LTC3374
1
3374fc
For more information www.linear.com/LTC3374
TYPICAL APPLICATION
FEATURES DESCRIPTION
8-Channel Parallelable
1A Buck DC/DCs
The LT C
®
3374 is a high efficiency multioutput power sup-
ply IC. The DC/DCs consist of eight synchronous buck
converters (1A each) all powered from independent 2.25V
to 5.5V input supplies.
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 reli-
able power-up sequencing. The LTC3374 is available in a
compact 38-lead 5mm × 7mm QFN package as well as a
38-lead TSSOP package.
8-Channel 1A Multioutput Buck Regulator
Buck Efficiency vs ILOAD
APPLICATIONS
n 8-Channel Independent Step-Down DC/DCs
n Master-Slave Configurable for Up to 4A per Output
Rail with a Single Inductor
n Independent VIN Supplies for Each DC/DC
(2.25V to 5.5V)
n All DC/DCs Have 0.8V to VIN Output Range
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
n General Purpose Multichannel Power Supplies
n Industrial/Automotive/Communications
L, LT , LT C , LT M , 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.
0.8V TO V
IN1
UP TO 1A
BUCK1
2.7V TO 5.5V
VIN1
BUCK2
VIN2
BUCK7
VIN7
BUCK8
VIN8
VCC
0.8V TO V
IN2
UP TO 1A
SLAVE
MASTER
SLAVE
MASTER
SLAVE
MASTER
EN1
EN2
EN3
EN4
EN5
EN6
EN7
EN8
PGOOD_ALL
TEMP
MODE
SYNC
0.8V TO V
IN7
UP TO 1A
0.8V TO V
IN8
UP TO 1A
RT
LTC3374
3374 TA01a
•
•
•
2.2µH
22µF
2.2µH
22µF
2.2µH
10µF
2.2µH
10µF
LOAD CURRENT (mA)
0
0
EFFICIENCY (%)
10
30
40
50
100
70
1000 2000
3374 TA01b
20
80
90
60
3000 4000
FORCED CONTINUOUS MODE
VIN = 3.3V, VOUT = 1.8V
fOSC = 1MHz, L = 3.3µH
1A BUCK
2A BUCK
3A BUCK
4A BUCK
LTC3374
2
3374fc
For more information www.linear.com/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
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
LTC3374
3
3374fc
For more information www.linear.com/LTC3374
PIN CONFIGURATION
ABSOLUTE MAXIMUM RATINGS
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
(Note 1)
13 14 15 16
TOP VIEW
39
GND
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
17 18 19
38 37 36 35 34 33 32
24
25
26
27
28
29
30
31
8
7
6
5
4
3
2
1FB1
VIN1
SW1
SW2
VIN2
FB2
FB3
VIN3
SW3
SW4
VIN4
FB4
FB8
VIN8
SW8
SW7
VIN7
FB7
FB6
VIN6
SW6
SW5
VIN5
FB5
EN1
EN2
TEMP
VCC
MODE
EN7
EN8
EN4
EN3
PGOOD_ALL
SYNC
RT
EN6
EN5
23
22
21
20
9
10
11
12
TJMAX = 150°C, θJA = 34°C/W
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
TOP VIEW
FE PACKAGE
38-LEAD PLASTIC TSSOP
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
TEMP
EN2
EN1
FB1
VIN1
SW1
SW2
VIN2
FB2
FB3
VIN3
SW3
SW4
VIN4
FB4
EN4
EN3
PGOOD_ALL
SYNC
VCC
MODE
EN7
EN8
FB8
VIN8
SW8
SW7
VIN7
FB7
FB6
VIN6
SW6
SW5
VIN5
FB5
EN5
EN6
RT
39
GND
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 LT C 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.
