LTC3374
8-Channel Parallelable
1A Buck DC/DCs
FEATURES
DESCRIPTION
8-Channel Independent Step-Down DC/DCs
n Master-Slave Configurable for Up to 4A per Output
Rail with a Single Inductor
n Independent V Supplies for Each DC/DC
IN
(2.25V to 5.5V)
n All DC/DCs Have 0.8V to V Output Range
IN
n Precision Enable Pin Thresholds for Autonomous
Sequencing
n 1MHz to 3MHz Programmable/Synchronizable
Oscillator Frequency (2MHz Default)
n Die Temperature Monitor Output
n Thermally-Enhanced 38-Lead QFN (5mm × 7mm)
and TSSOP Packages
The LTC®3374 is a high efficiency multioutput power supply IC. The DC/DCs consist of eight synchronous buck
converters (1A each) all powered from independent 2.25V
to 5.5V input supplies.
n
APPLICATIONS
General Purpose Multichannel Power Supplies
Industrial/Automotive/Communications
n
n
The DC/DCs may be used independently or in parallel to
achieve higher currents of up to 4A per output with a shared
inductor. The common buck switching frequency may be
programmed with an external resistor, synchronized to an
external oscillator, or set to a default internal 2MHz clock.
The operating mode for all DC/DCs may be programmed
via the MODE pin.
To reduce input noise the buck converters are phased in
90° steps. Precision enable pin thresholds provide reliable power-up sequencing. The LTC3374 is available in a
compact 38-lead 5mm × 7mm QFN package as well as a
38-lead TSSOP package.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
TYPICAL APPLICATION
8-Channel 1A Multioutput Buck Regulator
VIN1
BUCK1
VCC
2.2µH
22µF
LTC3374
VIN2
BUCK2
Buck Efficiency vs ILOAD
100
MASTER
90
2.2µH
SLAVE
22µF
EN1
EN2
EN3
EN4
VIN7
EN5
BUCK7
EN6
EN7
EN8
PGOOD_ALL
TEMP
MODE
VIN8
BUCK8
0.8V TO VIN1
UP TO 1A
MASTER
2.2µH
•
•
•
SLAVE
10µF
0.8V TO VIN7
UP TO 1A
70
60
50
30
20
0
SLAVE
10µF
1A BUCK
2A BUCK
3A BUCK
4A BUCK
FORCED CONTINUOUS MODE
VIN = 3.3V, VOUT = 1.8V
fOSC = 1MHz, L = 3.3µH
40
10
MASTER
2.2µH
80
0.8V TO VIN2
UP TO 1A
EFFICIENCY (%)
2.7V TO 5.5V
0
0.8V TO VIN8
UP TO 1A
2000
1000
3000
LOAD CURRENT (mA)
4000
3374 TA01b
SYNC
RT
3374 TA01a
3374fc
For more information www.linear.com/LTC3374
1
LTC3374
TABLE OF CONTENTS
Features...................................................... 1
Applications................................................. 1
Typical Application ......................................... 1
Description.................................................. 1
Absolute Maximum Ratings............................... 3
Pin Configuration........................................... 3
Order Information........................................... 3
Electrical Characteristics.................................. 4
Typical Performance Characteristics.................... 6
Pin Functions............................................... 11
Block Diagram.............................................. 13
Operation................................................... 14
Buck Switching Regulators...................................... 14
Buck Regulators with Combined Power Stages....... 14
Power Failure Reporting Via PGOOD_ALL Pin......... 15
Temperature Monitoring and Overtemperature
Protection................................................................ 15
Programming the Operating Frequency................... 15
2
Applications Information................................. 17
Buck Switching Regulator Output Voltage
and Feedback Network............................................. 17
Buck Regulators...................................................... 17
Combined Buck Regulators..................................... 17
Input and Output Decoupling Capacitor Selection... 17
PCB Considerations................................................. 19
Package Description...................................... 23
Revision History........................................... 25
Typical Application........................................ 26
Related Parts............................................... 26
3374fc
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LTC3374
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN1-8, FB1-8, EN1-8, VCC, PGOOD_ALL,
SYNC, RT, MODE.......................................... –0.3V to 6V
TEMP................... –0.3V to Lesser of (VCC + 0.3V) or 6V
IPGOOD_ALL................................................................5mA
Operating Junction Temperature Range
(Notes 2, 3)............................................. –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
PIN CONFIGURATION
TOP VIEW
FB1
35 EN8
EN7
36 EN7
4
MODE
38 37 36 35 34 33 32
3
VCC
37 MODE
EN1
TEMP
38 VCC
2
EN2
1
EN2
EN1
TEMP
EN8
TOP VIEW
FB1 1
31 FB8
VIN1 2
30 VIN8
VIN1
5
34 FB8
SW1 3
29 SW8
SW1
6
33 VIN8
SW2 4
28 SW7
SW2
7
32 SW8
VIN2 5
27 VIN7
VIN2
8
31 SW7
FB2 6
26 FB7
FB2
9
25 FB6
FB3 10
39
GND
FB3 7
VIN3 8
24 VIN6
SW3 9
23 SW6
SW4 10
22 SW5
VIN4 11
21 VIN5
20 FB5
FB4 12
VIN3 11
28 FB6
27 VIN6
SW4 13
26 SW6
VIN4 14
25 SW5
FB4 15
24 VIN5
EN4 16
23 FB5
EN3 17
22 EN5
PGOOD_ALL 18
21 EN6
EN5
EN6
RT
SYNC
PGOOD_ALL
EN3
EN4
29 FB7
SW3 12
13 14 15 16 17 18 19
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
TJMAX = 150°C, θJA = 34°C/W
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
30 VIN7
39
GND
SYNC 19
20 RT
FE PACKAGE
38-LEAD PLASTIC TSSOP
TJMAX = 150°C, θJA = 25°C/W
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3374EUHF#PBF
LTC3374EUHF#TRPBF
3374
38-Lead (5mm × 7mm) Plastic QFN
–40°C to 125°C
LTC3374IUHF #PBF
LTC3374IUHF#TRPBF
3374
38-Lead (5mm × 7mm) Plastic QFN
–40°C to 125°C
LTC3374HUHF #PBF
LTC3374HUHF#TRPBF
3374
38-Lead (5mm × 7mm) Plastic QFN
–40°C to 150°C
LTC3374EFE #PBF
LTC3374EFE#TRPBF
LTC3374FE
38-Lead Plastic TSSOP
–40°C to 125°C
LTC3374IFE #PBF
LTC3374IFE#TRPBF
LTC3374FE
38-Lead Plastic TSSOP
–40°C to 125°C
LTC3374HFE #PBF
LTC3374HFE#TRPBF
LTC3374FE
38-Lead Plastic TSSOP
–40°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
3374fc
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3
LTC3374
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VCC = VIN1-8 = 3.3V, unless otherwise specified.
