LTC3370
4-Channel 8A Configurable
Buck DC/DCs
Features
Description
8 × 1A Power Stages Configurable as 2, 3, or 4 Output
Channels
n 8 Unique Output Configurations (1A to 4A Per Channel)
n Independent V Supplies for Each DC/DC
IN
(2.25V to 5.5V)
n Low Total No Load Supply Current:
n Zero Current In Shutdown (All Channels Off)
n 63µA One Channel Active in Burst Mode® Operation
n 18µA Per Additional Channel
n Precision Enable Pin Thresholds for Autonomous
Sequencing
n 1MHz to 3MHz RT Programmable Frequency
(2MHz Default) or PLL Synchronization
n Temp Monitor Indicates Die Temperature
n PGOODALL Pin Indicates All Enabled Bucks Are in
Regulation
n 32-Lead 5mm × 5mm QFN Package
The LTC®3370 is a highly flexible multioutput power
supply IC. The device includes four synchronous buck
converters, configured to share eight 1A power stages,
each of which is powered from independent 2.25V to
5.5V inputs.
n
Applications
General Purpose Multichannel Power Supplies:
Automotive, Industrial, Distributed Power Systems
n
The DC/DCs are assigned to one of eight power configurations via pin programmable C1-C3 pins. 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 PLL/MODE pin for Burst Mode or forced continuous
mode operation. A PGOODALL output indicates when all
enabled DC/DCs are within a specified percentage of their
final output value.
To reduce input noise, the buck converters are phased
in 90° steps. Precision enable pin thresholds facilitate
reliable power-up sequencing. The LTC3370 is available
in a 32-lead 5mm × 5mm QFN package.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Typical Application
90
2.7V TO 5.5V
80
VINE
VINF
2.25V TO 5.5V
2.2µH
324k
SWA
SWB
SWE
SWF
806k
649k
FB1
EN1
FB3
EN3
649k
EFFICIENCY (%)
VOUT1
1.2V/2A
VINA
VINB
2.25V TO 5.5V
2.2µH
VCC
VOUT3
1.8V/2A
VOUT2
1.5V/2A
2.2µH
715k
VINC
VIND
VING
VINH
SWC
SWD
SWG
SWH
FB2
EN2
649k
665k
FB4
EN4
309k
PLL/MODE
TEMP
RT
PGOODALL
402k
C1 C2 C3
GND
3370 TA01a
60
Burst Mode OPERATION
VIN = 3.3V
VOUT = 1.8V
f OSC = 1MHz
L = 3.3µH
50
40
30
1A BUCK
2A BUCK
3A BUCK
4A BUCK
10
2.5V TO 5.5V
2.2µH
70
20
LTC3370
2.25V TO 5.5V
Buck Efficiency vs ILOAD
100
0
VOUT4
2.5V/2A
1
10
100
1000
LOAD CURRENT (mA)
4000
3370 TA01b
C3
C2
C1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
BUCK1 BUCK2 BUCK3 BUCK4
2A
3A
3A
4A
3A
4A
4A
4A
2A
1A
1A
1A
2A
–
–
–
2A
2A
1A
1A
–
2A
1A
–
2A
2A
3A
2A
3A
2A
3A
4A
3370fb
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1
LTC3370
Table of Contents
Features............................................................................................................................. 1
Applications........................................................................................................................ 1
Typical Application ................................................................................................................ 1
Description......................................................................................................................... 1
Absolute Maximum Ratings...................................................................................................... 3
Order Information.................................................................................................................. 3
Pin Configuration.................................................................................................................. 3
Electrical Characteristics......................................................................................................... 4
Typical Performance Characteristics........................................................................................... 6
Pin Functions......................................................................................................................12
Block Diagram.....................................................................................................................14
Operation..........................................................................................................................15
Buck Switching Regulators.....................................................................................................................................15
Buck Regulators with Combined Power Stages......................................................................................................15
