19-2622; Rev 0; 10/02
1MHz, All-Ceramic, 2.6V to 5.5V Input,
1.5A PWM Step-Down DC-to-DC Regulators
General Description
The MAX1951/MAX1952 high-efficiency, DC-to-DC
step-down switching regulators deliver up to 1.5A of
output current. The devices operate from an input volt-
age range of 2.6V to 5.5V and provide an output volt-
age from 0.8V to V
IN
, making the MAX1951/MAX1952
ideal for on-board postregulation applications. The
MAX1951 total output error is less than 1% over load,
line, and temperature.
The MAX1951/MAX1952 operate at a fixed frequency of
1MHz with an efficiency of up to 94%. The high operating
frequency minimizes the size of external components.
Internal soft-start control circuitry reduces inrush current.
Short-circuit and thermal-overload protection improve
design reliability.
The MAX1951 provides an adjustable output from 0.8V
to V
IN
, whereas the MAX1952 has a preset output of
1.8V. Both devices are available in a space-saving 8-pin
SO package.
o
Compact 0.385in
2
Circuit Footprint
o
10µF Ceramic Input and Output Capacitors, 2µH
Inductor
o
Efficiency Up to 94%
o
1% Output Accuracy Over Load, Line, and
Temperature (MAX1951)
o
Guaranteed 1.5A Output Current at +85°C
o
Operate from 2.6V to 5.5V Supply
o
Adjustable Output from 0.8V to V
IN
(MAX1951)
o
Preset Output of 1.8V (1.5% Accuracy) (MAX1952)
o
Internal Digital Soft-Soft
o
Short-Circuit and Thermal-Overload Protection
Features
MAX1951/MAX1952
Applications
ASIC/DSP/µP/FPGA Core and I/O Voltages
Set-Top Boxes
Cellular Base Stations
Networking and Telecommunications
PART
MAX1951ESA
Ordering Information
TEMP RANGE
PIN-
PACKAGE
OUTPUT
Adj 0.8V to V
IN
Fixed 1.8V
-40°C to +80°C 8 SO
MAX1952ESA-18
-40°C to +80°C 8 SO
Pin Configuration
Typical Operating Circuit
INPUT
2.6V TO 5.5V
IN
LX
OUTPUT
0.8V TO V
IN
, 1.5A
TOP VIEW
V
CC
1
REF
GND
2
3
8
7
IN
LX
PGND
COMP
ON
OFF
MAX1951
V
CC
FB
MAX1951
MAX1952
6
5
FB
4
COMP
PGND
REF
GND
SO
OPTIONAL
________________________________________________________________
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.
1MHz, All-Ceramic, 2.6V to 5.5V Input,
1.5A PWM Step-Down DC-to-DC Regulators
MAX1951/MAX1952
ABSOLUTE MAXIMUM RATINGS
IN, V
CC
to GND ........................................................-0.3V to +6V
COMP, FB, REF to GND .............................-0.3V to (V
CC
+ 0.3V)
LX to Current (Note 1).........................................................±4.5A
PGND to GND .............................................Internally Connected
Continuous Power Dissipation (TA = +85°C)
8-Pin SO (derate 12.2mW/°C above +70°C)................976mW
Operating Temperature Range
MAX195_ ESA..................................................-40°C to +85°C
Junction Temperature Range ............................-40°C to +150°C
Storage Temperature Range .............................-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.
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.
ELECTRICAL CHARACTERISTICS
(V
IN
= V
CC
= 3.3V, PGND = GND, FB in regulation, C
REF
= 0.1µF,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at
T
A
= +25°C.)
