MAXIM MAX8537, MAX858538, MAX858539 User Manual
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 generate 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 pointof-load supplies. Each buck controller can source or
sink up to 25A of current, while the termination reference can supply up to 15mA output.
The MAX8537/MAX8538/MAX8539 use constantfrequency voltage-mode architecture with operating
frequencies of 200kHz to 1.4MHz. An internal highbandwidth (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 efficiency and cost. The MAX8537/MAX8538/MAX8539
have a 1% accurate reference. The second synchronous buck controller in the MAX8537/MAX8539 and the
VTTR amplifier generate 1/2 V
DDQ
voltage for VTTand
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 setting 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.
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
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 VTT= 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
Dual-Synchronous Buck Controllers for Point-of-
Load, Tracking, and DDR Memory Power Supplies
________________________________________________________________ Maxim Integrated Products 1
19-3141; Rev 1; 6/05
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.
EVALUATION KIT
AVAILABLE
Ordering Information
Pin Configurations appear at end of data sheet.
+Denotes lead-free package.
PART TEMP RANGE
MAX8537EEI -40°C to +85°C 28 QSOP
M AX 8537E E I+ -40°C to +85°C 28 QSOP
MAX8538EEI -40°C to +85°C 28 QSOP
M AX 8538E E I+ -40°C to +85°C 28 QSOP
MAX8539EEI -40°C to +85°C 28 QSOP
M AX 8539E E I+ -40°C to +85°C 28 QSOP
PIN-
PACKAGE
OPERATION
Out-of-phase
tracking
Out-of-phase
tracking
Out-of-phase
nontracking
Out-of-phase
nontracking
In-phase
tracking
In-phase
tracking
MAX8537/MAX8538/MAX8539
Dual-Synchronous Buck Controllers for Point-ofLoad, Tracking, and DDR Memory Power Supplies
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
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
ELECTRICAL CHARACTERISTICS
(V+ = 12V, EN_ = VL, BST_ = 6V, LX_ = 1V, VL load = 0mA, CVL= 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, TA= 0°C to +85°C, unless
otherwise noted.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
GENERAL
V+ Operating Range VL regulator drops out below 5.5V (Note 1) 4.5 23.0 V
V+/ VL Operating Range VL is externally generated (Note 1) 4.5 5.5 V
V+ Operating Supply Current IL(VL) = 0, FB_ forced 50mV above threshold 3.5 7 mA
V+ Standby Supply Current IL(VL) = 0, BST_ = VL, EN = LX_ = FB_ = 0V 350 700 µA
VL REGULATOR
Output Voltage 5.5V < V+ < 23V, 1mA < I
VL Undervoltage-Lockout Trip
Level
Output Current
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
Thermal Shutdown Rising temperature, typical hysteresis = 10°C +160 °C
CURRENT-LIMIT THRESHOLD (all current limits are tested at V+ = VL = 4.5V and 5.5V)
ILIM Sink Current ILIM_ = LX - 200mV, 1.8V < LX < 23V, BST = LX +5V 180 200 220 µA
SOFT-START
Soft-Start Source Current SS_ = 100mV -7 -5 -3 µA
Soft-Start Sink Current SS_ = 0.8 or REFIN 3 5 7 µA
Soft-Start Full-Scale Voltage
FREQUENCY
Low End of Range R
Intermediate Range R
High End of Range R
= 100kΩ, V+ = VL = 5V 160 200 240 kHz
FREQ
= 20kΩ, V+ = VL = 5V 800 1000 1200 kHz
FREQ
= 14.3kΩ, V+ = VL = 5V 1120 1400 1680 kHz
FREQ
R
= 100kΩ 95
FREQ
R
= 20kΩ 80 Maximum Duty Cycle
FREQ
R
= 14.3kΩ 72
FREQ
< 70mA 4.75 5 5.25 V
LOAD
4.18 4.3 4.42 V
70 mA
0.8 or
REFIN
V
%
MAX8537/MAX8538/MAX8539
Dual-Synchronous Buck Controllers for Point-of-
