19-2966; Rev 0; 10/03
Dual 180° Out-of-Phase Buck Controllers with
Sequencing/Prebias Startup and POR
General Description
The MAX1858A/MAX1875A/MAX1876A dual, synchro-
nized, step-down controllers generate two outputs from
input supplies ranging from 4.5V to 23V. Each output is
adjustable from sub-1V to 18V and supports loads of 10A
or higher. Input voltage ripple and total RMS input ripple
current are reduced by synchronized 180° out-of-phase
operation.
The switching frequency is adjustable from 100kHz to
600kHz with an external resistor. Alternatively, the con-
troller can be synchronized to an external clock gener-
ated by another MAX1858A/MAX1875A/MAX1876A or a
system clock. One MAX1858A/MAX1875A/MAX1876A
can be set to generate an in-phase, or 90° out-of-
phase, clock signal for synchronization with additional
controllers. This allows two controllers to operate either
as an interleaved two- or four-phase system with each
output shifted by 90°. The MAX1858A/MAX1875A/
MAX1876A feature soft-start. The MAX1858A also fea-
tures first-on/last-off power sequencing and soft-stop.
The MAX1858A/MAX1875A/MAX1876A eliminate the
need for current-sense resistors by utilizing the low-side
MOSFET’s on-resistance as a current-sense element.
This protects the DC-DC components from damage dur-
ing output-overload conditions or output short-circuit
faults without requiring a current-sense resistor.
Adjustable foldback current limit reduces power dissipa-
tion during short-circuit conditions. The MAX1858A/
MAX1876A include a power-on reset (POR) output to sig-
nal the system when both outputs reach regulation.
The MAX1858A/MAX1875A/MAX1876A ensure that the
output voltage does not swing negative when the input
power is removed or when EN is driven low. The
MAX1875A/MAX1876A also allow prebias startup with-
out discharging the output.
The MAX1858A/MAX1875A/MAX1876A are available in a
24-pin QSOP package. Use the MAX1875 evaluation kit
or the MAX1858 evaluation kit to evaluate the
MAX1858A/MAX1875A/MAX1876A.
♦
4.5V to 23V Input Supply Range
♦
0 to 18V Output Voltage Range (Up to 10A)
♦
Adjustable Lossless Foldback Current Limit
♦
Adjustable 100kHz to 600kHz Switching
Frequency
♦
Optional Synchronization
♦
Clock Output for Master/Slave Synchronization
♦
4 x 90° Out-of-Phase Step-Down Converters
(Using Two Controllers, Figure 7)
♦
Prebias Startup (MAX1875A/MAX1876A)
♦
Power Sequencing (MAX1858A)
♦
RST
Output with 140ms Minimum Delay
(MAX1858A/MAX1876A)
♦
Fixed-Frequency Pulse-Width Modulation (PWM)
Operation
Features
MAX1858A/MAX1875A/MAX1876A
Ordering Information
PART
MAX1858AEEG
MAX1875AEEG
MAX1876AEEG
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
24 QSOP
24 QSOP
24 QSOP
Pin Configuration
TOP VIEW
COMP2 1
FB2 2
ILIM2 3
OSC 4
V+ 5
REF 6
GND 7
CKO 8
SYNC 9
ILIM1 10
FB1 11
COMP1 12
24 EN
23 DH2
22 LX2
21 BST2
20 DL2
Applications
Network Power Supplies
Telecom Power Supplies
DSP, ASIC, and FPGA Power Supplies
Set-Top Boxes
Broadband Routers
Servers
Desknote Computers
MAX1858A
MAX1875A
MAX1876A
19 V
L
18 PGND
17 DL1
16 BST1
15 LX1
14 DH1
13 RST (N.C.)
QSOP
() ARE FOR THE MAX1875A ONLY
________________________________________________________________
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.
Dual 180° Out-of-Phase Buck Controllers with
Sequencing/Prebias Startup and POR
MAX1858A/MAX1875A/MAX1876A
ABSOLUTE MAXIMUM RATINGS
V+ to GND ..............................................................-0.3V to +25V
PGND to GND .......................................................-0.3V to +0.3V
V
L
to GND ..................-0.3V to the lower of +6V and (V+ + 0.3V)
BST1, BST2 to GND ...............................................-0.3V to +30V
LX1 to BST1..............................................................-6V to +0.3V
LX2 to BST2..............................................................-6V to +0.3V
DH1 to LX1 ..............................................-0.3V to (V
BST1
+ 0.3V)
DH2 to LX2 ..............................................-0.3V to (V
BST2
+ 0.3V)
DL1, DL2 to PGND........................................-0.3V to (V
L
+ 0.3V)
CKO, REF, OSC, ILIM1, ILIM2,
COMP1, COMP2 to GND ..........................-0.3V to (V
L
+ 0.3V)
FB1, FB2,
RST,
SYNC, EN to GND...........................-0.3V to +6V
VL to GND Short Circuit .............................................Continuous
REF to GND Short Circuit ...........................................Continuous
Continuous Power Dissipation (T
A
= +70°C)
24-Pin QSOP (derate 9.4mW/°C above +70°C)...........762mW
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 = ILIM_ = V
L
, SYNC = GND, I
VL
= 0mA, PGND = GND, C
REF
= 0.22µF, C
VL
= 4.7µF (ceramic), R
OSC
= 60kΩ,
compensation components for COMP_ are from Figure 1,
T
A
= -40°C to +85°C
(Note 1), unless otherwise noted.)
