19-2431; Rev 0; 7/02
KIT
ATION
EVALU
BLE
AVAILA
Dual 180° Out-of-Phase PWM Step-
Down Controllers with POR
General Description
Features
o
Two Independent Output Voltages
o
180° Out-of-Phase Operation
o
90° Out-of-Phase Operation
(Using Two MAX1875/MAX1876s)
o
Foldback Current Limit
o
4.75V to 23V Input Supply Range
o
0 to 18V Output-Voltage Range (Up to 10A)
o
>90% Efficiency
o
Fixed-Frequency Pulse-Width Modulation (PWM)
Operation
o
Adjustable 100kHz to 600kHz Switching
Frequency
o
External SYNC Input
o
Clock Output for Master/Slave Synchronization
o
Soft-Start and Soft-Stop
o
RST
Output with 140ms Minimum Delay (MAX1876)
o
Lossless Current Limit (No Sense Resistor)
MAX1875/MAX1876
The MAX1875/MAX1876 dual, synchronized, step-down
controller generates two outputs from input supplies
ranging from 4.75V 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 to another MAX1875/MAX1876 or a system clock.
One MAX1875/MAX1876 can be set to generate an in-
phase, or 90° out-of-phase, clock signal for synchro-
nization with additional controllers. This allows two
controllers to operate either as an interleaved two- or
four-phase system with each output shifted by 90°.
These devices also feature soft-start and soft-stop.
The MAX1875/MAX1876 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 during output-
overload conditions or when output short-circuit faults
without requiring a current-sense resistor. Adjustable
foldback current limit reduces power dissipation during
short-circuit conditions. The MAX1876 includes a
power-on reset output to signal the system when both
outputs reach regulation.
The MAX1875/MAX1876 are available in a 24-pin QSOP
package. An evaluation kit is available to speed designs.
Ordering Information
PART
MAX1875EEG
MAX1876EEG
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
24 QSOP
24 QSOP
Applications
Network Power Supplies
Telecom Power Supplies
DSP, ASIC, and FPGA Power Supplies
Set-Top Boxes
Broadband Routers
Servers
Pin Configuration
TOP VIEW
COMP2 1
FB2 2
ILIM2 3
OSC 4
V+ 5
REF 6
GND 7
24 EN
23 DH2
22 LX2
21 BST2
20 DL2
MAX1875/
MAX1876
19 V
L
18 PGND
17 DL1
16 BST1
15 LX1
14 DH1
13 RST
(MAX1876 ONLY)
Typical Operating Circuit appears at end of data sheet.
CKO 8
SYNC 9
ILIM1 10
FB1 11
COMP1 12
QSOP
________________________________________________________________
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 PWM Step-
Down Controllers with POR
MAX1875/MAX1876
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
Trip Level
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 3)
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 2)
V
L
= V+ (Note 2)
V
L
unloaded, no MOSFETs connected
EN = LX_ = FB_ = 0V
R
OSC
= 60kΩ
ILIM_ = V
L
PGND - LX_
R
ILIM_
= 100kΩ
R
ILIM_
= 600kΩ
5.5V < V+ < 23V, 1mA < I
LOAD
< 50mA
75
32
225
4.75
4.4
Rising temperature, typical hysteresis = 10°C
4.75
4.75
3.5
0.3
160
100
50
300
5
4.55
125
62
375
5.25
4.7
23
5.5
6
0.6
V
mA
mA
°C
mV
mV
mV
V
V
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
Dual 180° Out-of-Phase PWM Step-
Down Controllers with 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 (MAX1876 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
= 4.75V
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
Internal oscillator nominal frequency must be set to half
of the SYNC frequency
(Note 3)
(Note 3)
High
Low
MIN
200
100
100
100
TYP
MAX
1200
UNITS
kHz
ns
ns
MAX1875/MAX1876
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:
Guaranteed by design and not production tested.
_______________________________________________________________________________________
3
Dual 180° Out-of-Phase PWM Step-
Down Controllers with POR
MAX1875/MAX1876
Typical Operating Characteristics
(Circuit of Figure 1, V
IN
= 12V, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD
MAX1875 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
OUT2
OUT1
MAX1875 toc02
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
1
LOAD (A)
10
OUT2
OUT1
1.0
100
0
5
LOAD (A)
10
15
V
L
VOLTAGE ACCURACY
vs. LOAD CURRENT
MAX1875 toc03
SWITCHING FREQUENCY vs. R
OSC
MAX1875 toc04
0.5
600
500
400
300
200
100
0
0
V
L
VOLTAGE ACCURACY
-0.5
-1.0
-1.5
-2.0
0
50
100
150
LOAD CURRENT (mA)
SWITCHING FREQUENCY (kHz)
0
10
20
30
R
OSC
(kΩ)
40
50
60
LOAD TRANSIENT RESPONSE (OUTPUT 1)
MAX1875 toc05
LOAD TRANSIENT RESPONSE (OUTPUT 2)
MAX1875 toc06
V
OUT2
50mV/div
AC-COUPLED
V
OUT1
50mV/div
AC-COUPLED
10A
I
OUT1
0A
10µs/div
10µs/div
V
OUT1
50mV/div
AC-COUPLED
V
OUT2
50mV/div
AC-COUPLED
10A
I
OUT2
0A
4
_______________________________________________________________________________________
Dual 180° Out-of-Phase PWM Step-
Down Controllers with POR
MAX1875/MAX1876
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V
IN
= 12V, T
A
= +25°C, unless otherwise noted.)
SOFT-START AND SOFT-STOP WAVEFORM
MAX1875 toc07
RESET TIMEOUT (MAX1876 ONLY)
MAX1875 toc08
OUT-OF-PHASE WAVEFORM
MAX1875 toc09
5V/div
5V
EN
0V
EN
0
V
OUT2
V
OUT2
1V/div
0V
V
OUT2
1V/div
0V
0V
V
OUT1
0V
V
RST
0V
V
OUT1
20mV/div
12V
V
LX1
0V
12V
V
LX2
0V
V
OUT2
20mV/div
1µs/div
1ms/div
100ms/div
EXTERNALLY SYNCHRONIZED
SWITCHING WAVEFORM
MAX1875 toc10
CKO OUTPUT WAVEFORM
5V
V
SYNC
0V
5V
V
CK0
0V
10V
V
LX1
0V
V
OUT1
10mV/div
AC-COUPLED
MAX1875 toc11
CKO OUTPUT WAVEFORM
MAX1875 toc12
SYNC = GND
5V
V
CK0
0V
10V
V
LX1
0V
V
OUT1
10mV/div
AC-COUPLED
400ns/div
SYNC = V
L
5V
V
CK0
0V
10V
V
LX1
0V
V
OUT1
10mV/div
400ns/div
400ns/div
SHORT-CIRCUIT CURRENT FOLDBACK
AND RECOVERY
MAX1875 toc13
I
OUT1
= 10A(5A/div)
V
OUT1
= 1.8V(1V/div)
SHORT
V
OUT2
V
OUT2
= 2.5V(1V/div)
I
OUT2
= 10A(5A/div)
4ms/div
_______________________________________________________________________________________
5
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