Power Failure Reporting Via PGOODALL Pin..........................................................................................................16
Temperature Monitoring and Overtemperature Protection......................................................................................16
Programming the Operating Frequency..................................................................................................................16
Applications Information........................................................................................................17
Buck Switching Regulator Output Voltage and Feedback Network.........................................................................17
Buck Regulators.....................................................................................................................................................17
Combined Buck Power Stages................................................................................................................................17
Input and Output Decoupling Capacitor Selection..................................................................................................17
PCB Considerations................................................................................................................................................19
Typical Applications..............................................................................................................20
Package Description.............................................................................................................23
Typical Application...............................................................................................................24
Related Parts......................................................................................................................24
2
3370fb
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LTC3370
FB4
EN4
RT
PLL/MODE
VCC
TOP VIEW
TEMP
VINA-H, FB1-4, EN1-4, VCC, PGOODALL,
RT, PLL/MODE, C1-3.................................... –0.3V to 6V
TEMP................... –0.3V to Lesser of (VCC + 0.3V) or 6V
IPGOODALL..................................................................5mA
Operating Junction Temperature Range
(Notes 2, 3)............................................. –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
Pin Configuration
EN1
(Note 1)
FB1
Absolute Maximum Ratings
32 31 30 29 28 27 26 25
VINA 1
24 VINH
SWA 2
23 SWH
SWB 3
22 SWG
VINB 4
21 VING
33
GND
VINC 5
20 VINF
SWC 6
19 SWF
SWD 7
18 SWE
VIND 8
17 VINE
FB3
EN3
PGOODALL
C3
C2
C1
FB2
EN2
9 10 11 12 13 14 15 16
UH PACKAGE
32-LEAD (5mm × 5mm) PLASTIC QFN
TJMAX = 150°C, θJA = 34°C/W, θJC = 3°C/W
EXPOSED PAD (PIN 33) IS GND, MUST BE SOLDERED TO PCB
Order Information
(http://www.linear.com/product/LTC3370#orderinfo)
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3370EUH#PBF
LTC3370EUH#TRPBF
3370
32-Lead (5mm × 5mm) Plastic QFN
–40°C to 125°C
LTC3370IUH#PBF
LTC3370IUH#TRPBF
3370
32-Lead (5mm × 5mm) Plastic QFN
–40°C to 125°C
LTC3370HUH#PBF
LTC3370HUH#TRPBF
3370
32-Lead (5mm × 5mm) Plastic QFN
–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.
3370fb
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3
LTC3370
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 = VINA-H = 3.3V, unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
VCC
VCC Voltage Range
VCC(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
One Buck Active
PLL/MODE = 0V, RT = 400k, VFB(BUCK) = 0.85V
PLL/MODE = 2MHz
fOSC
Internal Oscillator Frequency
VRT = VCC, PLL/MODE = 0V
VRT = VCC, PLL/MODE = 0V
RT = 400k, PLL/MODE = 0V
l
l
1.8
1.75
1.8
l
2.7
l
l
2.325
2.425
fPLL/MODE
Synchronization Frequency
tLOW, tHIGH > 40ns
l
1
VPLL/MODE
PLL/MODE Level High
PLL/MODE Level Low
For Synchronization
For Synchronization
l
l
1.2
VRT
RT Servo Voltage
RT = 400k
l
780
180
TYP
MAX
UNITS
5.5
V
2.45
2.55
2.575
2.675
V
V
0
2.5
µA
45
170
70
250
µA
µA
2
2
2
2.2
2.25
2.2
MHz
MHz
MHz
3
MHz
0.4
V
V
800
820
mV
220
260
mV
Temp Monitor
VTEMP(ROOM)
TEMP Voltage at 25°C
ΔVTEMP/°C
VTEMP Slope
OT
Overtemperature Shutdown
170
°C
OT Hyst
Overtemperature Hysteresis
10
°C
7
mV/°C
1A Buck Regulators
VIN
Buck Input Voltage Range
VOUT
Buck Output Voltage Range
VIN(UVLO)