Load, Tracking, and DDR Memory Power Supplies
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 12V, EN_ = VL, BST_ = 6V, LX_ = 1V, VL load = 0mA, CVL= 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, TA= 0°C to +85°C, unless
otherwise noted.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
R
= 100kΩ 2.4 4
FREQ
R
= 20kΩ 12 18Minimum Duty Cycle
FREQ
R
= 14.3kΩ 16 25
FREQ
DH_ Minimum Off-Time 140 200 ns
DH_ Minimum On-Time 120 ns
%
ERROR AMPLIFIER
FB_ Input Bias Current V
_ = 0.8V 250 nA
FB
FB1 Input-Voltage Set Point Over line and load 0.792 0.800 0.808 V
FB2 Input-Voltage Set Point
Op-Amp Open-Loop Voltage
Gain
Op-Amp Gain Bandwidth 25 MHz
Op-Amp Output-Voltage Slew
Rate
MAX8538 0.792 0.800 0.808
MAX8537/MAX8539, REFIN = 0.9V 0.894 0.900 0.906
COMP_ = 1.3V to 2.3V 72 >80 dB
15 V/µs
V
DRIVERS
Break-Before-Make Time 30 ns
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
0.9 2.5 Ω
1.3 2.5 Ω
0.7 1.5 Ω
1.6 2.8 Ω
LOGIC INPUTS (EN_)
Input Low Level 4.5V < VL < 5.5V 0.8 V
Input High Level 4.5V < VL < 5.5V 2.4 V
Input Bias Current 0V to 5.5V -1 +0.1 +1 µA
VTTR
VTTR Output Voltage Range Source or sink 15mA 0.5 2.5 V
VTTR Output Accuracy -15mA ≤ I
≤ +15mA, REFIN = 0.9V or 1.25V -1.0 REFIN +1.0 %
VTTR
REFIN
REFIN Input Bias Current REFIN = 0.9V or 1.25V -250 +250 nA
MAX8537/MAX8538/MAX8539
Dual-Synchronous Buck Controllers for Point-ofLoad, Tracking, and DDR Memory Power Supplies
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 12V, EN_ = VL, BST_ = 6V, LX_ = 1V, VL load = 0mA, CVL= 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, TA= 0°C to +85°C, unless
otherwise noted.)
ELECTRICAL CHARACTERISTICS (Note 2)
(V+ = 12V, EN_ = VL, BST_ = 6V, LX_ = 1V, VL load = 0mA, CVL= 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, TA= -40°C to +85°C,
unless otherwise noted.)
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.
PARAMETER CONDITIONS MIN TYP MAX UNITS
REFIN Input Voltage Range 0.5 2.5 V
REFIN Undervoltage-Lockout Trip
Level
OUTPUT-VOLTAGE FAULT COMPARATORS
Upper FB2 Fault Threshold Rising voltage, hysteresis = 15mV 115 117 120
Lower FB2 Fault Threshold Falling voltage, hysteresis = 15mV 68 70 72
Upper FB1 Fault Threshold Rising voltage, hysteresis = 15mV 115 117 120
Lower FB1 Fault Threshold Falling voltage, hysteresis = 15mV 68 70 72
POWER-OK OUTPUT (POK_)
POK_ Delay 64
Upper FB2 POK_ Threshold Rising voltage, hysteresis = 20mV 110 112 114
Lower FB2 POK_ Threshold Falling voltage, hysteresis = 20mV 86 88 90
Rising and falling edge, hysteresis = 15mV 0.4 0.45 0.5 V
Upper FB1 POK_ Threshold Rising voltage, hysteresis = 20mV 110 112 114
Lower FB1 POK_ Threshold Falling voltage, hysteresis = 20mV 86 88 90
POK_ Output Low Level I
POK_ Output High Leakage POK_ = 5.5V 1 µA
= 2mA 0.4 V
SINK
% of
REFIN
% of
REFIN
% of
0.8V
% of
0.8V
Clock
cycles
% of
REFIN
% of
REFIN
% of
0.8V
% of
0.8V
PARAMETER CONDITIONS MIN TYP MAX UNITS
V+ Operating Range VL regulator drops out below 5.5V (Note 1) 4.75 23.00 V
FB_ Input-Voltage Set Point Over line and load 0.788 0.800 0.812 V
FB2 Input-Voltage Set Point MAX8537/MAX8539, REFIN = 0.9V 0.891 0.900 0.909 V
VTTR Output Accuracy -15mA < I
≤ +15mA, REFIN = 0.9V or 1.25V -1 REFIN +1 %
VTTR
MAX8537/MAX8538/MAX8539
Dual-Synchronous Buck Controllers for Point-of-
Load, Tracking, and DDR Memory Power Supplies
_______________________________________________________________________________________ 5
Typical Operating Characteristics
(Circuit of Figure 1, TA= +25°C, 400kHz switching frequency, VIN= 12V, unless otherwise noted.)
