19-4113; Rev 1; 10/10
Single/Multiphase, Step-Down,
DC-DC Converter Delivers Up to 25A Per Phase
General Description
The MAX8686 current-mode, synchronous PWM step-
down regulator with integrated MOSFETs operates from
a 4.5V to 20V input supply and generates an adjustable
output voltage from 0.7V to 5.5V while delivering up to
25A per phase.
The MAX8686 employs a peak current-mode architec-
ture that operates with an adjustable switching frequency
from 300kHz to 1MHz. An adjustable current-limit thresh-
old allows for optimization for different applications with
different load currents. Inductor current sense is
achieved either using an external sense resistor or using
a lossless inductor current-sense scheme. The foldback
and hiccup current limit reduces the power dissipation
during overload or short-circuit conditions and allows for
autorecovery when the fault condition is removed.
The MAX8686 offers the ability to start up monotonically
even when there is a prebias output voltage. In addi-
tion, an adjustable soft-start capability allows for a con-
trolled turn-on. The MAX8686 features an accurate 1%
reference and offers a reference input that allows for a
higher accuracy reference to be used for voltage track-
ing applications such as DDR memory.
The MAX8686 can be paralleled (up to eight) together
in a true multiphase mode to deliver up to 200A of out-
put current. When operating in this mode, this device
achieves better than 10% current balance between
phases at full load. The MAX8686 supports program-
mable phase shedding to improve system efficiency
during light load conditions.
Other features include an enable input and a power-OK
(POK) indicator used for power sequencing. The
MAX8686 also features latch overvoltage protection
that turns on the low-side MOSFET when the output
voltage exceeds 120% of the nominal voltage. The
MAX8686 is offered in a thermally enhanced 40-pin,
6mm x 6mm TQFN package.
Features
o
Operating Range from 4.5V to 20V Input Supply
o
1% Reference Voltage Accuracy Over Temperature
o
Reference Input (REFIN) for Output Tracking or
System Reference Voltage
o
Adjustable Switching Frequency from 300kHz
to 1MHz
o
Single/Multiphase Operation Delivers Up to
25A/200A with Integrated MOSFETs
o
Adjustable Current Limit
o
Monotonic Output Voltage at Startup (Prebias)
o
Output Sink and Source Current Capability
o
Adjustable Soft-Start
o
Thermal-Overload Protection
o
Output Overvoltage Protection
o
Thermally Enhanced 6mm x 6mm TQFN
Package (4W)
MAX8686
Ordering Information
PART
MAX8686ETL+
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
40 TQFN-EP*
+Denotes
a lead-free package.
*EP
= Exposed pad.
Typical Application Circuit
V
IN
= 12V
IN
BST
V
OUT
= 1.2V/25A
PGND
LX
Applications
POL Power Supplies
Module Replacements
Telecom Equipment
Networking Equipment
Servers
DDR Memory
ENABLE
INPUT
REFIN
MAX8686
RS+
RS-
CS+
CS-
POK
POK
OUTPUT
PHASE/REFO
COMP
EN/SLOPE
FREQ
SS GND
ILIM
Pin Configuration appears at end of data sheet.
________________________________________________________________
Maxim Integrated Products
1
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.
Single/Multiphase, Step-Down,
DC-DC Converter Delivers Up to 25A Per Phase
MAX8686
ABSOLUTE MAXIMUM RATINGS
IN, INA to PGND.....................................................-0.3V to +22V
BST, DH to LX...........................................................-0.3V to +6V
BST to PGND..........................................................-0.3V to +28V
LX to PGND...........................-0.3V to (V
IN
+ 0.3V) (-2V for 50ns)
BST to VL................................................................-0.3V to +22V
AVL to GND.................................................-0.3V to (V
VL
+ 0.3V)
COMP, ILIM, FREQ, PHASE/REFO, RS+, RS-, POK, REFIN,
