19-3165; Rev 1; 5/06
IT
TION K
VALUA
E
BLE
AVAILA
Dual, Interleaved, Fixed-Frequency Step-Down
Controller with a Dynamically Adjustable Output
General Description
The MAX1549 dual pulse-width modulation (PWM) step-
down controller provides the high efficiency, excellent
transient response, and high DC-output accuracy nec-
essary for generating low-voltage chipset and RAM
power supplies in notebook computers. The controller
employs a fixed-frequency, current-mode PWM archi-
tecture that does not require complex compensation.
The MAX1549 also interleaves the dual step-down regu-
lators, minimizing the input capacitor requirements.
The MAX1549 features differential current-sense inputs
for accurately sensing the inductor current across an
external current-sense resistor in series with the output
to ensure reliable overload protection. Alternatively, the
controller can provide overload protection using loss-
less inductor current-sensing methods, lowering power
dissipation and reducing system cost.
Single-stage buck conversion allows the MAX1549 to
directly step down high-voltage batteries for the highest
possible efficiency. Very low output-voltage applica-
tions require two-stage conversion—stepping down
from another system supply rail instead of the battery.
The MAX1549 powers chipsets and graphics processor
cores that require dynamically adjustable output voltages,
or generates the active termination bus that must track
the input reference. The main step-down controller
(OUT1) regulates the dedicated reference input (REFIN)
voltage generated by a resistive voltage-divider from the
MAX1549’s reference. The MAX1549 also includes inter-
nal open-drain pulldowns with logic-level control inputs to
dynamically adjust the REFIN resistive-divider ratio. When
a transition occurs on these control inputs, the controller
enters forced-PWM mode and blanks the power-good
(PGOOD1) output and output fault protection. OUT2 uses
a Dual-Mode™ feedback input to provide either fixed
2.5V/1.8V or adjustable output voltage regulation. The
MAX1549 is available in a 40-pin, 6mm x 6mm thin QFN
package.
Features
♦
Interleaved, Fixed-Frequency, Current-Mode
Control Architecture
♦
1% V
OUT
Accuracy Over Line and Load
♦
Main Output (OUT1)
0.5V to 2.0V Adjustable Output
External Reference Input for Dynamically
Selectable Output Voltages
Four Digitally Selectable Output Voltages
Power-Good and Fault Blanking During
Transitions
♦
Second Output (OUT2)
2.5V/1.8V Fixed or 0.5V to 2.7V Adjustable
Output
♦
Accurate Differential Current-Sense Inputs
♦
100kHz/200kHz/300kHz/400kHz Selectable
Switching Frequency
♦
Output Overvoltage/Undervoltage Protection
♦
Soft-Start and Soft-Shutdown
♦
Drives Large Synchronous-Rectifier FETs
♦
2V ±0.6% Reference Output
♦
Separate Enable Inputs with Accurate Threshold
Voltages
♦
Separate Power-Good Window Comparators
MAX1549
Ordering Information
PART
MAX1549ETL
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
40 Thin QFN 6mm x 6mm
Pin Configuration
PGOOD1
Applications
Notebook Computers
Dynamically Adjustable Chipset Supplies
Video/GPU Core Supplies
DDR Memory Termination
CPU Core or V
CC
Supplies
Fixed Chipset/RAM Supplies
Active Termination Buses
TOP VIEW
REFIN
CSH1
OUT1
CSL1
OD3
OD2
OD1
40 39 38 37 36 35 34 33 32 31
N.C.
DH1
GND
N.C.
REF
V
CC
CC1
ILIM1
ILIM2
G0
G1
FBLANK
1
2
3
4
5
6
7
8
9
10
11 12 13 14 15 16 17 18 19 20
30
29
28
27
LX1
BST1
SKIP
DL1
V
DD
N.C.
DL2
PGND
BST2
LX2
MAX1549
26
25
24
23
22
21
PGOOD2
FSEL
CSH2
CSL2
OUT2
Dual Mode is a trademark of Maxim Integrated Products, Inc.
THIN QFN
6mm x 6mm
________________________________________________________________
Maxim Integrated Products
DH2
N.C.
ON1
ON2
FB2
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.