SYMBOL
PARAMETER
VVCC
VCC Voltage Range
VVCC_UVLO
Undervoltage Threshold on VCC
VCC Voltage Falling
VCC Voltage Rising
IVCC_ALLOFF
VCC Input Supply Current
All Switching Regulators in Shutdown
IVCC
VCC Input Supply Current
At Least 1 Buck Active
SYNC = 0V, RT = 400k, VFB_BUCK = 0.85V
SYNC = 2MHz
fOSC
Internal Oscillator Frequency
VRT = VCC, SYNC = 0V
VRT = VCC, SYNC = 0V
RRT = 400k, SYNC = 0V
fSYNC
Synchronization Frequency
VSYNC
SYNC Level High
SYNC Level Low
VRT
RT Servo Voltage
CONDITIONS
MIN
l
2.7
l
l
2.35
2.45
l
l
tLOW, tHIGH > 40ns
RRT = 400k
1.8
1.75
1.8
TYP
MAX
5.5
V
2.45
2.55
2.55
2.65
V
V
8
18
µA
45
200
75
275
µA
µA
2
2
2
2.2
2.25
2.2
MHz
MHz
MHz
3
MHz
1
l
l
1.2
l
780
800
UNITS
0.4
V
V
820
mV
Temperature Monitor
VTEMP(ROOM)
TEMP Voltage at 25°C
150
mV
∆VTEMP/°C
VTEMP Slope
6.75
mV/°C
OT
Overtemperature Shutdown
165
°C
OT Hyst
Overtemperature Hysteresis
10
°C
Temperature Rising
1A Buck Regulators
VBUCK
Buck Input Voltage Range
VOUT
Buck Output Voltage Range
VIN_UVLO
Undervoltage Threshold on VIN
VIN Voltage Falling
VIN Voltage Rising
IVIN_BUCK
Burst Mode® Operation
Forced Continuous Mode Operation
Shutdown Input Current
Shutdown Input Current
VFB_BUCK = 0.85V (Note 4)
ISW_BUCK = 0µA, VFB_BUCK = 0V
All Switching Regulators in Shutdown
At Least One Other Buck Active
IFWD
PMOS Current Limit
(Note 5)
VFB
Feedback Regulation Voltage
IFB
Feedback Leakage Current
l
l
l
l
VFB_BUCK = 0.85V
2.25
5.5
V
VFB
VIN
V
2.05
2.15
2.15
2.25
V
V
18
400
0
1
50
550
1
2
µA
µA
µA
µA
1.95
2.05
2.0
2.3
2.7
A
780
800
820
mV
50
nA
–50
DMAX
Maximum Duty Cycle
VFB_BUCK = 0V
RPMOS
PMOS On-Resistance
ISW_BUCK = 100mA
300
mΩ
RNMOS
NMOS On-Resistance
ISW_BUCK = 100mA
300
mΩ
ILEAKP
PMOS Leakage Current
EN_BUCK = 0
–2
2
µA
ILEAKN
NMOS Leakage Current
EN_BUCK = 0
–2
2
µA
3
ms
l
100
tSS
Soft-Start Time
(Note 6)
VPGOOD(FALL)
Falling PGOOD Threshold Voltage
% of Regulated VFB
92.5
%
VPGOOD(HYS)
PGOOD Hysteresis
% of Regulated VFB
1
%
l
0.25
%
1
Buck Regulators Combined
IFWD2
PMOS Current Limit
2 Buck Converters Combined (Note 5)
4.6
A
IFWD3
PMOS Current Limit
3 Buck Converters Combined (Note 5)
6.9
A
IFWD4
PMOS Current Limit
4 Buck Converters Combined (Note 5)
9.2
A
4
3374fc
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LTC3374
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VCC = VIN1-8 = 3.3V, unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Interface Logic Pins (PGOOD_ALL, MODE)
IOH
Output High Leakage Current
PGOOD_ALL 5.5V at Pin
–1
VOL
Output Low Voltage
PGOOD_ALL 3mA into Pin
VIH
Input High Threshold
MODE
l
VIL
Input Low Threshold
MODE
l
1
0.1
0.4
1.2
µA
V
V
0.4
V
Interface Logic Pins (EN1, EN2, EN3, EN4, EN5, EN6, EN7, EN8)
VHI_ALLOFF
Enable Rising Threshold
All Regulators Disabled
l
VEN_HYS
Enable Falling Hysteresis
Enable Rising Threshold
At Least One Regulator Enabled
l
VHI
IEN
Enable Pin Leakage Current
EN = VCC = VIN = 5.5V
400
730
1200
60
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC3374 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC3374E is guaranteed to meet specifications from
0°C to 85°C junction temperature. Specifications over the –40°C to
125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3374I is guaranteed over the –40°C to 125°C operating junction
temperature range and the LTC3374H is guaranteed over the –40°C to
150°C operating junction temperature range. High junction temperatures
degrade operating lifetimes; operating lifetime is derated for junction
temperatures greater than 125°C. Note that the maximum ambient
temperature consistent with these specifications is determined by
specific operating conditions in conjunction with board layout, the rated
package thermal impedance and other environmental factors. The junction
temperature (TJ in °C) is calculated from ambient temperature (TA in °C)
and power dissipation (PD in Watts) according to the formula:
TJ = TA + (PD • θJA)
where θJA (in °C/W) is the package thermal impedance.
380
–1
400
mV
mV
420
mV
1
µA
Note 3: The LTC3374 includes overtemperature protection which protects
the device during momentary overload conditions. Junction temperatures
will exceed 150°C when overtemperature protection is active. Continuous
operation above the specified maximum operating junction temperature
may impair device reliability.
Note 4: Static current, switches not switching. Actual current may be
higher due to gate charge losses at the switching frequency.
Note 5: The current limit features of this part are intended to protect the
IC from short term or intermittent fault conditions. Continuous operation
above the maximum specified pin current rating may result in device
degradation over time.
Note 6: The soft-start is the time from the first top switch turn on, after an
enable rising, until the feedback has reached 90% of its nominal regulation
voltage.
3374fc
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5
LTC3374
TYPICAL PERFORMANCE CHARACTERISTICS
Buck VIN Undervoltage Threshold
vs Temperature
2.30
2.65
2.25
2.60
VCC RISING
2.55
2.50
VCC FALLING
2.45
60
ALL REGULATORS
55 IN SHUTDOWN
50
2.20
VIN RISING
2.15
2.10
VIN FALLING
2.05
2.40
2.30
–50 –25
1.90
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
0
25 50 75 100 125 150
TEMPERATURE (°C)
fOSC (MHz)
IVCC (µA)
240
VCC = 3.3V
200
VCC = 2.7V
160
0
25 50 75 100 125 150
TEMPERATURE (°C)
0
–50 –25
0
VCC = 5.5V
VCC = 3.3V
VCC = 2.7V
0
25 50 75 100 125 150
TEMPERATURE (°C)
3374 G05
3374 G06
Oscillator Frequency vs VCC
VRT = VCC
2.15
2.15
2.10
2.10
2.05
2.05
fOSC (MHz)
fOSC (MHz)
1.95
2.20
2.00
1.95
1.90
VCC = 5.5V
VCC = 3.3V
VCC = 2.7V
1.85
0
25 50 75 100 125 150
TEMPERATURE (°C)
VRT = VCC
2.00
RRT = 402k
1.95
1.90
1.85
1.80
2.7
3374 G07
6
2.00
1.80
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
Default Oscillator Frequency
vs Temperature
1.80
–50 –25
2.05
1.85
3374 G04
2.20
RRT = 402k
1.90
80
40
0
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
2.10
120
25
0
2.15
VCC = 5.5V
280
IVCC (µA)
2.20
320
VCC = 2.7V
VCC = 2.7V
RT Programmed Oscillator
Frequency vs Temperature
AT LEAST ONE BUCK ENABLED
360 SYNC = 2MHz
50
VCC = 5.5V
3374 G03
400
VCC = 5.5V
VCC = 3.3V
0
–50 –25
VCC Supply Current
vs Temperature
AT LEAST ONE BUCK ENABLED
SYNC = 0V
FB = 850mV
VCC = 3.3V
20
3374 G02
VCC Supply Current
vs Temperature
75
30
25
5
3374 G01
100
35
10
1.95
0
45
40
15
2.00
2.35
125
VCC Supply Current
vs Temperature
IVCC_ALLOFF (µA)
2.70
UV THRESHOLD (V)
UV THRESHOLD (V)
VCC Undervoltage Threshold
vs Temperature
3.1
3.5
3.9 4.3
VCC (V)
4.7
5.1
5.5
3374 G08
3374fc
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LTC3374
TYPICAL PERFORMANCE CHARACTERISTICS
VCC = 3.3V
3.5
1200
3.0
1000
2.5
800
VTEMP (mV)
2.0
1.5
