19-3141; Rev 1; 6/05
KIT
ATION
EVALU
BLE
AVAILA
Dual-Synchronous Buck Controllers for Point-of-
Load, Tracking, and DDR Memory Power Supplies
General Description
The MAX8537/MAX8539 controllers provide a complete
power-management solution for both double-data-rate
(DDR) and combiner supplies. The MAX8537 and
MAX8539 are configured for out-of-phase and in-phase
DDR power-supply operations, respectively, and gener-
ate three outputs: the main memory voltage (V
DDQ
), the
tracking sinking/sourcing termination voltage (V
TT
), and
the termination reference voltage (V
TTR
). The MAX8538
is configured as a dual out-of-phase controller for point-
of-load supplies. Each buck controller can source or
sink up to 25A of current, while the termination refer-
ence can supply up to 15mA output.
The MAX8537/MAX8538/MAX8539 use constant-
frequency voltage-mode architecture with operating
frequencies of 200kHz to 1.4MHz. An internal high-
bandwidth (25MHz) operational amplifier is used as an
error amplifier to regulate the output voltage. This
allows fast transient response, reducing the number of
output capacitors. An all-N-FET design optimizes effi-
ciency and cost. The MAX8537/MAX8538/MAX8539
have a 1% accurate reference. The second synchro-
nous buck controller in the MAX8537/MAX8539 and the
VTTR amplifier generate 1/2 V
DDQ
voltage for V
TT
and
V
TTR
, and track the V
DDQ
within ±1%.
This family of controllers uses a high-side current-sense
architecture for current limiting. ILIM pins allow the set-
ting of an adjustable, lossless current limit for different
combinations of load current and R
DSON
. Alternately,
more accurate overcurrent limit is achieved by using
a sense resistor in series with the high-side FET.
Overvoltage protection is achieved by latching off the
high-side MOSFET and latching on the low-side MOSFET
when the output voltage exceeds 17% of its set output.
Independent enable, power-good, and soft-start features
enhance flexibility.
Features
♦
MAX8537/MAX8539: Complete DDR Supplies
♦
MAX8538: Dual Nontracking Controller
♦
Out-of-Phase (MAX8537/MAX8538) or In-Phase
(MAX8539) Operation
♦
4.5V to 23V Wide Input Range (Operate Down to
1.8V Input with External 5V Supply)
♦
Tracking Supply Maintains V
TT
= V
TTR
= 1/2 V
DDQ
♦
Adjustable Output from 0.8V to 3.6V with 1%
Accuracy
♦
VTTR Reference Sources and Sinks Up to 15mA
♦
200kHz to 1.4MHz Adjustable Switching
Frequency
♦
♦
♦
♦
All-Ceramic Design Achievable
>90% Efficiency
Independent POK_ and EN_
Adjustable Soft-Start and Soft-Stop for Each
Output
♦
Lossless Adjustable-Hiccup Current Limit
♦
Output Overvoltage Protection
♦
28-Pin QSOP Package
MAX8537/MAX8538/MAX8539
Ordering Information
PART
MAX8537EEI
MAX8537EEI+
MAX8538EEI
MAX8538EEI+
MAX8539EEI
MAX8539EEI+
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
28 QSOP
28 QSOP
28 QSOP
28 QSOP
28 QSOP
28 QSOP
OPERATION
Out-of-phase
tracking
Out-of-phase
tracking
Out-of-phase
nontracking
Out-of-phase
nontracking
In-phase
tracking
In-phase
tracking
Applications
DDR Memory Power Supplies
Notebooks and Desknotes
Servers and Storage Systems
Broadband Routers
XDSL Modems and Routers
Power DSP Core Supplies
Power Combiner in Advanced VGA Cards
Networking Systems
RAMBUS Memory Power Supplies
+Denotes
lead-free package.
Pin Configurations appear at end of data sheet.