Undervoltage Threshold on VIN
VIN Voltage Falling
VIN Voltage Rising
IVIN
Burst Mode Operation Input Current
Forced Continuous Mode Operation
Input Current
Shutdown Input Current
VFB = 0.85V (Note 4)
ISW(BUCK) = 0µA, FB = 0V
IFWD
PMOS Current Limit
(Note 5)
1.9
2.3
2.7
A
VFB1
Feedback Regulation Voltage for Buck 1
l
792
800
808
mV
VFB
Feedback Regulation Voltage for
Bucks 2-4
l
780
800
820
mV
IFB
Feedback Leakage Current
VFB = 0.85V
50
nA
l
2.25
l
VFB
l
l
1.95
2.05
5.5
V
VIN
V
2.05
2.15
2.15
2.25
V
V
18
400
30
600
µA
µA
0
2.5
µA
–50
DMAX
Maximum Duty Cycle
VFB = 0V
RPMOS
PMOS On-Resistance
ISW = 100mA
RNMOS
NMOS On-Resistance
ISW = –100mA
ILEAKP
PMOS Leakage Current
EN = 0
–2
2
µA
ILEAKN
NMOS Leakage Current
EN = 0
–2
2
µA
tSS
Soft-Start Time
VPGOOD(FALL)
Falling PGOOD Threshold for Buck 1
4
PGOOD Hysteresis for Bucks 1 to 4
100
%
300
mΩ
240
mΩ
1
% of Regulated VFB
Falling PGOOD Threshold for Bucks 2 to 4 % of Regulated VFB
VPGOOD(HYS)
l
% of Regulated VFB
ms
96.8
98
99.2
%
93
95
97
%
0.3
%
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LTC3370
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 = VINA-H = 3.3V, unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Buck Regulators Combined
IFWD2
PMOS Current Limit
2 Buck Power Stages Combined (Note 5)
4.6
A
IFWD3
PMOS Current Limit
3 Buck Power Stages Combined (Note 5)
6.9
A
IFWD4
PMOS Current Limit
4 Buck Power Stages Combined (Note 5)
9.2
A
Interface Logic Pins (PGOODALL, PLL/MODE, CT, C1, C2, C3)
IOH
Output High Leakage Current
PGOODALL 5.5V at Pin
VOL
Output Low Voltage
PGOODALL 3mA into Pin
VIL
C1, C2, C3 Input Low Threshold
l
VIH
PLL/MODE, CT, C1, C2, C3 Input High
Threshold
l
VIL
PLL/MODE Input Low Threshold
l
0.1
1
µA
0.4
V
0.4
V
VCC – 0.4
V
VCC – 1.2
V
Interface Logic Pins (EN1, EN2, EN3, EN4)
VHI(ALLOFF)
Enable Rising Threshold
All Regulators Disabled
l
730
1200
mV
VHI
Enable Rising Threshold
At Least One Regulator Enabled
l
400
420
mV
VLO
Enable Falling Threshold
IEN
Enable Pin Leakage Current
340
EN = 3.3V
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 LTC3370 is tested under pulsed load conditions such that
TJ ≈ TA. The LTC3370E 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
LTC3370I is guaranteed over the –40°C to 125°C operating junction
temperature range. The LTC3370H 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 the 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.
375
mV
1
µA
Note 3: The LTC3370 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.
3370fb
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5
LTC3370
Typical Performance Characteristics
3000
90
2500
EFFICIENCY (%)
70
Burst Mode OPERATION
VIN = 3.3V
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
40
30
10
1
2000
1000
500
0
125
2.25
100
1
5
35
65
95
TEMPERATURE (°C)
125
155
3370 G03
VCC Supply Current vs
Temperature
400
AT LEAST ONE BUCK ENABLED
PLL/MODE = 0V
FB = 850mV
AT LEAST ONE BUCK ENABLED
360 PLL/MODE = 2MHz
320
VIN FALLING
75
240
IVCC (µA)
IVCC (µA)
UV THRESHOLD (V)
2.10
50
200
160
120
25
1.90
–55
–25
5
35
65
95
TEMPERATURE (°C)
125
0
–55
155
–25
3370 G04
125
0
–55
155
2.20
1.95
VCC = 2.7V
VCC = 3.3V
VCC = 5.5V
2.10
2.15
2.10
2.00
2.00
1.85
1.85
155
3371 G07
1.80
–55
RT = 400k
1.95
1.95
1.85
125
VRT = VCC
2.05
2.05
1.90
5
35
65
95
TEMPERATURE (°C)
155
Oscillator Frequency vs VCC
1.90
–25
125
2.20
1.90
1.80
–55
5
35
65
95
TEMPERATURE (°C)
fOSC (MHz)
2.00
VRT = VCC
2.15
f OSC (MHz)
2.05
–25
3370 G06
Default Oscillator Frequency vs
Temperature
VCC = 2.7V
VCC = 3.3V
VCC = 5.5V
2.10
5
35
65
95
TEMPERATURE (°C)
VCC = 2.7V
VCC = 3.3V
VCC = 5.5V
40
3370 G05
RT Programmed Oscillator
Frequency vs Temperature
RT = 400k
80
VCC = 2.7V
VCC = 3.3V
VCC = 5.5V
1.95
6
–25
280
2.00
fOSC (MHz)
2.30
–55
10
100
1000
LOAD CURRENT (mA)
VIN RISING
2.05
VCC FALLING
2.45
VCC Supply Current vs
Temperature
2.30
2.15
2.50
3370 G02
Buck VIN Undervoltage Threshold
vs Temperature
2.15
VCC RISING
2.55
2.35
3370 G01
2.20
2.60
1A BUCK
2A BUCK
3A BUCK
4A BUCK
1500
10
100
1000
LOAD CURRENT (mA)
2.20
2.65
2.40
1A BUCK
2A BUCK
3A BUCK
4A BUCK
20
0
POWER LOSS (mW)
80
2.70
Burst Mode OPERATION
VIN = 3.3V
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
UV THRESHOLD (V)
100
50
VCC Undervoltage Threshold vs
Temperature
Buck Power Loss vs ILOAD
Buck Efficiency vs ILOAD
60
TA = 25°C, unless otherwise noted.