Enable Threshold vs Temperature
900
850
400 ACTUAL VTEMP
200
0.5
0
–200
EN FALLING
600
550
450
IDEAL VTEMP
0
50
415
20
40
60
80 100 120
TEMPERATURE (°C)
400
–50 –25
140
0
25 50 75 100 125 150
TEMPERATURE (°C)
3374 G11
Buck VIN Supply Current
vs Temperature
550
Burst Mode OPERATION
FB = 850mV
40
IVIN_BURST (µA)
410
405
EN RISING
EN FALLING
390
30
VIN = 5.5V
20
VIN = 2.25V
VIN = 3.3V
10
385
FORCED CONTINUOUS MODE
500 FB = 0V
450
VIN = 5.5V
400
VIN = 3.3V
350
VIN = 2.25V
300
250
200
150
100
50
0
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
0
3374 G12
1.86
0
25 50 75 100 125 150
TEMPERATURE (°C)
3374 G13
3374 G14
PMOS Current Limit
vs Temperature
VOUT vs Temperature
1.88
0
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
2.6
FORCED CONTINUOUS MODE
ILOAD = 0mA
VIN = 3.3V
2.5
1.84
1.82
1.80
1.78
2.4
VIN = 5.5V
IFWD (A)
0
VOUT (V)
EN THRESHOLD (mV)
650
Buck VIN Supply Current
vs Temperature
420
380
–50 –25
EN RISING
700
3374 G10
Enable Pin Precision Threshold
vs Temperature
395
750
500
3374 G09
400
ALL REGULATORS DISABLED
VCC = 3.3V
800
600
1.0
0
250 300 350 400 450 500 550 600 650 700 750 800
RRT (kΩ)
VTEMP vs Temperature
IVIN_FORCED_CONTINUOUS (µA)
fOSC (MHz)
1400
EN THRESHOLD (mV)
Oscillator Frequency vs RT
4.0
VIN = 2.25V
VIN = 3.3V
2.3
2.2
1.76
2.1
1.74
1.72
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
2.0
–50 –25
3374 G15
0
25 50 75 100 125 150
TEMPERATURE (°C)
3374 G16
3374fc
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7
LTC3374
TYPICAL PERFORMANCE CHARACTERISTICS
450
450
RDS(ON) (mΩ)
400
350
300
300
200
200
150
–50 –25
150
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
100
100
90
90
FORCED
CONTINUOUS
MODE
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
30
20
10
0
1
10
100
LOAD CURRENT (mA)
0
3374 G19
90
Burst Mode
OPERATION
70
50
40
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
30
20
10
1000
10
100
LOAD CURRENT (mA)
1
Burst Mode
OPERATION
80
FORCED
CONTINUOUS
MODE
60
0
1000
100
70
FORCED
CONTINUOUS
MODE
60
50
40
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
30
20
10
0
1000
10
100
LOAD CURRENT (mA)
1
3374 G21
1000
3374 G22
3A Buck Efficiency vs ILOAD,
VOUT = 2.5V
100
100
90
90
80
80
Burst Mode
OPERATION
70
60
FORCED
CONTINUOUS
MODE
50
40
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
30
20
10
1
10
100
LOAD CURRENT (mA)
1000
EFFICIENCY (%)
EFFICIENCY (%)
10
100
LOAD CURRENT (mA)
1
2A Buck Efficiency vs ILOAD,
VOUT = 2.5V
3374 G20
Burst Mode
OPERATION
70
60
50
40
20
10
0
FORCED
CONTINUOUS
MODE
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
30
1
3374 G23
8
0
25 50 75 100 125 150
TEMPERATURE (°C)
3A Buck Efficiency vs ILOAD,
VOUT = 1.8V
0
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
30
10
80
EFFICIENCY (%)
EFFICIENCY (%)
Burst Mode
80 OPERATION
50
50
40
2A Buck Efficiency vs ILOAD,
VOUT = 1.8V
70
FORCED
CONTINUOUS
MODE
60
3374 G18
1A Buck Efficiency vs ILOAD,
VOUT = 2.5V
40
70
20
3374 G17
60
80
350
250
Burst Mode OPERATION
90
400
250
0
100
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
500
EFFICIENCY (%)
500
RDS(ON) (mΩ)
550
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
1A Buck Efficiency vs ILOAD,
VOUT = 1.8V
NMOS RDS(ON) vs Temperature
EFFICIENCY (%)
550
PMOS RDS(ON) vs Temperature
10
100
LOAD CURRENT (mA)
1000
3374 G24
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LTC3374
TYPICAL PERFORMANCE CHARACTERISTICS
1A Buck Efficiency vs Frequency
(Forced Continuous Mode)
4A Buck Efficiency vs ILOAD,
VOUT = 2.5V
100
100
100
90
90
90
80
80
60
50
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
20
10
0
1
60
FORCED
CONTINUOUS
MODE
50
40
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
30
20
10
0
10
100
1000
LOAD CURRENT (mA)
3374 G25
70
EFFICIENCY (%)
ILOAD = 20mA
60
50
40
30
1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
FREQUENCY (MHz)
Burst Mode
OPERATION
60
50
3374 G27
30
10
0
1.804
10
100
LOAD CURRENT (mA)
1
VIN = 5.5V
1.808
VOUT = 1.8V
VIN = 3.3V
fOSC = 1MHz
L = 3.3µH
fOSC = 2MHz
L = 2.2µH
fOSC = 3MHz
L = 1µH
40
3
3
1.812
VIN = 3.3V
1.800
1.796
VIN = 2.25V
1.792
1.788
DROPOUT
1.784
1.780
1000
1
10
100
1.820
1.815
1.812
3374 G30
1A Buck Regulator Line Regulation
(Forced Continuous Mode)
1.820
fOSC = 2MHz
1.816 L = 2.2µH
1000
LOAD CURRENT (mA)
3374 G29
4A Buck Regulator Load Regulation
(Forced Continuous Mode)
fOSC = 2MHz
L = 2.2µH
1.810
VIN = 5.5V
1.805
1.804
VIN = 3.3V
1.800
1.796
1.800
ILOAD = 100mA
ILOAD = 500mA
1.795
VIN = 2.25V
1.792
1.790
1.788
DROPOUT
1.784
1.780
1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
FREQUENCY (MHz)
1A Buck Regulator Load Regulation
(Forced Continuous Mode)
FORCED
CONTINUOUS
MODE
3374 G28
1.808
1
fOSC = 2MHz
1.816 L = 2.2µH
VOUT (V)
1
VOUT = 1.8V
ILOAD = 100mA
L = 3.3µH
1.820
20
VOUT = 1.8V
VIN = 3.3V
L = 3.3µH
VOUT (V)
EFFICIENCY (%)
80
70
0
0
90
ILOAD = 500mA
10
30
10
100
80
20
40
1A Buck Efficiency vs ILOAD
(Across Operating Frequency)
ILOAD = 100mA
90
50
3374 G26
1A Buck Efficiency vs Frequency
(Forced Continuous Mode)
100
60
20
10
100
1000
LOAD CURRENT (mA)
1
VIN = 3.3V
VIN = 5.5V
70
VOUT (V)
FORCED
CONTINUOUS
40
MODE
30
70
VIN = 2.25V
80
Burst Mode
OPERATION
EFFICIENCY (%)
Burst Mode
OPERATION
70
EFFICIENCY (%)
EFFICIENCY (%)
4A Buck Efficiency vs ILOAD,
VOUT = 1.8V
1
10
100
1.785
1000
1.780
2.25
2.75
3.25
3.75
4.25
4.75
5.25
VIN (V)
LOAD CURRENT (mA)
3374 G31
3374 G32
3374fc
For more information www.linear.com/LTC3374
9
LTC3374
TYPICAL PERFORMANCE CHARACTERISTICS
4A Buck Regulator No-Load
Start-Up Transient (Forced
Continuous Mode)
1A Buck Regulator No-Load
Start-Up Transient (Burst Mode
Operation)
VOUT
500mV/DIV
INDUCTOR
CURRENT
500mA/DIV
EN 2V/DIV
VOUT
500mV/DIV
VOUT
100mV/DIV
AC-COUPLED
INDUCTOR
CURRENT
500mA/DIV
INDUCTOR
CURRENT
200mA/DIV
0mA
EN 2V/DIV
VIN = 3.3V
200µs/DIV
3374 G33
VIN = 3.3V
1A Buck Regulator, Transient
Response (Forced Continuous
Mode)
VOUT
100mV/DIV
AC-COUPLED
INDUCTOR
CURRENT
200mA/DIV
0mA
50µs/DIV
LOAD STEP = 100mA TO 700mA
VIN = 3.3V
VOUT = 1.8V
10
1A Buck Regulator, Transient
Response (Burst Mode Operation)
3374 G36
200µs/DIV
3374 G34
4A Buck Regulator, Transient
Response (Forced Continuous
Mode)
4A Buck Regulator, Transient
Response (Burst Mode Operation)
VOUT
100mV/DIV
AC-COUPLED
VOUT
100mV/DIV
AC-COUPLED
INDUCTOR
CURRENT
1A/DIV
0mA
INDUCTOR
CURRENT
1A/DIV
0mA
50µs/DIV
LOAD STEP = 400mA TO 2.8A
VIN = 3.3V
VOUT = 1.8V
3374 G37
3374 G35
50µs/DIV
LOAD STEP = 100mA TO 700mA
VIN = 3.3V
VOUT = 1.8V
50µs/DIV
LOAD STEP = 400mA TO 2.8A
VIN = 3.3V
VOUT = 1.8V
3374 G38
3374fc
For more information www.linear.com/LTC3374
LTC3374
PIN FUNCTIONS
(QFN/TSSOP)
FB1 (Pin 1/Pin 4): Buck Regulator 1 Feedback Pin. Receives
feedback by a resistor divider connected across the output.