PARAMETER
IN AND V
CC
IN Voltage Range
Supply Current
Shutdown Current
V
CC
Undervoltage Lockout
Threshold
REF
REF Voltage
REF Load Regulation
REF Line Regulation
REF Shutdown Resistance
COMP
COMP Transconductance
COMP Clamp Voltage, Low
COMP Clamp Voltage, High
COMP Shutdown Resistance
COMP Shutdown Threshold
COMP Startup Current
FB
Output Voltage Range
(MAX1951)
FB Regulation Voltage
(Error Amp Only)
FB Input Resistance
FB Input Bias Current
When using external feedback resistors to drive FB
V
COMP
= 1V to 2V,
I
OUT
= 0 to 1.5A
V
IN
= 2.6V to 5.5V
V
IN
= 2.8V to 5.5V
MAX1951
MAX1952
MAX1952
MAX1951
0.8
0.787
1.773
13
-0.1
0.795
1.8
18
V
IN
0.803
1.827
28
+0.1
V
V
kΩ
µA
From FB to COMP, V
COMP
= 1.25V
V
IN
= 2.6V to 5.5V, V
FB
= 1.3V
V
IN
= 2.6V to 5.5V, V
FB
= 1.1V
From COMP to GND, V
IN
= 2V
When LX starts/stops switching
COMP = GND
COMP rising
COMP falling
0.17
15
MAX1951
MAX1952
40
26.7
0.6
1.97
60
40
1
2.15
15
0.6
0.4
25
40
80
53.3
1.2
2.28
30
1
µS
V
V
Ω
V
µA
I
REF
= 0, V
IN
= 2.6V to 5.5V
I
REF
= 0 to 40µA, V
IN
= 2.6V to 5.5V
I
REF
= 20µA, V
IN
= 2.6V to 5.5V
From REF to GND, COMP = GND
1.96
2
0.01
0.01
12
2.03
0.2
0.4
22
V
%
%
Ω
Switching with no load, LX floating
COMP = GND
When LX starts/stops switching
V
CC
rising
V
CC
falling
2
V
IN
= 5.5V
2.6
6
0.5
2.35
2.25
5.5
10
1.0
2.5
V
mA
mA
V
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
1MHz, All-Ceramic, 2.6V to 5.5V Input,
1.5A PWM Step-Down DC-to-DC Regulators
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CC
= 3.3V, PGND = GND, FB in regulation, C
REF
= 0.1µF,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at
T
A
= +25°C.)
PARAMETER
LX
V
IN
= 5V
LX On-Resistance, PMOS
V
IN
= 3.3V
V
IN
= 2.6V
V
IN
= 5V
LX On-Resistance, NMOS
LX Current-Sense
Transimpedance
LX Current-Limit Threshold
LX Leakage Current
LX Switching Frequency
LX Maximum Duty Cycle
LX Minimum Duty Cycle
V
IN
= 3.3V
V
IN
= 2.6V
From LX to COMP, V
IN
= 2.6V to 5.5V
Duty cycle = 100%, V
IN
= 2.6V to 5.5V
V
IN
= 5.5V
V
IN
= 2.6V to 5.5V
V
COMP
= 1.5V, LX = high-Z, V
IN
= 2.6V to 5.5V
V
COMP
= 1V, V
IN
= 2.6V to 5.5V
T
J
rising
T
J
falling
High side
Low side
V
LX
= 5.5V
LX = GND
-10
0.85
100
15
160
145
1
1.1
0.16
2.4
116
140
163
93
106
116
0.24
3.1
-0.6
10
0.35
4.5
Ω
A
µA
MHz
%
%
206
mΩ
266
mΩ
CONDITIONS
MIN
TYP
MAX
UNITS
MAX1951/MAX1952
THERMAL CHARACTERISTICS
Thermal-Shutdown Threshold
When LX starts/stops switching
°C
ELECTRICAL CHARACTERISTICS
(V
IN
= V
CC
= 3.3V, PGND = GND, FB in regulation, C
REF
= 0.1µF,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
IN AND V
CC
IN Voltage Range
Supply Current
Shutdown Current
V
CC
Undervoltage Lockout
Threshold
REF
REF Voltage
REF Load Regulation
REF Line Regulation
REF Shutdown Resistance
I
REF
= 0, V
IN
= 2.6V to 5.5V
I
REF
= 0 to 40µA, V
IN
= 2.6V to 5.5V
I
REF
= 20µA, V
IN
= 2.6V to 5.5V
From REF to GND, COMP = GND
1.95
2.03
0.2
0.4
22
V
%
%
Ω
Switching with no load, V
IN
= 5.5V
COMP = GND
When LX starts/stops switching
V
CC
rising
V
CC
falling
1.95
2.6
5.5
10
1
2.5
V
mA
mA
V
CONDITIONS
MIN
TYP
MAX
UNITS
_______________________________________________________________________________________
3
1MHz, All-Ceramic, 2.6V to 5.5V Input,
1.5A PWM Step-Down DC-to-DC Regulators
MAX1951/MAX1952
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CC
