MAXIM MAX1945R, MAX1945S User Manual
General Description
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
VCCat 3.3V/5V, the input voltage can be as low as
2.25V. The MAX1945R/MAX1945S are ideal for onboard 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 synchronized 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 outof-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.
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
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
MAX1945R/MAX1945S
1MHz, 1% Accurate, 6A Internal Switch
Step-Down Regulators
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
IN
FB
REF
COMP
LX
BST
GND
V
CC
PGND
INPUT
2.6V TO 5.5V
FBSEL
CTL1
CTL2
SYNC
SYNCOUT
OUTPUT
0.8V TO
0.85 x V
IN
,
6A
VOLTAGE
MARGINING
ON/OFF
SYNCHRONIZATION
CLOCK
V
DD
MAX1945R
MAX1945S
180° OUT-OF-PHASE
Typical Operating Circuit
19-2640; Rev 1; 7/04
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.
*EP = Exposed pad.
Pin Configuration appears at end of data sheet.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-PACKAGE
MAX1945REUI -40°C to +85°C 28 TSSOP-EP*
MAX1945SEUI -40°C to +85°C 28 TSSOP-EP*
MAX1945R/MAX1945S
1MHz, 1% Accurate, 6A Internal Switch
Step-Down Regulators
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN= VCC= V
CTL1
= V
CTL2
= VDD= 3.3V, SYNC = GND, FBSEL = High-Z, VFB= 0.7V, C
REF
= 0.22µF, TA= 0°C to +85°C, unless
otherwise noted. Typical values are at +25°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.
CTL1, CTL2, IN, SYNC, VCC, VDDto 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
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
IN/V
CC
Input Voltage V
IN
2.6 5.5 V
V
IN
= 3.3V 12 20
IN Supply Current I
IN
SYNC = VCC (1MHz),
no load
V
IN
= 5.5V 48
mA
V
CC
= 3.3V 2 3
VCC Supply Current I
CC
SYNC = VCC (1MHz)
V
CC
= 5.5V 3
mA
V
DD
= 3.3V 5 8
VDD Supply Current I
DD
SYNC = VCC (1MHz)
V
DD
= 5.5V 10
mA
Total Shutdown Current from IN,
V
CC
, and V
DD
I
TOTAL
V
IN
= VCC = V
DD
= V
BST
- V
LX
= 5.5V,
CTL1 = CTL2 = GND
500 µA
VCC rising
VCC Undervoltage Lockout
Threshold
V
UVLO
When LX starts/stops
switching
V
CC
falling
V
V
DD
V
DD
Shutdown Supply Current
V
IN
= V
DD
= V
BST
= 5.5V, V
LX
= 5.5V or 0,
CTL1 = CTL2 = GND
10 µA
BST
BST Shutdown Supply Current I
BST
V
IN
= V
DD
= V
BST
= 5.5V, V
LX
= 5.5V or 0,
CTL1 = CTL2 = GND
10 µA
REF
REF Voltage V
REF
I
REF
= 0, V
IN
= 2.6V to 5.5V
V
REF Shutdown Resistance From REF to GND, CTL1 = CTL2 = GND 10 100 Ω
COMP
30 55 85
FBSEL = GND
COMP Transconductance
From FB to COMP,
V
COMP
= 1.25V
FBSEL = V
CC
9.6
µS
COMP Clamp Voltage Low
V
LOW_
CLAMP
V
IN
= 2.6V to 5.5V, V
FB
= 0.9V 0.5 0.8 1.1 V
COMP Clamp Voltage High
V
HIGH_
CLAMP
V
IN
= 2.6V to 5.5V, V
FB
= 0.7V
V
COMP Shutdown Resistance
10 100 Ω
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.
From COMP to GND, CTL1 = CTL2 = GND
2.20 2.35
1.97 2.00 2.04
FBSEL = High-Z
13.3 24.4 37.8
1.90 2.15 2.40
2.40 2.55
17.6 27.2
MAX1945R/MAX1945S
1MHz, 1% Accurate, 6A Internal Switch
Step-Down Regulators
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN= VCC= V
CTL1
= V
CTL2
= VDD= 3.3V, SYNC = GND, FBSEL = High-Z, VFB= 0.7V, C
REF
= 0.22µF, TA= 0°C to +85°C, unless
otherwise noted. Typical values are at +25°C.)
