19-3973; Rev 0; 1/06
KIT
ATION
EVALU
BLE
AVAILA
4.5V to 28V Input Current-Mode Step-
Down Controller with Adjustable Frequency
General Description
Features
♦
Operates from 4.5V to 28V Supply
♦
1% FB Voltage Accuracy Over Temperature
♦
Adjustable Output Voltage Down to 0.7V or REFIN
♦
Adjustable Switching Frequency or External
Synchronization from 200kHz to 1.2MHz
♦
180° Phase-Shifted Clock Output
♦
Adjustable Overcurrent Limit
♦
Adjustable Foldback Current Limit
♦
Adjustable Slope Compensation
♦
Selectable Current-Limit Mode: Latch-Off or
Automatic Recovery
♦
Monotonic Output-Voltage Rise at Startup
♦
Output Sources and Sinks Current
♦
Enable Input
♦
Power-OK (POK) Output
♦
Adjustable Soft-Start
♦
Independently Adjustable Overvoltage Protection
MAX8650
The MAX8650 synchronous PWM buck controller oper-
ates from a 4.5V to 28V input and generates an
adjustable 0.7V to 5.5V output voltage at loads up to 25A.
The MAX8650 uses a peak current-mode control archi-
tecture with an adjustable (200kHz to 1.2MHz) constant
switching frequency and is externally synchronizable. The
IC’s current limit uses the inductor’s DC resistance to
improve efficiency or an external sense resistor for high
accuracy. The current-limit threshold is adjusted with an
external resistor. Foldback-type current limit can be
implemented to reduce the power dissipation in overload
or short-circuit conditions. Short-circuit protection is
provided based on sensing the current in the low-side
MOSFET. A reference input is provided for use with a
high-accuracy external reference or for double-data-rate
(DDR)-tracking applications.
Monotonic prebiased startup is available for a safe-start
in applications where the output capacitor may have an
initial charge. This feature prevents the output from
pulling low during startup, which is a common charac-
teristic of conventional buck regulators.
A 180° out-of–phase synchronization output is available
for synchronizing with another converter.
Applications
Base Stations
DDR
Network and Telecom Power Modules
Storage
IBA Applications
Servers
Pin Configuration appears at end of data sheet.
Ordering Information
PART
MAX8650EEG+
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
24 QSOP
PKG
CODE
E24-1
+Denotes
lead-free package.
Typical Operating Circuit
R2
R1
SYNC
ON EN
OFF
POK
SYNCO
1
11
24
3
23
R3
22
21
C3
R4
C4
R5
20
16
19
18
R7
17
FSYNC
EN
POK
SYNCO
MAX8650EEG
SCOMP
ILIM2
REFIN
VL
SS
IN
ILIM1
AVL
COMP
CS+
FB
CS-
OVP
GND
MODE
BST
DH
6
LX
DL
PGND
7
8
9
10
12
14
15
13
C11
C7
C8
C10
R9
C9
Q2
R8
C6
2
4
5
C2
L1
Q1
C5
D2
V
IN
7V TO 28V
C1
V
OUT
0.7V TO 5.5V
R6
________________________________________________________________
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.
