19-2640; Rev 1; 7/04
IT
TION K
VALUA
E
BLE
AVAILA
1MHz, 1% Accurate, 6A Internal Switch
Step-Down Regulators
General Description
Features
♦
6A PWM Step-Down Regulator with 95%
Efficiency
♦
1MHz/500kHz Switching for Small External
Components
♦
0.76in
2
Complete 6A Regulator Footprint
♦
External Components’ Height <3mm
♦
±1% Output Accuracy over Load, Line, and
Temperature
♦
Operate from 2.6V to 5.5V Supply
♦
Operate from 2.5V Input with V
CC
at 3.3V/5V
♦
Preset Output Voltage of 1.8V or 2.5V
♦
Adjustable Output from 0.8V to 85% of Input
♦
Voltage Margining: ±4% (MAX1945R) or ±9%
(MAX1945S)
♦
Synchronize to External Clock
♦
SYNCOUT Provides 180-Degree Out-of-Phase
Clock Output
♦
All-Ceramic or Electrolytic Capacitor Designs
PART
MAX1945REUI
MAX1945SEUI
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
MAX1945R/MAX1945S
The MAX1945R/MAX1945S high-efficiency pulse-width
modulation (PWM) switching regulators deliver up to 6A
of output current. The devices operate from an input
supply range of 2.6V to 5.5V and provide selectable
output voltages of 1.8V, 2.5V, and adjustable output
voltages from 0.8V to 85% of the supply voltage. With
V
CC
at 3.3V/5V, the input voltage can be as low as
2.25V. The MAX1945R/MAX1945S are ideal for on-
board post-regulation applications. Total output voltage
error is less than ±1% over load, line, and temperature.
The MAX1945R/MAX1945S operate at a selectable
fixed frequency (500kHz or 1MHz) or can be synchro-
nized to an external clock (400kHz to 1.2MHz). The
high operating frequency minimizes the size of external
components. The high bandwidth of the internal error
amplifier provides excellent transient response. The
MAX1945R/MAX1945S have internal dual N-channel
MOSFETs to lower heat dissipation at heavy loads. Two
MAX1945R/MAX1945Ss can operate 180 degrees out-
of-phase of each other to minimize input capacitance.
The devices provide output voltage margining for
board-level testing. The MAX1945R provides a ±4%
voltage margining. The MAX1945S provides a ±9%
voltage margining.
The MAX1945R/MAX1945S are available in 28-pin
TSSOP-EP packages and are specified over the -40°C
to +85°C industrial temperature range. An evaluation kit
is available to speed designs.
Ordering Information
PIN-PACKAGE
28 TSSOP-EP*
28 TSSOP-EP*
Applications
Low-Voltage, High-Density Distributed Power
Supplies
ASIC, CPU, and DSP Core Voltages
RAM Power Supply
Base Station, Telecom, and Networking
Equipment Power Supplies
Server and Notebook Power Supplies
*EP
= Exposed pad.
Typical Operating Circuit
INPUT
2.6V TO 5.5V
BST
IN
V
DD
V
CC
MAX1945R
MAX1945S
PGND
LX
OUTPUT
0.8V TO
0.85 x V
IN
,
6A
VOLTAGE
MARGINING
ON/OFF
CTL1
CTL2
SYNC
FB
SYNCOUT
180° OUT-OF-PHASE
REF
GND
SYNCHRONIZATION
CLOCK
COMP
FBSEL
Pin Configuration appears at end of data sheet.
________________________________________________________________
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.
1MHz, 1% Accurate, 6A Internal Switch
Step-Down Regulators
MAX1945R/MAX1945S
ABSOLUTE MAXIMUM RATINGS
CTL1, CTL2, IN, SYNC, V
CC
, V
DD
to GND ...............-0.3V to +6V
SYNCOUT, COMP, FB, FBSEL,
REF to GND ............................................-0.3V to (V
CC
+ 0.3V)
LX Current (Note 1) .....................................................-9A to +9A
BST to LX..................................................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +85°C)
(derate 23.8mW/°C above +70°C) .............................1191mW
Operating Temperature Range ...........................-40°C to +85°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.
Note 1:
LX has 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.
