19-3154; Rev 1; 5/05
KIT
ATION
EVALU
BLE
AVAILA
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit
General Description
The MAX1954A synchronous current-mode, pulse-
width modulation (PWM) buck controller is pin compati-
ble with the popular MAX1954 and is suitable for
applications where cost and size are critical.
The MAX1954A operates from an input voltage range of
3.0V to 13.2V, independent of the IC supply. The output
voltage is adjustable down to 0.8V. The IC operates at
a fixed 300kHz switching frequency and provides up to
25A of output current with efficiency up to 95%. This
controller has excellent transient response resulting in
smaller output capacitance.
The MAX1954A features foldback current limiting that
greatly reduces input current and component power
dissipation during output overload or short-circuit
conditions.
The compensation and shutdown control (COMP) input,
in addition to providing compensation to the error
amplifier, can be pulled low to shut down the converter.
An input undervoltage lockout is provided to ensure
proper operation during power sags to prevent the
external power MOSFETs from overheating. Internal
digital soft-start is included to reduce inrush current
and save an external capacitor.
The MAX1954A is available in a tiny 10-pin µMAX
®
package to minimize PC board space.
♦
Current-Mode Controller
♦
Fixed-Frequency PWM
♦
Foldback Current Limit
♦
Output Down to 0.8V with
±1%
FB Accuracy
♦
3.0V to 13.2V Input Voltage
♦
300kHz Switching Frequency
♦
25A Output-Current Capability
♦
93% Efficiency
♦
All-N-Channel-MOSFET Design for Low Cost
♦
No Current-Sense Resistor Needed
♦
Internal Digital Soft-Start
♦
Small 10-Pin µMAX Package
Features
MAX1954A
Applications
Printers and Scanners
Graphic Cards and Video Cards
PCs and Servers
Microprocessor Cores
Low-Voltage Distributed Power
Telecom/Networks
PART
MAX1954AEUB
MAX1954AEUB+
Ordering Information
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
10 µMAX
10 µMAX
+Denotes
lead-free package.
Pin Configuration
TOP VIEW
HSD
1
COMP
FB
GND
IN
2
3
4
5
10
BST
9
LX
DH
PGND
DL
MAX1954A
8
7
6
µMAX is a registered trademark of Maxim Integrated Products, Inc.
µMAX
________________________________________________________________
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, Current-Mode PWM Buck
Controller with Foldback Current Limit
MAX1954A
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 to GND..............................................................-0.3V to 14V
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
10-Pin µMAX (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
= 0°C to +85°C,
unless otherwise noted.)
PARAMETER
GENERAL
Operating Input Voltage Range
HSD Voltage Range
Quiescent Supply Current
Standby Supply Current
Undervoltage-Lockout Trip Level
DC-DC CONTROLLER
Output-Voltage Adjust Range
(V
OUT
)
ERROR AMPLIFIER
FB Regulation Voltage
Transconductance
Voltage Gain
FB Input Leakage Current
FB Input Common-Mode Range
COMP Output-Voltage Swing
Current-Sense Amplifier
Voltage Gain
Current-Limit Threshold
OSCILLATOR
Switching Frequency
Maximum Duty Cycle
Minimum Duty Cycle
MAX1954A
Measured at DH
V
COMP
= 1.25V, LX = GND, V
BST
= V
IN
= 3.3V
240
89
300
91
2.5
360
93
3
kHz
%
%
V
PGND
- V
LX
V
FB
= 0.8V
V
FB
= 0V
V
FB
= 0.9V
-0.1
0.80
3.15
110
21
3.5
135
36
-1.0
70
+0.8
110
200
50
500
+1.5
2.36
3.85
145
51
+1.0
160
%
µS
V/ V
NA
V
V
V/V
mV
Maximum output voltage depends on external components
and maximum duty cycle
0.8
V
(Note 1)
V
FB
= 1.5V
V
IN
= V
BST
= 5.5V, V
HSD
= 13.2V, LX = unconnected,
COMP = GND
Falling V
IN
, 50mV (typ) hysteresis
2.5
2.7
3.0
3.0
1
5.5
13.2
2
2
2.9
V
V
mA
mA
V
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 5V, V
BST
- V
LX
= 5V,
T
A
= 0°C to +85°C,
unless otherwise noted.)