CS+, CS- to GND ..................................-0.3V to (V
AVL
+ 0.3V)
VL to PGND ..............................................................-0.3V to +6V
EN/SLOPE to GND ...................................................-0.3V to +6V
RTN to PGND to GND to GFREQ ..........................-0.3V to +0.3V
IN Continuous Current.....................................................20A
RMS
LX Continuous Current ....................................................25A
RMS
Continuous Power Dissipation (T
A
= +70°C) (Note 1)
40-Pin TQFN (derate 50mW/°C above +70°C) ..........4000mW
θ
JC
(thermal resistance from junction to exposed pad)
(Note 1) ......................................................................3.5°C/W
θ
JT
(thermal resistance from junction to top) (Note 1) ...3.9°C/W
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
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 see
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
= V
INA
= 12V, VL = AVL, V
REFIN
= 1V, V
RS+
- V
RS-
= 1V, V
RS-
= 0V, V
EN/SLOPE
= 1.25V, V
CS+
= V
CS-
= 1V, R
ILIM
= 122kΩ, C
VL
= 1μF,
C
AVL
= 0.22μF, C
FREQ
= 270pF, T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
GENERAL
Operating Input-Voltage Range
Operating Input-Voltage Range
IN/INA Shutdown Supply Current
IN/INA Quiescent Supply Current
AVL Undervoltage Lockout Trip
Level
VL Output Voltage
SOFT-START (SS)
SS Shutdown Resistance
SS Soft-Start Current
V
EN/SLOPE
= 0V (master mode)
V
SS
= 0.4V and 1.1V, T
A
= -40°C to +85°C
Measured at PHASE/REFO (master mode),
T
A
= -40°C to +85°C
V
RS-
= V
AVL
(slave mode), V
PHASE
= 0.3V and 2.5V,
T
A
= -40°C to +85°C
V
REFIN
= 0.7V or 3.3V
19
20
25
100
31
Ω
μA
V
INA
= V
IN
, T
A
= -40°C to +85°C
V
IN
= V
INA
= V
VL
= V
AVL
, T
A
= -40°C to +85°C
V
EN/SLOPE
= 0V,
V
IN
= V
INA
= 20V
T
A
= +25°C
T
A
= +85°C
6
4.5
450
500
5.5
4.2
4.35
4.03
5.2
5.4
5.5
6.6
4.45
20
5.5
V
V
μA
mA
V
V
CONDITIONS
MIN
TYP
MAX
UNITS
V
RS+
= 1.1V, no switching; V
IN
= V
INA
= 20V,
T
A
= -40°C to +85°C
Rising, T
A
= -40°C to +85°C
Falling
6V
≤
V
IN
= V
INA
≤
20V, 1mA
≤
I
VL
≤
30mA,
T
A
= -40°C to +85°C
PHASE COMPARATOR AND REFERENCE (PHASE/REFO)
Reference Output Voltage
PHASE Comparator Offset
REFIN INPUT
REFIN Input Bias Current
REFIN Input Voltage Range
-500
0
+500
3.3
nA
V
3.267
-20
3.300
3.333
+20
V
mV
2
_______________________________________________________________________________________
Single/Multiphase, Step-Down,
DC-DC Converter Delivers Up to 25A Per Phase
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
INA
= 12V, VL = AVL, V
REFIN
= 1V, V
RS+
- V
RS-
= 1V, V
RS-
= 0V, V
EN/SLOPE
= 1.25V, V
CS+
= V
CS-
= 1V, R
ILIM
= 122kΩ, C
VL
= 1μF,
C
AVL
= 0.22μF, C
FREQ
= 270pF, T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
ERROR AMPLIFIER
Remote-Sense Accuracy
(Including Error Amplifier Offset)
Transconductance
COMP Source Current
COMP Sink Current
COMP Shutdown Resistance
RS+/RS- Input Leakage Current
RS+ Input Common-Mode Range V
IN
= V
INA
= V
VL
= V
AVL
= 4.5V, V
RS-
= 100mV
RS- Input Common-Mode Range
CURRENT-SENSE AMPLIFIER
Input Offset Voltage
Current-Sense Amplifier Gain
Input Bias Current
CURRENT LIMIT
ILIM Output Current
Current-Limit Threshold
COMP Clamp Voltage High
COMP Clamp Voltage Low
Maximum Peak Positive Current
Threshold
V
ILIM
= 2V, T
A
= -40°C to +85°C
Measure as V
CS+
- V
CS-
(T
A
= -40°C to +85°C)
V
REFIN
= 3.3V, V
RS+
- V
RS-
= 3.35V
R
ILIM
= 275kΩ, no slope compensation
R
ILIM
= 122kΩ
R
ILIM
= 275kΩ
9
16
38
3.6
0.54
10
20
45
3.8
0.6
54
11
23
52
4.0
0.66
μA
mV
V
V
mV
Measure at CS+ and CS-, V
CS+
= V
CS-
= 0.7V and 5.5V
(T
A
= -40°C to +85°C)
V
CS-
= 0 to 5V, V
CS+
- V
CS-
= 30mV,
T
A
= -40°C to +85°C
V
CS+
= V
CS-
= 5.5V and 0V
-1.5
29.0
-4
30.5
+1.5
32.0
+4
mV
V/V
μA
0
-100
Measure as V
RS+
- V
RS-
(T
A
= -40°C to +85°C)
T
A
= -40°C to +85°C
V