Operating Junction Temperature Range
(Notes 2, 3) ............................................ –40°C to 150°C
Storage Temperature Range .................. –65°C to 150°C
LTC3374
4
3374fc
For more information www.linear.com/LTC3374
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.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VVCC VCC Voltage Range l2.7 5.5 V
VVCC_UVLO Undervoltage Threshold on VCC VCC Voltage Falling
VCC Voltage Rising
l
l
2.35
2.45
2.45
2.55
2.55
2.65
V
V
IVCC_ALLOFF VCC Input Supply Current All Switching Regulators in Shutdown 8 18 µA
IVCC VCC Input Supply Current At Least 1 Buck Active
SYNC = 0V, RT = 400k, VFB_BUCK = 0.85V
SYNC = 2MHz
45
200
75
275
µA
µA
fOSC Internal Oscillator Frequency VRT = VCC, SYNC = 0V
VRT = VCC, SYNC = 0V
RRT = 400k, SYNC = 0V
l
l
1.8
1.75
1.8
2
2
2
2.2
2.25
2.2
MHz
MHz
MHz
fSYNC Synchronization Frequency tLOW, tHIGH > 40ns 1 3 MHz
VSYNC SYNC Level High
SYNC Level Low
l
l
1.2
0.4
V
V
VRT RT Servo Voltage RRT = 400k l780 800 820 mV
Temperature Monitor
VTEMP(ROOM) TEMP Voltage at 25°C 150 mV
∆VTEMP/°C VTEMP Slope 6.75 mV/°C
OT Overtemperature Shutdown Temperature Rising 165 °C
OT Hyst Overtemperature Hysteresis 10 °C
1A Buck Regulators
VBUCK Buck Input Voltage Range l2.25 5.5 V
VOUT Buck Output Voltage Range VFB VIN V
VIN_UVLO Undervoltage Threshold on VIN VIN Voltage Falling
VIN Voltage Rising
l
l
1.95
2.05
2.05
2.15
2.15
2.25
V
V
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
18
400
0
1
50
550
1
2
µA
µA
µA
µA
IFWD PMOS Current Limit (Note 5) 2.0 2.3 2.7 A
VFB Feedback Regulation Voltage l780 800 820 mV
IFB Feedback Leakage Current VFB_BUCK = 0.85V –50 50 nA
DMAX Maximum Duty Cycle VFB_BUCK = 0V l100 %
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
tSS Soft-Start Time (Note 6) l0.25 1 3 ms
VPGOOD(FALL) Falling PGOOD Threshold Voltage % of Regulated VFB 92.5 %
VPGOOD(HYS) PGOOD Hysteresis % of Regulated VFB 1 %
Buck Regulators Combined
IFWD2PMOS Current Limit 2 Buck Converters Combined (Note 5) 4.6 A
IFWD3PMOS Current Limit 3 Buck Converters Combined (Note 5) 6.9 A
IFWD4PMOS Current Limit 4 Buck Converters Combined (Note 5) 9.2 A
LTC3374
5
3374fc
For more information www.linear.com/LTC3374
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.
ELECTRICAL CHARACTERISTICS
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.
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 1 µA
VOL Output Low Voltage PGOOD_ALL 3mA into Pin 0.1 0.4 V
VIH Input High Threshold MODE l1.2 V
VIL Input Low Threshold MODE l0.4 V
Interface Logic Pins (EN1, EN2, EN3, EN4, EN5, EN6, EN7, EN8)
VHI_ALLOFF Enable Rising Threshold All Regulators Disabled l400 730 1200 mV
VEN_HYS Enable Falling Hysteresis 60 mV
VHI Enable Rising Threshold At Least One Regulator Enabled l380 400 420 mV
IEN Enable Pin Leakage Current EN = VCC = VIN = 5.5V –1 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.
LTC3374
6
3374fc
For more information www.linear.com/LTC3374
TYPICAL PERFORMANCE CHARACTERISTICS
VCC Supply Current
vs Temperature
VCC Supply Current
vs Temperature
RT Programmed Oscillator
Frequency vs Temperature
Default Oscillator Frequency
vs Temperature Oscillator Frequency vs VCC
VCC Undervoltage Threshold
vs Temperature
Buck VIN Undervoltage Threshold
vs Temperature
VCC Supply Current
vs Temperature
TEMPERATURE (°C)
–50
UV THRESHOLD (V)
2.50
2.60
150
3374 G01
2.40
2.30 050 100
–25 25 75 125
2.70
2.45
2.55
2.35
2.65
VCC RISING
VCC FALLING
TEMPERATURE (°C)
–50
UV THRESHOLD (V)
2.10
2.20
150
3374 G02
2.00
1.90 050 100
–25 25 75 125
2.30
2.05
2.15
1.95
2.25
VIN RISING
VIN FALLING
TEMPERATURE (°C)
–50
IVCC_ALLOFF (µA)
30
45
50
150
3374 G03
25
20
0050 100
–25 25 75 125
10
60
55
40
35
15
5
ALL REGULATORS
IN SHUTDOWN
VCC = 5.5V
VCC = 2.7V
