19-2623; Rev 0; 1/03
KIT
ATION
EVALU
E
BL
AVAILA
1.6V to 5.5V Input, 0.5% Accurate, Dual
180° Out-of-Phase Step-Down Controllers
General Description
Features
o
Operates from a 1.6V to 5.5V Supply (MAX1956)
o
0.5% Output Accuracy
o
0.8V to 0.9V
IN
Output Range
o
Up to 25A per Phase Output Current
o
On-Chip Boost Regulator Provides 5V Gate Drive
o
Up to 93% Efficiency
o
180° Out-of-Phase Operation
o
±4% Voltage Margining
o
Lossless, Foldback Current Limit
o
Selectable Voltage Sequencing
o
Synchronizable to External Clock
o
Digital Soft-Start and Soft-Stop
o
Small 28-Pin, 5mm
✕
5mm Thin QFN Package
MAX1955/MAX1956
The MAX1955/MAX1956 are dual-output, fixed-frequency,
voltage-mode, pulse-width modulated (PWM) step-down
controllers with 0.5% output accuracy. Each controller
switches at a constant 600kHz and is 180° out-of-phase
with the other controller, reducing input ripple current
and the number of input capacitors.
An on-chip bias supply generates a 5V gate drive to
deliver up to 25A output current per phase with low-cost
N-channel MOSFETs at up to 93% efficiency. Lossless
adjustable current limit eliminates expensive current-
sense resistors and improves efficiency. Foldback current
limit reduces power dissipation during short-circuit
conditions and handles transient overloads better than
controllers using hiccup-mode short-circuit protection.
Output voltage margining shifts output voltage by
±4% from the nominal value to simplify system test.
Outputs also can be powered up and down in select-
able sequences to meet core and logic supply-rail
requirements.
The MAX1955/MAX1956 are available in a 28-lead thin
QFN package with exposed pad.
Ordering Information
PART
MAX1955ETI
MAX1956ETI
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
28 Thin QFN-EP*
28 Thin QFN-EP*
Applications
Base Stations
Telecom and Network Equipment
Servers
DSP, ASIC, µP, and FPGA Supplies
INPUT
1.6V TO 5.5V
*EP
= Exposed pad.
Pin Configuration appears at end of data sheet.
Typical Operating Circuit
VDD
IN
LXB
BST1
OUTPUT 1
0.8V TO 0.9V
IN
UP TO 25A
DH1
LX1
V
DD
BST2
DH2
LX2
MAX1956
OUTPUT 2
0.8V TO 0.9V
IN
UP TO 25A
DL2
FB2
DL1
PGND
FB1
COMP1
SEQ
GND
SYNCHRONIZATION
CLOCK
ON/OFF
VOLTAGE
MARGINING
ILIM1
SYNC
EN
ILIM2
AV
DD
VDD
COMP2
REF
________________________________________________________________
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.
1.6V to 5.5V Input, 0.5% Accurate, Dual
180° Out-of-Phase Step-Down Controllers
MAX1955/MAX1956
ABSOLUTE MAXIMUM RATINGS
IN, AVDD, SYNC, EN, ILIM_, FB_, SEQ to GND.......-0.3V to +6V
COMP_, REF to GND..............................-0.3V to (V
AVDD
+ 0.3V)
LXB to GND ..............................................-0.3V to (V
VDD
+ 0.3V)
DL_ to GND ...............................(V
PGND
- 0.3V) to (V
VDD
+ 0.3V)
BST_ to GND ..........................................................-0.3V to +12V
DH1 to LX1 ...............................................-0.3V to (BST1 + 0.3V)
DH2 to LX2 ...............................................-0.3V to (BST2 + 0.3V)
LX1 to BST1..............................................................-6V to +0.3V
LX2 to BST2..............................................................-6V to +0.3V
PGND to GND or VDD to AVDD ............................-0.3V to +0.3V
REF Short-Circuit to GND...........................................Continuous
I
VDD
...................................................................................250mA
Continuous Power Dissipation* (T
A
= +70°C)
28-Lead Thin QFN
(derate 20.8mW/°C above +70°C)................................1667mW
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
*Exposed
pad soldered to PC board.
