19-0726; Rev 4; 10/11
KIT
ATION
EVALU
BLE
AVAILA
Dual, 5A, 2MHz Step-Down Regulators
General Description
Features
o
27mΩ On-Resistance Internal MOSFETs
o
Dual, 5A, PWM Step-Down Regulators
o
Fully Protected Against Overcurrent,
Short Circuit, and Overtemperature
o
±1% Output Accuracy Over Load, Line,
and Temperature
o
Operates from 2.25V to 3.6V Supply
o
REFIN on One Channel for Tracking or
External Reference
o
Integrated Boost Diodes
o
Adjustable Output from 0.6V to 0.9 x V
IN
o
Soft-Start Reduces Inrush Supply Current
o
0.5MHz to 2MHz Adjustable Switching,
or FSYNC Input
o
All-Ceramic-Capacitor Design
o
180° Out-of-Phase Operation Reduces Input
Ripple Current
o
Individual Enable Inputs and PWRGD Outputs
o
Safe-Start into Prebiased Output
o
Available in 5mm x 5mm Thin QFN Package
o
Sink/Source Current in DDR Applications
MAX8855/MAX8855A
The MAX8855/MAX8855A high-efficiency, dual step-down
regulators are capable of delivering up to 5A at each out-
put. The devices operate from a 2.25V to 3.6V supply, and
provide output voltages from 0.6V to 0.9 x V
IN
, making them
ideal for on-board point-of-load applications. Total output
error is less than ±1% over load, line, and temperature.
The MAX8855/MAX8855A operate in PWM mode with a
switching frequency ranging from 0.5MHz to 2MHz, set
by an external resistor. It can also be synchronized to
an external clock in the same frequency range. Two
internal switching regulators operate 180° out-of-phase
to reduce the input ripple current, and consequently
reduce the required input capacitance. The high
operating frequency minimizes the size of external
components. High efficiency, internal dual-nMOS
design keeps the board cool under heavy loads. The
voltage-mode control architecture and the high-band-
width (> 15MHz typ) voltage-error amplifier allow a type
III compensation scheme to be utilized to achieve fast
response under both line and load transients, and also
allow for ceramic output capacitors.
Programmable soft-start reduces input inrush current.
Two enable inputs allow the turning on/off of each out-
put individually, resulting in great flexibility for system-
level designs. A reference input is provided to facilitate
output-voltage tracking applications. The MAX8855/
MAX8855A are available in a 32-pin TQFN (5mm x 5mm)
package with 0.8mm max height.
Ordering Information
PART
MAX8855ETJ+
MAX8855AETJ+
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
32 TQFN-EP*
32 TQFN-EP*
Applications
ASIC/CPU/DSP Power Supplies
DDR Power Supplies
Set-Top Box Power Supplies
Printer Power Supplies
Network Power Supplies
+Denotes
a lead(Pb)-free/RoHS-compliant package.
*EP
= Exposed pad.
Typical Operating Circuit
INPUT1
2.25V TO 3.6V
IN1 IN2
BST1
BST2
LX1
LX2
INPUT2
2.25V TO 3.6V
OUTPUT1
1.2V / 5A
OUTPUT2
1.5V / 5A
PGND1
PGND2
MAX8855/
MAX8855A
FB1
FB2
COMP1
TYPE III
COMPENSATION
COMP2
TYPE III
COMPENSATION
PWRGD1 PWRGD2
ON
OFF
EN1
GND
EN2
OFF
ON
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.
Dual, 5A, 2MHz Step-Down Regulators
MAX8855/MAX8855A
ABSOLUTE MAXIMUM RATINGS
IN_, LX_, V
DD
, VDL, PWRGD_ to GND..................-0.3V to +4.5V
V
DD
, VDL to IN_.....................................................-0.3V to +4.5V
EN_, SS_, COMP_, FB_, REFIN, FSYNC to GND ......-0.3V to the
lower of (V
VDD
+ 0.3V) and (V
VDL
+ 0.3V)
Continuous LX_ Current (Note 1) ...................................5.5A
RMS
BST_ to LX_ ...........................................................-0.3V to +4.5V
PGND_ to GND......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
32-Pin TQFN (5mm x 5mm)
(derate 34.5mW/°C above +70°C) ..........................2758.6mW
Operating Ambient Temperature Range .............-40°C to +85°C
Operating Junction Temperature Range ...........-40°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
Note 1:
LX_ have internal clamp diodes to PGND_ and IN_. Applications that forward bias these diodes should take care not to
exceed the IC’s package power-dissipation limits.
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.
PACKAGE THERMAL CHARACTERISTICS (Note 2)
TQFN
Junction-to-Ambient Thermal Resistance (θ
JA
) ...........29°C/W
Junction-to-Case Thermal Resistance (θ
JC
) ...............1.7°C/W
Note 2:
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.