PARAMETER
SOFT-START
Soft-Start Period
Soft-Start Levels
FET DRIVERS
DH, DL Output Low Voltage
DH, DL Output High Voltage
DH Pullup/Pulldown,
DL Pullup On-Resistance
DL Pulldown On-Resistance
LX, BST, HSD Leakage Current
THERMAL PROTECTION
Thermal Shutdown
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, 15°C hysteresis
+160
°C
V
BST
= 18.7V, V
LX
= 13.2V, V
IN
= 5.5V, V
HSD
= 13.2V
I
SINK
= 10mA
I
SOURCE
= 10mA
V
IN
- 0.1V or
V
BST
- 0.1V
1.5
1
3
2
30
0.1
V
V
Ω
Ω
µA
3.4
12.5
ms
mV
CONDITIONS
MIN
TYP
MAX
UNITS
MAX1954A
ELECTRICAL CHARACTERISTICS
(V
IN
= 5V, V
BST
- V
LX
= 5V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
GENERAL
Operating Input Voltage Range
HSD Voltage Range
Quiescent Supply Current
Standby Supply Current
Undervoltage Lockout Trip Level
DC-DC CONTROLLER
Output-Voltage Adjust Range
(V
OUT
)
ERROR AMPLIFIER
FB Regulation Voltage
Transconductance
FB Input Leakage Current
FB Input Common-Mode Range
COMP Output-Voltage Swing
V
FB
= 0.9V
-0.1
0.8
-2.5
70
+1.0
160
500
+1.5
2.2
%
µS
NA
V
V
0.8
0.9 x V
IN
V
(Note 1)
V
FB
= 1.5V
V
IN
= V
BST
= 5.5V, V
HSD
= 13.2V, LX = unconnected,
COMP = GND
Rising V
IN
3% (typ) hysteresis
2.50
3.0
3.0
5.5
13.2
2
2
2.93
V
V
mA
mA
V
CONDITIONS
MIN
MAX
UNITS
_______________________________________________________________________________________
3
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit
MAX1954A
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 5V, V
BST
- V
LX
= 5V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
Current-Sense Amplifier
Voltage Gain
Current-Limit Threshold
OSCILLATOR
Switching Frequency
Maximum Duty Cycle
Minimum Duty Cycle
FET DRIVERS
DH, DL Output Low Voltage
DH, DL Output High Voltage
DH Pullup/Pulldown,
DL Pullup On-Resistance
DL Pulldown On-Resistance
LX, BST, HSD Leakage Current
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
V
BST
= 18.7V, V
LX
= 13.2V, V
IN
= 5.5V, V
HSD
= 13.2V
I
SINK
= 10mA
I
SOURCE
= 10mA
V
IN
- 0.1V or
V
BST
- 0.1V
3
2
30
0.1
V
V
Ω
Ω
µA
Measured at DH
V
COMP
= 1.25V, LX = GND, V
BST
= V
IN
= 3.3V
240
89
360
93
3
kHz
%
%
V
PGND
- V
LX
, MAX1954A
V
FB
= 0.8V
V
FB
= 0V
CONDITIONS
MIN
3.15
110
21
MAX
3.85
145
51
UNITS
V/V
mV
Note 1:
HSD and IN are externally connected for applications where HSD < 5.5V.
Note 2:
Specifications to -40°C are guaranteed by design and not production tested.
4
_______________________________________________________________________________________
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
EFFICIENCY
vs. LOAD CURRENT
MAX1954A toc01
MAX1954A
OUTPUT VOLTAGE
vs. LOAD CURRENT
MAX1954A toc02
OUTPUT VOLTAGE CHANGE
vs. INPUT VOLTAGE
MAX1954A toc03
100
V
OUT
= 2.5V
90
EFFICIENCY (%)
80
70
60
50
V
IN
= V
HSD
= 5V
40
0.1
1
LOAD CURRENT (A)
2.60
70
CHANGE IN OUTPUT VOLTAGE (mV)
50
30
10
-10
-30
-50
-70
V
OUT
= 0.8V
V
OUT
= 2.5V
V
OUT
= 1.5V
OUTPUT VOLTAGE (V)
2.55
2.50
2.45
V
IN
= V
HSD
= 5V
2.40
10
0
1
2
3
4
5
LOAD CURRENT (A)
V
IN
= V
HSD
I
OUT
= 5A
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
OUTPUT VOLTAGE
vs. INPUT VOLTAGE
MAX1954A toc04
OSCILLATOR FREQUENCY
vs. INPUT VOLTAGE
MAX1954A toc05
LOAD TRANSIENT
MAX1954A toc06
0.81
350
OSCILLATOR FREQUENCY (kHz)
OUTPUT VOLTAGE (V)
0.81
330
T
A
= -40°C
V
OUT
AC-COUPLED
100mV/div
310
5A
T
A
= +85°C
270
V
IN
= V
HSD
250
T
A
= +25°C
I
OUT
5A/µs
500mA
0.80
290
0.80
V
IN
= V
HSD
I
OUT
= 5A
0.79
10.8
11.4
12.0
INPUT VOLTAGE (V)
12.6
13.2
3.0
3.5
4.0
4.5
5.0
5.5
40µs/div
INPUT VOLTAGE (V)
_______________________________________________________________________________________
5
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