ELECTRICAL CHARACTERISTICS
(V
IN
= V
CC
= V
CTL1
= V
CTL2
= V
DD
= 3.3V, SYNC = GND, FBSEL = High-Z, V
FB
= 0.7V, C
REF
= 0.22µF,
T
A
= 0°C to +85°C,
unless
otherwise noted. Typical values are at +25°C.)
PARAMETER
IN/V
CC
Input Voltage
IN Supply Current
V
CC
Supply Current
V
DD
Supply Current
Total Shutdown Current from IN,
V
CC
, and V
DD
V
CC
Undervoltage Lockout
Threshold
V
DD
V
DD
Shutdown Supply Current
BST
BST Shutdown Supply Current
REF
REF Voltage
REF Shutdown Resistance
COMP
FBSEL = High-Z
COMP Transconductance
V
LOW_
CLAMP
SYMBOL
V
IN
I
IN
I
CC
I
DD
I
TOTAL
V
UVLO
CONDITIONS
MIN
2.6
TYP
MAX
5.5
UNITS
V
mA
mA
mA
µA
V
SYNC = V
CC
(1MHz),
no load
SYNC = V
CC
(1MHz)
SYNC = V
CC
(1MHz)
V
IN
= 3.3V
V
IN
= 5.5V
V
CC
= 3.3V
V
CC
= 5.5V
V
DD
= 3.3V
V
DD
= 5.5V
12
48
2
3
5
10
20
3
8
V
IN
= V
CC
= V
DD
= V
BST
- V
LX
= 5.5V,
CTL1 = CTL2 = GND
When LX starts/stops
switching
V
CC
rising
V
CC
falling
2.20
2.40
2.35
500
2.55
V
IN
= V
DD
= V
BST
= 5.5V, V
LX
= 5.5V or 0,
CTL1 = CTL2 = GND
10
µA
I
BST
V
IN
= V
DD
= V
BST
= 5.5V, V
LX
= 5.5V or 0,
CTL1 = CTL2 = GND
I
REF
= 0, V
IN
= 2.6V to 5.5V
From REF to GND, CTL1 = CTL2 = GND
30
13.3
9.6
0.5
1.90
1.97
2.00
10
55
24.4
17.6
0.8
2.15
10
10
µA
V
REF
2.04
100
85
37.8
27.2
1.1
2.40
100
V
Ω
From FB to COMP,
V
COMP
= 1.25V
FBSEL = GND
FBSEL = V
CC
µS
COMP Clamp Voltage Low
COMP Clamp Voltage High
COMP Shutdown Resistance
V
IN
= 2.6V to 5.5V, V
FB
= 0.9V
V
IN
= 2.6V to 5.5V, V
FB
= 0.7V
From COMP to GND, CTL1 = CTL2 = GND
V
V
Ω
V
HIGH_
CLAMP
2
_______________________________________________________________________________________
1MHz, 1% Accurate, 6A Internal Switch
Step-Down Regulators
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CC
= V
CTL1
= V
CTL2
= V
DD
= 3.3V, SYNC = GND, FBSEL = High-Z, V
FB
= 0.7V, C
REF
= 0.22µF,
T
A
= 0°C to +85°C,
unless
otherwise noted. Typical values are at +25°C.)