RS+
- V
RS-
= 1.3V
V
RS+
- V
RS-
= 0.7V
V
EN/SLOPE
= 0V
V
REFIN
= 3.3V
V
REFIN
= 0.7V
3.267
0.693
1.1
220
220
3.3
0.7
1.7
300
300
20
0.2
100
1.5
3.4
+100
3.333
0.707
2.6
V
mS
μA
μA
Ω
μA
V
mV
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8686
R
ILIM
= 275kΩ, V
REFIN
= 3.3V, V
RS+
- V
RS-
= 2V
_______________________________________________________________________________________
3
Single/Multiphase, Step-Down,
DC-DC Converter Delivers Up to 25A Per Phase
MAX8686
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
INA
= 12V, VL = AVL, V
REFIN
= 1V, V
RS+
- V
RS-
= 1V, V
RS-
= 0V, V
EN/SLOPE
= 1.25V, V
CS+
= V
CS-
= 1V, R
ILIM
= 122kΩ, C
VL
= 1μF,
C
AVL
= 0.22μF, C
FREQ
= 270pF, T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
OSCILLATOR (FREQ)
Source Current
Switching Frequency
Minimum On-Time
FREQ Discharge Resistance
Ramp Peak Voltage
SLOPE COMPENSATION (EN/SLOPE)
V
SLOPE
Range
SLOPE Source Current
THERMAL PROTECTION
Thermal Shutdown
Thermal-Shutdown Hysteresis
POWER-OK (POK)
POK Threshold
POK Output Voltage Low
POK Leakage Current
V
OUT
rising
V
OUT
falling
V
RS+
- V
RS-
= 0.8V, I
POK
= 2mA
V
POK
= 5.5V
V
REFIN
= 3.3V, V
RS+
rising, percentage of V
OUT
in
regulation
87
90
87
25
0.001
200
1
93
%V
OUT
mV
μA
Rising temperature
160
30
°C
°C
1.25
8
10
2.50
12
V
μA
2.60
V
FREQ
= 2V, T
A
= -40°C to +85°C
C
FREQ
= 180pF
C
FREQ
= 580pF
480
0.8
240
500
1
300
100
10
V
AVL
/2
50
2.85
520
1.2
360
μA
MHz
kHz
ns
Ω
V
CONDITIONS
MIN
TYP
MAX
UNITS
OVERVOLTAGE OUTPUT PROTECTION (OVP)
Overvoltage Fault Trip Level
ENABLE (EN/SLOPE)
EN Logic-High
EN Logic-Low
BST
Internal PMOS On-Resistance
8
Ω
1.2
0.7
V
V
115
120
125
%
Note 2:
Specifications to T
A
= -40°C are guaranteed by design and not production tested.
4
_______________________________________________________________________________________
Single/Multiphase, Step-Down,
DC-DC Converter Delivers Up to 25A Per Phase
Typical Operating Characteristics
(V
IN
= 12V, f
SW
= 500kHz, single phase, circuit of Figure 2, unless otherwise noted.)
SINGLE-PHASE EFFICIENCY
vs. LOAD CURRENT
MAX8686 toc01
MAX8686
SINGLE-PHASE EFFICIENCY
vs. LOAD CURRENT (V
IN
= 5V)
MAX8686 toc02
EFFICIENCY vs. LOAD CURRENT
270kHz
86
85
EFFICIENCY (%)
379kHz
MAX8686 toc03
95.0
V
OUT
= 3.3V
92.5
90.0
EFFICIENCY (%)
95.0
92.5
90.0
EFFICIENCY (%)
87.5
85.0
82.5
80.0
77.5
CIRCUIT OF FIGURE 3
AIRFLOW = 300 LFM
0
5
10
15
20
V
OUT
= 1.2V
V
OUT
= 1.8V
V
OUT
= 2.5V
87
87.5
85.0
82.5
80.0
77.5
AIRFLOW = 300 LFM
75.0
0
5
10
15
20
25
LOAD CURRENT (A)
V
OUT
= 1.8V
V
OUT
= 2.5V
84
83
82
81
80
AIRFLOW = 300 LFM
79
5
8
11
14
17
20
564kHz
467kHz
75.0
25
LOAD CURRENT (A)
LOAD CURRENT (A)
SWITCHING FREQUENCY
vs. CFREQ CAPACITANCE
MAX8686 toc04
CLOSED-LOOP FREQUENCY RESPONSE
(I
OUT
= 160A, 8 PHASES)
50
40
30
20
GAIN (dB)
10
0
-10
-20
-30
-40
-50
GAIN
PHASE
OUTPUT VOLTAGE vs. OUTPUT CURRENT
AIRFLOW = 300 LFM
144
108
PHASE (DEGREES)
72
36
0
-36
-72
-108
-144
-180
1.2005
1.2000
0
5
10
15
20
25
OUTPUT CURRENT (A)
OUTPUT VOLTAGE (V)
1.2035
1.2030
1.2025
1.2020
1.2015
1.2010
MAX8686 toc06
MAX8686 toc09
1300
1200
SWITCHING FREQUENCY (kHz)
1100
1000
900
800
700
600
500
400
300
200
MAX8686 toc05
180
1.2040
100 150 200 250 300 350 400 450 500 550 600 650 700
CFREQ CAPACITANCE (pF)
1
10
100
1k
FREQUENCY (kHz)
OUTPUT VOLTAGE vs. INPUT VOLTAGE
I
OUT
= 10A
MAX8686 toc07
OUTPUT LOAD TRANSIENT
MAX8686 toc08
SOFT-START WITH EN CONTROL
(I
OUT
= 10A)
EN
2V/div
1.30
OUTPUT VOLTAGE (V)
1.25
V
OUT
200mV/div
AC-COUPLED
SS
2V/div
1.20
I
OUT
42A/div
CIRCUIT OF FIGURE 4
AIRFLOW = 300 LFM
1.15
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
INPUT VOLTAGE (V)
100μs/div
V
OUT
500mV/div
POK
5V/div
CIRCUIT OF FIGURE 4
1ms/div
_______________________________________________________________________________________
5
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