19-2795; Rev 2; 6/07
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
General Description
The MAX8545/MAX8546/MAX8548 are voltage-mode
pulse-width-modulated (PWM), step-down DC-DC con-
trollers ideal for a variety of cost-sensitive applications.
They drive low-cost n-channel MOSFETs for both the
high-side switch and synchronous rectifier, and require
no external current-sense resistor. These devices can
supply output voltages as low as 0.8V.
The MAX8545/MAX8546/MAX8548 have a wide 2.7V to
28V input range, and do not need any additional bias
voltage. The output voltage can be precisely regulated
from 0.8V to 0.83 x V
IN
. These devices can provide effi-
ciency up to 95%. Lossless short-circuit and current-limit
protection is provided by monitoring the R
DS(ON)
of the
low-side MOSFET. The MAX8545 and MAX8548 have a
current-limit threshold of 320mV, while the MAX8546 has
a current-limit threshold of 165mV. All devices feature
foldback-current capability to minimize power dissipation
under short-circuit condition. Pulling the COMP/EN pin
low with an open-collector or low-capacitance, open-
drain device can shut down all devices.
The MAX8545/MAX8546 operate at 300kHz and the
MAX8548 operates at 100kHz. The MAX8545/MAX8546/
MAX8548 are compatible with low-cost aluminum elec-
trolytic capacitors. Input undervoltage lockout prevents
proper operation under power-sag operations to prevent
external MOSFETs from overheating. Internal soft-start is
included to reduce inrush current. These devices are
offered in space-saving 10-pin µMAX
®
packages.
♦
2.7V to 28V Input Range
♦
Foldback Short-Circuit Protection
♦
No Additional Bias Supply Needed
♦
0.8V to 0.83 x V
IN
Output
♦
Up to 95% Efficiency
♦
Low-Cost External Components
♦
No Current-Sense Resistor
♦
All n-Channel MOSFET Design
♦
Adaptive Gate Drivers Eliminate Shoot-Through
♦
Lossless Overcurrent and Short-Circuit
Protection
♦
300kHz Switching Frequency
(MAX8545/MAX8546)
♦
100kHz Switching Frequency (MAX8548)
♦
Pin-Compatible with the MAX1967
♦
Thermal Shutdown
Features
MAX8545/MAX8546/MAX8548
Selector Guide
PART
MAX8545
MAX8546
MAX8548
SWITCHING
FREQUENCY
(kHz)
300
300
100
CURRENT-LIMIT
THRESHOLD
(mV)
-320
-165
-320
Applications
Set-Top Boxes
Graphic Card and Video
Supplies
Desktops and Desknotes
PCI Express Power
Supplies
Telecom Power Supplies
Notebook Docking
Station Supplies
Cable Modems and
Routers
Networking Power
Supplies
Typical Operating Circuit
INPUT
2.7V TO 28V
V
CC
VL
V
IN
BST
DH
OUTPUT
0.8V TO
0.9 x V
IN
UP TO 6A
Ordering Information
PART
MAX8545EUB
MAX8545EUB+
MAX8546EUB
MAX8546EUB+
MAX8548EUB
MAX8548EUB+
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
10 µMAX
10 µMAX
10 µMAX
10 µMAX
10 µMAX
10 µMAX
PKG
CODE
U10-2
U10-2
U10-2
U10-2
U10-2
U10-2
OPTIONAL
OFF
ON
MAX8545
MAX8546
MAX8548
COMP/
EN
LX
DL
GND
FB
+Denotes
a lead-free package.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
Pin Configuration appears at end of data sheet.
1
________________________________________________________________
Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
MAX8545/MAX8546/MAX8548
ABSOLUTE MAXIMUM RATINGS
(All voltages referenced to GND unless otherwise noted.)