VIN1 (Pin 2/Pin 5): Buck Regulator 1 Input Supply. Bypass
to GND with a 10µF or larger ceramic capacitor.
SW1 (Pin 3/Pin 6): Buck Regulator 1 Switch Node. External
inductor connects to this pin.
SW2 (Pin 4/Pin 7): Buck Regulator 2 Switch Node. External
inductor connects to this pin.
VIN2 (Pin 5/Pin 8): Buck Regulator 2 Input Supply. Bypass
to GND with a 10µF or larger ceramic capacitor. May be
driven by an independent supply or must be shorted to VIN1
when buck regulator 2 is combined with buck regulator 1
for higher current.
FB2 (Pin 6/Pin 9): Buck Regulator 2 Feedback Pin. Receives
feedback by a resistor divider connected across the output.
Connecting FB2 to VIN2 combines buck regulator 2 with
buck regulator 1 for higher current. Up to four converters
may be combined in this way.
FB3 (Pin 7/Pin 10): Buck Regulator 3 Feedback Pin.
Receives feedback by a resistor divider connected across
the output. Connecting FB3 to VIN3 combines buck regulator 3 with buck regulator 2 for higher current. Up to four
converters may be combined in this way.
VIN3 (Pin 8/Pin 11): Buck Regulator 3 Input Supply. Bypass
to GND with a 10µF or larger ceramic capacitor. May be
driven by an independent supply or must be shorted to VIN2
when buck regulator 3 is combined with buck regulator 2
for higher current.
SW3 (Pin 9/Pin 12): Buck Regulator 3 Switch Node.
External inductor connects to this pin.
SW4 (Pin 10/Pin 13): Buck Regulator 4 Switch Node.
External inductor connects to this pin.
VIN4 (Pin 11/Pin 14): Buck Regulator 4 Input Supply.
Bypass to GND with a 10µF or larger ceramic capacitor.
May be driven by an independent supply or must be
shorted to VIN3 when buck regulator 4 is combined with
buck regulator 3 for higher current.
FB4 (Pin 12/Pin 15): Buck Regulator 4 Feedback Pin.
Receives feedback by a resistor divider connected across
the output. Connecting FB4 to VIN4 combines buck regulator 4 with buck regulator 3 for higher current. Up to four
converters may be combined in this way.
EN4 (Pin 13/Pin 16): Buck Regulator 4 Enable Input.
Active high.
EN3 (Pin 14/Pin 17): Buck Regulator 3 Enable Input.
Active high.
PGOOD_ALL (Pin 15/Pin 18): PGOOD Status Pin. Opendrain output. When the regulated output voltage of any
enabled switching regulator is more than 7.5% below its
programmed level, this pin is driven LOW. When all buck
regulators are disabled PGOOD_ALL is driven LOW.
SYNC (Pin 16/Pin 19): Oscillator Synchronization Pin. Driving SYNC with an external clock signal will synchronize all
switchers to the applied frequency. The slope compensation
is automatically adapted to the external clock frequency.
The absence of an external clock signal will enable the
frequency programmed by the RT pin. SYNC should be
held at ground if not used. Do not float.
RT (Pin 17/Pin 20): Oscillator Frequency Pin. This pin
provides two modes of setting the switching frequency.
Connecting a resistor from RT to ground will set the switching frequency based on the resistor value. If RT is tied to
VCC the internal 2MHz oscillator will be used. Do not float.
EN6 (Pin 18/Pin 21): Buck Regulator 6 Enable Input.
Active high.
EN5 (Pin 19/Pin 22): Buck Regulator 5 Enable Input.
Active high.
FB5 (Pin 20/Pin 23): Buck Regulator 5 Feedback Pin.
Receives feedback by a resistor divider connected across
the output. Connecting FB5 to VIN5 combines buck regulator 5 with buck regulator 4 for higher current. Up to four
converters may be combined in this way.
3374fc
For more information www.linear.com/LTC3374
11
LTC3374
PIN FUNCTIONS
(QFN/TSSOP)
VIN5 (Pin 21/Pin 24): Buck Regulator 5 Input Supply.
Bypass to GND with a 10µF or larger ceramic capacitor.
May be driven by an independent supply or must be
shorted to VIN4 when buck regulator 5 is combined with
buck regulator 4 for higher current.
VIN8 (Pin 30/Pin 33): Buck Regulator 8 Input Supply.
Bypass to GND with a 10µF or larger ceramic capacitor.
May be driven by an independent supply or must be
shorted to VIN7 when buck regulator 8 is combined with
buck regulator 7 for higher current.
SW5 (Pin 22/Pin 25): Buck Regulator 5 Switch Node.
External inductor connects to this pin.
FB8 (Pin 31/Pin 34): Buck Regulator 8 Feedback Pin.
Receives feedback by a resistor divider connected across
the output. Connecting FB8 to VIN8 combines buck regulator 8 with buck regulator 7 for higher current. Up to four
converters may be combined in this way.
SW6 (Pin 23/Pin 26): Buck Regulator 6 Switch Node.
External inductor connects to this pin.
VIN6 (Pin 24/Pin 27): Buck Regulator 6 Input Supply.
Bypass to GND with a 10µF or larger ceramic capacitor.
May be driven by an independent supply or must be
shorted to VIN5 when buck regulator 6 is combined with
buck regulator 5 for higher current.
EN8 (Pin 32/Pin 35): Buck Regulator 8 Enable Input.
Active high.
EN7 (Pin 33/Pin 36): Buck Regulator 7 Enable Input.