ELECTRICAL CHARACTERISTICS
(V
IN_
= V
VDD
= V
VDL
= 3.3V, V
FB_
= 0.5V, V
SS_
= V
REFIN
= 600mV, PGND_ = GND, R
FSYNC
= 10kΩ, L = 0.47μH, C
BST_
= 0.1μF,
C
SS_
= 0.022μF, PWRGD_ not connected; T
A
= -40°C to +85°C, typical values are at T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
IN1, IN2, VDL, VDD
IN_, VDL, and V
DD
Voltage Range
IN_ Supply Current
V
DD
+ VDL Supply Current
Shutdown Supply Current
(I
IN1
+ I
IN2
+ I
VDD
+ I
VDL
)
IN_, V
DD
Undervoltage Lockout Threshold
UVLO Monitors V
DD
, IN1, and IN2
IN_, V
DD
Undervoltage Lockout Deglitch
BST1, BST2
Shutdown BST_ Current
COMP1, COMP2
COMP_ Clamp Voltage, High
COMP_ Slew Rate
COMP_ Shutdown Resistance
From COMP_ to GND, V
EN
_ = 0V
V
VDD
= V
IN
_ = 2.25V to 3.6V, V
FB
_ = 0.7V
1.80
2.00
1.40
7
25
2.25
V
V/μs
Ω
V
IN
_ = V
VDD
= V
VDL
= V
BST
_ =
3.6V, V
EN
_ = 0V, V
LX
_ = 0 or 3.6V
T
A
= +25°C
T
A
= +85°C
0.02
2
μA
(Note 3)
1MHz switching, no load
1MHz switching, V
DD
= VDL
MAX8855
MAX8855A
V
IN
_ = 2.5V
V
IN
_ = 3.3V
V
VDD
= 2.5V
V
VDD
= 3.3V
2.35
2.25
1.9
2.8
7.2
10
0.3
2.0
1.8
1.9
2
2.2
15
11
3.60
3.60
3.5
5
V
mA
mA
μA
V
μs
CONDITIONS
MIN
TYP
MAX
UNITS
V
IN
_ = V
VDD
= V
VDL
= V
BST
_ - T
A
= +25°C
V
LX
_ = 3.6V, V
EN
_ = 0V
T
A
= +85°C
Rising
Falling
2
_______________________________________________________________________________________
Dual, 5A, 2MHz Step-Down Regulators
ELECTRICAL CHARACTERISTICS (continued)
(V
IN_
= V
VDD
= V
VDL
= 3.3V, V
FB_
= 0.5V, V
SS_
= V
REFIN
= 600mV, PGND_ = GND, R
FSYNC
= 10kΩ, L = 0.47μH, C
BST_
= 0.1μF,
C
SS_
= 0.022μF, PWRGD_ not connected; T
A
= -40°C to +85°C, typical values are at T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
ERROR AMPLIFIER
V
COMP
_ = 1V to
2V
V
VDD
= V
IN
_ = 2.5V to
3.3V (MAX8855)
0.594
V
VDD
= V
IN
_ = 2.25V to
3.3V (MAX8855A)
V
VDD
= V
IN
_ = 2.5V to
3.3V (MAX8855)
0.594
V
VDD
= V
IN
_ = 2.25V to
3.3V (MAX8855A)
0
1
V
FB
_ = 0.605V
T
A
= +25°C
T
A
= +85°C
T
A
= +25°C
T
A
= +85°C
V
VDD
= 2.35V to 2.6V
V
VDD
= 2.25V to 2.6V
0
0
40
37
90
65
V
VDD
-
1.65
V
V
VDD
-
1.70
31
34
27
29
7.0
8.3
-0.1
-10
-0.1
0.9
1.80
1.0
2.0
50
95
R
FSYNC
= 10kΩ
90
3
95
1.1
2.2
MHz
ns
ns
%
A
RMS
9.6
+0.1
μA
46
52
500
300
V
VDD
-
1.6
V
mA
nA
0.600
0.606
V
0.600
0.606
V
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8855/MAX8855A
FB_ Regulation Voltage
FB_ Regulation Voltage with External
Reference
V
COMP
_ = 1V to
2V
Error Amplifier Common-Mode-Input Range
Error Amplifier Maximum Output Current
FB_ Input Bias Current
REFIN, SS2
REFIN Input Bias Current
V
FB_
= 0.610V
MAX8855
REFIN Common-Mode Range
MAX8855A
V
VDD
= 2.6V to 3.6V
LX1, LX2 (ALL PINS COMBINED)
LX_ On-Resistance, High
LX_ On-Resistance, Low
LX_ Current-Limit Threshold
I
LX_
= -2A
I
LX_
= -2A
V
IN
_ = V
BST
_ - V
LX
_ = 3.3V
V
IN
_ = V
BST
_ - V
LX
_ = 2.5V
V
IN
_ = 3.3V
V
IN
_ = 2.5V
T
A
= +25°C
T
A
= +85°C
T
A
= +25°C
T
A
= +85°C
nA
mΩ
mΩ
A
High-side sourcing and freewheeling
V
IN
_ = 3.6V,
V
EN
_ = 0V
V
LX_
= 3.6V
V
LX_
= 0V
LX_ Leakage Current
LX_ Switching Frequency
LX_ Minimum Off-Time
LX_ Minimum On-Time
