19-1760; Rev 2; 9/05
KIT
ATION
EVALU
BLE
AVAILA
1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
General Description
The MAX1742/MAX1842 constant-off-time, pulse-width-
modulated (PWM) step-down DC-DC converters are ideal
for use in 5V and 3.3V to low-voltage conversion neces-
sary in notebook and subnotebook computers. These
devices feature internal synchronous rectification for high
efficiency and reduced component count. They require
no external Schottky diode. The internal 90mΩ PMOS
power switch and 70mΩ NMOS synchronous-rectifier
switch easily deliver continuous load currents up to 1A.
The MAX1742/MAX1842 produce a preset 2.5V, 1.8V, or
1.5V output voltage or an adjustable output from 1.1V to
V
IN
. They achieve efficiencies as high as 95%.
The MAX1742/MAX1842 use a unique current-mode,
constant-off-time, PWM control scheme, which includes
Idle Mode™ to maintain high efficiency during light-load
operation. The programmable constant-off-time architec-
ture sets switching frequencies up to 1MHz, allowing the
user to optimize performance trade-offs between effi-
ciency, output switching noise, component size, and
cost. Both devices are designed for continuous output
currents up to 1A. The MAX1742 uses a peak current
limit of 1.3A (min) and is suitable for applications requir-
ing small external component size and high efficiency.
The MAX1842 has a higher current limit of 3.1A (min)
and is intended for applications requiring an occasional
burst of output current up to 2.7A. Both devices also fea-
ture an adjustable soft-start to limit surge currents during
startup, a 100% duty cycle mode for low-dropout opera-
tion, and a low-power shutdown mode that disconnects
the input from the output and reduces supply current
below 1µA. The MAX1742/MAX1842 are available in 16-
pin QSOP packages.
For similar devices that provide continuous output cur-
rents up to 2A and 3A, refer to the MAX1644 and
MAX1623 data sheets.
♦
±1% Output Accuracy
♦
95% Efficiency
♦
Internal PMOS and NMOS Switches
90mΩ On-Resistance at V
IN
= 4.5V
110mΩ On-Resistance at V
IN
= 3V
♦
Output Voltage
2.5V, 1.8V, or 1.5V Pin Selectable
1.1V to V
IN
Adjustable
♦
3V to 5.5V Input Voltage Range
♦
600μA (max) Operating Supply Current
♦
<1μA Shutdown Supply Current
♦
Programmable Constant-Off-Time Operation
♦
1MHz (max) Switching Frequency
♦
Idle-Mode Operation at Light Loads
♦
Thermal Shutdown
♦
Adjustable Soft-Start Inrush Current Limiting
♦
100% Duty Cycle During Low-Dropout Operation
♦
Output Short-Circuit Protection
♦
16-Pin QSOP Package
Features
MAX1742/MAX1842
Ordering Information
PART
MAX1742EEE
MAX1742EEE+
MAX1842EEE
MAX1842EEE+
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
16 QSOP
16 QSOP
16 QSOP
+
Denotes lead-free package.
Applications
5V or 3.3V to Low-Voltage Conversion
CPU I/O Ring
Chipset Supplies
Notebook and Subnotebook Computers
INPUT
3V TO
5.5V
Typical Configuration
IN
10Ω
LX
OUTPUT
1.1V TO
V
IN
MAX1742
FB
MAX1842
V
CC
PGND
GND
SHDN
COMP
TOFF
FBSEL
REF
SS
1μF
0.01μF
2.2μF
470pF
Pin Configuration appears at end of data sheet.
Idle Mode is a trademark of Maxim Integrated Products.
________________________________________________________________
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.
1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
MAX1742/MAX1842
ABSOLUTE MAXIMUM RATINGS
V
CC
, IN to GND ........................................................-0.3V to +6V
Continuous Power Dissipation (T
A
= +70°C)
IN to V
CC
.............................................................................±0.3V
SSOP (derate 16.7mW/°C above +70°C;
GND to PGND.....................................................................±0.3V
part mounted on 1 in.
2
of 1oz. copper) ...............................1W
Operating Temperature Range ...........................-40°C to +85°C
All Other Pins to GND.................................-0.3V to (V
CC
+ 0.3V)
LX Current (Note 1).............................................................±4.7A
Storage Temperature Range .............................-65°C to +150°C
REF Short Circuit to GND Duration ............................Continuous
Lead Temperature (soldering, 10s) ................................ +300°C
ESD Protection .....................................................................±2kV
Note 1:
LX has internal clamp diodes to PGND and IN. Applications that forward-bias these diodes should take care not to exceed
the IC’s package power dissipation limits.
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
CC
= 3.3V, FBSEL = GND,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Input Voltage
SYMBOL
V
IN
, V
CC
FBSEL =
V
CC
T
A
= +25°C
to +85°C
T
A
= +0°C
to +85°C
T
A
= +25°C
to +85°C
T
A
= +0°C
to +85°C
T
A
= +25°C
to +85°C
T
A
= +0°C
to +85°C
T
A
= +25°C
to +85°C
T
A
= +0°C
to +85°C
CONDITIONS
MIN
3.0
2.500
2.487
1.500
1.492
1.800
1.791
1.089
1.084
V
REF
2
0.4
V
DO
V
REF
ΔV
REF
R
ON, P
R
ON, N
V
IN
= V
CC
= 3V, I
LOAD
= 1A
T
A
= +25°C to +85°C
T
A
= +0°C to +85°C
I
REF
= -1µA to +10µA
I
LX
= 0.5A
I
LX
= 0.5A
V
IN
= 4.5V
V
IN
= 3V
V
IN
= 4.5V
V
IN
= 3V
1.089
1.084
1.100
1.100
0.5
90
110
70
80
250
1.111
1.117
2
200
250
150
200
mΩ
2.525
2.525
1.515
1.515
1.818
1.818
1.100
1.100
TYP
MAX
5.5
2.550
2.563
1.530
1.538
V
1.836
1.845
1.111
1.117
V
IN
V
%
%
mV
V
mV
FBSEL =
REF
UNITS
V
Preset Output Voltage
V
OUT
V
IN
= 3V to
5.5V,
I
LOAD
= 0
to 1A for
MAX1742,
I
LOAD
= 0
to 2.5A for
MAX1842,
V
FB
= V
OUT
FBSEL =
unconnected
FBSEL =
GND
Adjustable Output Voltage
Range
AC Load Regulation Error
DC Load Regulation Error
Dropout Voltage
Reference Voltage
Reference Load Regulation
PMOS Switch
On-Resistance
NMOS Switch
On-Resistance
V
IN
= V
CC
= 3V to 5.5V, I
LOAD
= 0,
FBSEL = GND
2
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