Dual, Interleaved, Fixed-Frequency Step-Down
Controller with a Dynamically Adjustable Output
MAX1549
ABSOLUTE MAXIMUM RATINGS
V
CC
to GND ..............................................................-0.3V to +6V
V
DD
to PGND............................................................-0.3V to +6V
CSH_, CSL_, OUT_, PGOOD_,
OD_ to GND ...........................................-0.3V to (V
CC
+ 0.3V)
G0, G1, ILIM_, REFIN to GND ..................................-0.3V to +6V
FB2,
SKIP,
ON_ to GND ...........................................-0.3V to +6V
REF, CC1, FBLANK, FSEL to GND.............-0.3V to (V
CC
+ 0.3V)
DL1, DL2 to PGND .....................................-0.3V to (V
DD
+ 0.3V)
BST1, BST2 to PGND .............................................-0.3V to +36V
LX1 to BST1..............................................................-6V to +0.3V
DH1 to LX1 ..............................................-0.3V to (V
BST1
+ 0.3V)
LX2 to BST2..............................................................-6V to +0.3V
DH2 to LX2 ..............................................-0.3V to (V
BST2
+ 0.3V)
GND to PGND .......................................................-0.3V to +0.3V
REF Short Circuit to GND ...........................................Continuous
Continuous Power Dissipation (T
A
= +70°C)
40-Pin 6mm x 6mm Thin QFN (derated 26.3mW/°C
above +70°C).............................................................2105mW
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
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
(Circuit of Figure 1, V
CC
= V
DD
= 5V,
SKIP
= GND,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
INPUT SUPPLIES (Note 1)
Input Voltage Range
Quiescent Supply Current (V
CC
)
Quiescent Supply Current (V
DD
)
Shutdown Supply Current (V
CC
)
Shutdown Supply Current (V
DD
)
PWM CONTROLLERS
Main Output-Voltage Accuracy
(OUT1 Tracking)
V
REFIN
-
V
OUT1
With respect to
REFIN,
SKIP
=
V
CC
or GND
50% duty cycle
10% to 90% duty cycle
-5
-10
2.475
1.780
0.490
0.485
0.1
1
0.5
0.5
-1
-0.1
120
85
250
180
2.0
2.7
+1
+0.1
460
335
2.5
1.8
0.50
0
+5
mV
+10
2.525
1.820
0.510
0.515
V
V
%
%
V
µA
µA
kΩ
V
BIAS
I
CC
I
DD
V
CC
, V
DD
OUT1 and FB2 forced above their
regulation points
OUT1 and FB2 forced above their
regulation points
ON1 = ON2 = GND,
SKIP
= V
CC
ON1 = ON2 = GND
4.5
1.0
1.5
2.5
<1
5.5
1.8
5
5
5
V
mA
µA
µA
µA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Secondary Preset Output-Voltage
Accuracy (OUT2 Fixed)
Secondary Feedback-Voltage
Accuracy (FB2 Adjustable)
Load-Regulation Error
V
IN
Line-Regulation Error
Output Adjust Range
OUT1 Input Bias Current
FB2 Input Bias Current
OUT2 Input Resistance
V
OUT2
V
FB2
SKIP
= V
CC
, 50% FB2 = GND
duty cycle (Note 1) FB2 = V
CC
SKIP
= V
CC
(Note 1)
V
IN
= 2V to 28V
OUT1 (tracks REFIN)
OUT2
50% duty cycle
10% to 90% duty cycle
I
LOAD
= 0 to 3A,
SKIP
= V
CC
I
OUT1
I
FB2
R
OUT2
V
OUT1
= 0.5V to 2.0V
V
FB2
= 0 to 2.7V
FB2 = GND or adjustable
FB2 = V
CC
2
_______________________________________________________________________________________
Dual, Interleaved, Fixed-Frequency Step-Down