Active high.
FB6 (Pin 25/Pin 28): Buck Regulator 6 Feedback Pin.
Receives feedback by a resistor divider connected across
the output. Connecting FB6 to VIN6 combines buck regulator 6 with buck regulator 5 for higher current. Up to four
converters may be combined in this way.
MODE (Pin 34/Pin 37): Logic Input. MODE enables Burst
Mode functionality for all the buck switching regulators
when the pin is set low. When the pin is set high, all the
buck switching regulators will operate in forced continuous mode.
FB7 (Pin 26/Pin 29): Buck Regulator 7 Feedback Pin.
Receives feedback by a resistor divider connected across
the output. Connecting FB7 to VIN7 combines buck regulator 7 with buck regulator 6 for higher current. Up to four
converters may be combined in this way.
VCC (Pin 35/Pin 38): Internal Bias Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
VIN7 (Pin 27/Pin 30): Buck Regulator 7 Input Supply.
Bypass to GND with a 10µF or larger ceramic capacitor.
May be driven by an independent supply or must be
shorted to VIN6 when buck regulator 7 is combined with
buck regulator 6 for higher current.
SW7 (Pin 28/Pin 31): Buck Regulator 7 Switch Node.
External inductor connects to this pin.
SW8 (Pin 29/Pin 32): Buck Regulator 8 Switch Node.
External inductor connects to this pin.
12
TEMP (Pin 36/Pin 1): Temperature Indication Pin. TEMP
outputs a voltage of 150mV (typical) at room temperature. The TEMP voltage will change by 6.75mV/°C (typical)
giving an external indication of the LTC3374 internal die
temperature.
EN2 (Pin 37/Pin 2): Buck Regulator 2 Enable Input.
Active high.
EN1 (Pin 38/Pin 3): Buck Regulator 1 Enable Input.
Active high.
GND (Exposed Pad Pin 39/Exposed Pad Pin 39): Ground.
The exposed pad must be connected to a continuous
ground plane on the printed circuit board directly under
the LTC3374 for electrical contact and rated thermal
performance.
3374fc
For more information www.linear.com/LTC3374
LTC3374
BLOCK DIAGRAM
(Pin numbers reflect QFN package)
TOP LOGIC
VCC 35
15 PGOOD_ALL
SYNC 16
REF, CLK
RT 17
8 PGOOD
TEMP 36
BANDGAP,
OSCILLATOR,
UV, OT
TEMP MONITOR
34 MODE
30 VIN8
VIN1 2
SW1 3
FB1 1
BUCK REGULATOR 1
1A
BUCK REGULATOR 8
1A
MASTER/SLAVE LINES
MASTER/SLAVE LINES
27 VIN7
VIN2 5
FB2 6
BUCK REGULATOR 2
1A
BUCK REGULATOR 7
1A
MASTER/SLAVE LINES
24 VIN6
BUCK REGULATOR 3
1A
BUCK REGULATOR 6
1A
MASTER/SLAVE LINES
25 FB6
MASTER/SLAVE LINES
21 VIN5
VIN4 11
FB4 12
23 SW6
18 EN6
EN3 14
SW4 10
26 FB7
MASTER/SLAVE LINES
VIN3 8
FB3 7
28 SW7
33 EN7
EN2 37
SW3 9
31 FB8
32 EN8
EN1 38
SW2 4
29 SW8
BUCK REGULATOR 4
1A
BUCK REGULATOR 5
1A
EN4 13
22 SW5
20 FB5
19 EN5
MASTER/SLAVE LINES
GND (EXPOSED PAD)
39
3374 BD
3374fc
For more information www.linear.com/LTC3374
13
LTC3374
OPERATION
Buck Switching Regulators
The LTC3374 contains eight monolithic 1A synchronous
buck switching regulators. All of the switching regulators are internally compensated and need only external
feedback resistors to set the output voltage. The switching regulators offer two operating modes: Burst Mode
operation (when the MODE pin is set low) for higher
efficiency at light loads and forced continuous PWM mode
(when the MODE pin is set high) for lower noise at light
loads. The MODE pin collectively sets the operating mode
for all enabled buck switching regulators. In Burst Mode
operation at light loads, the output capacitor is charged
to a voltage slightly higher than its regulation point. The
regulator then goes into sleep mode, during which time
the output capacitor provides the load current. In sleep
most of the regulator’s circuitry is powered down, helping
conserve input power. When the output capacitor droops
below its programmed value, the circuitry is powered on
and another burst cycle begins. The sleep time decreases
as load current increases. In Burst Mode operation, the
regulator will burst at light loads whereas at higher loads
it will operate at constant frequency PWM mode operation.
In forced continuous mode, the oscillator runs continuously and the buck switch currents are allowed to reverse
under very light load conditions to maintain regulation.
This mode allows the buck to run at a fixed frequency with
minimal output ripple.
Each buck switching regulator has its own VIN, SW, FB
and EN pins to maximize flexibility. The enable pins have
two different enable threshold voltages that depend on
the operating state of the LTC3374. With all regulators
disabled, the enable pin threshold is set to 730mV (typical).
Once any regulator is enabled, the enable pin thresholds
of the remaining regulators are set to a bandgap-based
400mV and the EN pins are each monitored by a precision
comparator. This precision EN threshold may be used to
provide event-based sequencing via feedback from other
previously enabled regulators. All buck regulators have
forward and reverse-current limiting, soft-start to limit
inrush current during start-up, and short-circuit protection.
14
The buck switching regulators are phased in 90° steps to
reduce noise and input ripple. The phase step determines
the fixed edge of the switching sequence, which is when
the PMOS turns on. The PMOS off (NMOS on) phase
is subject to the duty cycle demanded by the regulator.
Bucks 1 and 2 are set to 0°, bucks 3 and 4 are set to 90°,
bucks 5 and 6 are set to 180°, and bucks 7 and 8 are set
to 270°. In shutdown all SW nodes are high impedance.
The buck regulator enable pins may be tied to VOUT voltages, through a resistor divider, to program power-up
sequencing.
Buck Regulators with Combined Power Stages
Up to four adjacent buck regulators may be combined
in a master-slave configuration by connecting their SW
pins together, connecting their VIN pins together, and
connecting the higher numbered bucks’ FB pin(s) to the
input supply. The lowest numbered buck is always the
master. In Figure 1, buck regulator 1 is the master. The
feedback network connected to the FB1 pin programs
the output voltage to 1.2V. The FB2 pin is tied to VIN1-2,
which configures buck regulator 2 as the slave. The SW1
and SW2 pins must be tied together, as must the VIN1
and VIN2 pins. The slave buck control circuitry draws no
current. The enable of the master buck (EN1) controls the
VIN
L1
VIN1
SW1
COUT
BUCK REGULATOR 1
(MASTER)
EN1
VOUT
1.2V
2A
400k
FB1
800k
VIN
VIN2
SW2
BUCK REGULATOR 2
(SLAVE)
FB2
EN2
VIN
3374 F01
Figure 1. Buck Regulators Configured as Master-Slave
3374fc
For more information www.linear.com/LTC3374
LTC3374
OPERATION
operation of the combined bucks; the enable of the slave
regulator (EN2) must be tied to ground.
Any combination of 2, 3, or 4 adjacent buck regulators
may be combined to provide either 2A, 3A, or 4A of average output load current. For example, buck regulator 1
and buck regulator 2 may run independently, while buck
regulators 3 and 4 may be combined to provide 2A, while
buck regulators 5 through 8 may be combined to provide
4A. Buck regulator 1 is never a slave, and buck regulator
8 is never a master. 15 unique output power stage configurations are possible to maximize application flexibility.