LX_ Maximum Duty Cycle
Maximum LX_ Output Current
R
FSYNC
= 10kΩ
R
FSYNC
= 4.75kΩ
_______________________________________________________________________________________
3
Dual, 5A, 2MHz Step-Down Regulators
MAX8855/MAX8855A
ELECTRICAL CHARACTERISTICS (continued)
(V
IN_
= V
VDD
= V
VDL
= 3.3V, V
FB_
= 0.5V, V
SS_
= V
REFIN
= 600mV, PGND_ = GND, R
FSYNC
= 10kΩ, L = 0.47μH, C
BST_
= 0.1μF,
C
SS_
= 0.022μF, PWRGD_ not connected; T
A
= -40°C to +85°C, typical values are at T
A
= +25°C, unless otherwise noted.) (Note 2)
PARAMETER
EN1, EN2
EN_ Logic-Low
EN_ Logic-High
EN_ Input Current
SS1, SS2
SS_ Charging Current
REFIN, SS2
Discharge Resistance
THERMAL SHUTDOWN
Thermal-Shutdown Threshold
(Independent Channels)
Thermal-Shutdown Hysteresis
+165
20
°C
°C
In shutdown or a fault condition
335
Ω
V
SS
_ = 300mV
5
8
11
μA
V
EN
_ = 0 or 3.6V,
V
VDD
= 3.6V
T
A
= +25°C
T
A
= +85°C
1.7
-1
0.01
+1
0.7
V
V
μA
CONDITIONS
MIN
TYP
MAX
UNITS
Note 2:
All devices 100% production tested at T
A
= +25°C. Limits over temperature are guaranteed by design.
Note 3:
V
VDD
must equal V
VDL
and be equal to or greater than V
IN
_.
Typical Operating Characteristics
(V
IN1
= V
IN2
= 3.3V, MAX8855/MAX8855A, circuit of Figure 6, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY
vs. LOAD CURRENT WITH 3.3V INPUT
MAX8855/MAX8855A toc01
EFFICIENCY
vs. LOAD CURRENT WITH 2.5V INPUT
MAX8855/MAX8855A toc02
SWITCHING FREQUENCY vs. R
FSYNC
2200
SWITCHING FREQUENCY (kHz)
2000
1800
1600
1400
1200
1000
800
600
400
MAX8855/MAX8855A toc03
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
100
1000
LOAD CURRENT (mA)
V
OUT_
= 2.5V
V
OUT_
= 1.2V
V
OUT_
= 1.8V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
V
OUT_
= 1.8V
V
OUT_
= 1.2V
2400
10,000
100
1000
LOAD CURRENT (mA)
10,000
3
6
9
12
R
FSYNC
(kΩ)
15
18
21
4
_______________________________________________________________________________________
Dual, 5A, 2MHz Step-Down Regulators
Typical Operating Characteristics (continued)
(V
IN1
= V
IN2
= 3.3V, MAX8855/MAX8855A, circuit of Figure 6, T
A
= +25°C, unless otherwise noted.)
SWITCHING FREQUENCY
vs. TEMPERATURE
MAX8855/MAX8855A toc04
MAX8855/MAX8855A
FEEDBACK VOLTAGE
vs. TEMPERATURE
608
FEEDBACK VOLTAGE (mV)
606
604
602
600
598
596
594
592
590
MAX8855/MAX8855A toc05
1100
1080
SWITCHING FREQUENCY (kHz)
1060
1040
1020
1000
980
960
940
920
900
-40
-15
10
35
60
610
85
-40
-15
10
35
60
85
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SHUTDOWN SUPPLY CURRENT (nA)
9
8
7
6
5
4
3
2
1
0
2.35
2.60
2.85
3.10
3.35
3.60
I
OUT_
1.5A
I
IN1
+ I
IN2
+ I
VDL
+ I
VDD
MAX8855/MAX8855A toc06
LOAD TRANSIENT
MAX8855/MAX8855A toc07
10
1.8V OUTPUT
V
OUT_
100mV/div
3.0A
1.5A
1A/div
20µs/div
SUPPLY VOLTAGE (V)
SWITCHING WAVEFORMS
MAX8855/MAX8855A toc08
SOFT-START AND SHUTDOWN
MAX8855/MAX8855A toc09
V
LX1
2V/div
V
EN2
5V/div
I
L1
2A/div
V
OUT2
1V/div
V
LX2
V
PWRGD2
2V/div
I
IN2
2V/div
I
L2
400ns/div
2A/div
400µs/div
3A LOAD
1A/div
_______________________________________________________________________________________
5
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