VCC = 3.3V
TEMPERATURE (°C)
–50
IVCC (µA)
100
150
3374 G04
50
0050 100
–25 25 75 125
25
125
75 VCC = 5.5V
VCC = 2.7V
AT LEAST ONE BUCK ENABLED
SYNC = 0V
FB = 850mV
VCC = 3.3V
TEMPERATURE (°C)
–50
fOSC (MHz)
1.95
2.10
150
3374 G06
1.85
1.80 050 100
–25 25 75 125
2.20
1.90
2.00
2.05
2.15
VCC = 5.5V
VCC = 3.3V
VCC = 2.7V
RRT = 402k
TEMPERATURE (°C)
–50
fOSC (MHz)
1.95
2.10
150
3374 G07
1.85
1.80 050 100
–25 25 75 125
2.20
1.90
2.00
2.05
2.15
VCC = 5.5V
VCC = 3.3V
VCC = 2.7V
VRT = VCC
VCC (V)
2.7
fOSC (MHz)
1.95
2.10
5.5
3374 G08
1.85
1.80 3.5 4.3 5.1
3.1 3.9 4.7
2.20
1.90
2.00
2.05
2.15
VRT = VCC
RRT = 402k
TEMPERATURE (°C)
–50
IVCC (µA)
320
280
150
3374 G05
160
120
0050 100
–25 25 75 125
80
40
400
360
240
200
VCC = 5.5V
VCC = 3.3V
VCC = 2.7V
AT LEAST ONE BUCK ENABLED
SYNC = 2MHz
LTC3374
7
3374fc
For more information www.linear.com/LTC3374
Oscillator Frequency vs RTEnable Threshold vs TemperatureVTEMP vs Temperature
TYPICAL PERFORMANCE CHARACTERISTICS
Buck VIN Supply Current
vs Temperature
Buck VIN Supply Current
vs Temperature
VOUT vs Temperature
Enable Pin Precision Threshold
vs Temperature
RRT (kΩ)
250
fOSC (MHz)
2.0
2.5
3.0
650 750700
3374 G09
1.5
1.0
0350 450 550
300 800
400 500 600
0.5
4.0
3.5
VCC = 3.3V
0
–200
VTEMP (mV)
0
400
1400
800
20 10080
200
1000
1200
600
40 60 120 140
ACTUAL VTEMP
IDEAL VTEMP
TEMPERATURE (°C)
3374 G10
TEMPERATURE (°C)
–50
400
EN THRESHOLD (mV)
450
550
600
650
900
750
050 75
3374 G11
500
800
850
700
–25 25 100 125 150
ALL REGULATORS DISABLED
VCC = 3.3V
EN RISING
EN FALLING
TEMPERATURE (°C)
–50
EN THRESHOLD (mV)
395
410
150
3374 G12
385
380 050 100
–25 25 75 125
420
390
400
405
415
EN RISING
EN FALLING
TEMPERATURE (°C)
–50
IVIN_BURST (µA)
40
150
3374 G13
10
01251007550250–25
50
20
30
Burst Mode OPERATION
FB = 850mV
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
TEMPERATURE (°C)
–50
IVIN_FORCED_CONTINUOUS (µA)
450
500
150
3374 G14
50
100
150
01251007550250–25
550
200
250
300
350
400
FORCED CONTINUOUS MODE
FB = 0V
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
TEMPERATURE (°C)
–50
VOUT (V)
1.84
1.86
150
3374 G15
1.72 1251007550250–25
1.88
1.74
1.76
1.78
1.80
1.82
FORCED CONTINUOUS MODE
ILOAD = 0mA
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
PMOS Current Limit
vs Temperature
TEMPERATURE (°C)
–50
IFWD (A)
2.5
150
3374 G16
2.1
2.2
2.0 1251007550250–25
2.6
2.3
2.4
VIN = 3.3V
LTC3374
8
3374fc
For more information www.linear.com/LTC3374
TYPICAL PERFORMANCE CHARACTERISTICS
2A Buck Efficiency vs ILOAD,
VOUT=2.5V
3A Buck Efficiency vs ILOAD,
VOUT=1.8V
3A Buck Efficiency vs ILOAD,
VOUT=2.5V
1A Buck Efficiency vs ILOAD,
VOUT=1.8V
1A Buck Efficiency vs ILOAD,
VOUT=2.5V
2A Buck Efficiency vs ILOAD,
VOUT=1.8V
LOAD CURRENT (mA)
1
40
EFFICIENCY (%)
50
60
70
80
10 100 1000
3374 G19
30
20
10
0
90
100 Burst Mode OPERATION
FORCED
CONTINUOUS
MODE
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
1
40
EFFICIENCY (%)
50
60
70
80
10 100 1000
3374 G20
30
20
10
0
90
100
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
1
40
EFFICIENCY (%)
50
60
70
80
10 100 1000
3374 G21
30
20
10
0
90
100
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
1
40
EFFICIENCY (%)
50
60
70
80
10 100 1000
3374 G22
30
20
10
0
90
100
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
1
40
EFFICIENCY (%)
50
60
70
80
10 100 1000
3374 G23
30
20
10
0
90
100
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
1
40
EFFICIENCY (%)
50
60
70
80
10 100 1000
3374 G24
30
20
10
0
90
100
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
PMOS RDS(ON) vs Temperature NMOS RDS(ON) vs Temperature
TEMPERATURE (°C)
0
25
50
75
100
125
150
150
200
250
300
350
400
450
500
550
R
DS(ON)
(mΩ)
3374 G17
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
TEMPERATURE (°C)
–50