PARAMETER
FB
FBSEL = GND
FB Regulation Voltage
(Error Amp Only)
Maximum Output Current
V
FB
I
FB_OUT
V
COMP
= 1V to 2V,
V
IN
= 2.6V to 5.5V
FBSEL = V
CC
FBSEL = High-Z
CTL1 = V
CC
,
CTL2 = V
CC
MAX1945R,
V
COMP
= 1V to 2V,
V
IN
= 2.6V to 5.5V
FB Voltage Margining Output
(Error Amp Only)
V
MARGIN_
MAX1945S,
V
COMP
= 1V to 2V,
V
IN
= 2.6V to 5.5V
CTL1 = GND,
CTL2 = V
CC
CTL1 = V
CC
,
CTL2 = GND
CTL1 = V
CC
,
CTL2 = V
CC
CTL1 = GND,
CTL2 = V
CC
CTL1 = V
CC
,
CTL2 = GND
FB Input Resistance
FB Input Bias Current
LX
LX On-Resistance High
LX On-Resistance Low
LX Current-Sense
Transresistance
LX Current-Limit Threshold
LX Leakage Current
LX Switching Frequency
LX Minimum Off-Time
LX Maximum Duty Cycle
I
LEAK_LX
f
SW
t
OFF
R
ON_HIGH_
V
IN
= V
BST
- V
LX
= 3.3V
LX
V
IN
= V
BST
- V
LX
= 2.6V
R
ON_LOW_
LX
MAX1945R/MAX1945S
SYMBOL
CONDITIONS
MIN
1.782
2.475
0.792
6
-1
3
-5
-1
8
-10
25
TYP
1.800
2.500
0.800
MAX
1.818
2.525
0.808
UNITS
V
A
V
IN
= 3.3V, V
OUT
= 1.8V, L = 1µH
+1
5
-3
%
+1
10
-8
50
0.01
26
30
26
30
100
0.10
43
50
43
50
65
12.8
-2
100
kΩ
µA
FB to GND, FBSEL = GND, or V
FB
= 1.8V,
or FBSEL = V
CC
, or V
FB
= 2.5V
FBSEL = High-Z, V
FB
= 0.7V
mΩ
mΩ
mΩ
A
µA
MHz
kHz
ns
%
V
IN
= 3.3V
V
IN
= 2.6V
From LX to COMP
Duty cycle =100%,
V
IN
= 2.6V/3.3V/5.5V
V
IN
= 5.5V,
CTL1 = CTL2 = GND
V
IN
= 2.6V/3.3V
V
IN
= 2.6V/3.3V
V
IN
= 2.6V/3.3V
SYNC = GND
SYNC = V
CC
90
80
High side
Low side
V
LX
= 5.5V
LX = GND
SYNC = V
CC
SYNC = GND
-100
0.8
400
43
8.0
-6
54
10.4
-4
1.0
500
155
1.2
600
180
_______________________________________________________________________________________
3
1MHz, 1% Accurate, 6A Internal Switch
Step-Down Regulators
MAX1945R/MAX1945S
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CC
= V
CTL1
= V
CTL2
= V
DD
= 3.3V, SYNC = GND, FBSEL = High-Z, V
FB
= 0.7V, C
REF
= 0.22µF,
T
A
= 0°C to +85°C,
unless
otherwise noted. Typical values are at +25°C.)
PARAMETER
LX Minimum Duty Cycle
RMS LX Output Current
FBSEL
FBSEL Input Threshold 1.8V
Where 1.8V feedback
switches in and out,
V
CC
= 2.6V/3.3V/5.5V
Where 2.5V feedback
switches in and out,
V
CC
= 2.6V/3.3V/5.5V
I
LOW_
FBSEL
SYMBOL
CONDITIONS
V
IN
= 2.6V/3.3V
SYNC = GND
SYNC = V
CC
MIN
TYP
8.8
17.6
MAX
10.5
6
UNITS
%
A
FBSEL rising
FBSEL falling
FBSEL rising
FBSEL falling
V
CC
-
0.22
-50
0.08
0.16
0.14
V
CC -
0.14
V
CC
-
0.16
-20
20
0.22
V
V
CC
-
0.08
FBSEL Input Threshold 2.5V
V
FBSEL Input Current Low
FBSEL Input Current High
CTL1 /CTL2
CTL1/CTL2 Input Threshold
CTL1/CTL2 Input Current
Soft-Start Period
Time from Nominal to Margin
High
Time from Nominal to Margin Low
SYNC
SYNC Capture Range
SYNC Pulse Width
SYNC Input Threshold
SYNC Input Current
SYNCOUT
SYNCOUT Frequency Range
FBSEL = GND
FBSEL = V
