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19-1760; Rev 2; 9/05
EVAALVUAAILTAIOBNLEKIT
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
VIN. 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.
Applications
5V or 3.3V to Low-Voltage Conversion
CPU I/O Ring
Chipset Supplies
Notebook and Subnotebook Computers
Pin Configuration appears at end of data sheet.
Idle Mode is a trademark of Maxim Integrated Products.
Features
±1% Output Accuracy
95% Efficiency
Internal PMOS and NMOS Switches
90mΩ On-Resistance at VIN = 4.5V
110mΩ On-Resistance at VIN = 3V
Output Voltage
2.5V, 1.8V, or 1.5V Pin Selectable
1.1V to VIN 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
Ordering Information
PART
MAX1742EEE
TEMP RANGE
-40°C to +85°C
MAX1742EEE+
MAX1842EEE
MAX1842EEE+
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
+ Denotes lead-free package.
PIN-PACKAGE
16 QSOP
16 QSOP
16 QSOP
16 QSOP
Typical Configuration
INPUT
3V TO
5.5V
10Ω
2.2μF
470pF
IN LX
MAX1742 FB
MAX1842
VCC PGND
SHDN
COMP
TOFF
GND
FBSEL
REF
SS
OUTPUT
1.1V TO
VIN
0.01μF
1μF
________________________________________________________________ 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.

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1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
ABSOLUTE MAXIMUM RATINGS
VCC, IN to GND ........................................................-0.3V to +6V
IN to VCC.............................................................................±0.3V
GND to PGND.....................................................................±0.3V
All Other Pins to GND.................................-0.3V to (VCC + 0.3V)
LX Current (Note 1).............................................................±4.7A
REF Short Circuit to GND Duration ............................Continuous
ESD Protection .....................................................................±2kV
Continuous Power Dissipation (TA = +70°C)
SSOP (derate 16.7mW/°C above +70°C;
part mounted on 1 in.2 of 1oz. copper) ...............................1W
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) ................................ +300°C
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
(VIN = VCC = 3.3V, FBSEL = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
Input Voltage
SYMBOL
VIN, VCC
CONDITIONS
FBSEL =
VCC
TA = +25°C
to +85°C
TA = +0°C
to +85°C
MIN
3.0
2.500
2.487
TYP
2.525
2.525
MAX
5.5
2.550
2.563
Preset Output Voltage
VOUT
VIN = 3V to
5.5V,
ILOAD = 0
to 1A for
MAX1742,
ILOAD = 0
to 2.5A for
MAX1842,
VFB = VOUT
FBSEL =
unconnected
FBSEL =
REF
TA = +25°C
to +85°C
TA = +0°C
to +85°C
TA = +25°C
to +85°C
TA = +0°C
to +85°C
1.500
1.492
1.800
1.791
1.515
1.515
1.818
1.818
1.530
1.538
1.836
1.845
FBSEL =
GND
TA = +25°C
to +85°C
TA = +0°C
to +85°C
1.089
1.084
1.100
1.100
1.111
1.117
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
VIN = VCC = 3V to 5.5V, ILOAD = 0,
FBSEL = GND
VDO
VREF
ΔVREF
RON, P
VIN = VCC = 3V, ILOAD = 1A
TA = +25°C to +85°C
TA = +0°C to +85°C
IREF = -1µA to +10µA
ILX = 0.5A
RON, N ILX = 0.5A
VIN = 4.5V
VIN = 3V
VIN = 4.5V
VIN = 3V
VREF
1.089
1.084
2
0.4
1.100
1.100
0.5
90
110
70
80
VIN
250
1.111
1.117
2
200
250
150
200
UNITS
V
V
V
%
%
mV
V
mV
mΩ
2 _______________________________________________________________________________________

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1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VCC = 3.3V, FBSEL = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP
Current-Limit Threshold
ILIMIT
MAX1742
MAX1842
1.3 1.5
3.1 3.6
RMS LX Output Current
Idle Mode Current Threshold
MAX1742
IIM MAX1842
0.1 0.3
0.3 0.6
Switching Frequency
f (Note 2)
No-Load Supply Current
Shutdown Supply Current
IIN + ICC VFB = 1.2V
ICC(SHDN) SHDN = GND
350
<1
PMOS Switch Off-Leakage
Current
IIN SHDN = GND
MAX
1.7
4.1
3.1
0.5
0.9
1
600
5
15
Thermal Shutdown Threshold
Undervoltage Lockout Threshold
FB Input Bias Current
Off-Time Default Period
Off-Time Startup Period
On-Time Period
SS Source Current
SS Sink Current
SHDN Input Current
SHDN Input Low Threshold
SHDN Input High Threshold
FBSEL Input Current
TSHDN
VUVLO
IFB
tOFF
tOFF
tON
ISS
ISS
I SHDN
VIL
VIH
Hysteresis = 15°C
VIN falling, hysteresis = 90mV
VFB = 1.2V
RTOFF = 110kΩ
RTOFF = 30.1kΩ
RTOFF = 499kΩ
FB = GND
(Note 2)
VSS = 1V
V SHDN = 0 to VCC
FBSEL = GND
FBSEL = REF
160
2.5 2.6 2.7
0 60 250
0.9 1.00 1.1
0.24 0.30 0.37
3.8 4.5 5.2
4 tOFF
0.4
456
100
-1 1
0.8
2.0
-4 +4
0.2
0.9 1.3
FBSEL Logic Thresholds
FBSEL = unconnected
0.7 VCC 0.7 VCC
- 0.2
+0.2
FBSEL = VCC
VCC
- 0.2
UNITS
A
A
A
MHz
µA
µA
µA
°C
V
nA
µs
µs
µs
µA
µA
µA
V
V
µA
V
_______________________________________________________________________________________ 3

