
V
IN
= 3.3V, V
OUT
= 1.5V,
I
LOAD
= 20mA TO 320mA
V
IN
AC-COUPLED
200mV/div
V
IN
AC-COUPLED
200mV/div
V
OUT
AC-COUPLED
100mV/div
I
L
200mA/div
V
OUT
AC-COUPLED
5mV/div
V
IN
= 3.8V to 4.2V,
V
OUT
= 1.5V, I
LOAD
= 250mA
4µs/div
V
IN
= 3.8V to 4.2V,
V
OUT
= 1.5V, I
LOAD
= 20mA
4µs/div
V
OUT
AC-COUPLED
5mV/div
I
LOAD
200mA/div
40µs/div
4
_______________________________________________________________________________________
Embedded System
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