19-3982; Rev 2; 10/10
KIT
ATION
EVALU
BLE
AVAILA
Highly Integrated, 25A, Wide-Input,
Internal MOSFET, Step-Down Regulator
General Description
The MAX8655 synchronous-PWM buck regulator oper-
ates from a 4.5V to 25V input and generates an output
voltage adjustable from 0.7V to 5.5V at loads up to 25A.
Integrated power MOSFETs provide a small footprint,
ease of layout, and reduced EMI. Removing the board
trace inductances ensures the highest efficiency at
high frequency.
The MAX8655 uses peak current-mode control architec-
ture with an adjustable (200kHz to 1MHz), constant-
switching frequency, which is externally synchronizable.
The MAX8655’s adjustable current limit uses the induc-
tor’s DC resistance to improve efficiency or an external
sense resistor for higher accuracy. Foldback type cur-
rent limit is available to reduce the power dissipation
under severe-overload or short-circuit conditions. A ref-
erence input is provided for use with a high-accuracy
external reference or for DDR and tracking applications.
Monotonic startup provides safe starting into a prebi-
ased output, where traditional step-down regulators
discharge the output capacitor during soft-start, creat-
ing a negative voltage at the output and possibly dam-
aging the load.
A 180° out-of-phase synchronization output is available
for synchronizing with another MAX8655.
An enable input is provided for on/off control and to
facilitate output sequencing. Output-voltage sensing for
programmable overvoltage protection is provided and
is independent of the feedback network to further
enhance the output overvoltage protection.
Overall, the MAX8655 provides enough flexibility for the
experienced user, as well as simplicity and ease of use
for non-power-supply engineers.
o
25A Output Current
o
Integrated Power MOSFETs
o
Operates from 4.5V to 25V Supply
o
1% FB Voltage Accuracy Over Temperature
o
Adjustable Output Voltage Down to 0.7V
o
Adjustable Switching Frequency and External
Synchronization from 200kHz to 1MHz
o
180° Phase-Shifted Synchronization
o
Adjustable Overcurrent Limit
o
Adjustable Slope Compensation
o
Selectable Current-Limit Mode: Latch-Off or
Automatic Recovery
o
Monotonic Output Voltage Rise at Startup into
Prebias Output
o
Output Sources and Sinks Current for DDR
Applications
o
Enable Input
o
Power-OK (POK) Output
o
Adjustable Soft-Start
o
Independently Adjustable Overvoltage Protection
Features
MAX8655
Typical Operating Circuit
Applications
ILIM2
SCOMP
COMP
Point-of-Load Power Supplies
Telecom Power
Networking
Nonisolated DC-DC Power Modules
Servers and Workstations
Notebook Computers
IBA Power Supplies
POWER-OK OUTPUT
POK
ILIM1
CS-
CS+
PVIN
IN
VL
VLGND
OUTPUT
0.7V TO 5.5V
UP TO 25A
LX
GND
FSYNC INPUT
FSYNC
SYNC OUTPUT
OFF
ENABLE INPUT
ON
SYNCO
MAX8655
EN
VL
BST
Ordering Information
PART
MAX8655ETN+
TEMP
RANGE
-40°C to +85°C
PIN-PACKAGE
56 TQFN-EP*
(8mm x 8mm)
LXB
INPUT 7V
TO 28V
PVIN
MODE
PGND
REFIN
AVL
AVL
+Denotes
a lead(Pb)-free/RoHS-compliant package.
*EP
= Exposed pad.
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.
