Rainbow Electronics MAX8548 User Manual
General Description
The MAX8545/MAX8546/MAX8548 are voltage-mode
pulse-width-modulated (PWM), step-down DC-DC controllers 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 VIN. These devices can provide efficiency 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, opendrain 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 electrolytic 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.
Applications
Features
♦ 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
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
________________________________________________________________ Maxim Integrated Products 1
Typical Operating Circuit
Ordering Information
Pin Configuration appears at end of data sheet.
19-2795; Rev 0; 7/03
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.
Selector Guide
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
PART TEMP RANGE PIN-PACKAGE
MAX8545EUB -40°C to +85°C 10 µMAX
MAX8546EUB -40°C to +85°C 10 µMAX
MAX8548EUB -40°C to +85°C 10 µMAX
PART
MAX8545 300kHz -320mV
MAX8546 300kHz -165mV
MAX8548 100kHz -320mV
SWITCHING
FREQUENCY
CURRENT-LIMIT
THRESHOLD
2.7V TO 28V
OFF
ON
OPTIONAL
INPUT
VLV
CC
IN
COMP/
EN
MAX8545
MAX8546
MAX8548
BSTV
GND
DH
LX
DL
FB
OUTPUT
0.8V TO
0.9 x V
UP TO 6A
IN
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN= VL= VCC= 5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°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.
(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 ......................................................................0 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
VIN Operating Range V
VIN Undervoltage Lockout
(UVLO) Trip Level
VIN Operating Supply Current VFB = 0.88V (no switching)
VL Output Voltage
Thermal Shutdown
OSCILLATOR
Frequency f
Minimum Duty Cycle DC
Maximum Duty Cycle DC
SOFT-START
Digital Ramp Period
Soft-Start Levels
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
VCC = VL, VIN separate from V
IN
VIN = VL = V
Rising and falling edge, hysteresis = 2% 2.35 2.50 2.66 V
OSC
MIN
MAX
5.5V < V
1mA < I
Rising temperature, typical
hysteresis = 10°C (Note 1)
MAX8545, MAX8546 250 300 360
MAX8548 80 100 120
DH output, MAX8545, MAX8546 5
MAX8548 10
DH output, MAX8545, MAX8546 83 86
MAX8548 90 95
MAX8545, MAX8546 6.6
MAX8548
MAX8545, MAX8546 V
MAX8548
< 28V, VCC = VL,
IN
LOAD
CC
CC
< 25mA
4.9 28.0
2.7 5.5
0.7
4.7 5 5.3 V
+160 °C
10.2
/ 64
OUT
V
/ 32
OUT
1.2 mA
V
kHz
%
%
ms
V
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN= VL= VCC= 5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
Note 1: Thermal shutdown disables the buck regulator when the die reaches this temperature. Soft-start is reset but the VL regulator
remains on.
ERROR AMPLIFIER
FB Regulation Voltage
FB to COMP/EN Gain
FB to COMP/EN
Transconductance
FB Input Bias Current V
COMP/EN Source Current V
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 1.6 4 Ω
DH On-Resistance in High State 2.5 5.5 Ω
DL On-Resistance in Low State 1.1 2.5 Ω
DL On-Resistance in High State 2.5 5.5 Ω
BST Leakage Current V
LX Leakage Current V
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
2.7V < VCC < 5.5V, 0°C to +85°C 0.787 0.800 0.815
2.7V < V
-5µA < I
FB
COMP/EN
LX to GND, MAX8545, MAX8548,
V
FB
LX to GND MAX8546, V
LX to GND, VFB = 0V,
MAX8545, MAX8548
MAX8546, LX to GND, V
Rising edge, DH going low to DL going high 96
Falling edge, DL going low to DH going high 28
BST
BST
< 5.5V, -40°C to +85°C 0.782 0.800 0.815
CC
4000 V / V
COMP/EN
= 0.88V 1 2 µA
= 0.8V
= 33V, V
= 33V, V
< +5µA 70 108 160 µS
= 0V 15 46 100 µA
-355 -320 -280
= 0.8V -185 -165 -140
FB
-105 -75 -45
= 0 -53 -38 -22
FB
= 28V, VFB = 0.88V 0 50 µA
LX
= 28V, VFB = 0.88V 33 100 µA
LX
V
mV
mV
ns
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
4 _______________________________________________________________________________________
Typical Operating Characteristics