PARAMETER
CONDITIONS
UNITS
FB
FBSEL = V
CC
FB Regulation Voltage
(Error Amp Only)
V
FB
V
COMP
= 1V to 2V,
V
IN
= 2.6V to 5.5V
V
Maximum Output Current
V
IN
= 3.3V, V
OUT
= 1.8V, L = 1µH 6 A
-1 +1
CTL2 = V
CC
35
MAX1945R,
V
COMP
= 1V to 2V,
V
IN
= 2.6V to 5.5V
-5 -3
-1 +1
CTL2 = V
CC
810
FB Voltage Margining Output
(Error Amp Only)
MAX1945S,
V
COMP
= 1V to 2V,
V
IN
= 2.6V to 5.5V
-10 -8
%
FB Input Resistance
FB to GND, FBSEL = GND, or V
FB
= 1.8V,
or FBSEL = V
CC
, or V
FB
= 2.5V
25 50 100 kΩ
FB Input Bias Current FBSEL = High-Z, V
FB
= 0.7V
µA
LX
V
IN
= V
BST
- V
LX
= 3.3V 26 43
LX On-Resistance High
R
ON_HIGH_
LX V
IN
= V
BST
- V
LX
= 2.6V 30 50
mΩ
V
IN
= 3.3V 26 43
LX On-Resistance Low
R
ON_LOW_
LX V
IN
= 2.6V 30 50
mΩ
LX Current-Sense
Transresistance
From LX to COMP 43 54 65 mΩ
High side 8.0
LX Current-Limit Threshold
Duty cycle =100%,
V
IN
= 2.6V/3.3V/5.5V
Low side -6 -4 -2
A
V
LX
= 5.5V 100
LX Leakage Current
V
IN
= 5.5V,
CTL1 = CTL2 = GND
LX = GND
µA
0.8 1.0
1.2
MHz
LX Switching Frequency f
SW
V
IN
= 2.6V/3.3V
600 kHz
LX Minimum Off-Time t
OFF
V
IN
= 2.6V/3.3V
180 ns
90
LX Maximum Duty Cycle VIN = 2.6V/3.3V
80
%
SYMBOL
I
FB_OUT
V
MARGIN_
MIN TYP MAX
FBSEL = GND 1.782 1.800 1.818
2.475 2.500 2.525
FBSEL = High-Z 0.792 0.800 0.808
CTL1 = VCC,
CTL2 = V
CC
CTL1 = GND,
CTL1 = VCC,
CTL2 = GND
CTL1 = VCC,
CTL2 = V
CC
CTL1 = GND,
CTL1 = VCC,
CTL2 = GND
0.01 0.10
I
LEAK_LX
-100
SYNC = V
CC
SYNC = GND 400 500
SYNC = GND
SYNC = V
CC
10.4 12.8
155
MAX1945R/MAX1945S
1MHz, 1% Accurate, 6A Internal Switch
Step-Down Regulators
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VIN= VCC= V
CTL1
= V
CTL2
= VDD= 3.3V, SYNC = GND, FBSEL = High-Z, VFB= 0.7V, C
REF
= 0.22µF, TA= 0°C to +85°C, unless
otherwise noted. Typical values are at +25°C.)