–25
5
35
65
95
TEMPERATURE (°C)
125
155
3370 G08
1.80
2.7
3.1
3.5
3.9 4.3
VCC (V)
4.7
5.1
5.5
3370 G09
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LTC3370
Typical Performance Characteristics
VTEMP vs Temperature
Oscillator Frequency vs RT
ILOAD = 0mA
1200 VCC = 3.3V
3.0
1000
1.5
600
1.0
200
0.5
0
0
250 300 350 400 450 500 550 600 650 700 750 800
RT (kΩ)
800
ACTUAL VTEMP
400
–200
–55
50
EN RISING
385
EN FALLING
375
–25
5
35
65
95
TEMPERATURE (°C)
125
155
125
20
0
–55
155
–25
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
–25
1.88
2.6
FORCED CONTINUOUS MODE
1.86 I LOAD = 0mA
5
35
65
95
TEMPERATURE (°C)
125
350
300
250
200
150
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
100
0
–55
155
–25
550
VIN = 3.3V
RDS(ON) (mΩ)
IFWD (A)
2.2
1.76
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
1.74
–25
5
35
65
95
TEMPERATURE (°C)
125
155
3370 G16
155
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
450
2.3
125
PMOS RDS(ON) vs Temperature
500
2.4
5
35
65
95
TEMPERATURE (°C)
3370 G15
1.84
1.78
155
400
50
2.5
1.82
125
FORCED CONTINUOUS MODE
500 FB = 0V
450
PMOS Current Limit vs
Temperature
1.80
5
35
65
95
TEMPERATURE (°C)
3370 G12
3370 G14
VOUT vs Temperature
VOUT (V)
EN FALLING
550
3370 G13
1.72
–55
500
Buck VIN Supply Current vs
Temperature
30
370
5
35
65
95
TEMPERATURE (°C)
550
350
–55
Burst Mode OPERATION
FB = 850mV
10
–25
600
400
IDEAL VTEMP
40
IVIN_BURST (µA)
EN THRESHOLD (mV)
400
365
–55
650
Buck VIN Supply Current vs
Temperature
405
380
700
3370 G11
Enable Pin Precision Threshold
vs Temperature
390
EN RISING
750
450
3370 G10
395
ALL REGULATORS DISABLED
VCC = 3.3V
850
800
VTEMP (mV)
2.0
900
EN THRESHOLD (mV)
VCC = 3.3V
3.5
2.5
fOSC (MHz)
Enable Threshold vs Temperature
1400
IVIN_FORCED_CONTINUOUS (µA)
4.0
TA = 25°C, unless otherwise noted.
400
350
300
250
2.1
2.0
–55
200
–25
5
35
65
95
TEMPERATURE (°C)
125
155
3370 G17
150
–55
–25
5
35
65
95
TEMPERATURE (°C)
125
155
3370 G18
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7
LTC3370
Typical Performance Characteristics
100
EFFICIENCY (%)
RDS(ON) (mΩ)
350
300
250
80
Burst Mode OPERATION
900 VOUT = 1.2V
fOSC = 2MHz
800 L = 2.2µH
70
700
60
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
50
40
30
20
200
10
150
–55
–25
5
35
65
95
TEMPERATURE (°C)
125
0
155
1000
Burst Mode OPERATION
90
1
70
700
30
20
FORCED
CONTINUOUS
MODE
10
0
1
POWER LOSS (mW)
EFFICIENCY (%)
40
600
VIN = 3.3V
400
300
0
100
1000
VIN = 5.5V
400
200
1
100
0
1
10
100
LOAD CURRENT (mA)
3370 G25
8
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
50
40
30
FORCED
CONTINUOUS
MODE
10
100
LOAD CURRENT (mA)
0
1000
1
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
10
100
LOAD CURRENT (mA)
3370 G24
1A Buck Power Loss vs ILOAD,
VOUT = 3.3V
Burst Mode OPERATION
900 VOUT = 3.3V
fOSC = 2MHz
800 L = 2.2µH
Burst Mode
OPERATION
70
60
VIN = 4.2V
VIN = 5.5V
VIN = 4.2V
VIN = 5.5V
50
40
30
0
1000
1000
FORCED
CONTINUOUS
MODE
10
1000
60
1A Buck Efficiency vs ILOAD,
VOUT = 3.3V
20
VIN = 5.5V
Burst Mode
OPERATION
70
10
80
VIN = 2.7V
300
1A Buck Efficiency vs ILOAD,
VOUT = 2.5V
20
90
EFFICIENCY (%)
POWER LOSS (mW)
Burst Mode OPERATION
900 VOUT = 2.5V
fOSC = 2MHz
800 L = 2.2µH
VIN = 3.3V
1000
3370 G23
1A Buck Power Loss vs ILOAD,
VOUT = 2.5V
600
10
100
LOAD CURRENT (mA)
80
100
1000
700
1
90
3370 G22
500
100
VIN = 2.25V
500
200
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
10
100