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
EN
= 3.3V; V
VDD
= V
AVDD
= 5V; V
PGND
= V
GND
= 0; C
REF
= 0.22µF; SEQ = SYNC = GND;
T
A
= 0°C to +85°C,
unless other-
wise noted. Typical values are at T
A
= +25°C.)
PARAMETER
IN Input Voltage Range
IN Input Voltage UVLO
FB Regulation Voltage
FB Regulation Voltage with
Positive Voltage Margining
FB Regulation Voltage with
Negative Voltage Margining
Line Regulation Error
Feedback Input Bias
Feedback Transconductance
COMP Source Current
COMP Sink Current
COMP Pulldown Resistance
Output Soft-Start Time
Step-Down Switching Frequency
SYNC Frequency Range
Maximum Duty Cycle
Minimum Duty Cycle
SYNC = GND (Note 3)
2 times step-down switching frequency
Measured at DH_
Measured at DH_
540
1080
90
93
7
In shutdown
4.27
600
660
1320
97
10
Percentage change from nominal regulation voltage
Percentage change from nominal regulation voltage
Note 2
-0.2
1
100
100
2
150
150
100
MAX1955
MAX1956 (Note 1)
Rise or fall
MAX1955, hysteresis = 35mV
MAX1956, hysteresis = 30mV
CONDITIONS
MIN
2.25
1.6
1.9
1.30
0.796
3
-5
0.8
4
-4
0.1
TYP
MAX
5.50
5.5
2.2
1.58
0.804
5
-3
0.3
+0.2
3
UNITS
V
V
V
%
%
%
µA
mS
µA
µA
Ω
ms
kHz
kHz
%
%
2
_______________________________________________________________________________________
1.6V to 5.5V Input, 0.5% Accurate, Dual
180° Out-of-Phase Step-Down Controllers
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
EN
= 3.3V; V
VDD
= V
AVDD
= 5V; V
PGND
= V
GND
= 0; C
REF
= 0.22µF; SEQ = SYNC = GND;
T
A
= 0°C to +85°C,
unless other-
wise noted. Typical values are at T
A
= +25°C.)
PARAMETER
V
DD
No-Load Supply Current
IN Supply Current
IN Shutdown Supply Current
REF Voltage
REF Load Regulation
Default Current-Limit Threshold
Adjustable Current-Limit
Threshold
Thermal-Shutdown Threshold
DH_ Gate-Driver
On-Resistance
DL_ Gate-Driver Pullup
On-Resistance
DL_ Gate-Driver Pulldown
On-Resistance
Dead Time (Adaptive)
SYNC Minimum Pulse Width
EN Voltage Range for Nominal
Output Voltage
EN Voltage Range for Positive
Voltage Margining
EN Voltage Range for Negative
Voltage Margining
EN Voltage Range for Shutdown
EN, SEQ, SYNC Input High
Voltage
SEQ, SYNC Input Low Voltage
EN, SEQ, SYNC Input Current
BST_ Leakage Current in
Shutdown
V
DD
Output Voltage
I
VDD
= 0 to 150mA
-1
-20
4.75
I
REF
= -50µA to +50µA
ILIM_ = V
DD
, measured from PGND to LX_
Measured from PGND to LX_
T
J
rising, 15°C hysteresis
Pulling up or down
DL_ high state
DL_ low state
DH_ falling to DL_ rising
DL_ falling to DH_ rising
High or low
Percentage of V
IN
Percentage of V
IN
Percentage of V
IN
Percentage of V
IN
(Note 4)
200
80
55
30
0
V
IN
- 0.5
0.5
+1
+20
5.50
90
100
70
45
20
R
ILIM_
= 100kΩ
R
ILIM_
= 400kΩ
127.5
60
240
150
75
300
160
1
1
0.35
23
26
1.8
1.8
0.65
1.267
1.28
CONDITIONS
Total of VDD1 + VDD2 + AVDD current, SYNC = GND,
no load on DH_ or DL_
MIN
TYP
20
35
MAX
32
100
20
1.293
0.01
172.5
90
360
UNITS
mA
µA
µA
V
V
mV
mV
°C
Ω
Ω
Ω
ns
ns
%
%
%
%
V
V
µA
µA
V
MAX1955/MAX1956
_______________________________________________________________________________________
3
1.6V to 5.5V Input, 0.5% Accurate, Dual
180° Out-of-Phase Step-Down Controllers