–25
0
25
50
75
100
125
150
150
200
250
300
350
400
450
500
550
R
DS(ON)
(mΩ)
3374 G18
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
LTC3374
9
3374fc
For more information www.linear.com/LTC3374
4A Buck Efficiency vs ILOAD,
VOUT=1.8V
4A Buck Efficiency vs ILOAD,
VOUT=2.5V
1A Buck Efficiency vs Frequency
(Forced Continuous Mode)
TYPICAL PERFORMANCE CHARACTERISTICS
1A Buck Efficiency vs Frequency
(Forced Continuous Mode)
1A Buck Efficiency vs ILOAD
(Across Operating Frequency)
1A Buck Regulator Load Regulation
(Forced Continuous Mode)
4A Buck Regulator Load Regulation
(Forced Continuous Mode)
1A Buck Regulator Line Regulation
(Forced Continuous Mode)
LOAD CURRENT (mA)
1
40
EFFICIENCY (%)
50
60
70
80
10 100 1000
3374 G25
30
20
10
0
90
100
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
LOAD CURRENT (mA)
1
40
EFFICIENCY (%)
50
60
70
80
10 100 1000
3374 G26
30
20
10
0
90
100
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
FREQUENCY (MHz)
1
EFFICIENCY (%)
60
80
100
2.6
3374 G27
40
20
50
70
90
30
10
01.4 1.8 2.2
1.2 2.8
1.6 22.4 3
VIN = 5.5V
VIN = 3.3VVIN = 2.25V
VOUT = 1.8V
ILOAD = 100mA
L = 3.3µH
FREQUENCY (MHz)
1
EFFICIENCY (%)
60
80
100
2.6
3374 G28
40
20
50
70
90
30
10
01.4 1.8 2.2
1.2 2.8
1.6 22.4 3
ILOAD = 100mA
ILOAD = 500mA
ILOAD = 20mA
VOUT = 1.8V
VIN = 3.3V
L = 3.3µH
LOAD CURRENT (mA)
1
40
EFFICIENCY (%)
50
60
70
80
10 100 1000
3374 G29
30
20
10
0
90
100
Burst Mode
OPERATION FORCED
CONTINUOUS
MODE
VOUT = 1.8V
VIN = 3.3V
fOSC = 1MHz
L = 3.3µH
fOSC = 2MHz
L = 2.2µH
fOSC = 3MHz
L = 1µH
VIN = 5.5V
DROPOUT
VIN = 3.3V
VIN = 2.25V
LOAD CURRENT (mA)
1
VOUT (V)
1.800
1.812
1000
3374 G30
1.792
1.788
1.784
1.780 10010
1.820
1.796
1.804
1.808
1.816
fOSC = 2MHz
L = 2.2µH
VIN = 5.5V
VIN = 3.3V
VIN = 2.25V
LOAD CURRENT (mA)
1
VOUT (V)
1.800
1.812
1000
3374 G31
1.792
1.788
1.784
1.780 10010
1.820
1.796
1.804
1.808
1.816
fOSC = 2MHz
L = 2.2µH
DROPOUT
ILOAD = 100mA
ILOAD = 500mA
VIN (V)
2.25 2.75
VOUT (V)
1.810
5.254.25 4.75
3374 G32
1.790
1.785
1.780 3.753.25
1.820
1.795
1.800
1.805
1.815
fOSC = 2MHz
L = 2.2µH
LTC3374
10
3374fc
For more information www.linear.com/LTC3374
TYPICAL PERFORMANCE CHARACTERISTICS
1A Buck Regulator, Transient
Response (Forced Continuous
Mode)
4A Buck Regulator, Transient
Response (Forced Continuous
Mode)
4A Buck Regulator, Transient
Response (Burst Mode Operation)
VOUT
100mV/DIV
AC-COUPLED
0mA
50µs/DIV
LOAD STEP = 100mA TO 700mA
VIN = 3.3V
VOUT = 1.8V
3374 G36
INDUCTOR
CURRENT
200mA/DIV
VOUT
100mV/DIV
AC-COUPLED
0mA
50µs/DIV
LOAD STEP = 400mA TO 2.8A
VIN = 3.3V
VOUT = 1.8V
3374 G37
INDUCTOR
CURRENT
1A/DIV
VOUT
100mV/DIV
AC-COUPLED
0mA
50µs/DIV
LOAD STEP = 400mA TO 2.8A
VIN = 3.3V
VOUT = 1.8V
3374 G38
INDUCTOR
CURRENT
1A/DIV
1A Buck Regulator No-Load
Start-Up Transient (Burst Mode
Operation)
4A Buck Regulator No-Load
Start-Up Transient (Forced
Continuous Mode)
1A Buck Regulator, Transient
Response (Burst Mode Operation)
VOUT
500mV/DIV
EN 2V/DIV
200µs/DIVVIN = 3.3V 3374 G33
INDUCTOR
CURRENT
500mA/DIV
VOUT
500mV/DIV
EN 2V/DIV
200µs/DIVVIN = 3.3V 3374 G34
INDUCTOR
CURRENT
500mA/DIV
VOUT
100mV/DIV
AC-COUPLED
0mA
50µs/DIV
LOAD STEP = 100mA TO 700mA
VIN = 3.3V
VOUT = 1.8V
3374 G35
INDUCTOR
CURRENT
200mA/DIV
LTC3374
11
3374fc
For more information www.linear.com/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 regula-
tor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 regula-
tor 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. Open-
drain 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. Driv-
ing 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 switch-
ing 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 regula-
tor 5 with buck regulator 4 for higher current. Up to four
converters may be combined in this way.