OVP
SS
FB
Highly Integrated, 25A, Wide-Input,
Internal MOSFET, Step-Down Regulator
MAX8655
ABSOLUTE MAXIMUM RATINGS
PVIN, IN, EN to GND ..............................................-0.3V to +30V
BST to LXB ............................................................-0.3V to +7.5V
LX, LXB to GND............ (-2.5V for < 50ns transient) -1V to +30V
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 to VLGND ......................................-0.3V to +0.3V
Operating Junction Temperature Range .......... -40°C to +125°C
Junction Temperature ......................................................+150°C
θ
JC
(thermal resistance from
junction to exposed pad) (Note 1) ...............................3.5°C/W
θ
JT
(thermal resistance from junction to the top) ............3.9°C/W
I
LX(RMS)
..................................................................................27A
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
Note 1:
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on package thermal considerations, refer to
www.maxim-ic.com/thermal-tutorial.
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, circuit of Figure 4, typical values are at T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
PVIN Operating Voltage Range
IN Operating Voltage Range
IN Quiescent Supply Current
Shutdown Supply Current
PVIN Shutdown Supply Current
AVL Undervoltage-Lockout
Threshold
Output-Voltage Adjust Range
VL Regulation Voltage
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
REF
= 0.625V
18
20
23
100
28
Ω
µA
VL = IN for V
IN
< 7V
V
FB
= 0.75V, no switching
EN = GND, V
IN
≤
28V
I
IN
+ I
VL
+ I
AVL
, EN = GND, V
AVL
= V
VL
= V
IN
= 5V
V
PVIN
= V
LX
= V
BST
V
AVL
rising, 3% typical hysteresis
Minimum output voltage is limited by minimum duty cycle
and external components
7V < V
IN
< 28V
5.5V < V
VL
< 7V, 1mA < I
LOAD
< 10mA
3.90
0.7
6.0
4.900
10
6.5
4.975
1
4.15
4.40
5.5
7.0
5.050
CONDITIONS
MIN
3
4.5
2
TYP
MAX
25
25.0
3
10
32
UNITS
V
V
mA
µA
µA
V
V
V
V
mA
Dual Mode is a trademark of Maxim Integrated Products, Inc.
2
_______________________________________________________________________________________
Highly Integrated, 25A, Wide-Input,
Internal MOSFET, Step-Down Regulator
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 12V, V
BST
- V
LX
= 6.5V, T
A
= -40°C to +85°C, circuit of Figure 4, typical values are at T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
ERROR AMPLIFIER
REFIN = AVL
FB Regulation Voltage
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-
)
Negative Current Limit
CS+, CS- Input Bias 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
SCOMP High Threshold
SCOMP Low Threshold
SCOMP Adjustment Range
SCOMP Input Leakage Current
V
SCOMP
= 1.25V to 2.5V
0.5
1.25
5
2.50
200
T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
231.25
113.77
231.25
113.77
110.70
250.00
123.00
250.00
123.00
123.00
268.75
132.23
268.75
132.23
132.23
V
AVL
-
0.5
V
V
V
nA
mV
R
ILIM1
= 24kΩ
ILIM1 = AVL
% of valley current limit
V
CS+
= V
CS-
= 0V or 5.5V
27.2
60
-90
-25
0
32
80
-120
36.8
92
-150
+25
5.5
mV
%
µA
V
V
CS+
- V
CS-
= 30mV, V
OUT
= 0 to 5.5V
12
V/V
From COMP to GND, V
EN
= 0V
V
FB
