19-3155; Rev 0; 5/04
Step-Down Controllers with Prebias Startup,
Lossless Sensing, Synchronization, and OVP
General Description
The MAX8543/MAX8544 current-mode, constant-fre-
quency PWM buck controllers operate from a 3V to
13.2V input supply and generate adjustable 0.8V to 0.9
x V
IN
output voltages at loads up to 25A. They feature
adjustable switching frequency and synchronization for
noise-sensitive applications.
The MAX8543/MAX8544 can start with (or without) a pre-
existing bias on the output, without discharging the out-
put. This feature simplifies tracking supply designs for
core and I/O applications and redundant supply designs.
The MAX8543/MAX8544 use the DC resistance of the
output inductor as the current-sense element for loss-
less, low-cost current sensing. The current-sense
threshold can be set to four discrete levels to accom-
modate inductors with different DC resistance values.
The MAX8544 features a power-OK monitor and two
MAX8544 controllers that can operate at 180° out-of-
phase for dual-output applications.
♦
Prebias Startup/Monotonic
♦
1% Output Accuracy
♦
Ceramic, Polymer, or Electrolytic Capacitors
♦
200kHz to 1MHz Adjustable Frequency
♦
160kHz to 1.2MHz Synchronization
♦
Lossless, Foldback Current Limit
♦
Overvoltage Protection
♦
Enable (On/Off)
♦
Adjustable Soft-Start
♦
MAX8544
Latch-Off/Autorecovery
Power-OK Monitor
Out-of-Phase Clock Output
Features
MAX8543/MAX8544
Applications
Base Stations
Networks and Telecom
Storage
Servers
PART
MAX8543EEE
MAX8544EEP
Ordering Information
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
20 QSOP
Pin Configurations appear at end of data sheet.
Typical Operating Circuit
INPUT 3V TO 13.2V
V
IN
= 3V
TO 5.5V
VL
ON
OFF
EN
FSYNC
OPTIONAL
SYNCHRONIZATION
SS
IN
BST
DH
LX
OUTPUT
0.8V TO 0.9 x V
IN
UP TO 25A
MAX8543
COMP
ILIM
GND
PGND
DL
CS+
CS-
POK (MAX8544)
FB
________________________________________________________________
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.
Step-Down Controllers with Prebias Startup,
Lossless Sensing, Synchronization, and OVP
MAX8543/MAX8544
ABSOLUTE MAXIMUM RATINGS
IN, EN, CS+, CS- to GND .......................................-0.3V to +14V
BST, DH to LX ..........................................................-0.3V to +6V
BST to GND ............................................................-0.3V to +20V
DL, COMP, ILIM2, SS, SYNCO,
FSYNC to GND .......................................-0.3V to (V
VL
+ 0.3V)
VL, FB, POK, ILIM1, ILIM, MODE to GND ................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C) .......666.7mW
20-Pin QSOP (derate 9.1mW/°C above +70°C) .......727.3mW
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
= 13.2V, V
BST
- V
LX
= 5V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Operating Input Voltage Range
Quiescent Supply Current
Shutdown Supply Current
VL Undervoltage-Lockout Trip Level
Output Voltage Adjust Range (V
OUT
)
VL Output Voltage
VL Output Current
VOLTAGE REFERENCE
SS Shutdown Resistance
SS Soft-Start Current
Soft-Start Ramp Time
ERROR AMPLIFIER
FB Regulation Voltage
Transconductance
COMP Shutdown Resistance
FB Input Leakage Current
FB Input Common-Mode Range
CURRENT-SENSE AMPLIFIER
V
ILIM1
= 0V
Voltage Gain
V
OUT
= 0 to 13V
V
ILIM1
= (1/3)V
VL
V
ILIM1
= (2/3)V
VL
V
ILIM1
= V
VL
CURRENT LIMIT
ILIM2 Output Current (MAX8544 Only)
ILIM1 Input Current
R
ILIM2
= 50kΩ to 200kΩ
V
ILIM1
= 0V or V
VL
4.5