LOAD CURRENT (mA)
VIN = 5.5V
3370 G21
EFFICIENCY (%)
80
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
300
0
1000
90
50
VIN = 3.3V
400
100
1A Buck Power Loss vs ILOAD,
VOUT = 1.8V
Burst Mode OPERATION
900 VOUT = 1.8V
fOSC = 2MHz
800 L = 2.2µH
60
500
3370 G20
1A Buck Efficiency vs ILOAD,
VOUT = 1.8V
Burst Mode OPERATION
VIN = 2.25V
600
200
VOUT = 1.2V
FORCED
CONTINUOUS fOSC = 2MHz
L = 2.2µH
MODE
10
100
1000
LOAD CURRENT (mA)
3370 G19
100
POWER LOSS (mW)
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
400
1A Buck Power Loss vs ILOAD,
VOUT = 1.2V
1A Buck Efficiency vs ILOAD,
VOUT = 1.2V
NMOS RDS(ON) vs Temperature
POWER LOSS (mW)
450
TA = 25°C, unless otherwise noted.
1
VOUT = 3.3V
fOSC = 2MHz
L = 2.2µH
10
100
LOAD CURRENT (mA)
1000
3370 G26
700
600
500
VIN = 5.5V
400
300
VIN = 4.2V
200
100
0
1
10
100
LOAD CURRENT (mA)
1000
3370 G27
3370fb
For more information www.linear.com/LTC3370
LTC3370
Typical Performance Characteristics
3A Buck Efficiency vs ILOAD,
VOUT = 1.8V
2A Buck Efficiency vs ILOAD,
VOUT = 2.5V
2A Buck Efficiency vs ILOAD,
VOUT = 1.8V
100
90
90
90
80
80
70 Burst Mode
OPERATION
60
70
50
40
30
20
0
1
10
100
LOAD CURRENT (mA)
60
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
50
40
30
20
VOUT = 1.8V
FORCED
CONTINUOUS fOSC = 2MHz
L = 2.2µH
MODE
10
80
Burst Mode
OPERATION
0
1
10
100
LOAD CURRENT (mA)
30
0
100
90
90
90
80
80
60
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
50
40
30
FORCED
CONTINUOUS
MODE
10
0
1
FORCED
CONTINUOUS
MODE
60
50
40
30
10
0
1000
VOUT = 1.8V
fOSC = 2MHz
L = 2.2µH
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
20
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
10
100
LOAD CURRENT (mA)
1
90
90
80
80
60
FORCED
CONTINUOUS
MODE
50
40
fOSC = 1MHz, L = 3.3µH
fOSC = 2MHz, L = 2.2µH
fOSC = 3MHz, L = 1µH
fOSC = 1MHz, L = 3.3µH
fOSC = 2MHz, L = 2.2µH
fOSC = 3MHz, L = 1µH
30
20
10
0
1
10
100
LOAD CURRENT (mA)
1000
3370 G34
70
50
10
100
LOAD CURRENT (mA)
100
1000
VIN = 3.3V
90
VIN = 3.3V
80
VIN = 5.5V
30
3370 G35
VIN = 2.25V
60
50
40
30
10
3
VIN = 5.5V
70
20
VOUT = 1.8V
ILOAD = 100mA
L = 3.3µH
1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
FREQUENCY (MHz)
1
3370 G33
VIN = 2.25V
40
0
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
VIN = 2.7V
VIN = 3.3V
VIN = 5.5V
30
1A Buck Efficiency vs Frequency
(Forced Continuous Mode)
50
10
VOUT = 2.5V
fOSC = 2MHz
L = 2.2µH
40
0
60
20
FORCED
CONTINUOUS
MODE
10
EFFICIENCY (%)
100
EFFICIENCY (%)
100
Burst Mode
OPERATION
60
1A Buck Efficiency vs Frequency
(Forced Continuous Mode)
VOUT = 1.8V
VIN = 3.3V
1000
4A Buck Efficiency vs ILOAD,
VOUT = 2.5V
70
3370 G32
1A Buck Efficiency vs ILOAD
(Across Operating Frequency)
Burst Mode
OPERATION
10
100
LOAD CURRENT (mA)
20
10
100
1000
LOAD CURRENT (mA)
3370 G31
70
1
80
Burst Mode
OPERATION
70
EFFICIENCY (%)
Burst Mode
OPERATION
VOUT = 1.8V
FORCED
CONTINUOUS fOSC = 2MHz
L = 2.2µH
MODE
3370 G30
4A Buck Efficiency vs ILOAD,
VOUT = 1.8V
EFFICIENCY (%)
EFFICIENCY (%)
40
100
70
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
50
3370 G29
3A Buck Efficiency vs ILOAD,
VOUT = 2.5V
20
EFFICIENCY (%)
60
10
1000
3370 G28
100
Burst Mode
OPERATION
70
20
VOUT = 2.5V
FORCED
CONTINUOUS fOSC = 2MHz
L = 2.2µH
MODE
10
1000
EFFICIENCY (%)
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
VIN = 2.25V
VIN = 3.3V
VIN = 5.5V
EFFICIENCY (%)
100
100
EFFICIENCY (%)
TA = 25°C, unless otherwise noted.