V
IN
to GND ............................................................-0.3V to +30V
V
CC
to GND .............................-0.3V, lower of 6V or (VL + 0.3V)
FB to GND ................................................................-0.3V to +6V
BST to GND ............................................................-0.3V to +36V
VL, DL, COMP to GND ..............................-0.3V to (V
CC
+ 0.3V)
BST to LX..................................................................-0.3V to +6V
DH to LX ....................................................-0.3V to (V
BST
+ 0.3V)
VL Short to GND ......................................................................5s
LX to GND ................................................................-1V to +30V
Input Current (any pin) .....................................................±50mA
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
= VL = V
CC
= 5V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
V
IN
Operating Range
V
IN
Undervoltage Lockout
(UVLO) Trip Level
V
IN
Operating Supply Current
VL Output Voltage
Thermal Shutdown
OSCILLATOR
Frequency
Minimum Duty Cycle
Maximum Duty Cycle
SOFT-START
Digital Ramp Period
Soft-Start Levels
MAX8545, MAX8546
MAX8548
MAX8545, MAX8546
MAX8548
6.6
10.2
V
OUT
/ 64
V
OUT
/ 32
ms
V
f
OSC
DC
MIN
DC
MAX
MAX8545, MAX8546
MAX8548
DH output, MAX8545, MAX8546
MAX8548
DH output, MAX8545, MAX8546
MAX8548
83
90
86
95
250
80
300
100
360
120
5
10
kHz
%
%
SYMBOL
V
IN
CONDITIONS
V
CC
= VL, V
IN
separate from V
CC
V
IN
= VL = V
CC
Rising and falling edge, hysteresis = 2%
V
FB
= 0.88V (no switching)
5.5V < V
IN
< 28V, V
CC
= VL,
1mA < I
LOAD
< 25mA
Rising temperature, typical
hysteresis = 10°C (Note 1)
4.7
MIN
4.9
2.7
2.35
2.50
0.7
5
+160
TYP
MAX
28.0
5.5
2.66
1.2
5.3
UNITS
V
V
mA
V
°C
2
_______________________________________________________________________________________
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= VL = V
CC
= 5V, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
ERROR AMPLIFIER
FB Regulation Voltage
FB to COMP/EN Gain
FB to COMP/EN
Transconductance
FB Input Bias Current
COMP/EN Source Current
Current-Limit Threshold Voltage
(Across Low-Side MOSFET)
Foldback Current-Limit Threshold
Voltage (Across Low-Side
MOSFET) When Output is Short
MOSFET DRIVERS
Break-Before-Make Time
DH On-Resistance in Low State
DH On-Resistance in High State
DL On-Resistance in Low State
DL On-Resistance in High State
BST Leakage Current
LX Leakage Current
V
BST
= 33V, V
LX
= 28V, V
FB
= 0.88V
V
BST
= 33V, V
LX
= 28V, V
FB
= 0.88V
Rising edge, DH going low to DL going high
Falling edge, DL going low to DH going high
96
28
1.6
2.5
1.1
2.5
0
33
4
5.5
2.5
5.5
50
100
ns
Ω
Ω
Ω
Ω
µA
µA
-5µA < I
COMP/EN
< +5µA
V
FB
= 0.88V
V
COMP/EN
= 0V
LX to GND, MAX8545, MAX8548,
V
FB
= 0.8V
LX to GND MAX8546, V
FB
= 0.8V
LX to GND, V
FB
= 0V,
MAX8545, MAX8548
MAX8546, LX to GND, V
FB
= 0
15
-355
-185
-105
-53
70
2.7V < V
CC
< 5.5V, 0°C to +85°C
2.7V < V
CC
< 5.5V, -40°C to +85°C
0.787
0.782
0.800
0.800
4000
108
1
46
-320
-165
-75
-38
160
2
100
-280
-140
-45
-22
mV
0.815
0.815
V
V /V
µS
µA
µA
mV
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8545/MAX8546/MAX8548
3
Note 1:
Thermal shutdown disables the buck regulator when the die reaches this temperature. Soft-start is reset but the VL regulator
remains on.