-1
5
5.5
+1
µA
µA
8.8
4.8
3.2
2.4
11
6
4
3
13.2
7.2
4.8
3.6
V/V
From COMP to GND, V
EN
= 0V
V
FB
= 0.9V
-0.1
0.792
70
0.8
110
20
5
0.808
160
100
100
+0.9
V
µS
Ω
nA
V
From SS to GND, V
EN
= 0V
V
REF
= 0.625V
Output from 0% to 100%, C
REF
= 0.01µF to 1µF
14
20
24
33
100
34
Ω
µA
ms/µF
CONDITIONS
VL connected to IN for V
IN
< 5.5V
V
FB
= 0.9V, no switching
EN = GND, MODE = GND, IN not connected to VL
EN = GND, VL = IN, MODE = GND
V
VL
rising, typical hysteresis is 80mV
(Note 1)
5.5V < V
IN
< 13.2V, 1mA < I
VL
< 75mA
2.52
0.8
4.5
5
5.5
75
2.7
MIN
3.0
2
TYP
MAX
13.2
3
10
20
2.88
UNITS
V
mA
µA
V
V
V
mA
2
_______________________________________________________________________________________
Step-Down Controllers with Prebias Startup,
Lossless Sensing, Synchronization, and OVP
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 13.2V, V
BST
- V
LX
= 5V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
CONDITIONS
V
CS+
- V
CS-
, V
ILIM1
= 0V
V
CS+
- V
CS-
, V
ILIM1
= (1/3)V
VL
V
CS+
- V
CS-
, V
ILIM1
= (2/3)V
VL
Current-Limit Threshold
V
CS+
- V
CS-
, V
ILIM1
= V
VL
V
LX
- V
PGND
, R
ILIM2
= 50kΩ (MAX8544 only)
V
LX
- V
PGND
, R
ILIM2
= 200kΩ (MAX8544 only)
V
LX
- V
PGND
, V
FB
= 0.8V (MAX8543 only)
V
LX
- V
PGND
, V
FB
= 0V (MAX8543 only)
Negative Current-Limit Threshold
CS+, CS- Input Current
CS+, CS- Input Common-Mode Range
OSCILLATOR
Switching Frequency
Minimum Off-Time
Minimum On-Time
FSYNC Synchronization Range
FSYNC Input High Pulse Width
FSYNC Input Low Pulse Width
FSYNC Rise/Fall Time
SYNCO Phase Shift from DH Rising
SYNCO Output Low Level
SYNCO Output High Level
MOSFET DRIVERS
DH On-Resistance, High State
DH On-Resistance, Low State
DL On-Resistance, High State
DL On-Resistance, Low State
Break-Before-Make Dead Time
LX, BST, IN Leakage Current
THERMAL PROTECTION
Thermal Shutdown
Thermal-Shutdown Hysteresis
Rising temperature
+160
15
°C
°C
(V
BST
- V
LX
) = 5V
(V
BST
- V
LX
) = 3V
(V
BST
- V
LX
) = 5V
(V
BST
- V
LX
) = 3V
V
VL
= 5V
V
VL
= 3V
V
VL
= 5V
V
VL
= 3V
Low-side off to high-side on
High-side off to low-side on
V
BST
= 18.7V, V
LX
= 13.2V, V
IN
= 13.2V
1
1.2
1
1.2
1
1.2
0.6
0.8
55
40
5
1.7
2.5
2.5
2.5
Ω
Ω
Ω
Ω
ns
µA
R
FSYNC
= 18.2kΩ, free-running mode,
at maximum duty cycle
I
SYNCO
= 5mA
I
SYNCO
= 5mA
V
VL
- 1V
165
180
R
FSYNC
= 18.2kΩ
R
FSYNC
= 158kΩ
Measured at DH
Measured at DH
160
100
100
100
195
0.4
150
800
1000
200
220
90
270
145
1200
1200
kHz
ns
ns
kHz
ns
ns
ns
Degrees
V
V
% of positive-direction current limit V
LX
- V
PGND
V
CS+
= V
CS-
= 0 or 5V
MIN
38.5
85
127.5
170
-42.5
-160
-110
-20
-25
-40
0
TYP
50
100
150
200
-50
-200
-130
-30
-50
MAX
56.5
115
172.5
230
-57.5
-240
-150
-40
-85
+40
13.2
%
µA
V
mV
UNITS
MAX8543/MAX8544
_______________________________________________________________________________________
3
Step-Down Controllers with Prebias Startup,
Lossless Sensing, Synchronization, and OVP
MAX8543/MAX8544
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 13.2V, V
BST
- V
LX
= 5V,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
POK
Power-OK Threshold
POK Output Voltage, Low
POK Leakage Current, High
OVERVOLTAGE PROTECTION (OVP)
Output Overvoltage Fault-Trip level
MODE CONTROL
MODE Logic-Level Low
MODE Logic-Level High
MODE Input Current
SHUTDOWN CONTROL
EN Logic-Level Low
EN Logic-Level High
EN Input Current
3V
≤
V
VL
≤
5.5V
3V
≤
V
VL
≤
5.5V
V
EN
= 0 or 5.5V
V
EN
= 13.2V
2
-1
1.5
+4
6
0.45
V
V
µA
3V
≤
V
VL
≤
5.5V