0
VOUT = 1.8V
ILOAD = 200mA
L = 3.3µH
1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
FREQUENCY (MHz)
3
3370 G36
3370fb
For more information www.linear.com/LTC3370
9
LTC3370
Typical Performance Characteristics
1A Buck Efficiency vs Frequency
(Forced Continuous Mode)
ILOAD = 100mA
90
ILOAD = 500mA
ILOAD = 20mA
70
60
50
40
30
1.820
1.816
1.816
1.812
1.812
1.800
1.796
VIN = 2.25V
10
1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8
FREQUENCY (MHz)
1.780
3
1
VIN = 3.3V
1.800
VIN = 2.25V
1.796
1.788
fOSC = 2MHz
L = 2.2µH
1.784
VIN = 5.5V
1.804
1.792
DROPOUT
1.788
VOUT = 1.8V
VIN = 3.3V
L = 3.3µH
1.808
VIN = 3.3V
VIN = 5.5V
1.804
1.792
20
0
1.820
1.808
VOUT (V)
EFFICIENCY (%)
80
4A Buck Regulator Load Regulation
(Forced Continuous Mode)
1A Buck Regulator Load Regulation
(Forced Continuous Mode)
VOUT (V)
100
TA = 25°C, unless otherwise noted.
fOSC = 2MHz
L = 2.2µH
1.784
10
100
LOAD CURRENT (mA)
3370 G37
1000
1.780
1
DROPOUT
10
100
1000
LOAD CURRENT (mA)
3370 G39
3370 G38
1A Buck Regulator Line Regulation
(Forced Continuous Mode)
1A Buck Regulator No-Load Start-Up
Transient (Forced Continuous Mode)
1A Buck Regulator No-Load Start-Up
Transient(Burst Mode Operation)
1.820
VIN = 3.3V
VOUT = 1.8V
1.815
VIN = 3.3V
VOUT = 1.8V
VOUT (V)
1.810
1.805
ILOAD = 100mA
1.800
ILOAD = 500mA
1.795
VOUT
500mV/DIV
VOUT
500mV/DIV
INDUCTOR
CURRENT
500mA/DIV
INDUCTOR
CURRENT
500mA/DIV
EN
2V/DIV
EN
2V/DIV
1.790
1.785
200µs/DIV
fOSC = 2MHz
L = 2.2µH
1.780
2.25
2.75
3.25
3.75 4.25
VIN (V)
4.75
3370 G41
200µs/DIV
3370 G42
5.25
3370 G40
4A Buck Regulator No-Load Start-Up
Transient (Burst Mode Operation)
1A Buck Regulator Transient
Response (Burst Mode Operation)
4A Buck Regulator No-Load Start-Up
Transient (Forced Continuous Mode)
VIN = 3.3V
VOUT = 1.8V
VIN = 3.3V
VOUT = 1.8V
VOUT
100mV/DIV
AC-COUPLED
VOUT
500mV/DIV
VOUT
500mV/DIV
INDUCTOR
CURRENT
500mA/DIV
INDUCTOR
CURRENT
500mA/DIV
INDUCTOR
CURRENT
200mA/DIV
EN
2V/DIV
EN
2V/DIV
0mA
200µs/DIV
3370 G43
200µs/DIV
3370 G44
50µs/DIV
3370 G45
LOAD STEP = 100mA TO 700mA
VIN = 3.3V
VOUT = 1.8V
10
3370fb
For more information www.linear.com/LTC3370
LTC3370
Typical Performance Characteristics
1A Buck Regulator Transient
Response (Forced Continuous
Mode)
TA = 25°C, unless otherwise noted.