LTC3374
12
3374fc
For more information www.linear.com/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.
SW5 (Pin 22/Pin 25): Buck Regulator 5 Switch Node.
External inductor connects to this pin.
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.
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 regula-
tor 6 with buck regulator 5 for higher current. Up to four
converters may be combined in this way.
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 regula-
tor 7 with buck regulator 6 for higher current. Up to four
converters may be combined in this way.
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.
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.
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 regula-
tor 8 with buck regulator 7 for higher current. Up to four
converters may be combined in this way.
EN8 (Pin 32/Pin 35): Buck Regulator 8 Enable Input.
Active high.
EN7 (Pin 33/Pin 36): Buck Regulator 7 Enable Input.
Active high.
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 continu-
ous mode.
VCC (Pin 35/Pin 38): Internal Bias Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
TEMP (Pin 36/Pin 1): Temperature Indication Pin. TEMP
outputs a voltage of 150mV (typical) at room tempera-
ture. 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.
LTC3374
13
3374fc
For more information www.linear.com/LTC3374
BLOCK DIAGRAM
(Pin numbers reflect QFN package)
13
39
EN4
12
FB4
10
SW4
11
VIN4
14
EN3
7
FB3
9
SW3
8
VIN3
37
EN2
6
FB2
4
SW2
MASTER/SLAVE LINES
MASTER/SLAVE LINES
MASTER/SLAVE LINES
MASTER/SLAVE LINES
GND (EXPOSED PAD)
MASTER/SLAVE LINES
MASTER/SLAVE LINES
MASTER/SLAVE LINES
5
VIN2
38
EN1
1
FB1
3
SW1
REF, CLK
8 PGOOD
2
19
20
22
21
18
25
23
24
33
26
28
27
32
31
29
30
VIN1
EN5
3374 BD
FB5
SW5
VIN5
EN6
FB6
SW6
VIN6
EN7
FB7
SW7
VIN7
EN8
FB8
SW8
VIN8
34 MODE
PGOOD_ALL
BUCK REGULATOR 4
1A
BUCK REGULATOR 3
1A
BUCK REGULATOR 2
1A
BUCK REGULATOR 1
1A
BUCK REGULATOR 5
1A
BUCK REGULATOR 6
1A
BUCK REGULATOR 7
1A
BUCK REGULATOR 8
1A
BANDGAP,
OSCILLATOR,
UV, OT
TEMP MONITOR
TOP LOGIC
17
RT
16
SYNC
36
TEMP
35
VCC 15
LTC3374
14
3374fc
For more information www.linear.com/LTC3374
OPERATION
Buck Switching Regulators
The LTC3374 contains eight monolithic 1A synchronous
buck switching regulators. All of the switching regula-
tors are internally compensated and need only external
feedback resistors to set the output voltage. The switch-
ing 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 continu-
ously 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.Figure 1. Buck Regulators Configured as Master-Slave
BUCK REGULATOR 1
(MASTER)
V
IN
V
IN
VIN
SW1
COUT
V
OUT
1.2V
2A
400k
L1
800k
FB1EN1
BUCK REGULATOR 2
(SLAVE)
SW2
EN2
VIN1
VIN2
FB2
3374 F01
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 volt-
ages, 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
LTC3374
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For more information www.linear.com/LTC3374
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 aver-
age 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 con-
figurations 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 sur-
rounding 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).
OPERATION
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 =
V
TEMP
+19mV
6.75mV
•1°C
(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:
fOSC =8 •1011 •ΩHz
R
T
(2)
While the LTC3374 is designed to function with operat-
ing 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
LTC3374
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OPERATION
regulators are locked to the appropriate phase of the ex-
ternal 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.