3V
≤
V
VL
≤
5.5V
V
MODE
= 0V
MODE = VL
1.8
-1
5
+1
10
0.4
V
V
µA
Rising edge compared to regulation set point;
triggers after one or two clock cycles
+110
+115
+120
%
V
FB
rising, percent of V
OUT
,
typical hysteresis is 3%
V
FB
= 0.6V, I
POK
= 2mA
V
POK
= 5.5V
88
91
25
0.001
94
200
1
%
mV
µA
CONDITIONS
MIN
TYP
MAX
UNITS
ELECTRICAL CHARACTERISTICS
(V
IN
= 13.2V, V
BST
- V
LX
= 5V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
Operating Input Voltage Range
Quiescent Supply Current
Shutdown Supply Current
VL Undervoltage-Lockout Trip Level
Output Voltage Adjust Range (V
OUT
)
VL Output Voltage
VL Output Current
VOLTAGE REFERENCE
SS Shutdown Resistance
SS Soft-Start Current
ERROR AMPLIFIER
FB Regulation Voltage
Transconductance
COMP Shutdown Resistance
FB Input Leakage Current
FB Input Common-Mode Range
From COMP to GND, V
EN
= 0V
V
FB
= 0.9V
-0.1
0.788
70
0.808
160
100
100
+0.9
V
µS
Ω
nA
V
From SS to GND, V
EN
= 0V
V
REF
= 0.625V
14
100
34
Ω
µA
CONDITIONS
VL connected to IN for V
IN
< 5.5V
V
FB
= 0.9V, no switching
EN = GND, MODE = GND, IN not connected to VL
EN = GND, VL = IN, MODE = GND
V
VL
rising, typical hysteresis is 80mV
(Note 1)
5.5V < V
IN
< 13.2V, 1mA < I
VL
< 75mA
2.52
0.8
4.5
5.5
75
MIN
3.0
MAX
13.2
3
10
20
2.88
UNITS
V
mA
µA
V
V
V
mA
4
_______________________________________________________________________________________
Step-Down Controllers with Prebias Startup,
Lossless Sensing, Synchronization, and OVP
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 13.2V, V
BST
- V
LX
= 5V,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 2)
PARAMETER
CURRENT-SENSE AMPLIFIER
V
ILIM1
= 0V
Voltage Gain
V
OUT
= 0 to 13V
V
ILIM1
= (1/3)V
VL
V
ILIM1
= (2/3)V
VL
V
ILIM1
= V
VL
CURRENT LIMIT
ILIM2 Output Current (MAX8544 Only)
ILIM1 Input Current
R
ILIM2
= 50kΩ to 200kΩ
V
ILIM1
= 0V or V
VL
V
CS+
- V
CS-
, V
ILIM1
= 0V
V
CS+
- V
CS-
, V
ILIM1
= (1/3)V
VL
V
CS+
- V
CS-
, V
ILIM1
= (2/3)V
VL
Current-Limit Threshold
V
CS+
- V
CS-
, V
ILIM1
= V
VL
V
LX
- V
PGND
, R
ILIM2
= 50kΩ (MAX8544 only)
V
LX
- V
PGND
, R
ILIM2
= 200kΩ (MAX8544 only)
V
LX
- V
PGND
, V
FB
= 0.8V (MAX8543 only)
V
LX
- V
PGND
, V
FB
= 0V (MAX8543 only)
Negative Current-Limit Threshold
CS+, CS- Input Current
CS+, CS- Input Common-Mode Range
OSCILLATOR
Switching Frequency
Minimum Off-Time
Minimum On-Time
FSYNC Synchronization Range
FSYNC Input High Pulse Width
FSYNC Input Low Pulse Width
FSYNC Rise/Fall Time
SYNCO Phase Shift from DH Rising
SYNCO Output Low Level
SYNCO Output High Level
MOSFET DRIVERS
DH On-Resistance, High State
DH On-Resistance, Low State
DL On-Resistance, High State
DL On-Resistance, Low State
LX, BST, IN Leakage Current
(V
BST
- V
LX
) = 5V
(V
BST
- V
LX
) = 5V
V
VL
= 5V
V
VL
= 5V
V
BST
= 18.7V, V
LX
= 13.2V, V
IN
= 13.2V
2.5
2.5
2.5
1.7
5
Ω
Ω
Ω
Ω
µA
R
FSYNC
= 18.2kΩ
I
SYNCO
= 5mA
I
SYNCO
= 5mA
V
VL
- 1V
165
R
FSYNC
= 18.2kΩ
Measured at DH
Measured at DH
160
100
100
100
195
0.4
800
150
1200
270
140
1200
kHz
ns
ns
kHz
ns
ns
ns
Degrees
V
V
% of positive-direction current limit V
LX
- V
PGND
V
CS+
= V
CS-
= 0V or 5V
4.2
-1
38.5
85
127.5
170
-40
-160
-110
-20
-25
-40
0
5.5
+1
56.5
115
172.5
230
-60
-240
-150
-40
-85
+40
13.2
%
µA
V
mV
µA
µA
8.8
4.8
3.2
2.4
13.2
7.2
4.8
3.6
V/V
CONDITIONS
MIN
MAX
UNITS
MAX8543/MAX8544
5
_______________________________________________________________________________________
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