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
VOUT
100mV/DIV
AC-COUPLED
INDUCTOR
CURRENT
200mA/DIV
INDUCTOR
CURRENT
1A/DIV
INDUCTOR
CURRENT
1A/DIV
0mA
0mA
0mA
50µs/DIV
LOAD STEP = 100mA TO 700mA
VIN = 3.3V
VOUT = 1.8V
3370 G46
50µs/DIV
3370 G47
LOAD STEP = 400mA TO 2.8A
VIN = 3.3V
VOUT = 1.8V
50µs/DIV
3370 G48
LOAD STEP = 400mA TO 2.8A
VIN = 3.3V
VOUT = 1.8V
Pin Functions
VINA (Pin 1): Power Stage A Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
SWA (Pin 2): Power Stage A Switch Node. External inductor connects to this pin.
SWB (Pin 3): Power Stage B Switch Node. External inductor connects to this pin.
VINB (Pin 4): Power Stage B Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
VINC (Pin 5): Power Stage C Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
SWC (Pin 6): Power Stage C Switch Node. External inductor connects to this pin.
SWD (Pin 7): Power Stage D Switch Node. External inductor connects to this pin.
VIND (Pin 8): Power Stage D Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
FB2 (Pin 9): Buck Regulator 2 Feedback Pin. Receives
feedback by a resistor divider connected across the output.
In configurations where Buck 2 is not used, FB2 should
be tied to ground.
EN2 (Pin 10): Buck Regulator 2 Enable Input. Active high.
In configurations where Buck 2 is not used, tie EN2 to
ground. Do not float.
C1 (Pin 11): Configuration Control Input Bit. With C2 and
C3, C1 configures the Buck output current power stage
combinations. C1 should either be tied to VCC or ground.
Do not float.
C2 (Pin 12): Configuration Control Input Bit. With C1 and
C3, C2 configures the Buck output current power stage
combinations. C2 should either be tied to VCC or ground.
Do not float.
C3 (Pin 13): Configuration Control Input Bit. With C1 and
C2, C3 configures the Buck output current power stage
combinations. C3 should either be tied to VCC or ground.
Do not float.
PGOODALL (Pin 14): PGOOD Status Pin (Active Low).
Open-drain output. When the regulated output voltage
of any enabled switching regulator is below its PGOOD
threshold level, this pin is driven LOW. This level is 98%
of the programmed output value for Buck 1 and 95% of
3370fb
For more information www.linear.com/LTC3370
11
LTC3370
Pin Functions
the programmed output value for Bucks 2-4. When all
buck regulators are disabled PGOODALL is driven LOW.
EN3 (Pin 15): Buck Regulator 3 Enable Input. Active high.
In configurations where Buck 3 is not used, tie EN3 to
ground. Do not float.
RT (Pin 27): Oscillator Frequency Pin. This pin provides
two modes of setting the switching frequency. Connecting
a resistor from RT to ground sets the switching frequency
based on the resistor value. If RT is tied to VCC the internal
2MHz oscillator is used. Do not float.
SWF (Pin 19): Power Stage F Switch Node. External
inductor connects to this pin.
PLL/MODE (Pin 28): Oscillator Synchronization and Buck
Mode Select Pin. Driving PLL/MODE with an external clock
signal synchronizes all switches to the applied frequency,
and the buck converters operate in forced continuous
mode. The slope compensation is automatically adapted
to the external clock frequency. The absence of an external
clock signal enables the frequency programmed by the
RT pin. When not synchronizing to an external clock this
input determines how the LTC3370 operates at light loads.
Pulling this pin to ground selects Burst Mode operation.
Tying this pin to VCC invokes forced continuous mode
operation. Do not float.
VINF (Pin 20): Power Stage F Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
VCC (Pin 29): Internal Bias Supply. Bypass to GND with a
10µF or larger ceramic capacitor.
VING (Pin 21): Power Stage G Input Supply. Bypass to
GND with a 10µF or larger ceramic capacitor.
TEMP (Pin 30): Temperature Indication Pin. TEMP outputs
a voltage of 220mV (typical) at 25°C. The TEMP voltage
increases by 7mV/°C (typical) at higher temperatures
giving an external indication of the LTC3370 internal die
temperature.
FB3 (Pin 16): Buck Regulator 3 Feedback Pin. Receives
feedback by a resistor divider connected across the output.
In configurations where Buck 3 is not used, FB3 should
be tied to ground.
VINE (Pin 17): Power Stage E Input Supply. Bypass to GND
with a 10µF or larger ceramic capacitor.
SWE (Pin 18): Power Stage E Switch Node. External
inductor connects to this pin.