CC
µA
50
µA
I
HIGH_
FBSEL
V
IL_CTL_
V
IH_CTL_
I
IL_CTL_
I
IH_CTL_
t
HIGH_4%
t
HIGH_9%
t
LOW_4%
t
LOW_9%
V
IN
= 2.6V to 5.5V
V
CTL1
or V
CTL2
= 0 or 5.5V, V
IN
= 5.5V
Time required for output to ramp up
+4%
+9%
-4%
-9%
V
IN
= 2.6V to 5.5V
0.4
-1
-1
2.9
0.95
1.0
1.6
+1
+1
3.7
160
360
450
1000
4.5
V
µA
ms
µs
µs
0.4
250
0.40
-1
0.4
V
CC
-
0.4
V
CC
-
0.05
0.95
1.0
1.2
MHz
ns
t
LO,
t
HI
V
IL_SYNC
V
IH_SYNC
I
IL,
I
IH
f
SYNCOUT
V
OH_SYNC
OUT
V
IN
= 2.6V to 5.5V
V
IN
= 2.6V to 5.5V
V
SYNC
= 0 or 5.5V, V
IN
= 5.5V
V
CC
= 2.6V to 5.5V
1.6
+1
1.2
V
µA
MHz
SYNCOUT Output Voltage
V
OL_SYNC
OUT
I
SYNCOUT
=
±1mA,
V
CC
= 2.6V to 5.5V
V
0.05
0.40
4
_______________________________________________________________________________________
1MHz, 1% Accurate, 6A Internal Switch
Step-Down Regulators
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CC
= V
CTL1
= V
CTL2
= V
DD
= 3.3V, SYNC = GND, FBSEL = High-Z, V
FB
= 0.7V, C
REF
= 0.22µF,
T
A
= 0°C to +85°C,
unless
otherwise noted. Typical values are at +25°C.)
PARAMETER
THERMAL SHUTDOWN
Thermal-Shutdown Hysteresis
Thermal-Shutdown Threshold
When LX stops switching
20
165
°C
°C
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX1945R/MAX1945S
ELECTRICAL CHARACTERISTICS
(V
IN
= V
CC
= V
CTL1
= V
CTL2
= V
DD
= 3.3V, SYNC = GND, FBSEL = High-Z, V
FB
= 0.7V, C
REF
= 0.22µF,
T
A
= -40°C to +85°C,
unless
otherwise noted.) (Note 2)
PARAMETER
IN/V
CC
Input Voltage
IN Supply Current
V
CC
Supply Current
V
DD
Supply Current
Total Shutdown Current from IN,
V
CC
, and V
DD
V
CC
Undervoltage Lockout
Threshold
V
DD
V
DD
Shutdown Supply Current
BST
BST Shutdown Supply Current
REF
REF Voltage
REF Shutdown Resistance
COMP
FBSEL = High-Z
COMP Transconductance
V
LOW_
CLAMP
SYMBOL
V
IN
I
IN
I
CC
I
DD
I
TOTAL
V
UVLO
CONDITIONS
MIN
2.6
TYP
MAX
5.5
20
4
8
500
2.55
UNITS
V
mA
mA
mA
µA
V
SYNC = V
CC
(1MHz),
no load
SYNC = V
CC
(1MHz)
SYNC = V
CC
(1MHz)
V
IN
= 3.3V
V
CC
= 3.3V
V
DD
= 3.3V
V
IN
= V
CC
= V
DD
= V
BST
- V
LX
= 5.5V,
CTL1 = CTL2 = GND
When LX starts/stops
switching
V
CC
rising
V
CC
falling
2.20
I
VDD
V
IN
= V
DD
= V
BST
= 5.5V, V
LX
= 5.5V or 0,
CTL1 = CTL2 = GND
10
µA
I
BST
V
IN
= V
DD
= V
BST
= 5.5V, V
LX
= 5.5V or 0,
CTL1 = CTL2 = GND
I
REF
= 0, V
IN
= 2.6V to 5.5V
From REF to GND, CTL1 = CTL2 = GND
30
13.3
9.6
0.5
1.90
1.96
10
µA
V
REF
2.04
100
85
37.8
27.2
1.1
2.40
100
V
Ω
From FB to COMP,
V
COMP
= 1.25V
FBSEL = GND
FBSEL = V
CC
µS
COMP Clamp Voltage Low
COMP Clamp Voltage High
COMP Shutdown Resistance
V
IN
= 2.6V to 5.5V, V
FB
= 0.9V
V
IN
= 2.6V to 5.5V, V
FB
= 0.7V
From COMP to GND, CTL1 = CTL2 = GND
V
V
Ω
V
HIGH_
CLAMP
_______________________________________________________________________________________
5
微控制器 MCU
