19-2373; Rev 0; 4/02
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
General Description
The MAX1953/MAX1954/MAX1957 is a family of versa-
tile, economical, synchronous current-mode, pulse-width
modulation (PWM) buck controllers. These step-down
controllers are targeted for applications where cost and
size are critical.
The MAX1953 operates at a fixed 1MHz switching fre-
quency, thus significantly reducing external component
size and cost. Additionally, excellent transient response
is obtained using less output capacitance. The MAX1953
operates from low 3V to 5.5V input voltage and can sup-
ply up to 10A of output current. Selectable current limit is
provided to tailor to the external MOSFETs’ on-resistance
for optimum cost and performance. The output voltage is
adjustable from 0.8V to 0.86V
IN
.
With the MAX1954, the drain-voltage range on the high-
side FET is 3V to 13.2V and is independent of the supply
voltage. It operates at a fixed 300kHz switching frequen-
cy and can be used to provide up to 25A of output cur-
rent with high efficiency. The output voltage is adjustable
from 0.8V to 0.86V
HSD
.
The MAX1957 features a tracking output voltage range of
0.4V to 0.86V
IN
and is capable of sourcing or sinking
current for applications such as DDR bus termination
and PowerPC™/ASIC/DSP core supplies. The MAX1957
operates from a 3V to 5.5V input voltage and at a fixed
300kHz switching frequency.
The MAX1953/MAX1954/MAX1957 provide a COMP pin
that can be pulled low to shut down the converter in
addition to providing compensation to the error amplifier.
An input undervoltage lockout (ULVO) is provided to
ensure proper operation under power-sag conditions to
prevent the external power MOSFETs from overheating.
Internal digital soft-start is included to reduce inrush cur-
rent. The MAX1953/MAX1954/MAX1957 are available in
tiny 10-pin µMAX packages.
o
Low-Cost Current-Mode Controllers
o
Fixed-Frequency PWM
o
MAX1953
1MHz Switching Frequency
Small Component Size, Low Cost
Adjustable Current Limit
o
MAX1954
3V to 13.2V Input Voltage
25A Output Current Capability
93% Efficiency
300kHz Switching Frequency
o
MAX1957
Tracking 0.4V to 0.86V
IN
Output Voltage Range
Sinking and Sourcing Capability of 3A
o
Shutdown Feature
o
All N-Channel MOSFET Design for Low Cost
o
No Current-Sense Resistor Needed
o
Internal Digital
†
Soft-Start
o
Thermal Overload Protection
o
Small 10-Pin µMAX Package
Features
MAX1953/MAX1954/MAX1957
Ordering Information
PART
MAX1953EUB
MAX1954EUB
MAX1957EUB
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
10 µMAX
10 µMAX
10 µMAX
Pin Configurations
TOP VIEW
Applications
Printers and Scanners
Graphic Cards and Video Cards
PCs and Servers
Microprocessor Core Supply
Low-Voltage Distributed Power
Telecommunications and Networking
ILIM
1
COMP
FB
GND
IN
2
3
4
5
10
BST
9
LX
DH
PGND
DL
MAX1953EUB
8
7
6
µMAX
†Patent
Pending
PowerPC is a trademark of Motorola, Inc.
Pin Configurations continued at end of data sheet.