= 0.7V
-0.1
V
REFIN
= 0.7V to 1.5V
0.693
V
REFIN
-
0.00375
70
0.7
V
REFIN
110
20
5
0.707
V
REFIN
+
0.00375
160
100
50
+1.5
V
µS
Ω
nA
V
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8655
_______________________________________________________________________________________
3
Highly Integrated, 25A, Wide-Input,
Internal MOSFET, Step-Down Regulator
MAX8655
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 12V, V
BST
- V
LX
= 6.5V, T
A
= -40°C to +85°C, circuit of Figure 4, typical values are at T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
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
SYNCO Output Low Level
SYNCO Output High Level
FSYNC Input Low
FSYNC Input High
THERMAL PROTECTION
Thermal Shutdown
Thermal-Shutdown Hysteresis
POK
POK Threshold
POK Output Voltage, Low
POK Leakage Current, High
OVP
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
REFIN = AVL
V
REFIN
= 0.7V to 1.5V
V
OVP
= 0.8V
770
110
800
115
840
120
500
mV
%
nA
REFIN = AVL, V
FB
rising, typical hysteresis is 3%
V
REFIN
= 0.75V to 1.5V, V
FB
rising, typical hysteresis is 3%
V
FB
= 0.6V, I
POK
= 2mA
V
POK
= 5.5V
629
88.7
650
91.7
25
671
94.7
200
1
mV
%
mV
µA
Rising temperature
+160
15
°C
°C
2.5
I
SYNCO
= 5mA
I
SYNCO
= -5mA
V
AVL
- 1V
0.4
180
0.4
R
FSYNC
= 21.0kΩ
R
FSYNC
= 143kΩ
Measured at LX
Measured at LX
160
100
100
100
800
160
1000
200
235
75
100
1200
1200
240
kHz
ns
ns
kHz
ns
ns
ns
Degrees
V
V
V
V
CONDITIONS
MIN
TYP
MAX
UNITS
Note 2:
Specifications are 100% production tested at T
A
= +85°C. Limits over the operating temperature range are guaranteed by
design.
4
_______________________________________________________________________________________
Highly Integrated, 25A, Wide-Input,
Internal MOSFET, Step-Down Regulator
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
MAX8655
LOAD REGULATION
(CIRCUIT OF FIGURE 4)
MAX8655 toc01
LINE REGULATION
(CIRCUIT OF FIGURE 4)
MAX8655 toc02
FB VOLTAGE vs. EXPOSED PAD TEMPERATURE
(CIRCUIT OF FIGURE 4)
7.5A LOAD
0.715
0.710
FB VOLTAGE (V)
0.705
0.700
0.695
0.690
0.685
0.680
MAX8655 toc03
3.34
3.33
OUTPUT VOLTAGE (V)
3.32
3.31
3.30
3.29
3.28
3.27
3.26
0
5
10
15
LOAD CURRENT (A)
V
IN
= 12V
3.34
12A LOAD
3.33
OUTPUT VOLTAGE (V)
3.32
3.31
3.30
3.29
3.28
3.27
3.26
0.720
20
25
5
10
15
INPUT VOLTAGE (V)
20
-40
0
40
80
EXPOSED PAD TEMPERATURE (°C)
120
OSCILLATOR FREQUENCY vs. INPUT VOLTAGE
(CIRCUIT OF FIGURE 4)
MAX8655 toc04
STEP-LOAD RESPONSE
(CIRCUIT OF FIGURE 3)
MAX8655 toc05
400
390
OSCILLATOR FREQUENCY (kHz)
380
370
360
350
340
330
320
310
300
8
13
18
23
INPUT VOLTAGE (V)
T
A
= +85°C
T
A
= +25°C
R
FSYNC
= 76.8kΩ
T
A
= -40°C
V
OUT
= 1.2V
V
OUT
50mV/div
(AC-COUPLED)
I
OUT
5A/div
28
40µs/div
POWER-UP WAVEFORMS
(CIRCUIT OF FIGURE 4)
MAX8655 toc06
POWER-DOWN WAVEFORMS
(CIRCUIT OF FIGURE 4)
MAX8655 toc07
ENABLE WAVEFORMS
(CIRCUIT OF FIGURE 4)
MAX8655 toc08
V
POK
10V/div
5V/div
V
IN
10V/div
V
POK
5V/div
V
EN
1V/div
V
IN
V
OUT
5A/div
I
LX
I
LX
2ms/div
10A/div
V
POK
V
OUT
2V/div
V
OUT
I
LX
2ms/div
5V/div
5V/div
2V/div
10A/div
200µs/div
_______________________________________________________________________________________
5
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