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.
LTC3374
17
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For more information www.linear.com/LTC3374
APPLICATIONS INFORMATION
Buck Switching Regulator Output Voltage
and Feedback Network
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.
Figure 2. Feedback Components
BUCK
SWITCHING
REGULATOR
VOUT
C
OUT
(OPTIONAL)
CFF
R2
R1
FB
3374 F02
+
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.
Combined Buck Regulators
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 capaci-
tor 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
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.
LTC3374
18
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For more information www.linear.com/LTC3374
APPLICATIONS INFORMATION
Table 1. Recommended Inductors for 1A Buck Regulators
PART NUMBER L (µH) MAX IDC (A) MAX DCR (mΩ) SIZE IN mm (L × W × H) MANUFACTURER
IHLP1212ABER1R0M-11 1.0 3 38 3 × 3.6 × 1.2 Vishay
1239AS-H-1R0N 1 2.5 65 2.5 × 2.0 × 1.2 Toko
XFL4020-222ME 2.2 3.5 23.5 4 × 4 × 2.1 CoilCraft
1277AS-H-2R2N 2.2 2.6 84 3.2 × 2.5 × 1.2 Toko
IHLP1212BZER2R2M-11 2.2 3 46 3 × 3.6 × 1.2 Vishay
XFL4020-332ME 3.3 2.8 38.3 4 × 4 × 2.1 CoilCraft
IHLP1212BZER3R3M-11 3.3 2.7 61 3 × 3.6 × 1.2 Vishay
Table 2. Recommended Inductors for 2A Buck Regulators
PART NUMBER L (µH) MAX IDC (A) MAX DCR (mΩ) SIZE IN mm (L × W × H) MANUFACTURER
XFL4020-102ME 1.0 5.1 11.9 4 × 4 × 2.1 CoilCraft
74437324010 1 5 27 4.45 × 4.06 × 1.8 Wurth Elektronik
XAL4020-222ME 2.2 5.6 38.7 4 × 4 × 2.1 CoilCraft
FDV0530-2R2M 2.2 5.3 15.5 6.2 × 5.8 × 3 Toko
IHLP2020BZER2R2M-11 2.2 5 37.7 5.49 × 5.18 × 2 Vishay
XAL4030-332ME 3.3 5.5 28.6 4 × 4 × 3.1 CoilCraft
FDV0530-3R3M 3.3 4.1 34.1 6.2 × 5.8 × 3 Toko
Table 3. Recommended Inductors for 3A Buck Regulators
PART NUMBER L (µH) MAX IDC (A) MAX DCR (mΩ) SIZE IN mm (L × W × H) MANUFACTURER
XAL4020-102ME 1.0 8.7 14.6 4 × 4 × 2.1 CoilCraft
FDV0530-1R0M 1 8.4 11.2 6.2 × 5.8 × 3 Toko
XAL5030-222ME 2.2 9.2 14.5 5.28 × 5.48 × 3.1 CoilCraft
IHLP2525CZER2R2M-01 2.2 8 20 6.86 × 6.47 × 3 Vishay
74437346022 2.2 6.5 20 7.3 × 6.6 × 2.8 Wurth Elektonik
XAL5030-332ME 3.3 8.7 23.3 5.28 × 5.48 × 3.1 CoilCraft
SPM6530T-3R3M 3.3 7.3 27 7.1 × 6.5 × 3 TDK
Table 4. Recommended Inductors for 4A Buck Regulators
PART NUMBER L (µH) MAX IDC (A) MAX DCR (mΩ) SIZE IN mm (L × W × H) MANUFACTURER
XAL5030-122ME 1.2 12.5 9.4 5.28 × 5.48 × 3.1 CoilCraft
SPM6530T-1R0M120 1 14.1 7.81 7.1 × 6.5 × 3 TDK
XAL5030-222ME 2.2 9.2 14.5 5.28 × 5.48 × 3.1 CoilCraft
SPM6530T-2R2M 2.2 8.4 19 7.1 × 6.5 × 3 TDK
IHLP2525EZER2R2M-01 2.2 13.6 20.9 6.86 × 6.47 × 5 Vishay
XAL6030-332ME 3.3 8 20.81 6.36 × 6.56 × 3.1 CoilCraft
FDVE1040-3R3M 3.3 9.8 10.1 11.2 × 10 × 4 Toko
LTC3374
19
3374fc
For more information www.linear.com/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 capaci-
tors 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.