Power Failure Reporting Via PGOOD_ALL Pin
Power failure conditions are reported back via the
PGOOD_ALL pin. All buck switching regulators have an
internal power good (PGOOD) signal. When the regulated
output voltage of an enabled switcher rises above 93.5%
of its programmed value, the PGOOD signal will transition
high. When the regulated output voltage falls below
92.5% of its programmed value, the PGOOD signal is
pulled low. If any internal PGOOD signal stays low for
greater than 100µs, then the PGOOD_ALL pin is pulled
low, indicating to a microprocessor that a power failure
fault has occurred. The 100µs filter time prevents the pin
from being pulled low due to a transient.
An error condition that pulls the PGOOD_ALL pin low
is not latched. When the error condition goes away, the
PGOOD_ALL pin is released and is pulled high if no other
error condition exists. If no buck switching regulators are
enabled, then PGOOD_ALL will be pulled low.
Temperature Monitoring and Overtemperature
Protection
To prevent thermal damage to the LTC3374 and its surrounding components, the LTC3374 incorporates an
overtemperature (OT) function. When the LTC3374 die
temperature reaches 165°C (typical) all enabled buck
switching regulators are shut down and remain in shutdown
until the die temperature falls to 155°C (typical).
The temperature may be read back by the user by sampling
the TEMP pin analog voltage. The temperature, T, indicated
by the TEMP pin voltage is given by:
T=
VTEMP +19mV
•1°C
6.75mV
(1)
If none of the buck switching regulators are enabled, then
the temperature monitor is shut down to further reduce
quiescent current.
Programming the Operating Frequency
Selection of the operating frequency is a trade-off between
efficiency and component size. High frequency operation
allows the use of smaller inductor and capacitor values.
Operation at lower frequencies improves efficiency by
reducing internal gate charge losses but requires larger
inductance values and/or capacitance to maintain low
output voltage ripple.
The operating frequency for all of the LTC3374 regulators
is determined by an external resistor that is connected
between the RT pin and ground. The operating frequency
can be calculated by using the following equation:
8 •1011 • ΩHz
fOSC =
RT
(2)
While the LTC3374 is designed to function with operating frequencies between 1MHz and 3MHz, it has safety
clamps that will prevent the oscillator from running faster
than 4MHz (typical) or slower than 250kHz (typical). Tying
the RT pin to VCC sets the oscillator to the default internal
operating frequency of 2MHz (typical).
The LTC3374’s internal oscillator can be synchronized
through an internal PLL circuit, to an external frequency
by applying a square wave clock signal to the SYNC pin.
During synchronization, the top MOSFET turn-on of buck
switching regulators 1 and 2 are locked to the rising edge
of the external frequency source. All other buck switching
3374fc
For more information www.linear.com/LTC3374
15
LTC3374
OPERATION
regulators are locked to the appropriate phase of the external frequency source (see Buck Switching Regulators).
The synchronization frequency range is 1MHz to 3MHz.
After detecting an external clock on the first rising edge of
the SYNC pin, the PLL starts up at the current frequency
being programmed by the RT pin. The internal PLL then
requires a certain number of periods to gradually settle
until the frequency at SW matches the frequency and
phase of SYNC.
16
When the external clock is removed the LTC3374 needs
approximately 5µs to detect the absence of the external
clock. During this time, the PLL will continue to provide
clock cycles before it recognizes the lack of a SYNC input.
Once the external clock removal has been identified, the
oscillator will gradually adjust its operating frequency to
match the desired frequency programmed at the RT pin.
SYNC should be connected to ground if not used.
3374fc
For more information www.linear.com/LTC3374
LTC3374
APPLICATIONS INFORMATION
Buck Switching Regulator Output Voltage
and Feedback Network
Combined Buck Regulators
The output voltage of the buck switching regulators is
programmed by a resistor divider connected from the
switching regulator’s output to its feedback pin and is
given by VOUT = VFB(1 + R2/R1) as shown in Figure 2.
Typical values for R1 range from 40k to 1M. The buck
regulator transient response may improve with optional
capacitor CFF that helps cancel the pole created by the
feedback resistors and the input capacitance of the FB
pin. Experimentation with capacitor values between 2pF
and 22pF may improve transient response.
VOUT
BUCK
SWITCHING
REGULATOR
R2
FB
CFF
+
COUT
(OPTIONAL)
R1
3374 F02
Figure 2. Feedback Components
A single 2A buck regulator is available by combining two
adjacent 1A buck regulators together. Likewise a 3A or 4A
buck regulator is available by combining any three or four
adjacent buck regulators respectively. Tables 2, 3, and 4
show recommended inductors for these configurations.
The input supply needs to be decoupled with a 22µF capacitor while the output needs to be decoupled with a 47µF
capacitor for a 2A combined buck regulator. Likewise for
3A and 4A configurations the input and output capacitance
must be scaled up to account for the increased load. Refer
to the Capacitor Selection section for details on selecting
a proper capacitor.
In many cases, any extra unused buck converters may be
used to increase the efficiency of the active regulators.
In general the efficiency will improve for any regulators
running close to their rated load currents. If there are
unused regulators, the user should look at their specific
applications and current requirements to decide whether
to add extra stages.
Input and Output Decoupling Capacitor Selection
Buck Regulators
All eight buck regulators are designed to be used with
inductors ranging from 1µH to 3.3µH depending on the
lowest switching frequency that the buck regulator must
operate at. To operate at 1MHz a 3.3µH inductor should
be used, while to operate at 3MHz a 1µH inductor may be
used. Table 1 shows some recommended inductors for
the buck regulators.
The input supply needs to be decoupled with a 10µF
capacitor while the output needs to be decoupled with a
22µF capacitor. Refer to the Capacitor Selection section
for details on selecting a proper capacitor.
The LTC3374 has individual input supply pins for each
buck switching regulator and a separate VCC pin that
supplies power to all top level control and logic. Each of
these pins must be decoupled with low ESR capacitors
to GND. These capacitors must be placed as close to
the pins as possible. Ceramic dielectric capacitors are a
good compromise between high dielectric constant and
stability versus temperature and DC bias. Note that the
capacitance of a capacitor deteriorates at higher DC bias.
It is important to consult manufacturer data sheets and
obtain the true capacitance of a capacitor at the DC bias
voltage it will be operated at. For this reason, avoid the
use of Y5V dielectric capacitors. The X5R/X7R dielectric
capacitors offer good overall performance.
The input supply voltage Pins 2/5, 5/8, 8/11, 11/14, 21/24,
24/27, 27/30, 30/33, and 35/38 (QFN/TSSOP packages)
all need to be decoupled with at least 10µF capacitors.