PARAMETER
CONDITIONS
UNITS
8.8
LX Minimum Duty Cycle VIN = 2.6V/3.3V
%
RMS LX Output Current 6A
FBSEL
FBSEL Input Threshold 1.8V
Where 1.8V feedback
switches in and out,
V
CC
= 2.6V/3.3V/5.5V
V
V
CC -
V
CC
-
FBSEL Input Threshold 2.5V
Where 2.5V feedback
switches in and out,
V
CC
= 2.6V/3.3V/5.5V
V
CC
-
V
CC
-
V
FBSEL Input Current Low
I
LOW_
FBSEL
FBSEL = GND -50 -20 µA
FBSEL Input Current High
I
HIGH_
FBSEL
FBSEL = V
CC
20 50 µA
CTL1 /CTL2
0.4
CTL1/CTL2 Input Threshold
V
IN
= 2.6V to 5.5V
1.0 1.6
V
-1 +1
CTL1/CTL2 Input Current
V
CTL1
or V
CTL2
= 0 or 5.5V, V
IN
= 5.5V
-1 +1
µA
Soft-Start Period Time required for output to ramp up 2.9 3.7 4.5 ms
+4%
Time from Nominal to Margin
High
+9%
µs
-4%
Time from Nominal to Margin Low
-9%
µs
SYNC
SYNC Capture Range V
IN
= 2.6V to 5.5V 0.4 1.2
MHz
SYNC Pulse Width
t
LO, tHI
V
IN
= 2.6V to 5.5V
ns
SYNC Input Threshold
V
IN
= 2.6V to 5.5V
1.0 1.6
V
SYNC Input Current I
IL, IIH
V
SYNC
= 0 or 5.5V, V
IN
= 5.5V -1 +1 µA
SYNCOUT
SYNCOUT Frequency Range
V
CC
= 2.6V to 5.5V 0.4 1.2
MHz
V
OH_SYNC
OUT
V
CC
-
0.4
V
CC
-
SYNCOUT Output Voltage
V
OL_SYNC
OUT
I
SYNCOUT
= ±1mA, V
CC
= 2.6V to 5.5V
V
SYMBOL
MIN TYP MAX
SYNC = GND
SYNC = V
CC
FBSEL rising 0.16 0.22
FBSEL falling 0.08 0.14
10.5
17.6
FBSEL rising
FBSEL falling
0.22
0.14
0.16
0.08
V
IL_CTL_
V
IH_CTL_
I
IL_CTL_
I
IH_CTL_
t
HIGH_4%
t
HIGH_9%
t
t
V
V
LOW_4%
LOW_9%
IL_SYNC
IH_SYNC
250
0.40 0.95
f
SYNCOUT
0.95
160
360
450
1000
0.05
0.05 0.40
MAX1945R/MAX1945S
1MHz, 1% Accurate, 6A Internal Switch
Step-Down Regulators
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS (continued)
(VIN= VCC= V
CTL1
= V
CTL2
= VDD= 3.3V, SYNC = GND, FBSEL = High-Z, VFB= 0.7V, C
REF
= 0.22µF, TA= 0°C to +85°C, unless
otherwise noted. Typical values are at +25°C.)
PARAMETER
CONDITIONS
UNITS
THERMAL SHUTDOWN
Thermal-Shutdown Hysteresis 20 °C
Thermal-Shutdown Threshold When LX stops switching
°C
ELECTRICAL CHARACTERISTICS
(VIN= VCC= V
CTL1
= V
CTL2
= VDD= 3.3V, SYNC = GND, FBSEL = High-Z, VFB= 0.7V, C
REF
= 0.22µF, TA= -40°C to +85°C, unless
otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
IN/V
CC
Input Voltage V
IN
2.6 5.5 V
IN Supply Current I
IN
SYNC = VCC (1MHz),
no load
V
IN
= 3.3V 20 mA
VCC Supply Current I
CC
SYNC = VCC (1MHz) V
CC
= 3.3V 4 mA
VDD Supply Current I
DD
SYNC = VCC (1MHz) V
DD
= 3.3V 8 mA
Total Shutdown Current from IN,
V
CC
, and V
DD
I
TOTAL
V
IN
= VCC = V
DD
= V
BST
- V
LX
= 5.5V,
CTL1 = CTL2 = GND
500 µA
VCC rising
VCC Undervoltage Lockout
Threshold
V
UVLO
When LX starts/stops