4.5V to 28V Input Current-Mode Step-Down
Controller with Adjustable Frequency
MAX8650
ABSOLUTE MAXIMUM RATINGS
IN, EN to GND ........................................................-0.3V to +30V
BST to LX...............................................................-0.3V to +7.5V
DH to LX ....................................................-0.3V to (V
BST
+ 0.3V)
LX to GND .................... -1V (-2.5V for < 50ns transient) to +30V
DL to PGND.................................................-0.3V to (V
VL
+ 0.3V)
ILIM2, ILIM1, SYNCO, FSYNC, OVP,
SCOMP to GND .....................................-0.3V to (V
AVL
+ 0.3V)
VL to PGND ...........................................................-0.3V to +7.5V
AVL, FB, POK, COMP, SS, MODE, REFIN to GND .....-0.3V to +6V
CS+, CS- to GND .....................................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
24-Pin QSOP (derate 9.5mW/°C above +70°C)..........762mW
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
= 12V, V
BST
- V
LX
= 6.5V, T
A
= -40°C to +85°C. Typical values are at T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
Operating Input Voltage Range
Quiescent Supply Current
Shutdown Supply Current
I
IN
+ I
VL
+ I
AVL
AVL Undervoltage-Lockout Trip
Level
Output Voltage Adjust Range
VL Regulation Voltage
VL Output Current
AVL Regulation Voltage
AVL Output Current
SOFT-START
SS Shutdown Resistance
SS Soft-Start Current
REFIN INPUT
REFIN Dual Mode™ Threshold
REFIN Input Bias Current
REFIN Input Voltage Range
V
REFIN
= 0.7V to 1.5V
V
AVL
-
1.0V
-250
0
V
AVL
+250
1.5
V
nA
V
From SS to GND, V
EN
= 0V
V
SS
= 0.625V
18
20
23
100
28
Ω
µA
5.5V < V
VL
< 7V, 1mA < I
LOAD
< 10mA
VL = IN for V
IN
< 7V
V
FB
= 0.75V, no switching
EN = GND, V
IN
≤
28V
EN = GND, V
AVL
= V
VL
= V
IN
= 5V
V
AVL
rising, 3% typ hysteresis
Minimum output voltage is limited by minimum duty cycle
and external components
7V < V
IN
< 28V, 1mA < I
LOAD
< 40mA
3.90
0.7
6.0
40
4.900
10
4.975
5.050
6.5
4.15
CONDITIONS
MIN
4.5
2
TYP
MAX
28.0
3
10
32
4.40
5.5
7.0
UNITS
V
mA
µA
V
V
V
mA
V
mA
Dual Mode is a trademark of Maxim Integrated Products, Inc.
2
_______________________________________________________________________________________
4.5V to 28V Input Current-Mode Step-Down
Controller with Adjustable Frequency
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 12V, V
BST
- V
LX
= 6.5V, T
A
= -40°C to +85°C. Typical values are at T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
ERROR AMPLIFIER
REFIN = AVL
FB Regulation Voltage
V
REFIN
= 0.7V to 1.5V
0.693
0.7
0.707
V
REFIN
+
0.00375
160
100
50
+1.5
12
27.2
68.0
-42.5
-170
-90
-25
0
32.0
80.0
-50.0
-200
-120
36.8
92.0
-57.5
-230
-150
+25
5.5
V
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8650
V
REFIN
-
V
REFIN
0.00375
70
110
20
5
-0.1
Transconductance
COMP Shutdown Resistance
FB Input Leakage Current
FB Input Common-Mode Range
CURRENT-SENSE AMPLIFIER
Voltage Gain
CURRENT LIMIT
Peak Current-Limit
Threshold (V
CS+
- V
CS-
)
Valley Current-Limit Threshold
(V
LX
- V
PGND
)
Negative Current-Limit Threshold
CS+, CS- Input Current
CS+, CS- Input Common-Mode
Range
SLOPE COMPENSATION
V
SCOMP
= 2.5V
Slope Compensation at Maximum
Duty Cycle
V
SCOMP
= 1.25V
SCOMP = AVL
SCOMP = GND, T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