1
________________________________________________________________
Maxim Integrated Products
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-Synchronous Buck Controllers for Point-of-
Load, Tracking, and DDR Memory Power Supplies
MAX8537/MAX8538/MAX8539
ABSOLUTE MAXIMUM RATINGS
V+ to GND ..............................................................-0.3V to +25V
AVL, VL to GND........................................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
FB_, EN_, POK_ to GND...........................................-0.3V to +6V
REFIN, VTTR, FREQ, SS_, COMP_ to GND....-0.3V to (AVL + 0.3V)
BST_, ILIM_ to GND ...............................................-0.3V to +30V
DH1 to LX1 ...............................................-0.3V to (BST1 + 0.3V)
DH2 to LX2 ...............................................-0.3V to (BST2 + 0.3V)
LX_ to BST_ ..............................................................-6V to +0.3V
LX_ to GND................................................................-2V to +25V
DL_ to PGND ................................................-0.3V to (VL + 0.3V)
Continuous Power Dissipation (T
A
= +70°C)
28-Pin QSOP (derate 10.8mW/°C above +70°C)........860mW
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
(V+ = 12V, EN_ = VL, BST_ = 6V, LX_ = 1V, VL load = 0mA, C
VL
= 10µF (ceramic), REFIN = 1.25V, PGND = AGND = FB_ = ILIM_ =
0V, C
SS
= 10nF, C
VTTR
= 1µF, R
FREQ
= 20kΩ, DH_ = open, DL_ = open, POK_ = open, circuit of Figure 1,
T
A
= 0°C to +85°C,
unless
otherwise noted.)
PARAMETER
GENERAL
V+ Operating Range
V+/ VL Operating Range
V+ Operating Supply Current
V+ Standby Supply Current
VL REGULATOR
Output Voltage
VL Undervoltage-Lockout Trip
Level
Output Current
Thermal Shutdown
ILIM Sink Current
SOFT-START
Soft-Start Source Current
Soft-Start Sink Current
Soft-Start Full-Scale Voltage
FREQUENCY
Low End of Range
Intermediate Range
High End of Range
Maximum Duty Cycle
R
FREQ
= 100kΩ, V+ = VL = 5V
R
FREQ
= 20kΩ, V+ = VL = 5V
R
FREQ
= 14.3kΩ, V+ = VL = 5V
R
FREQ
= 100kΩ
R
FREQ
= 20kΩ
R
FREQ
= 14.3kΩ
160
800
1120
95
80
72
%
200
1000
1400
240
1200
1680
kHz
kHz
kHz
SS_ = 100mV
SS_ = 0.8 or REFIN
-7
3
-5
5
0.8 or
REFIN
-3
7
µA
µA
V
5.5V < V+ < 23V, 1mA < I
LOAD
< 70mA
Rising edge, hysteresis = 550mV (typ) (trip level is
typically 85% of VL)
This is for gate current of DL_ /DH_ drivers, C(VL) =
1µF/10mA ceramic capacitor
Rising temperature, typical hysteresis = 10°C
ILIM_ = LX - 200mV, 1.8V < LX < 23V, BST = LX +5V
180
+160
200
220
4.75
4.18
5
4.3
5.25
4.42
70
V
V
mA
°C
µA
VL regulator drops out below 5.5V (Note 1)
VL is externally generated (Note 1)
IL(VL) = 0, FB_ forced 50mV above threshold
IL(VL) = 0, BST_ = VL, EN = LX_ = FB_ = 0V
4.5
4.5
3.5
350
23.0
5.5
7
700
V
V
mA
µA
CONDITIONS
MIN
TYP
MAX
UNITS
CURRENT-LIMIT THRESHOLD
(all current limits are tested at V+ = VL = 4.5V and 5.5V)
2
_______________________________________________________________________________________
Dual-Synchronous Buck Controllers for Point-of-
Load, Tracking, and DDR Memory Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 12V, EN_ = VL, BST_ = 6V, LX_ = 1V, VL load = 0mA, C
VL
= 10µF (ceramic), REFIN = 1.25V, PGND = AGND = FB_ = ILIM_ =
0V, C
SS
= 10nF, C
VTTR
= 1µF, R
FREQ
= 20kΩ, DH_ = open, DL_ = open, POK_ = open, circuit of Figure 1,
T
A
= 0°C to +85°C,
unless
otherwise noted.)