3374fc
For more information www.linear.com/LTC3374
17
LTC3374
APPLICATIONS INFORMATION
Table 1. Recommended Inductors for 1A Buck Regulators
L (µH)
MAX IDC (A)
MAX DCR (mΩ)
SIZE IN mm (L × W × H)
1.0
3
38
3 × 3.6 × 1.2
1239AS-H-1R0N
1
2.5
65
2.5 × 2.0 × 1.2
XFL4020-222ME
2.2
3.5
23.5
4 × 4 × 2.1
1277AS-H-2R2N
2.2
2.6
84
3.2 × 2.5 × 1.2
IHLP1212BZER2R2M-11
2.2
3
46
3 × 3.6 × 1.2
XFL4020-332ME
3.3
2.8
38.3
4 × 4 × 2.1
IHLP1212BZER3R3M-11
3.3
2.7
61
3 × 3.6 × 1.2
SIZE IN mm (L × W × H)
PART NUMBER
IHLP1212ABER1R0M-11
MANUFACTURER
Vishay
Toko
CoilCraft
Toko
Vishay
CoilCraft
Vishay
Table 2. Recommended Inductors for 2A Buck Regulators
PART NUMBER
L (µH)
MAX IDC (A)
MAX DCR (mΩ)
XFL4020-102ME
1.0
5.1
11.9
4 × 4 × 2.1
1
5
27
4.45 × 4.06 × 1.8
XAL4020-222ME
2.2
5.6
38.7
4 × 4 × 2.1
FDV0530-2R2M
2.2
5.3
15.5
6.2 × 5.8 × 3
IHLP2020BZER2R2M-11
2.2
5
37.7
5.49 × 5.18 × 2
XAL4030-332ME
3.3
5.5
28.6
4 × 4 × 3.1
FDV0530-3R3M
3.3
4.1
34.1
6.2 × 5.8 × 3
74437324010
MANUFACTURER
CoilCraft
Wurth Elektronik
CoilCraft
Toko
Vishay
CoilCraft
Toko
Table 3. Recommended Inductors for 3A Buck Regulators
L (µH)
MAX IDC (A)
MAX DCR (mΩ)
SIZE IN mm (L × W × H)
1.0
8.7
14.6
4 × 4 × 2.1
FDV0530-1R0M
1
8.4
11.2
6.2 × 5.8 × 3
XAL5030-222ME
2.2
9.2
14.5
5.28 × 5.48 × 3.1
IHLP2525CZER2R2M-01
2.2
8
20
6.86 × 6.47 × 3
74437346022
2.2
6.5
20
7.3 × 6.6 × 2.8
XAL5030-332ME
3.3
8.7
23.3
5.28 × 5.48 × 3.1
SPM6530T-3R3M
3.3
7.3
27
7.1 × 6.5 × 3
PART NUMBER
XAL4020-102ME
MANUFACTURER
CoilCraft
Toko
CoilCraft
Vishay
Wurth Elektonik
CoilCraft
TDK
Table 4. Recommended Inductors for 4A Buck Regulators
L (µH)
MAX IDC (A)
MAX DCR (mΩ)
SIZE IN mm (L × W × H)
1.2
12.5
9.4
5.28 × 5.48 × 3.1
1
14.1
7.81
7.1 × 6.5 × 3
XAL5030-222ME
2.2
9.2
14.5
5.28 × 5.48 × 3.1
SPM6530T-2R2M
2.2
8.4
19
7.1 × 6.5 × 3
IHLP2525EZER2R2M-01
2.2
13.6
20.9
6.86 × 6.47 × 5
XAL6030-332ME
3.3
8
20.81
6.36 × 6.56 × 3.1
FDVE1040-3R3M
3.3
9.8
10.1
11.2 × 10 × 4
PART NUMBER
XAL5030-122ME
SPM6530T-1R0M120
18
MANUFACTURER
CoilCraft
TDK
CoilCraft
TDK
Vishay
CoilCraft
Toko
3374fc
For more information www.linear.com/LTC3374
LTC3374
APPLICATIONS INFORMATION
PCB Considerations
When laying out the printed circuit board, the following
list should be followed to ensure proper operation of the
LTC3374:
1. The exposed pad of the package (Pin 39) should connect
directly to a large ground plane to minimize thermal and
electrical impedance.
2. All the input supply pins should each have a decoupling
capacitor.
3. The connections to the switching regulator input supply
pins and their respective decoupling capacitors should
be kept as short as possible. The GND side of these
capacitors should connect directly to the ground plane
of the part. These capacitors provide the AC current
to the internal power MOSFETs and their drivers. It is
important to minimize inductance from these capacitors
to the VIN pins of the LTC3374.
4. The switching power traces connecting SW1, SW2, SW3,
SW4, SW5, SW6, SW7, and SW8 to their respective
inductors should be minimized to reduce radiated EMI
and parasitic coupling. Due to the large voltage swing
of the switching nodes, high input impedance sensitive
nodes, such as the feedback nodes, should be kept far
away or shielded from the switching nodes or poor
performance could result.
5. The GND side of the switching regulator output capacitors should connect directly to the thermal ground plane
of the part. Minimize the trace length from the output
capacitor to the inductor(s)/pin(s).
6. In a combined buck regulator application the trace length
of switch nodes to the inductor must be kept equal to
ensure proper operation.
3374fc
For more information www.linear.com/LTC3374
19
LTC3374
APPLICATIONS INFORMATION
3.3V TO 5.5V
10µF 3.3V
1A
2.2µH
22µF
VIN8
VIN1
SW1
SW8
FB1
FB8
1.02M
806k
324k
3.0V TO 5.5V
10µF 3.0V
1A
2.2µH
22µF
2.25V TO 5.5V
2.2µH
22µF
1.8V
1A
10µF
1.5V
1A
10µF
1.2V
1A
10µF
1.0V
1A
10µF
649k
VIN2
VIN7
SW2
SW7
FB2
FB7
2.25V TO 5.5V
2.2µH
1.0M
715k
365k
22µF
806k
LTC3374
2.5V TO 5.5V
10µF 2.5V
1A
2.2µH
22µF
VIN3
VIN6
SW3
SW6
FB3
FB6
1.02M
232k
475k
2.25V TO 5.5V
10µF 2.0V
1A
2.2µH
22µF
VIN4
VIN5
SW4
SW5
FB4
FB5
2.25V TO 5.5V
2.2µH
255k
665k
22µF
1.02M
EN1
EN2
EN3
EN4
EN5
EN6
EN7
EN8
SYNC
MODE
RT
402k
22µF
464k
1.0M
MICROPROCESSOR
CONTROL
2.25V TO 5.5V
2.2µH
VCC
2.7V TO 5.5V
10µF
PGOOD_ALL
TEMP
EXPOSED PAD
MICROPROCESSOR
CONTROL
3374 F03
Figure 3. Detailed Front Page Application
20
3374fc
For more information www.linear.com/LTC3374
LTC3374
APPLICATIONS INFORMATION
VIN
5.5V TO 36V
CIN
22µF
100k
INTVCC
VIN
INTVCC
2.2µF
PGOOD
PLLIN/MODE
LTC2955TS8-1
VIN
EN
KILL
INT
PB
MICROPROCESSOR
CONTROL
ILIM
PGND
470pF
FREQ
34.8k
0.1µF
1M
ITH
SENSE+
–
TRACK/SS SENSE
EXTVCC
SGND
VFB
22µF
2.5V
1A
22µF
5V
6A
100k
MTOP, MBOT: Si7850DP
L1 COILCRAFT SER1360-802KL
COUT: SANYO 10TPE330M
D1: DFLS1100
19.1k
VIN8
SW1
SW8
FB1
FB8
10µF
2.2µH
324k
2.2µH
COUT
330µF
1nF
324k
649k
10µF
RSENSE
7mΩ
MBOT
BG
VIN1
2.2µH
L1
8µH
SW
SGND
10µF
MTOP
0.1µF
LTC3891
RUN
BOOST
TMR GND ON
1.2V
1A
D1
TG
22µF
1.2V
1A
649k
VIN2
VIN7
SW2
SW7
10µF
2.2µH
665k
665k
FB2
2.5V
1A
22µF
FB7
309k
309k
LTC3374
10µF
1.8V
1A
2.2µH
22µF
VIN3
VIN6
SW3
SW6
10µF
2.2µH
590k
590k
FB3
FB6
475k
1.6V
1A
475k
VIN4
10µF
2.2µH
22µF
VIN5
SW4
SW5
10µF
2.2µH
511k
511k
FB4
511k
MODE
SYNC
EN1
EN2
EN3
EN4
EN5
EN6
EN7
EN8
RT
402k
1.6V
1A
22µF
FB5
511k
MICROPROCESSOR
CONTROL
1.8V
1A
22µF
VCC
PGOOD_ALL
TEMP
10µF
MICROPROCESSOR
CONTROL
EXPOSED PAD
3374 F04
Figure 4. Buck Regulators with Sequenced Start-Up Driven from a High Voltage Upstream Buck Converter
3374fc
For more information www.linear.com/LTC3374
21
LTC3374
APPLICATIONS INFORMATION
2.7V TO 5.5V
10µF
2.5V
4A
2.2µH
100µF
665k
VIN1
VIN6
SW1
SW2
SW3
SW4
FB1
SW8
SW7
SW6
2.2µH
324k
10µF
FB6
309k
10µF
68µF
1.2V
3A
649k
VIN2
VIN7
FB2
FB7
10µF
LTC3374
10µF
10µF
VIN3
VIN8
FB3
FB8
VIN4
VIN5
SW5
10µF
2.2µH
511k
FB4
EN1
EN5
EN6
SYNC
MODE
10µF
FB5
511k
EN2
EN3
EN4
EN7
EN8
MICROPROCESSOR
CONTROL
22µF
1.6V
1A
VCC
PGOOD_ALL
TEMP
10µF
MICROPROCESSOR
CONTROL
RT
EXPOSED PAD
3374 F05
Figure 5. Combined Buck Regulators with Common Input Supply
22
3374fc
For more information www.linear.com/LTC3374
LTC3374
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/product/LTC3374#packaging for the most recent package drawings.