MAX1955/MAX1956
ELECTRICAL CHARACTERISTICS
(V
IN
= V
EN
= 3.3V; V
VDD
= V
AVDD
= 5V; PGND = GND = 0; C
REF
= 0.22µF; SYNC = GND;
T
A
= -40°C to +85°C,
unless otherwise
noted.) (Note 5)
PARAMETER
IN Input Voltage Range
IN Input Voltage UVLO
FB Regulation Voltage
FB Regulation Voltage with
Positive Voltage Margining
FB Regulation Voltage with
Negative Voltage Margining
Line Regulation Error
FB_ Input Bias
Feedback Transconductance
COMP_ Source Current
COMP_ Sink Current
COMP_ Pulldown Resistance
Step-Down Switching Frequency
SYNC Frequency Range
Maximum Duty Cycle
Minimum Duty Cycle
V
DD
Quiescent Supply Current
IN Quiescent Supply Current
IN Shutdown Supply Current
REF Voltage
REF Load Regulation
Default Current-Limit Threshold
Adjustable Current-Limit
Threshold
I
REF
= -50µA to +50µA
ILIM_ = V
DD
; measured from PGND to LX_
Measured from PGND to LX_
R
ILIM_
= 100kΩ
R
ILIM_
= 400kΩ
127.5
60
240
1.267
In shutdown
SYNC = GND (Note 3)
2 times step-down switching frequency
Measured at DH_
Measured at DH_
Total of VDD1 + VDD2 + AVDD current, SYNC = GND,
no load on DH_ or DL_
540
1080
90
Percentage change from nominal regulation voltage
Percentage change from nominal regulation voltage
(Note 2)
-0.2
1.0
100
100
100
660
1320
97
10
32
100
20
1.293
0.01
172.5
90
360
MAX1955
MAX1956 (Note 1)
Rise or fall
MAX1955
MAX1956
CONDITIONS
MIN
2.25
1.6
1.9
1.30
0.794
+3
-5
TYP
MAX
5.50
5.5
2.2
1.58
0.806
+5
-3
0.3
+0.2
3.1
UNITS
V
V
V
%
%
%
µA
mS
µA
µA
Ω
kHz
kHz
%
%
mA
µA
µA
V
V
mV
mV
4
_______________________________________________________________________________________
1.6V to 5.5V Input, 0.5% Accurate, Dual
180° Out-of-Phase Step-Down Controllers
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
EN
= 3.3V; V
VDD
= V
AVDD
= 5V; PGND = GND = 0; C
REF
= 0.22µF; SYNC = GND;
T
A
= -40°C to +85°C,
unless otherwise
noted.) (Note 5)
PARAMETER
DH_ Gate-Driver On-Resistance
DL_ Gate-Driver Pullup
On-Resistance
DL_ Gate-Driver Pulldown
On-Resistance
SYNC Minimum Pulse Width
EN Voltage Range for Nominal
Output Voltage
EN Voltage Range for Positive
Voltage Margining
EN Voltage Range for Negative
Voltage Margining
EN Voltage Range for Shutdown
EN, SEQ, SYNC Input High
Voltage
SEQ, SYNC Input Low Voltage
EN, SEQ, SYNC Input Current
BST_ Leakage Current in
Shutdown
V
DD
Output Voltage
I
VDD
= 0 to 150mA
-1
-20
4.75
Pulling up or down
DL_ high state
DL_ low state
High or low
Percentage of V
IN
Percentage of V
IN
Percentage of V
IN
Percentage of V
IN
(Note 4)
200
80
55
30
0
V
IN
- 0.5
0.5
+1
+20
5.50
100
70
45
20
CONDITIONS
MIN
TYP
MAX
1.8
1.8
0.65
UNITS
Ω
Ω
Ω
ns
%
%
%
%
V
V
µA
µA
V
MAX1955/MAX1956
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
IN input voltage must not drop below minimum voltage because of ripple or transient conditions.
Guaranteed by design.
Boost frequency is 2x step-down frequency.
For proper startup, EN must exceed V
IN
- 0.5V.
Specifications to -40°C are guaranteed by design but not production tested.
_______________________________________________________________________________________
5
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