LTC3374
20
3374fc
For more information www.linear.com/LTC3374
Figure 3. Detailed Front Page Application
LTC3374
EXPOSED PAD
2.2µH
VIN1
SW1
FB1
VIN8
SW8
FB8
3374 F03
2.2µH
806k
649k
1.02M
324k
10µF
3.3V TO 5.5V
1.8V
1A
3.3V
1A 22µF 22µF
10µF
2.25V TO 5.5V
2.2µH
VIN2
SW2
FB2
VIN7
SW7
FB7
2.2µH
715k
806k
1.0M
365k
10µF
3.0V TO 5.5V
1.5V
1A
3.0V
1A 22µF 22µF
10µF
2.25V TO 5.5V
2.2µH
VIN3
SW3
FB3
VIN6
SW6
FB6
2.2µH
232k
464k
1.02M
475k
10µF
2.5V TO 5.5V
1.2V
1A
2.5V
1A 22µF 22µF
10µF
2.25V TO 5.5V
2.2µH
VIN4
SW4
FB4
402k
RT
EN1
EN2
EN3
EN4
EN5
EN6
EN7
EN8
SYNC
MODE
VIN5
SW5
FB5
VCC
PGOOD_ALL
TEMP
MICROPROCESSOR
CONTROL
2.2µH
255k
1.02M
1.0M
665k
10µF
2.25V TO 5.5V
1.0V
1A
2.0V
1A 22µF 22µF
2.7V TO 5.5V
MICROPROCESSOR
CONTROL
10µF
2.25V TO 5.5V
10µF
APPLICATIONS INFORMATION
LTC3374
21
3374fc
For more information www.linear.com/LTC3374
APPLICATIONS INFORMATION
Figure 4. Buck Regulators with Sequenced Start-Up Driven from a High Voltage Upstream Buck Converter
LTC3374
EXPOSED PAD
2.2µH
VIN1
SW1
FB1
VIN8
SW8
FB8
3374 F04
2.2µH
324k
649k
324k
1M
649k
10µF
1.2V
1A
2.5V
1A
1.8V
1A
1.6V
1A
1.2V
1A
10µF
10µF
10µF 10µF
10µF
10µF
10µF
22µF 22µF
22µF
22µF
2.5V
1A
1.8V
1A
1.6V
1A
22µF
22µF
22µF
22µF
2.2µH
VIN2
SW2
FB2
VIN7
SW7
FB7
2.2µH
665k
309k
665k
309k
2.2µH
VIN3
SW3
FB3
VIN6
SW6
FB6
2.2µH
590k
475k
590k
475k
2.2µH
VIN4
SW4
FB4
402k
RT
EN1
EN2
EN3
EN4
EN5
EN6
EN7
EN8
VIN5
SW5
FB5
VCC
PGOOD_ALL
TEMP
2.2µH
511k
511k
511k
511k
MICROPROCESSOR
CONTROL
10µF
SYNC
MODE
0.1µF
CIN
22µF
V
IN
5.5V TO 36V
INTVCC
34.8k
470pF
100k
100k
MTOP, MBOT: Si7850DP
L1 COILCRAFT SER1360-802KL
COUT: SANYO 10TPE330M
D1: DFLS1100
19.1k
2.2µF
D1
0.1µF
FREQ
ITH
SGND
SGND
LTC3891
VIN
PGOOD
PLLIN/MODE
ILIM
INTVCC
PGND
L1
8µH RSENSE
7mΩ
BOOST
SW
BG
SENSE+
SENSE–
EXTVCC
VFB
TG MTOP
MBOT
1nF
COUT
330µF
5V
6A
TRACK/SS
RUN
VIN EN
KILL
INT
PB
TMR GND ON
LTC2955TS8-1
MICROPROCESSOR
CONTROL
MICROPROCESSOR
CONTROL
LTC3374
22
3374fc
For more information www.linear.com/LTC3374
APPLICATIONS INFORMATION
Figure 5. Combined Buck Regulators with Common Input Supply
LTC3374
EXPOSED PAD
2.2µH
VIN1
SW1
SW2
SW3
SW4
FB1
VIN6
SW8
SW7
SW6
FB6
3374 F05
2.2µH
324k
649k
665k
309k
1.2V
3A
2.5V
4A
2.7V TO 5.5V
100µF 68µF
10µF10µF
10µF
10µF
10µF
10µF
10µF
10µF
VIN2
FB2
VIN7
FB7
VIN3
FB3
VIN8
FB8
2.2µH
VIN4
FB4
RT
EN2
EN3
EN4
EN7
EN8
EN1
EN5
EN6
SYNC
MODE
VIN5
SW5
FB5
PGOOD_ALL
TEMP
VCC
MICROPROCESSOR
CONTROL
511k
511k
1.6V
1A
22µF
10µF
MICROPROCESSOR
CONTROL
LTC3374
23
3374fc
For more information www.linear.com/LTC3374
PACKAGE DESCRIPTION
5.00 ± 0.10
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE
OUTLINE M0-220 VARIATION WHKD
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
PIN 1
TOP MARK
(SEE NOTE 6)
37
1
2
38
BOTTOM VIEW—EXPOSED PAD
5.50 REF
5.15 ± 0.10
7.00
± 0.10
0.75 ± 0.05
R = 0.125
TYP
R = 0.10
TYP
0.25 ± 0.05
(UH) QFN REF C 1107
0.50 BSC
0.200 REF
0.00 – 0.05
RECOMMENDED SOLDER PAD LAYOUT
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
3.00 REF
3.15 ± 0.10
0.40 ±0.10
0.70 ± 0.05
0.50 BSC
5.5 REF
3.00 REF 3.15 ± 0.05
4.10 ± 0.05
5.50 ± 0.05 5.15 ± 0.05
6.10 ± 0.05
7.50 ± 0.05
0.25 ± 0.05
PACKAGE
OUTLINE
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
PIN 1 NOTCH
R = 0.30 TYP OR
0.35 × 45°
CHAMFER
UHF Package
38-Lead Plastic QFN (5mm × 7mm)
(Reference LTC DWG # 05-08-1701 Rev C)
Please refer to http://www.linear.com/product/LTC3374#packaging for the most recent package drawings.