UHF Package
38-Lead Plastic QFN (5mm × 7mm)
(Reference LTC DWG # 05-08-1701 Rev C)
0.70 ± 0.05
5.50 ± 0.05
5.15 ± 0.05
4.10 ± 0.05
3.00 REF
3.15 ± 0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
5.5 REF
6.10 ± 0.05
7.50 ± 0.05
RECOMMENDED SOLDER PAD LAYOUT
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
0.75 ± 0.05
5.00 ± 0.10
PIN 1 NOTCH
R = 0.30 TYP OR
0.35 × 45° CHAMFER
3.00 REF
37
0.00 – 0.05
38
0.40 ±0.10
PIN 1
TOP MARK
(SEE NOTE 6)
1
2
5.15 ± 0.10
5.50 REF
7.00 ± 0.10
3.15 ± 0.10
(UH) QFN REF C 1107
0.200 REF 0.25 ± 0.05
0.50 BSC
R = 0.125
TYP
R = 0.10
TYP
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE
OUTLINE M0-220 VARIATION WHKD
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
3374fc
For more information www.linear.com/LTC3374
23
LTC3374
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/product/LTC3374#packaging for the most recent package drawings.
FE Package
38-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1772 Rev C)
Exposed Pad Variation AA
4.75 REF
38
9.60 – 9.80*
(.378 – .386)
4.75 REF
(.187)
20
6.60 ±0.10
4.50 REF
2.74 REF
SEE NOTE 4
6.40
2.74
REF (.252)
(.108)
BSC
0.315 ±0.05
1.05 ±0.10
0.50 BSC
RECOMMENDED SOLDER PAD LAYOUT
4.30 – 4.50*
(.169 – .177)
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN MILLIMETERS
(INCHES)
3. DRAWING NOT TO SCALE
24
1
0.25
REF
19
1.20
(.047)
MAX
0° – 8°
0.50
(.0196)
BSC
0.17 – 0.27
(.0067 – .0106)
TYP
0.05 – 0.15
(.002 – .006)
FE38 (AA) TSSOP REV C 0910
4. RECOMMENDED MINIMUM PCB METAL SIZE
FOR EXPOSED PAD ATTACHMENT
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
3374fc
For more information www.linear.com/LTC3374
LTC3374
REVISION HISTORY
REV
DATE
DESCRIPTION
A
11/13
Modified Figure 5 – removed a resistor.
PAGE NUMBER
22
B
06/15
Modified Typical Application circuit
1
Changed part marking on TSSOP package
3
Changed typical specifications: RPMOS and RNMOS
4
Added conditions for VPGOOD specifications
C
10/15
4
Modified various curves
8, 9
Modified Temperature Monitoring section
15
Modified 2A inductor table
18
Added Related Parts
26
Added Note 6 to tSS specification
4, 5
Modified conditions graphs G27, G28
9
3374fc
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection
of its circuits
as described
herein will not infringe on existing patent rights.
For more
information
www.linear.com/LTC3374
25
LTC3374
TYPICAL APPLICATION
Combined Bucks with 3MHz Switch Frequency and Sequenced Power Up
2.25V TO 5.5V
10µF
10µF
10µF
2V
3A
1µH
68µF
649k
VIN1
VIN8
FB8
VIN2
FB2
VIN7
VIN3
FB3
SW7
SW8
SW1
SW2
SW3
FB7
1.2V
1A
VIN6
FB6
VIN4
VIN5
10µF
1µH
SW5
SW6
SW4
324k
FB4
10µF
1.02M
47µF
2.5V
2A
FB5
475k
VCC
PGOOD_ALL
MICROPROCESSOR
CONTROL
3.3V
2A
2.5V TO 5.5V
10µF
649k
2.7V TO 5.5V
47µF
324k
1µH
22µF
1.02M
LTC3374
FB1
10µF
10µF
1µH
432k
2.25V TO 5.5V
3.3V TO 5.5V
10µF
TEMP
SYNC
MODE
EN1
EN4
EN5
EN7
RT
267k
EXPOSED PAD
EN2
EN3
EN6
EN8
3374 TA02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC3370/
LTC3371
4-Channel Configurable DC/DC 4 Synchronous Buck Regulators with 8 × 1A Power Stages. Can Connect Up to Four Power Stages
with 8 × 1A Power Stages
in Parallel to Make a Single Inductor, High Current Output (4A Maximum), 8 Output Configurations
Possible, Precision PGOODALL Indication (LTC3370) or Precision RST Monitoring with Windowed
Watchdog Timer (CT Programmable, LTC3371), 38-Lead (5mm × 7mm × 0.75mm) QFN and TSSOP
Packages (LTC3371) and 32-Lead (5mm × 5mm × 0.75mm) QFN Package (LTC3371).
LTC3589
8-Output Regulator with
Sequencing and I2C
Triple I2C Adjustable High Efficiency Step-Down DC/DC Converters: 1.6A, 1A, 1A. High Efficiency 1.2A
Buck-Boost DC/DC Converter, Triple 250mA LDO Regulators. Pushbutton On/Off Control with System
Reset, Flexible Pin-Strap Sequencing Operation. I2C and Independent Enable Control Pins, Dynamic
Voltage Scaling and Slew Rate Control. Selectable 2.25MHz or 1.12MHz Switching Frequency, 8µA
Standby Current, 40-Pin 6mm × 6mm × 0.75mm QFN.
LTC3675
7-Channel Configurable High
Power PMIC
Four Monolithic Synchronous Buck DC/DCs (1A/1A/500mA/500mA). Buck DC/DCs Can Be Paralleled
to Deliver Up to 2× Current with a Single Inductor. Independent 1A Boost and 1A Buck-Boost DC/DCs,
Dual String I2C Controlled 40V LED Driver. I2C Programmable Output Voltage, Operating Mode, and
Switch Node Slew Rate for All DC/DCs. I2C Read Back of DC/DC, LED Driver, Fault Status, Pushbutton
On/Off/Reset, Always-On 25mA LDO. Low Quiescent Current: 16µA (All DC/DCs Off), 4mm × 7mm ×
0.75mm 44-Lead QFN Package.
LTC3375
8-Channel Programmable
Configurable 1A DC/DC
8 × 1A Synchronous Buck Regulators. Can Connect Up to Four Power Stages in Parallel to Make
a Single Inductor, High Current Output (4A Maximum), 15 Output Configurations Possible,
7mm × 7mm QFN-48 Package
26 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTC3374
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LTC3374
3374fc
LT 1015 REV C • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2013
工商网监
湘ICP备2023018690号