________________________________________________________________
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-Cost, High-Frequency, Current-Mode PWM
Buck Controller
MAX1953/MAX1954/MAX1957
ABSOLUTE MAXIMUM RATINGS
IN, FB to GND...........................................................-0.3V to +6V
LX to BST..................................................................-6V to +0.3V
BST to GND ............................................................-0.3V to +20V
DH to LX ....................................................-0.3V to (V
BST
+ 0.3V)
DL, COMP to GND.......................................-0.3V to (V
IN
+ 0.3V)
HSD, ILIM, REFIN to GND ........................................-0.3V to 14V
PGND to GND .......................................................-0.3V to +0.3V
I
DH
, I
DL
................................................................±100mA (RMS)
Continuous Power Dissipation (T
A
= +70°C)
(derate 5.6mW/°C above +70°C) ..................................444mW
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
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
= 5V, V
BST
- V
LX
= 5V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Operating Input Voltage Range
HSD Voltage Range
Quiescent Supply Current
MAX1954 only (Note 2)
V
FB
= 1.5V, no switching
V
IN
= V
BST
= 5.5V, V
HSD
= 13.2V,
COMP = GND
Rising and falling V
IN
, 3% hysteresis
2.50
0.8
CONDITIONS
MIN
3.0
3.0
1
220
220
2.78
TYP
MAX
5.5
13.2
2
350
350
2.95
0.86 x
V
IN
0.8
0.8
V
REFIN
110
5
5
-0.1
MAX1957 only
ILIM = GND (MAX1953 only)
V
ILIM
= V
IN
or ILIM = open (MAX1953 only)
MAX1954/MAX1957
-0.1
5.67
3.15
6.3
3.5
0.812
0.812
V
REFIN
+ 8mV
160
500
500
1.5
1.5
6.93
3.85
µS
nA
nA
V
V
V/V
V/V
V
UNITS
V
V
mA
µA
µA
V
V
Standby Supply Current (MAX1953/ MAX1957) V
IN
= V
BST
= 5.5V, COMP = GND
Standby Supply Current (MAX1954)
Undervoltage Lockout Trip Level
Output Voltage Adjust Range (V
OUT
)
ERROR AMPLIFIER
T
A
= 0°C to +85°C
(MAX1953/MAX1954)
FB Regulation Voltage
T
A
= -40°C to +85°C
(MAX1953/MAX1954)
MAX1957 only
Transconductance
FB Input Leakage Current
REFIN Input Bias Current
FB Input Common-Mode Range
REFIN Input Common-Mode Range
Current-Sense Amplifier Voltage Gain Low
Current-Sense Amplifier Voltage Gain
V
FB
= 0.9V
V
REFIN
= 0.8V, MAX1957 only
0.788
0.776
V
REFIN
- 8mV
70
2
_______________________________________________________________________________________
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 5V, V
BST
- V
LX
= 5V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
ILIM Input Impedance
MAX1953 only
V
PGND
- V
LX
, ILIM = GND (MAX1953 only)
Current-Limit Threshold
V
PGND
- V
LX
, ILIM = open (MAX1953 only)
V
PGND
- V
LX
, ILIM = IN (MAX1953 only)
V
PGND
– V
LX
(MAX1954/MAX1957 only)
OSCILLATOR
Switching Frequency
Maximum Duty Cycle
Minimum Duty Cycle
SOFT-START
Soft-Start Period
FET DRIVERS
DH On-Resistance, High State
DH On-Resistance, Low State
DL On-Resistance, High State
DL On-Resistance, Low State
LX, BST Leakage Current
LX, BST, HSD Leakage Current
THERMAL PROTECTION
Thermal Shutdown
Thermal Shutdown Hysteresis
SHUTDOWN CONTROL
COMP Logic Level Low
COMP Logic Level High
COMP Pullup Current
3V < V
IN
< 5.5V
3V < V
IN
< 5.5V
0.8
100
0.25
V
V
µA
Rising temperature
160
15
°C
°C
V
BST
= 10.5V, V
LX
= V
IN
= 5.5V,
MAX1953/MAX1957
V
BST
= 18.7V, V
LX
= 13.2V, V
IN
= 5.5V
V
HSD
= 13.2V (MAX1954 only)
2
1.5
2
0.8
3
3
3
2
20
30
Ω
Ω
Ω
Ω
µA
µA
MAX1953
MAX1954/MAX1957
4
3.4
ms
MAX1953
MAX1954/MAX1957
Measured at DH
MAX1953, measured at DH
MAX1954/MAX1957, measured at DH
0.8
240
86
1
300
89
15
4.5
1.2
360
96
18
5.5
MHz
kHz
%
%
CONDITIONS
MIN
50
85
190
290
190
TYP
125
105
210
320
210
MAX
200
125
235
350
235
mV
UNITS
kΩ
MAX1953/MAX1954/MAX1957
Note 1:
Specifications to -40°C are guaranteed by design and not production tested.
Note 2:
HSD and IN are externally connected for applications where V
HSD
< 5.5V.