V
100
95
V
= 2.5V
DDQ
90
85
80
75
70
EFFICIENCY (%)
65
60
55
50
1100
SENSE RESISTOR = 0
V
= 1.8V
DDQ
10
LOAD CURRENT (A)
V
IN
= 12V
Ω
MAX8537 toc01
EFFICIENCY vs. LOAD CURRENT
DDQ
VTT vs. LOAD CURRENT
1.30
VIN = 12V
1.29
1.28
1.27
1.26
TT
V
1.25
1.24
1.23
1.22
1.21
1.20
015
LOAD CURRENT (A)
12963
MAX8537 toc04
V
EFFICIENCY vs. LOAD CURRENT
DDQ
100
95
V
= 2.5V
DDQ
90
85
80
75
70
EFFICIENCY (%)
65
60
55
50
1100
V
1.30
VIN = 12V
1.29
1.28
1.27
1.26
TTR
1.25
V
1.24
1.23
1.22
1.21
1.20
025
SENSE RESISTOR = 3m
V
= 1.8V
DDQ
10
LOAD CURRENT (A)
vs. LOAD CURRENT
TTR
LOAD CURRENT (mA)
Ω
= 12V
V
IN
2015105
2.55
MAX8537 toc02
2.53
2.51
DDQ
V
2.49
2.47
2.45
2.6
2.5
2.4
MAX8537 toc05
2.3
2.2
2.1
2.0
1.9
1.8
1.7
OUTPUT VOLTAGE (V)
1.6
1.5
1.4
1.3
1.2
V
vs. LOAD CURRENT
DDQ
VIN = 12V
0
LOAD CURRENT (A)
2015105
OUTPUT VOLTAGE vs. INPUT VOLTAGE
V
DDQ
I
= 20A
OUT_VDDQ
= 12A
I
OUT_VTT
= 15mA
I
OUT_VTTR
VTT AND V
TTR
12 14
13
INPUT VOLTAGE (V)
MAX8537 toc03
MAX8537 toc06
POWER-UP
4ms/div
MAX8537 toc07
V+
5V/div
V
DDQ
1V/div
V
TT
8.5V/div
V
TTR
8.5V/div
V
IN
V
DDQ
V
TT
V
VTTR
POWER-DOWN
4ms/div
MAX8537 toc08
5V/div
2V/div
2V/div
2V/div
STARTUP AND SHUTDOWN
1ms/div
MAX8537 toc09
EN1/EN2
5V/div
V
DDQ
2V/div
V
TT
1V/div
V
TTR
1V/div
MAX8537/MAX8538/MAX8539
Dual-Synchronous Buck Controllers for Point-ofLoad, Tracking, and DDR Memory Power Supplies
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA= +25°C, 400kHz switching frequency, VIN= 12V, unless otherwise noted.)