(VIN= VL= VCC= 5V, typical values are at TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc01
LOAD CURRENT (A)
(CIRCUIT OF FIGURE 1; TABLE 1a)
EFFICIENCY (%)
10.1
10
20
30
40
50
60
70
80
90
100
0
0.01 10
VIN = 3.3V
V
OUT
= 1.2V
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc02
LOAD CURRENT (A)
(CIRCUIT OF FIGURE 1; TABLE 1a)
EFFICIENCY (%)
10.1
10
20
30
40
50
60
70
80
90
100
0
0.01 10
VIN = 5V
V
OUT
= 1.8V
V
OUT
= 3.3V
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc03
LOAD CURRENT (A)
(CIRCUIT OF FIGURE 2; TABLE 2a)
EFFICIENCY (%)
10.1
10
20
30
40
50
60
70
80
90
100
0
0.01 10
V
OUT
= 1.8V
V
OUT
= 3.3V
VIN = 12V
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc04
LOAD CURRENT (A)
(CIRCUIT OF FIGURE 2; TABLE 2a)
EFFICIENCY (%)
10.1
10
20
30
40
50
60
70
80
90
100
0
0.01 10
VIN = 17V
V
OUT
= 3.3V
V
OUT
= 1.8V
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc05
LOAD CURRENT (A)
EFFICIENCY (%)
10.1
10
20
30
40
50
60
70
80
90
100
0
0.01 10
V
OUT
= 1.8V
V
OUT
= 1.2V
VIN = 3.3V
(CIRCUIT OF FIGURE 1; TABLE 1b)
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc06
LOAD CURRENT (A)
EFFICIENCY (%)
10.1
10
20
30
40
50
60
70
80
90
100
0
0.01 10
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.8V
V
OUT
= 1.2V
VIN = 5V
(CIRCUIT OF FIGURE 1; TABLE 1b)
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc07
LOAD CURRENT (A)
EFFICIENCY (%)
10.1
10
20
30
40
50
60
70
80
90
100
0
0.01 10
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.8V
V
OUT
= 1.2V
VIN = 12V
(CIRCUIT OF FIGURE 2; TABLE 2b)
EFFICIENCY vs. LOAD CURRENT
MAX8545/46/48 toc08
LOAD CURRENT (A)
EFFICIENCY (%)
10.1
10
20
30
40
50
60
70
80
90
100
0
0.01 10
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.8V
V
OUT
= 1.2V
VIN = 17V
(CIRCUIT OF FIGURE 2; TABLE 2b)
CHANGE IN OUTPUT VOLTAGE
vs. LOAD CURRENT
MAX8545/46/48 toc09
LOAD CURRENT (A)
OUTPUT VOLTAGE (V)
5432
2.485
2.490
2.495
2.500
2.505
2.510
2.515
2.520
2.480
16
V
OUT
= 2.5V
V
IN
= 12V
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
_______________________________________________________________________________________ 5
Typical Operating Characteristics (continued)
(VIN= VL= VCC= 5V, typical values are at TA = +25°C, unless otherwise noted.)
1.84
1.83
1.82
1.81
1.80
OUTPUT VOLTAGE (V)
1.79
1.78
CHANGE IN OUTPUT VOLTAGE
vs. INPUT VOLTAGE
2.5
INPUT VOLTAGE (V)
FREQUENCY vs. INPUT VOLTAGE
310
306
302
I
= 6V
LOAD
4.54.03.53.0
V
= 2.5V
OUT
NO LOAD
MAX8545/
MAX8546
MAX8545/46/48 toc10
MAX8545/46/48 toc12
2.52
2.51
2.50
OUTPUT VOLTAGE (V)
2.49
2.48
10
310
306
302
CHANGE IN OUTPUT VOLTAGE
vs. INPUT VOLTAGE
I
= 6V
LOAD
18 20 22 24161412
INPUT VOLTAGE (V)
FREQUENCY vs. TEMPERATURE
VIN = 12V
= 2.5V
V
OUT
NO LOAD
MAX8545/
MAX8546
MAX8545/46/48 toc11
MAX8545/46/48 toc13
298
FREQUENCY (kHz)
294
290
2.70 28.00
INPUT VOLTAGE (V)
22.9417.8812.827.76
LOAD TRANSIENT RESPONSE
VIN = 17V
= 2.5V
V
OUT
0
40µs/div
298
FREQUENCY (kHz)
294
290
-40.00 85.00
TEMPERATURE (°C)
MAX8545 toc14
V
OUT
AC COUPLED
100mV/div
I
OUT
5A/div
60.0035.0010.00-15.00
MAX8545/MAX8546/MAX8548
Low-Cost, Wide Input Range, Step-Down
Controllers with Foldback Current Limit
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VIN= VL= VCC= 5V, typical values are at TA = +25°C, unless otherwise noted.)
V
OUT
1V/div
V
IN
5V/div
INDUCTOR
CURRENT
5A/div
1ms/div
START-UP WAVEFORM
MAX8545 toc15
I
LOAD
= 3A
V
OUT
1V/div
V
IN
5V/div
INDUCTOR
CURRENT
2A/div
2ms/div
SHUTDOWN WAVEFORM
MAX8545 toc16
I
LOAD
= 3A
V
OUT
2V/div
V
IN
5V/div
I
IN
10A/div
I
OUT
5A/div
SHORT-CIRCUIT WAVEFORM
MAX8545 toc18
V
OUT
2V/div
V
IN
20V/div
I
IN
2A/div
INDUCTOR
CURRENT
5A/div
1ms/div
0
0
0
0
SHORT-CIRCUIT WAVEFORM
MAX8545 toc17
GAIN AND PHASE vs. FREQUENCY
MAX8545/46/48 toc19
FREQUENCY (kHz)
GAIN (dB)
PHASE (DEGREES)
101
-120
-100
-80
-60
-40
-20
0
20
40
60
-140
0.1 100
180
150
120
90
60
30
VIN = 17V, V
OUT
= 2.5V
I
LOAD
= 6A
GAIN
PHASE
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