SCOMP High Threshold
SCOMP Low Threshold
SCOMP Adjustment Range
SCOMP Input Leakage Current
OSCILLATOR
Switching Frequency
Minimum Off-Time
Minimum On-Time
R
FSYNC
= 21.0kΩ
R
FSYNC
= 143kΩ
Measured at DH
Measured at DH
V
SCOMP
= 1.25V to 2.5V
R
ILIM1
= 24kΩ
ILIM1 = AVL
R
ILIM2
= 50kΩ
R
ILIM2
= 200kΩ
% of (typ) positive direction current limit (V
LX
- V
PGND
)
V
CS+
= V
CS-
= 0V or 5.5V
V
OUT
= 0 to 5.5V, V
CS+
- V
CS-
= 30mV
From COMP to GND, V
EN
= 0V
V
FB
= 0.7V
µS
Ω
nA
V
V/V
mV
mV
%
µA
V
231.25
113.77
231.25
113.77
110.70
0.5
1.25
250.00
123.00
250.00
123.00
123.00
268.75
132.23
268.75
132.23
132.23
V
AVL
- 0.5
2.5
V
V
V
nA
mV
5
800
160
1000
200
235
75
200
1200
240
100
kHz
ns
ns
_______________________________________________________________________________________
3
4.5V to 28V Input Current-Mode Step-Down
Controller with Adjustable Frequency
MAX8650
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 12V, V
BST
- V
LX
= 6.5V, T
A
= -40°C to +85°C. Typical values are at T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
FSYNC Synchronization Range
FSYNC Input-High Pulse Width
FSYNC Input-Low Pulse Width
FSYNC Rise/Fall Time
SYNCO Phase Shift
SYNCO Output Low Level
SYNCO Output High Level
FSYNC Pin Threshold
for SYNC Mode
FSYNC Input Low
FSYNC Input High
FET 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 Leakage Current
THERMAL PROTECTION
Thermal Shutdown
Thermal-Shutdown Hysteresis
Rising temperature
+160
15
°C
°C
V
BST
- V
LX
= 6.5V
V
BST
- V
LX
= 5V
V
BST
- V
LX
= 6.5V
V
BST
- V
LX
= 5V
V
VL
= 6.5V
V
VL
= 5V
V
VL
= 6.5V
V
VL
= 5V
Low side off to high side on, high side off to low side on
V
BST
= 35V, V
LX
= 28V, V
IN
= 28V
1.13
1.4
1.0
1.3
1.6
1.7
0.8
0.85
20
1.8
2.2
2
2.2
2.5
2.8
1.5
1.5
30
5
Ω
Ω
Ω
Ω
ns
µA
2.5
I
SYNCO
= 5mA
I
SYNCO
= 5mA
V
AVL
-
1V
1.7
2.5
0.4
180
0.4
CONDITIONS
MIN
160
100
100
100
TYP
MAX
1200
UNITS
kHz
ns
ns
ns
Degrees
V
V
V
V
V
4
_______________________________________________________________________________________
4.5V to 28V Input Current-Mode Step-Down
Controller with Adjustable Frequency
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 12V, V
BST
- V
LX
= 6.5V, T
A
= -40°C to +85°C. Typical values are at T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
POK
Power-OK Threshold
POK Output Voltage, Low
POK Leakage Current, High
OVP
REFIN = AVL
OVP Threshold Voltage
OVP Leakage Current, High
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
4.5V
≤
V
AVL
≤
5.5V
4.5V
≤
V
AVL
≤
5.5V
V
EN
= 0V
V
EN
= 28V
2
-1
1.5
+1
6.0
0.45
V
V
µA
4.5V
≤
V
AVL
≤
5.5V
4.5V
≤
V
AVL
≤
5.5V
V
MODE
= 0 to V
AVL
1.8
-1
+1
0.4
V
V
µA
V
REFIN
= 0.7V to 1.5V
V
OVP
= 0.8V
770
110
800
115
840
120
500
mV
% of
V
REFIN
nA
REFIN = AVL, V
FB
rising, typical hysteresis is 3%
V
REFIN
= 0.7V to 1.5V, V
FB
rising, typical hysteresis is 3%
V
FB
= 0.6V, I
POK
= 2mA
V
POK
= 5.5V
629.0
88.7
650.0
91.7
25
671.0
94.7
200
1
mV
% of
mV
µA
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8650
Note 1:
Specifications are 100% production tested at TA = +85°C. Limits over the operating temperature range are guaranteed
by design.
_______________________________________________________________________________________
5
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