PARAMETER
R
FREQ
= 100kΩ
Minimum Duty Cycle
DH_ Minimum Off-Time
DH_ Minimum On-Time
ERROR AMPLIFIER
FB_ Input Bias Current
FB1 Input-Voltage Set Point
FB2 Input-Voltage Set Point
Op-Amp Open-Loop Voltage
Gain
Op-Amp Gain Bandwidth
Op-Amp Output-Voltage Slew
Rate
DRIVERS
Break-Before-Make Time
DH1, DH2 On-Resistance in Low
State
DH1, DH2 On-Resistance in High
State
DL1, DL2 On-Resistance in Low
State
DL1, DL2 On-Resistance in High
State
LOGIC INPUTS (EN_)
Input Low Level
Input High Level
Input Bias Current
VTTR
VTTR Output Voltage Range
VTTR Output Accuracy
REFIN
REFIN Input Bias Current
REFIN = 0.9V or 1.25V
-250
+250
nA
Source or sink 15mA
-15mA
≤
I
VTTR
≤
+15mA, REFIN = 0.9V or 1.25V
0.5
-1.0
REFIN
2.5
+1.0
V
%
4.5V < VL < 5.5V
4.5V < VL < 5.5V
0V to 5.5V
2.4
-1
+0.1
+1
0.8
V
V
µA
30
0.9
1.3
0.7
1.6
2.5
2.5
1.5
2.8
ns
Ω
Ω
Ω
Ω
V
FB
_ = 0.8V
Over line and load
MAX8538
MAX8537/MAX8539, REFIN = 0.9V
COMP_ = 1.3V to 2.3V
0.792
0.792
0.894
72
0.800
0.800
0.900
>80
25
15
250
0.808
0.808
0.906
nA
V
V
dB
MHz
V/µs
R
FREQ
= 20kΩ
R
FREQ
= 14.3kΩ
CONDITIONS
MIN
TYP
2.4
12
16
140
120
MAX
4
18
25
200
ns
ns
%
UNITS
MAX8537/MAX8538/MAX8539
_______________________________________________________________________________________
3
Dual-Synchronous Buck Controllers for Point-of-
Load, Tracking, and DDR Memory Power Supplies
MAX8537/MAX8538/MAX8539
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 12V, EN_ = VL, BST_ = 6V, LX_ = 1V, VL load = 0mA, C
VL
= 10µF (ceramic), REFIN = 1.25V, PGND = AGND = FB_ = ILIM_ =
0V, C
SS
= 10nF, C
VTTR
= 1µF, R
FREQ
= 20kΩ, DH_ = open, DL_ = open, POK_ = open, circuit of Figure 1,
T
A
= 0°C to +85°C,
unless
otherwise noted.)
PARAMETER
REFIN Input Voltage Range
REFIN Undervoltage-Lockout Trip
Level
Rising and falling edge, hysteresis = 15mV
CONDITIONS
MIN
0.5
0.4
0.45
TYP
MAX
2.5
0.5
UNITS
V
V
OUTPUT-VOLTAGE FAULT COMPARATORS
Upper FB2 Fault Threshold
Lower FB2 Fault Threshold
Upper FB1 Fault Threshold
Lower FB1 Fault Threshold
POWER-OK OUTPUT (POK_)
POK_ Delay
Upper FB2 POK_ Threshold
Lower FB2 POK_ Threshold
Upper FB1 POK_ Threshold
Lower FB1 POK_ Threshold
POK_ Output Low Level
POK_ Output High Leakage
Rising voltage, hysteresis = 20mV
Falling voltage, hysteresis = 20mV
Rising voltage, hysteresis = 20mV
Falling voltage, hysteresis = 20mV
I
SINK
= 2mA
POK_ = 5.5V
110
86
110
86
64
112
88
112
88
114
90
114
90
0.4
1
Clock
cycles
% of
REFIN
% of
REFIN
% of
0.8V
% of
0.8V
V
µA
Rising voltage, hysteresis = 15mV
Falling voltage, hysteresis = 15mV
Rising voltage, hysteresis = 15mV
Falling voltage, hysteresis = 15mV
115
68
115
68
117
70
117
70
120
72
120
72
% of
REFIN
% of
REFIN
% of
0.8V
% of
0.8V
ELECTRICAL CHARACTERISTICS (Note 2)
(V+ = 12V, EN_ = VL, BST_ = 6V, LX_ = 1V, VL load = 0mA, C
VL
= 10µF (ceramic), REFIN = 1.25V, PGND = AGND = FB_ = ILIM_ =
0V, C
SS
= 10nF, C
VTTR
= 1µF, R
FREQ
= 20kΩ, DH_ = open, DL_ = open, POK_ = open, circuit of Figure 1,
T
A
= -40°C to +85°C,
unless otherwise noted.)