_______________________________________________________________________________________
3
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
MAX1953/MAX1954/MAX1957
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
MAX1953
EFFICIENCY vs. LOAD CURRENT
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
0.1
1
LOAD CURRENT (A)
V
OUT
= 2.5V
CIRCUIT OF FIGURE 1
10
V
IN
= 5V
V
IN
= 3.3V
MAX1953 toc01
MAX1954
EFFICIENCY vs. LOAD CURRENT
MAX1953 toc02
MAX1957
EFFICIENCY vs. LOAD CURRENT
MAX1953 toc03
100
100
V
OUT
= 2.5V
90
EFFICIENCY (%)
80
70
60
50
40
0.1
1
LOAD CURRENT (A)
V
OUT
= 1.7V
100
90
EFFICIENCY (%)
80
70
60
50
40
0.1
1
LOAD CURRENT (A)
V
OUT
= 1.25V
V
IN
= 5V
CIRCUIT OF FIGURE 2
10
V
IN
= 5V
CIRCUIT OF FIGURE 3
10
MAX1954
EFFICIENCY vs. LOAD CURRENT
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
0
5
10
V
IN
= 12V
CIRCUIT OF FIGURE 4
15
20
25
V
OUT
= 1.8V
MAX1953 toc04
MAX1953
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1953 toc05
100
2.60
OUTPUT VOLTAGE (V)
2.55
V
IN
= 5V
2.50
V
IN
= 3.3V
2.45
CIRCUIT OF FIGURE 1
2.40
0
0.5
1.0
1.5
2.0
2.5
3.0
LOAD CURRENT (A)
LOAD CURRENT (A)
MAX1954
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1953 toc06
MAX1954
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1953 toc07
2.60
1.80
2.55
OUTPUT VOLTAGE (V)
1.75
OUTPUT VOLTAGE (V)
2.50
V
HSD
= V
IN
= 5V
2.45
1.70
V
HSD
= V
IN
= 5V
1.65
2.40
CIRCUIT OF FIGURE 2
2.35
0
1
2
3
4
5
6
LOAD CURRENT (A)
1.60
CIRCUIT OF FIGURE 2
1.55
0
1
2
3
4
5
6
LOAD CURRENT (A)
4
_______________________________________________________________________________________
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
MAX1953/MAX1954/MAX1957
Typical Operating Characteristics (continued)
(T
A
= +25°C, unless otherwise noted.)
MAX1957
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1953 toc08
MAX1953
OUTPUT VOLTAGE vs. INPUT VOLTAGE
MAX1953 toc09
MAX1954
OUTPUT VOLTAGE vs. INPUT VOLTAGE
MAX1953 toc10
1.35
2.60
1.76
1.74
OUTPUT VOLTAGE (V)
1.72
1.70
1.68
1.66
I
LOAD
= 5A
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
1.30
2.55
I
LOAD
= 3A
2.50
I
LOAD
= 0
2.45
I
LOAD
= 0
1.25
V
IN
= 5V
1.20
1.15
-3
-2
-1
0
CIRCUIT OF FIGURE 3
1
2
3
CIRCUIT OF FIGURE 1
2.40
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
1.64
3.0
3.5
4.0
CIRCUIT OF FIGURE 2
4.5
5.0
5.5
LOAD CURRENT (A)
INPUT VOLTAGE (V)
MAX1954
OUTPUT VOLTAGE vs. INPUT VOLTAGE
MAX1953 toc11
MAX1957
OUTPUT VOLTAGE vs. INPUT VOLTAGE
MAX1953 toc12
2.52
2.51
OUTPUT VOLTAGE (V)
I
LOAD
= 0
2.50
2.49
2.48
2.47
CIRCUIT OF FIGURE 2
2.46
3.0
3.5
4.0
4.5
5.0
1.29
1.27
OUTPUT VOLTAGE (V)
I
LOAD
= 0
1.25
I
LOAD
= 5A
1.23
I
LOAD
= 3A
1.21
CIRCUIT OF FIGURE 3
1.19
5.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
MAX1953
FREQUENCY vs. INPUT VOLTAGE
MAX1953 toc13
MAX1954/MAX1957
FREQUENCY vs. INPUT VOLTAGE
315
310
FREQUENCY (kHz)
305
300
295
290
285
T
A
= +85°C
T
A
= +25°C
T
A
= -40°C
V
OUT
= 1.25V
MAX1953 toc14
320
1.06
1.04
V
OUT
= 2.5V
FREQUENCY (MHz)
T
A
= -40°C
1.02
1.00
0.98
0.96
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
T
A
= +85°C
T
A
= +25°C
280
275
270
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
_______________________________________________________________________________________
5
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