PARAMETER
GENERAL
V+ Operating Range
V+ Operating Supply Current
V+ Standby Supply Current
Thermal Shutdown
Current-Limit Threshold
V
L
REGULATOR
Output Voltage
V
L
Undervoltage Lockout Rising
Trip Level
V
L
Undervoltage Lockout
Hysteresis
REFERENCE
Output Voltage
Reference Load Regulation
SOFT-START
Digital Ramp Period
Soft-Start Steps
FREQUENCY
Low End of Range
High End of Range
DH_ Minimum Off-Time
R
OSC
= 60kΩ
R
OSC
= 10kΩ
R
OSC
= 10kΩ
0°C to +85°C
-40°C to +85°C
84
80
540
100
100
600
250
115
120
660
303
kHz
kHz
ns
Internal 6-bit DAC for one converter to ramp from 0V to
full scale (Note 4)
1024
64
DC-DC
clocks
Steps
I
REF
= 0µA
0µA < I
REF
< 50µA
1.98
0
2.00
4
2.02
10
V
mV
(Note 3)
(Note 2)
V
L
= V+ (Note 2)
V
L
unloaded, no MOSFETs connected
EN = LX_ = FB_ = 0V
Rising temperature, typical hysteresis = 10°C
ILIM_ = V
L
PGND - LX_
R
ILIM_
= 100kΩ
R
ILIM_
= 600kΩ
5.5V < V+ < 23V, 1mA < I
LOAD
< 50mA
75
32
225
4.75
4.1
4.5
4.5
3.5
0.3
+160
100
50
300
5
4.2
100
125
62
375
5.25
4.3
V
V
mV
mV
23.0
5.5
6
0.6
V
mA
mA
°C
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
Dual 180° Out-of-Phase Buck Controllers with
Sequencing/Prebias Startup and POR
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 12V, EN = ILIM_ = V
L
, SYNC = GND, I
VL
= 0mA, PGND = GND, C
REF
= 0.22µF, C
VL
= 4.7µF (ceramic), R
OSC
= 60kΩ,
compensation components for COMP_ are from Figure 1,
T
A
= -40°C to +85°C
(Note 1), unless otherwise noted.)
PARAMETER
SYNC Range
SYNC Input Pulse Width
SYNC Rise/Fall Time
ERROR AMPLIFIER
FB_ Input Bias Current
FB_ Input Voltage Set Point
FB_ to COMP_ Transconductance
DRIVERS
DL_, DH_ Break-Before-Make Time C
LOAD
= 5nF
DH_ On-Resistance
DL_ On-Resistance
LOGIC INPUTS (EN, SYNC)
Input Low Level
Input High Level
Input High/Low Bias Current
LOGIC OUTPUTS (CKO)
Output Low Level
Output High Level
COMP_
Pulldown Resistance During
Shutdown and Current Limit
RST
OUTPUT (MAX1858A/MAX1876A ONLY)
Output-Voltage Trip Level
Output Low Level
Output Leakage
Reset Timeout Period
FB_ to Reset Delay
Both FBs must be over this to allow the reset timer to
start; there is no hysteresis
V
L
= 5V, sinking 3.2mA
V
L
= 1V, sinking 0.4mA
V+ = V
L
= 5V, V
RST
= 5.5V, V
FB
= 1V
V
FB_
= 1V
FB_ overdrive from 1V to 0.85V
140
315
4
0.87
0.9
0.93
0.4
0.3
1
560
V
V
µA
ms
µs
17
Ω
V
L
= 5V, sinking 5mA
V
L
= 5V, sourcing 5mA
4.0
0.4
V
V
Typical 15% hysteresis, V
L
= 4.5V
V
L
= 5.5V
V
EN
= 0 or 5.5V
2.4
-1
+0.1
+1
0.8
V
V
µA
Low
High
Low
High
30
1.5
3
0.6
3
2.5
5
1.5
5
ns
Ω
Ω
0°C to +85°C
-40°C to +85°C
0°C to +85°C
-40°C to +85°C
0.985
0.98
1.25
1.2
1.00
1.00
1.8
1.8
250
1.015
1.02
2.70
2.9
nA
V
mS
CONDITIONS
Switching frequency must be set to half of the SYNC
frequency
(Note 4)
(Note 4)
High
Low
MIN
200
100
100
100
TYP
MAX
1200
UNITS
kHz
ns
ns
MAX1858A/MAX1875A/MAX1876A
Note 1:
Specifications to -40°C are guaranteed by design and not production tested.
Note 2:
Operating supply range is guaranteed by V
L
line regulation test. Connect V+ to V
L
for 5V operation.