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1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
ELECTRICAL CHARACTERISTICS
(VIN = VCC = 3.3V, FBSEL = GND, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 3)
PARAMETER
Input Voltage
Preset Output Voltage
SYMBOL
VIN
VOUT
CONDITIONS
ILOAD = 0 to 1A
for MAX1742,
ILOAD = 0 to 2.5A
for MAX1842,
VFB = VOUT
VIN = 3V to 5.5V,
FBSEL = VCC
FBSEL = unconnected
FBSEL = REF
FBSEL = GND
Adjustable Output Voltage
Range
VIN = VCC = 3V to 5.5V, ILOAD = 0,
FBSEL = GND
Reference Voltage
PMOS Switch
On-Resistance
NMOS Switch
On-Resistance
Current-Limit Threshold
VREF
RON, P
ILX = 0.5A
RON, N
ILIMIT
ILX = 0.5A
MAX1742
MAX1842
VIN = 4.5V
VIN = 3V
VIN = 4.5V
VIN = 3V
Idle Mode Current Threshold
No-Load Supply Current
FB Input Bias Current
Off-Time Default Period
IIM
IIN + ICC
IFB
tOFF
MAX1742
MAX1842
VFB = 1.2V
VFB = 1.2V
RTOFF = 110kΩ
Note 2: Recommended operating frequency, not production tested.
Note 3: Specifications from 0°C to -40°C are guaranteed by design, not production tested.
MIN
3.0
2.475
1.485
1.782
1.078
VREF
1.078
1.2
2.9
0.05
0.2
0
0.85
MAX UNITS
5.5 V
2.575
1.545
1.854
1.122
V
VIN V
1.122
200
250
150
200
1.8
4.3
0.55
1.0
600
300
1.15
V
mΩ
A
µA
nA
µs
4 _______________________________________________________________________________________

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1A/2.7A, 1MHz, Step-Down Regulators with
Synchronous Rectification and Internal Switches
(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics
MAX1742
EFFICIENCY vs. OUTPUT CURRENT
(VIN = 5.0V, L = 6.0μH)
100
95 VOUT = 2.5V, RTOFF = 47kΩ, f = 926kHz
90 VOUT = 1.8V, RTOFF = 75kΩ,
85 f = 833kHz
80
75
70
65
60
55
50
0.001
VOUT = 1.5V, RTOFF = 100kΩ, f = 692kHz
0.01 0.1
OUTPUT CURRENT (A)
1
MAX1742
EFFICIENCY vs. OUTPUT CURRENT
(VIN = 3.3V, L = 3.9μH)
100
95 VOUT = 2.5V, RTOFF = 36kΩ, f = 456kHz
90
85
80
75
70 VOUT = 1.8V, RTOFF = 43kΩ, f = 869kHz
65
60
55 VOUT = 1.5V, RTOFF = 56kΩ, f = 833kHz
50
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
MAX1742
EFFICIENCY vs.OUTPUT CURRENT
(fPWM = 270kHz)
100
95
VIN = 5V, VOUT = 1.8V,
L = 15μH, RTOFF = 240kΩ
90
85
80
75
70
65
60 VIN = 3.3V, VOUT = 1.8V,
L = 10μH, RTOFF = 160kΩ
55
50
0.001
0.01 0.1
OUTPUT CURRENT (A)
1
MAX1742
NORMALIZED OUTPUT ERROR
vs. OUTPUT CURRENT
0.5
0.4
0.3
0.2 VIN = 5V, VOUT = 1.5V, L = 6μH
0.1
0
-0.1
-0.2 VIN = 3.3V, VOUT = 1.5V
-0.3
-0.4
-0.5
0.001
0.01 0.1
OUTPUT CURRENT (A)
1
MAX1742
SWITCHING FREQUENCY
vs. OUTPUT CURRENT
1100
1000
VIN = 5V, VOUT = 2.5V, L = 6μH
900
800
700
600
500
400 VIN = 5V, VOUT = 1.5V, L = 6μH
300
200 VIN = 3.3V, VOUT = 1.5V, L = 3.9μH
100
0
0 0.2 0.4 0.6 0.8 1.0
OUTPUT CURRENT (A)
_______________________________________________________________________________________ 5