Controller with a Dynamically Adjustable Output
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
CC
= V
DD
= 5V,
SKIP
= GND,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
OUT_ Discharge-Mode
On-Resistance
OUT_ Synchronous-Rectifier
Discharge-Mode Turn-On Level
FSEL = GND
Operating Frequency
f
OSC
(Note 2)
FSEL = REF
FSEL = open
FSEL = V
CC
Minimum On-Time
Maximum Duty Cycle
Soft-Start Ramp Time
REFERENCE (REF)
Reference Voltage
Reference Load Regulation
REF Lockout Voltage
REFIN Voltage Range
REFIN Input Bias Current
FAULT DETECTION
Output Overvoltage
Trip Threshold
Output Overvoltage
Fault-Propagation Delay
Output Undervoltage-Protection
Trip Threshold
Output Undervoltage-Protection
Blanking Time
Output Undervoltage
Fault-Propagation Delay
PGOOD_ Lower Trip Threshold
PGOOD_ Upper Trip Threshold
PGOOD_ Propagation Delay
PGOOD_ Output Low Voltage
PGOOD_ Leakage Current
I
PGOOD
_
t
PGOOD
_
t
BLANK
t
UVP
With respect to error-comparator threshold,
hysteresis = 1%
With respect to error-comparator threshold,
hysteresis = 1%
OUT1 and FB2 forced 2% beyond PGOOD_
trip threshold
I
SINK
= 4mA
OUT1 = REFIN and V
FB2
= 0.5V (PGOOD_
high impedance), PGOOD_ forced to 5.5V
-12.5
+7.5
t
OVP
With respect to error-comparator threshold
OUT1 and FB2 forced 2% above trip
threshold
With respect to error-comparator threshold
From rising edge of ON_
65
12
14.5
10
70
4096 /
f
OSC
10
-10
+10
10
0.3
1
-7.5
+12.5
75
17
%
µs
%
s
µs
%
%
µs
V
µA
V
REF
∆V
REF
V
REFIN
I
REFIN
V
CC
= 4.5V to
5.5V, I
REF
= 0
T
A
= +25°C
T
A
= 0°C to +85°C
1.988
1.985
1.980
1.95
0.5
-50
2.0
+50
2.00
2.00
2.012
2.015
2.020
V
V
V
V
nA
t
ON(MIN)
D
MAX
t
SS
Measured from the rising edge of ON_ to
full scale
(Note 3)
91
93
512 /
f
OSC
SYMBOL
R
DISCHARGE
0.2
70
170
270
350
CONDITIONS
MIN
TYP
12
0.3
100
200
300
400
MAX
40
0.4
130
230
330
450
200
ns
%
s
kHz
UNITS
Ω
V
MAX1549
I
REF
= -10µA to +100µA
V
REF(UVLO)
Rising edge, hysteresis = 350mV
_______________________________________________________________________________________
3
Dual, Interleaved, Fixed-Frequency Step-Down
Controller with a Dynamically Adjustable Output
MAX1549
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
CC
= V
DD
= 5V,
SKIP
= GND,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Fault-Blanking Time
Thermal-Shutdown Threshold
V
CC
Undervoltage-Lockout
Threshold
CURRENT LIMIT
ILIM_ Adjustment Range
Current-Limit Input Range
CSH_/CSL_ Input Bias Current
Current-Limit Threshold (Fixed)
Current-Limit Threshold
(Adjustable)
Current-Limit Threshold
(Zero Crossing)
V
LIMIT
V
LIMIT
V
CSH
_, V
CSL
_
V
CSH
_ = V
CSL
_ = 0 to 2.7V
V
CSH
_ - V
CSL
_, ILIM_ = V
CC
V
ILIM
_ = 2.0V
V
CSH
_ - V
CSL
_
V
ILIM
_ = 1.0V
V
ILIM
_ = 0.5V
V
ZX
V
PGND
- V
LX
_,
SKIP
= GND
ILIM_ = V
CC
Idle-Mode™ Threshold
V
CSH
_ - V
CSL
_
With respect to
current-limit
threshold
-0.1
R
DH
R
DL
I
DH
BST_ - LX_ forced to 5V
DL_, high state
DL_, low state
DH_ forced to 2.5V, BST_ - LX_ forced to 5V
1.5
1.5
0.5
1
1
3
35
26
10
OD_ high impedance, V
OD