I
OUT_VDDQ
I
OUT_VTT
= 20A
= 8A
POWER-OK
2ms/div
MAX8537 toc10
V
DDQ
2V/div
POK1
5V/div
V
TT
1V/div
POK2
5V/div
VTT LOAD-TRANSIENT RESPONSE
-8A
8A
di/dt = 1A/µs
I
OUT_VDDQ
I
OUT_VTTR
200µs/div
VTT STARTUP AND SHUTDOWN
2ms/div
MAX8537 toc13
V
TT
AC-COUPLED
50mV/div
V
TTR
AC-COUPLED
50mV/div
V
DDQ
AC-COUPLED
50mV/div
V
TT_IOUT
10A/div
= 20A
= 15mA
MAX8537 toc11
EN2
5V/div
V
TT
1V/div
V
TTR
1V/div
V
DDQ
2V/div
V
= 2.5V AT 20A BODE PLOT,
DDQ
180
160
140
120
100
80
60
dB (DEGREES)
40
20
0
-20
-40
100 1M
20A
10A
V
IN
VTT_I
V
TTR
= 12V
kHz
V
LOAD TRANSIENT
DDQ
AND V
di/dt
= 12A
OUT
= 15mA
200µs/div
100k10k1k
TRACKING
TT
= 5A/µs
MAX8537 toc12
MAX8537 toc14
V
DDQ
100mV/div
V
TT
50mV/div
V
TTR
50mV/div
V
DDQ_IOUT
10A/div
VTT = 1.25V AT 12A BODE PLOT,
150
125
100
75
50
dB (DEGREES)
25
0
-25
-50
2
10
IN
MAX8537 toc15
3
10
4
10
Hz
5
10
6
10
SHORT CIRCUIT AND RECOVERY
V
OUT1
V
OUT2
I
L1
I
IN
MAX8537 toc16
10ms/div
= 12V
V
1V/div
1V/div
10V/div
5A/div
MAX8537/MAX8538/MAX8539
Dual-Synchronous Buck Controllers for Point-of-
Load, Tracking, and DDR Memory Power Supplies
_______________________________________________________________________________________ 7
Pin Description
NAME
PIN
1 BST2 BST2
2 DH2 DH2 High-Side Gate-Driver Output for Step-Down 2. Swings from LX2 to BST2.
3 LX2 LX2
4 ILIM2 ILIM2
5 POK1 POK1
6 DL2 DL2 Low-Side Gate-Driver Output for Step-Down 2. Swings from PGND to VL.
7 POK2 POK2
8 EN2 EN2 Enable Input for Step-Down 2 (also for VTTR for the MAX8537 and MAX8539)
9 EN1 EN1 Enable Input for Step-Down 1
10 FREQ FREQ
11 COMP2 COMP2 Compensation Pin for Step-Down 2. Connect to compensation networks.
12 FB2 FB2
13 SS2 SS2 Soft-Start for Step-Down 2. Connect a capacitor to GND to set the soft-start time.
14
15 GND GND Analog Ground for Internal Circuitry
16 SS1 SS1 Soft-Start for Step-Down 1. Connect a capacitor to GND to set the soft-start time.
17 FB1 FB1
18 COMP1 COMP1 Compensation Pin for Step-Down 1. Connect to compensation networks.
19
20 AVL AVL
21 V+ V+ Input Supply Voltage
(MAX8537/
MAX8539)
REFIN —
— N.C. For the MAX8538, connect pin 14 to GND.
VTTR —
— GND Analog Ground for Internal Circuitry
NAME
(MAX8538)
FUNCTION
Bootstrap Input to Power Internal High-Side Driver for Step-Down 2. Connect to an
external capacitor and diode according to Figure 1.
External Inductor Input for Step-Down 2. Connect to the switched side of the inductor.
LX2 serves as the lower supply-voltage rail for the DH2 high-side gate driver and the
current-limit circuitry.
Output Current-Limit Setting for Step-Down 2. Connect a resistor from ILIM2 to the
drain of the step-down 2 high-side MOSFET, or to the junction of the source of the
high-side MOSFET and the current-sense resistor to set the current-limit threshold.
See the Current-Limit Setting section.
Open-Drain Output. High impedance when step-down 1 is within 12% of its regulation
voltage. POK1 is pulled low in shutdown.
Open-Drain Output. High impedance when step-down 2 is within 12% of its regulation
voltage. POK2 is pulled low in shutdown or if REFIN is undervoltage.
Frequency Adjust. Connect a resistor from this pin to ground to set the frequency. The
range of the FREQ resistor is 163kΩ, 20kΩ, and 100kΩ (corresponding to 1.4MHz,
1.0MHz, and 200kHz).
Feedback Input for Step-Down 2 with V
impedance <40kΩ.
Reference Input for V
common-mode voltage range is 0.5V to 2.5V. Current through the divider-resistors
must be ≥100µA.
Feedback Input for Step-Down 1 with 0.8V Threshold. User must have impedance
<40kΩ.
VTTR Output Capable of Sourcing and Sinking Up to 15mA. Always bypass with a 1µF
ceramic capacitor (or larger) to GND.
Analog VL Input Pin. Connect to VL through a 4.7Ω resistor. Bypass with a 0.1µF (or
larger) ceramic capacitor to GND.
TT
and V
. Connect it to a resistor-divider from V
TTR
as the Threshold. User must have
REFIN
DDQ
. REFIN
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