Note 3:
When V
L
falls and UVLO is tripped, the device is latched and V
L
must be discharged below 2.5V before normal operation
can resume.
Note 4:
Guaranteed by design and not production tested.
_______________________________________________________________________________________
3
Dual 180° Out-of-Phase Buck Controllers with
Sequencing/Prebias Startup and POR
MAX1858A/MAX1875A/MAX1876A
Typical Operating Characteristics
(Circuit of Figure 1, V
IN
= 12V, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD
MAX1858A/75A/76A toc01
OUTPUT VOLTAGE ACCURACY vs. LOAD
0.8
OUTPUT VOLTAGE ACCURACY (%)
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
-2.0
0
5
LOAD (A)
10
15
0
OUT2
OUT1
MAX1858A/75A/76A toc02
V
L
VOLTAGE ACCURACY
vs. LOAD CURRENT
MAX1858A/75A/76A toc03
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
1
LOAD (A)
10
OUT2
OUT1
1.0
0.5
0
V
L
VOLTAGE ACCURACY
-0.5
-1.0
-1.5
100
50
100
150
LOAD CURRENT (mA)
SWITCHING FREQUENCY vs. R
OSC
MAX1858A/75A/76A toc04
LOAD TRANSIENT RESPONSE (OUTPUT 1)
MAX1858A/75A/76A toc05
LOAD TRANSIENT RESPONSE (OUTPUT 2)
MAX1858A/75A/76A toc06
600
500
400
300
200
100
0
0
10
20
30
R
OSC
(kΩ)
40
50
SWITCHING FREQUENCY (kHz)
V
OUT2
50mV/div
AC-COUPLED
V
OUT1
50mV/div
AC-COUPLED
10A
I
OUT1
0A
10µs/div
V
OUT1
50mV/div
AC-COUPLED
V
OUT2
50mV/div
AC-COUPLED
10A
I
OUT2
0A
10µs/div
60
SOFT-START AND SOFT-STOP WAVEFORM
(MAX1858A ONLY)
MAX1858A/75A/76A toc07
SOFT-START AND SOFT-STOP WAVEFORM
(MAX1858A ONLY)
MAX1858A/75A/76A toc08
10V
EN
0V
V
OUT1
1V/div
I
OUT1
= 300mA
0V
V
OUT2
1V/div
I
OUT2
= 300mA
0V
EN PULLED HIGH BEFORE V
OUT1
REACHES 0V.
5V
EN
0V
V
OUT1
1V/div
I
OUT1
= 300mA
0V
V
OUT2
1V/div
I
OUT2
= 300mA
0V
2ms/div
2ms/div
4
_______________________________________________________________________________________
Dual 180° Out-of-Phase Buck Controllers with
Sequencing/Prebias Startup and POR
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
IN
= 12V, T
A
= +25°C, unless otherwise noted.)
START AND STOP WAVEFORM
(MAX1875A/MAX1876A ONLY)
MAX1858A/75A/76A toc09
MAX1858A/MAX1875A/MAX1876A
INPUT POWER REMOVAL
10V
EN
0V
V
OUT1
1V/div
I
OUT1
= 300mA
0V
V
OUT2
1V/div
I
OUT2
= 300mA
0V
MAX1858A/75A/76A toc10
RESET TIMEOUT
(MAX1858A/MAX1876A ONLY)
MAX1858A/75A/76A toc11
V
IN
10V/div
0V
V
OUT1
1V/div
I
OUT1
= 300mA
0V
V
OUT2
1V/div
I
OUT2
= 300mA
0V
5ms/div
100ms/div, 5V/div
EN
0
V
OUT2
0V
V
OUT1
0V
V
RST
0V
PREBIAS STARTUP
2ms/div
OUT-OF-PHASE WAVEFORM
MAX1858A/75A/76A toc12
EXTERNALLY SYNCHRONIZED
SWITCHING WAVEFORM
MAX1858A/75A/76A toc13
CKO OUTPUT WAVEFORM
5V
V
SYNC
0V
5V
V
CK0
0V
10V
V
LX1
0V
V
OUT1
10mV/div
AC-COUPLED
MAX1858A/75A/76A toc14
V
OUT1
20mV/div
12V
V
LX1
0V
12V
V
LX2
0V
V
OUT2
20mV/div
1µs/div
400ns/div
SYNC = GND
5V
V
CK0
0V
10V
V
LX1
0V
V
OUT1
10mV/div
AC-COUPLED
400ns/div
CKO OUTPUT WAVEFORM
MAX1858A/75A/76A toc15
SHORT-CIRCUIT CURRENT FOLDBACK
AND RECOVERY
MAX1858A/75A/76A toc16
SYNC = V
L
5V
V
CK0
0V
10V
V
LX1
0V
V
OUT1
10mV/div
SHORT
V
OUT2
I
OUT1
= 10A (5A/div)
V
OUT1
= 1.8V (1V/div)
V
OUT2
= 2.5V (1V/div)
I
OUT2
= 10A (5A/div)
400ns/div
4ms/div
_______________________________________________________________________________________
5
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