_______________________________________________________________________________________
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
MAX8545/MAX8546/MAX8548
Typical Operating Characteristics
(V
IN
= VL = V
CC
= 5V, typical values are at T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc01
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc02
EFFICIENCY vs. LOAD CURRENT
90
80
EFFICIENCY (%)
70
60
50
40
30
20
V
OUT
= 1.8V
V
OUT
= 3.3V
MAX8545/46/48 toc03
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
(CIRCUIT OF FIGURE 1; TABLE 1a)
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
(CIRCUIT OF FIGURE 1; TABLE 1a)
V
OUT
= 3.3V
V
OUT
= 1.8V
100
(CIRCUIT OF FIGURE 2; TABLE 2a)
V
IN
= 3.3V
V
OUT
= 1.2V
0.1
1
10
LOAD CURRENT (A)
10
0
0.01
0.1
1
V
IN
= 5V
10
10
0
0.01
0.1
1
V
IN
= 12V
10
LOAD CURRENT (A)
LOAD CURRENT (A)
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc04
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc05
EFFICIENCY vs. LOAD CURRENT
90
80
EFFICIENCY (%)
70
60
50
40
30
20
V
OUT
= 1.2V
MAX8545/46/48 toc06
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
(CIRCUIT OF FIGURE 2; TABLE 2a)
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
(CIRCUIT OF FIGURE 1; TABLE 1b)
100
(CIRCUIT OF FIGURE 1; TABLE 1b)
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.8V
V
OUT
= 3.3V
V
OUT
= 1.8V
V
OUT
= 1.8V
V
OUT
= 1.2V
V
IN
= 17V
0.1
1
10
10
0
0.01
0.1
1
V
IN
= 3.3V
10
10
0
0.01
0.1
1
LOAD CURRENT (A)
V
IN
= 5V
10
LOAD CURRENT (A)
LOAD CURRENT (A)
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc07
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc08
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.8V
90
80
EFFICIENCY (%)
70
60
50
40
30
20
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.8V
2.515
OUTPUT VOLTAGE (V)
2.510
2.505
2.500
2.495
2.490
2.485
V
OUT
= 2.5V
V
IN
= 12V
V
OUT
= 1.2V
V
OUT
= 1.2V
V
IN
= 12V
0.1
1
10
10
0
0.01
0.1
1
LOAD CURRENT (A)
V
IN
= 17V
10
2.480
1
2
3
4
5
6
LOAD CURRENT (A)
LOAD CURRENT (A)
4
_______________________________________________________________________________________
MAX8545/46/48 toc09
100
(CIRCUIT OF FIGURE 2; TABLE 2b)
100
(CIRCUIT OF FIGURE 2; TABLE 2b)
CHANGE IN OUTPUT VOLTAGE
vs. LOAD CURRENT
2.520
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
Typical Operating Characteristics (continued)
(V
IN
= VL = V
CC
= 5V, typical values are at T
A
= +25°C, unless otherwise noted.)
CHANGE IN OUTPUT VOLTAGE
vs. INPUT VOLTAGE
MAX8545/46/48 toc10
MAX8545/MAX8546/MAX8548
CHANGE IN OUTPUT VOLTAGE
vs. INPUT VOLTAGE
I
LOAD
= 6A
2.51
MAX8545/46/48 toc11
1.84
I
LOAD
= 6A
1.83
OUTPUT VOLTAGE (V)
1.82
1.81
1.80
1.79
1.78
2.5
3.0
3.5
4.0
4.5
INPUT VOLTAGE (V)
2.52
OUTPUT VOLTAGE (V)
2.50
2.49
2.48
10
12
14
16
18
20
22
24
INPUT VOLTAGE (V)
FREQUENCY vs. INPUT VOLTAGE
MAX8545/46/48 toc12
FREQUENCY vs. TEMPERATURE
V
IN
= 12V
V
OUT
= 2.5V
NO LOAD
MAX8545/
MAX8546
MAX8545/46/48 toc13
310
V
OUT
= 2.5V
NO LOAD
MAX8545/
MAX8546
310
306
FREQUENCY (kHz)
306
FREQUENCY (kHz)
302
302
298
298
294
294
290
2.70
7.76
12.82
17.88
22.94
28.00
INPUT VOLTAGE (V)
290
-40.00
-15.00
10.00
35.00
60.00
85.00
TEMPERATURE (°C)
LOAD TRANSIENT RESPONSE
MAX8545 toc14
V
IN
= 17V
V
OUT
= 2.5V
V
OUT
AC COUPLED
100mV/div
0
40μs/div
I
OUT
5A/div
_______________________________________________________________________________________
5
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