switching
V
CC
falling
V
V
DD
V
DD
Shutdown Supply Current I
VDD
V
IN
= V
DD
= V
BST
= 5.5V, V
LX
= 5.5V or 0,
CTL1 = CTL2 = GND
10 µA
BST
BST Shutdown Supply Current I
BST
V
IN
= V
DD
= V
BST
= 5.5V, V
LX
= 5.5V or 0,
CTL1 = CTL2 = GND
10 µA
REF
REF Voltage V
REF
I
REF
= 0, V
IN
= 2.6V to 5.5V
V
REF Shutdown Resistance From REF to GND, CTL1 = CTL2 = GND 100 Ω
COMP
30 85
FBSEL = GND
COMP Transconductance
From FB to COMP,
V
COMP
= 1.25V
FBSEL = V
CC
9.6
µS
COMP Clamp Voltage Low
V
LOW_
CLAMP
V
IN
= 2.6V to 5.5V, V
FB
= 0.9V 0.5 1.1 V
COMP Clamp Voltage High
V
HIGH_
CLAMP
V
IN
= 2.6V to 5.5V, V
FB
= 0.7V
V
COMP Shutdown Resistance
100 Ω
SYMBOL
MIN TYP MAX
165
2.20
1.96 2.04
FBSEL = High-Z
13.3 37.8
1.90 2.40
From COMP to GND, CTL1 = CTL2 = GND
2.55
27.2
MAX1945R/MAX1945S
1MHz, 1% Accurate, 6A Internal Switch
Step-Down Regulators
6 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VIN= VCC= V
CTL1
= V
CTL2
= VDD= 3.3V, SYNC = GND, FBSEL = High-Z, VFB= 0.7V, C
REF
= 0.22µF, TA= -40°C to +85°C, unless
otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
FB
FBSEL = GND
FBSEL = V
CC
FB Regulation Voltage
(Error Amp Only)
V
FB
V
COMP
= 1V to 2V,
V
IN
= 2.6V to 5.5V
V
Maximum Output Current
V
IN
= 3.3V, V
OUT
= 1.8V, L = 1µH 6 A
CTL2 = V
CC
2.5 5.5
MAX1945R,
V
COMP
= 1V to 2V,
V
IN
= 2.6V to 5.5V
CTL2 = V
CC
7.5
FB Voltage Margining Output
(Error Amp Only)
MAX1945S,
V
COMP
= 1V to 2V,
V
IN
= 2.6V to 5.5V
%
FB Input Resistance
FB to GND, FBSEL = GND, or V
FB
= 1.8V,
or FBSEL = V
CC
, or V
FB
= 2.5V
25 100 kΩ
FB Input Bias Current FBSEL = High-Z, V
FB
= 0.7V 0.1 µA
LX
V
IN
= V
BST
- V
LX
= 3.3V 43
LX On-Resistance High
R
ON_
V
IN
= V
BST
- V
LX
= 2.6V 50
mΩ
V
IN
= 3.3V 43
LX On-Resistance Low
R
ON_
V
IN
= 2.6V 50
mΩ
LX Current-Sense
Transresistance
From LX to COMP 43 65 mΩ
High side 8.0
LX Current-Limit Threshold
Duty cycle =100%,
V
IN
= 2.6V/3.3V/5.5V
Low side -6 -2
A
V
LX
= 5.5V 100
LX Leakage Current
V
IN
= 5.5V,
CTL1 = CTL2 = GND
LX = GND
µA
0.8 1.2
MHz
LX Switching Frequency f
SW
V
IN
= 2.6V/3.3V
600 kHz
LX Minimum Off-Time t
OFF
V
IN
= 2.6V/3.3V 180 ns
90
LX Maximum Duty Cycle VIN = 2.6V/3.3V
80
%
I
FB_OUT
1.773 1.827
2.462 2.538
FBSEL = High-Z 0.788 0.812
CTL1 = VCC,
CTL2 = V
CC
-1.5 +1.5
CTL1 = GND,
V
MARGIN_
HIGH_LX
LOW_LX
I
LEAK_LX
CTL1 = VCC,
CTL2 = GND
CTL1 = VCC,
CTL2 = V
CC
CTL1 = GND,
CTL1 = VCC,
CTL2 = GND
SYNC = V
CC
SYNC = GND 400
-5.5 -2.5
-1.5 +1.5
-10.5 -7.5
-100
SYNC = GND
SYNC = V
CC
10.5
12.8
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