= 3.3V, PGND = GND, FB in regulation, C
REF
= 0.1µF,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
COMP
COMP Transconductance
COMP Clamp Voltage, Low
COMP Clamp Voltage, High
COMP Shutdown Resistance
COMP Shutdown Threshold
COMP Startup Current
FB
Output Voltage Range
(MAX1951)
FB Regulation Voltage
(Error Amp Only)
FB Input Resistance
FB Input Bias Current
LX
LX On-Resistance, PMOS
LX On-Resistance, NMOS
LX Current Sense
LX Current-Limit Threshold
LX Leakage Current
LX Switching Frequency
LX Maximum Duty Cycle
From LX to COMP, V
IN
= 2.6V to 5.5V
Duty cycle = 100%, V
IN
= 2.6V to 5.5V, high side
V
IN
= 5.5V
V
IN
= 2.6V to 5.5V
V
COMP
= 1.5V, LX = Hi-Z, V
IN
= 2.6V to 5.5V
V
LX
= 5.5V
LX = GND
-10
0.8
100
1.1
0.16
2.4
266
206
0.35
4.5
10
mΩ
mΩ
Ω
A
µA
MHz
%
When using external feedback resistors to drive FB
V
COMP
= 1V to 2V, V
IN
= 2.6V to 5.5V
From FB to GND
MAX1951
MAX1952
MAX1952
MAX1951
0.8
0.783
1.764
10
-0.1
V
IN
0.807
1.836
30
+0.1
V
V
kΩ
µA
From FB to COMP, V
COMP
= 1.25V
V
IN
= 2.6V to 5.5V, V
FB
= 1.3V
V
IN
= 2.6V to 5.5V, V
FB
= 1.1V
From COMP to GND, V
IN
= 2V
When LX starts/stops switching
COMP = GND
COMP rising
COMP falling
0.17
14
40
MAX1951
MAX1952
40
26.7
0.6
1.97
80
53.3
1.2
2.28
30
1.2
µS
V
V
Ω
V
µA
CONDITIONS
MIN
TYP
MAX
UNITS
Note 2:
Specifications to -40°C are guaranteed by design and not production tested.
Note 3:
The LX output is designed to provide 2A RMS current.
4
_______________________________________________________________________________________
1MHz, All-Ceramic, 2.6V to 5.5V Input,
1.5A PWM Step-Down DC-to-DC Regulators
MAX1951/MAX1952
Typical Operating Characteristics
(Typical values are at V
IN
= V
CC
= 5V, V
OUT
= 1.5V, I
OUT
= 1.5A, and T
A
= +25°C, unless otherwise noted. See Figure 2.)
EFFICIENCY vs. LOAD CURRENT
(V
CC
= V
IN
= 5V)
MAX 1951 toc01
EFFICIENCY vs. LOAD CURRENT
(V
CC
= V
IN
= 3.3V)
MAX 1951 toc02
REF VOLTAGE
vs. REF OUTPUT CURRENT
MAX1951 toc03
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
10
V
OUT
= 3.3V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
V
OUT
= 2.5V
1.995
1.994
REF VOLTAGE (V)
1.993
1.992
1.991
1.990
1.989
T
A
= -40°C
T
A
= +85°C
T
A
= +25°C
V
OUT
= 2.5V
V
OUT
= 1.5V
V
OUT
= 1.8V
V
OUT
= 1.5V
V
OUT
= 0.8V
V
OUT
= 0.8V
100
1000
10,000
10
100
1000
10,000
0
5
10
15
20
25
30
35
40
LOAD CURRENT (mA)
LOAD CURRENT (mA)
REF OUTPUT CURRENT (µA)
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX1951 toc04
OUTPUT VOLTAGE DEVIATION
vs. LOAD CURRENT
MAX1951 toc05
1.20
1.15
SWITCHING FREQUENCY (MHz)
1.10
1.05
1.00
0.95
0.90
0.85
0.80
2.6
3.1
3.6
4.1
4.6
5.1
T
A
= -40°C
T
A
= +25°C
T
A
= +85°C
OUTPUT VOLTAGE DEVIATION (mV)
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
0
V
OUT
= 2.5V
V
OUT
= 3.3V
V
OUT
= 0.8V
V
OUT
= 1.8V
5.6
0.4
0.8
LOAD CURRENT (A)
1.2
1.6
INPUT VOLTAGE (V)
LOAD TRANSIENT RESPONSE
MAX1951 toc06
LOAD TRANSIENT RESPONSE
MAX1951 toc07
OUTPUT VOLTAGE:
100mV/div,
AC-COUPLED
OUTPUT VOLTAGE:
100mV/div,
AC-COUPLED
OUTPUT CURRENT:
0.5A/div
V
IN
= 5V
V
OUT
= 2.5V
I
OUT
= 0.5 TO 1A
40µs/div
OUTPUT CURRENT:
0.5A/div
V
IN
= 3.3V
V
OUT
= 1.5V
I
OUT
= 0.5 TO 1A
40µs/div
0
0
_______________________________________________________________________________________
5
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