LTC3374
24
3374fc
For more information www.linear.com/LTC3374
PACKAGE DESCRIPTION
4.75
(.187) REF
FE38 (AA) TSSOP REV C 0910
0.09 – 0.20
(.0035 – .0079)
0° – 8°
0.25
REF
0.50 – 0.75
(.020 – .030)
4.30 – 4.50*
(.169 – .177)
119
20
REF
9.60 – 9.80*
(.378 – .386)
38
1.20
(.047)
MAX
0.05 – 0.15
(.002 – .006)
0.50
(.0196)
BSC 0.17 – 0.27
(.0067 – .0106)
TYP
RECOMMENDED SOLDER PAD LAYOUT
0.315 ±0.05
0.50 BSC
4.50 REF
6.60 ±0.10
1.05 ±0.10
4.75 REF
2.74 REF
2.74
(.108)
MILLIMETERS
(INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN
3. DRAWING NOT TO SCALE
SEE NOTE 4
4. RECOMMENDED MINIMUM PCB METAL SIZE
FOR EXPOSED PAD ATTACHMENT
6.40
(.252)
BSC
FE Package
38-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1772 Rev C)
Exposed Pad Variation AA
Please refer to http://www.linear.com/product/LTC3374#packaging for the most recent package drawings.
LTC3374
25
3374fc
For more information www.linear.com/LTC3374
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 11/13 Modified Figure 5 – removed a resistor. 22
B 06/15 Modified Typical Application circuit
Changed part marking on TSSOP package
Changed typical specifications: RPMOS and RNMOS
Added conditions for VPGOOD specifications
Modified various curves
Modified Temperature Monitoring section
Modified 2A inductor table
Added Related Parts
1
3
4
4
8, 9
15
18
26
C 10/15 Added Note 6 to tSS specification
Modified conditions graphs G27, G28
4, 5
9
LTC3374
26
3374fc
For more information www.linear.com/LTC3374
LINEAR TECHNOLOGY CORPORATION 2013
LT 1015 REV C • PRINTED IN USA
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
LTC3370/
LTC3371
4-Channel Configurable DC/DC
with 8 × 1A Power Stages
4 Synchronous Buck Regulators with 8 × 1A Power Stages. Can Connect Up to Four 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
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC3374
LTC3374
EXPOSED PAD
VIN1
10µF
VIN8
FB8
VIN6
FB6
VIN5
VIN4
VIN7
VIN2
FB2
10µF
10µF 10µF
1µH
1µH
10µF
10µF
47µF
SW7
SW8
SW5
SW6
FB5
RT
FB7
VIN3
FB3
FB1
SW1
SW2
SW3
10µF
10µF
68µF
47µF
1.02M
324k
1µH
1.02M
475k
267k
3374 TA02
649k
432k
1µH
FB4
VCC
PGOOD_ALL
TEMP
SYNC
MODE
EN1
EN4
EN5
EN7
EN2
EN3
EN6
EN8
SW4
22µF
10µF
MICROPROCESSOR
CONTROL
2.7V TO 5.5V
2.25V TO 5.5V
2.25V TO 5.5V 3.3V TO 5.5V
2.5V TO 5.5V
3.3V
2A
2.5V
2A
1.2V
1A
2V
3A
324k
649k
Combined Bucks with 3MHz Switch Frequency and Sequenced Power Up