_ = 5.5V
Rising edge, hysteresis = 600mV
SKIP,
G0, G1 hysteresis =
600mV
High
Low
2.4
2.4
0.8
2.6
100
100
2.8
10
0.25
0
-0.15
65
170
91
42
70
200
100
50
3
15
20
+0.1
6
6
2.7
20
V
REF
2.7
+0.15
75
230
109
58
mV
mV
%
µA
Ω
Ω
A
A
A
ns
mV
V
V
µA
mV
SYMBOL
t
FBLANK
T
SHDN
V
CC(UVLO)
CONDITIONS
FBLANK = V
CC
FBLANK = open
FBLANK = REF
Hysteresis = 15°C
Rising edge, PWM disabled below this
level, hysteresis = 50mV
4.1
MIN
110
60
22
TYP
150
100
50
+165
4.25
4.4
MAX
190
140
75
°C
V
µs
UNITS
ILIM_ Leakage Current
GATE DRIVERS
DH_ Gate-Driver On-Resistance
DL_ Gate-Driver On-Resistance
DH_ Gate-Driver Source/Sink
Current
DL_ Gate-Driver Source Current
DL_ Gate-Driver Sink Current
Dead Time
INPUTS AND OUTPUTS
OD_ On-Resistance
OD_ Leakage Current
ON_ Logic Input Threshold
Logic Input Voltage
R
OD
_
I
OD
_
I
DL (SOURCE)
DL_ forced to 2.5V
I
DL (SINK)
t
DEAD
DL_ forced to 2.5V
DL_ rising
DH_ rising
Ω
nA
V
V
Idle Mode is a trademark of Maxim Integrated Products, Inc.
4
_______________________________________________________________________________________
Dual, Interleaved, Fixed-Frequency Step-Down
Controller with a Dynamically Adjustable Output
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V
CC
= V
DD
= 5V,
SKIP
= GND,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Logic Input Current
Dual-Mode Threshold Voltage
SYMBOL
CONDITIONS
ON_,
SKIP,
G0, G1
FB2
High
Low
High
Four-Level Input Logic Levels
FSEL, FBLANK
Open
REF
Low
Four-Level Logic Input Current
FSEL, FBLANK forced to GND or V
CC
-3
MIN
-1
1.9
0.05
V
CC
-
0.4V
3.15
1.65
2.0
0.1
TYP
MAX
+1
2.1
0.15
UNITS
µA
V
MAX1549
3.85
2.35
0.5
+3
V
µA
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V
CC
= V
DD
= 5V,
SKIP
= GND,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 4)
PARAMETER
INPUT SUPPLIES (Note 1)
Input Voltage Range
Quiescent Supply Current (V
CC
)
Quiescent Supply Current (V
DD
)
Shutdown Supply Current (V
CC
)
Shutdown Supply Current (V
DD
)
PWM CONTROLLERS
Main Output-Voltage Accuracy
(OUT1 Tracking)
Secondary Preset Output-Voltage
Accuracy (OUT2 Fixed)
Secondary Feedback-Voltage
Accuracy (FB2 Adjustable)
Output Adjust Range
OUT2 Input Resistance
OUT_ Discharge-Mode
On-Resistance
OUT_ Synchronous-Rectifier
Discharge-Mode Turn-On Level
R
OUT2
R
DISCHARGE
0.2
V
REFIN
-
V
OUT1
V
OUT2
V
FB2
With respect to
50% duty cycle
REFIN,
SKIP
= V
CC
10% to 90% duty cycle
or GND
SKIP
= V
CC
, 50%
duty cycle (Note 1)
SKIP
= V
CC
(Note 1)
OUT1 (tracks REFIN)
OUT2
FB2 = GND or adjustable
FB2 = V
CC
FB2 = GND
FB2 = V
CC
50% duty cycle
10% to 90% duty cycle
-8
-10
2.470
1.775
0.490
0.485
0.5
0.5
120
85
+8
mV
+10
2.530
1.825
0.510
0.515
2.0
2.7
460
335
40
0.4
V
V
V
kΩ
Ω
V
V
BIAS
I
CC
I
DD
V
CC,
V
DD
OUT1 and FB2 forced above their
regulation points
OUT1 and FB2 forced above their
regulation points
ON1 = ON2 = GND,
SKIP
= V
CC
ON1 = ON2 = GND
4.5
5.5
1.8
5
5
5
V
mA
µA
µA
µA
SYMBOL
CONDITIONS
MIN
MAX
UNITS
_______________________________________________________________________________________
5
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