PARAMETER
V+ Operating Range
FB_ Input-Voltage Set Point
FB2 Input-Voltage Set Point
VTTR Output Accuracy
Over line and load
MAX8537/MAX8539, REFIN = 0.9V
-15mA < I
VTTR
≤
+15mA, REFIN = 0.9V or 1.25V
CONDITIONS
VL regulator drops out below 5.5V (Note 1)
MIN
4.75
0.788
0.891
-1
0.800
0.900
REFIN
TYP
MAX
23.00
0.812
0.909
+1
UNITS
V
V
V
%
Note 1:
Operating supply range is guaranteed by the VL line-regulation test. User must short V+ to VL if a fixed 5V supply is used
(i.e., if V+ is less than 5.5V).
Note 2:
Specifications to -40°C are guaranteed by design, not production tested.
4
_______________________________________________________________________________________
Dual-Synchronous Buck Controllers for Point-of-
Load, Tracking, and DDR Memory Power Supplies
Typical Operating Characteristics
(Circuit of Figure 1, T
A
= +25°C, 400kHz switching frequency, V
IN
= 12V, unless otherwise noted.)
V
DDQ
EFFICIENCY vs. LOAD CURRENT
MAX8537 toc01
MAX8537/MAX8538/MAX8539
V
DDQ
EFFICIENCY vs. LOAD CURRENT
MAX8537 toc02
V
DDQ
vs. LOAD CURRENT
V
IN
= 12V
MAX8537 toc03
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
1
V
DDQ
= 2.5V
SENSE RESISTOR = 0Ω
V
IN
= 12V
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
V
DDQ
= 2.5V
SENSE RESISTOR = 3mΩ
V
IN
= 12V
2.55
2.53
2.51
V
DDQ
= 1.8V
V
DDQ
2.49
2.47
2.45
1
10
LOAD CURRENT (A)
100
0
5
10
15
20
LOAD CURRENT (A)
V
DDQ
= 1.8V
10
LOAD CURRENT (A)
100
V
TT
vs. LOAD CURRENT
MAX8537 toc04
V
TTR
vs. LOAD CURRENT
MAX8537 toc05
OUTPUT VOLTAGE vs. INPUT VOLTAGE
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
12
V
DDQ
I
OUT
_V
DDQ
= 20A
I
OUT
_V
TT
= 12A
I
OUT
_V
TTR
= 15mA
MAX8537 toc06
1.30
1.29
1.28
1.27
1.26
1.25
1.24
1.23
1.22
1.21
1.20
0
V
IN
= 12V
1.30
1.29
1.28
1.27
1.26
V
TTR
1.25
1.24
1.23
1.22
1.21
1.20
V
IN
= 12V
OUTPUT VOLTAGE (V)
V
TT
V
TT
AND V
TTR
13
INPUT VOLTAGE (V)
14
3
6
9
12
15
0
5
10
15
20
25
LOAD CURRENT (A)
LOAD CURRENT (mA)
POWER-UP
MAX8537 toc07
POWER-DOWN
MAX8537 toc08
STARTUP AND SHUTDOWN
MAX8537 toc09
V+
V
IN
5V/div
V
DDQ
1V/div
V
DDQ
V
TT
8.5V/div
V
TTR
8.5V/div V
TT
5V/div
EN1/EN2
5V/div
2V/div
V
DDQ
2V/div
V
TT
1V/div
V
TTR
1V/div
1ms/div
2V/div
V
VTTR
2V/div
4ms/div
4ms/div
_______________________________________________________________________________________
5
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