SWG (Pin 22): Power Stage G Switch Node. External
inductor connects to this pin.
SWH (Pin 23): Power Stage H Switch Node. External
inductor connects to this pin.
VINH (Pin 24): Power Stage H Input Supply. Bypass to
GND with a 10µF or larger ceramic capacitor.
FB4 (PIN 25): Buck Regulator 4 Feedback Pin. Receives
feedback by a resistor divider connected across the output.
EN4 (Pin 26): Buck Regulator 4 Enable Input. Active high.
Do not float.
12
EN1 (Pin 31): Buck Regulator 1 Enable Input. Active high.
Do not float.
FB1 (Pin 32): Buck Regulator 1 Feedback Pin. Receives
feedback by a resistor divider connected across the output.
GND (Exposed Pad Pin 33): Ground. The exposed pad
should be connected to a continuous ground plane on the
printed circuit board directly under the LTC3370.
3370fb
For more information www.linear.com/LTC3370
LTC3370
Block Diagram
29
VCC
BANDGAP OT
27
28
14
RT
PLL/MODE
4
REF
UVLO
UV
TEMP
MONITOR
TEMP
CLK
OSCILLATOR
MODE
SD
PGOODALL
VINA
4 PGOOD
PGOOD LOGIC
1A POWER
STAGE A
SWA
VINB
SD
REF
CLK
1A POWER
STAGE B
MODE
4
32
EN1
FB1
1A POWER
STAGE C
9
EN2
FB2
1A POWER
STAGE D
16
EN3
FB3
BUCK REGULATOR 2
CONTROL
1A POWER
STAGE E
26
25
FB4
1A POWER
STAGE F
BUCK REGULATOR 3
CONTROL
12
1A POWER
STAGE H
GND
(EXPOSED PAD)
C3
C2
SWG
VINH
CONFIGURATION LINES
11
SWF
VING
1A POWER
STAGE G
BUCK REGULATOR 4
CONTROL
C1
SWE
VINF
VING
EN4
SWD
VINE
VINE
15
SWC
VIND
BUCK REGULATOR 1
CONTROL
VIND
10
SWB
VINC
VINB
31
30
13
33
C3
C2
C1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
SWH
1
2
4
3
5
6
8
7
17
18
20
19
21
22
24
23
3370 BD
BUCK1 BUCK2 BUCK3 BUCK4
2A
3A
3A
4A
3A
4A
4A
4A
2A
1A
1A
1A
2A
–
–
–
2A
2A
1A
1A
–
2A
1A
–
2A
2A
3A
2A
3A
2A
3A
4A
3370fb
For more information www.linear.com/LTC3370
13
LTC3370
Operation
Buck Switching Regulators
The LTC3370 contains eight monolithic 1A synchronous
buck switching channels. These are controlled by up to
four current mode regulator controllers. 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 (PLL/MODE = LOW) for higher efficiency
at light loads and forced continuous PWM mode (PLL/
MODE = HIGH or switching) for lower noise at light loads.
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 a sleep state, 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 bursts at light loads whereas at
higher loads it operates 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 can operate at an independent VIN voltage and has its own FB and EN pin to maximize flexibility. The enable pins have two different enable
threshold voltages that depend on the operating state of
the LTC3370. 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 eventbased 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. Buck 1
is set to 0°, Buck 2 is set to 90°, Buck 3 is set to 270°, and
Buck 4 is set to 180°. 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.
The buck switching regulators feature a controlled shutdown scheme where the inductor current ramps down to
zero through the NMOS switch. If any event causes the
buck regulator to shut down (EN = LOW, OT, VINA-H or VCC
UVLO) the NMOS switch turns on until the inductor current
reaches 0mA (typical). Then, the switch pin becomes Hi-Z.
Buck Regulators with Combined Power Stages
Up to four adjacent buck regulators may be combined in
a master-slave configuration by setting the configuration
via the C1, C2, and C3 pins. These pins should either be
tied to ground or pin strapped to VCC in accordance with
the desired configuration code (Table 1). Any combined
SW pins must be tied together, as must any of the combined VIN pins. EN1 and FB1 are utilized by Buck 1, EN2
and FB2 by Buck 2, EN3 and FB3 by Buck 3, and EN4 and
FB4 by Buck 4. If any buck is not used or is not available
in the desired configuration, then the associated FB and
EN pins must be tied to ground.
Any available combination of 2, 3, or 4 adjacent Buck
regulators serve to provide up to either 2A, 3A, or 4A
of average output load current. For example, code 110
(C3C2C1) configures Buck 1 to operate as a 4A regulator through VIN/SW pairs A, B, C, and D, while Buck 2
is disabled, Buck 3 operates as a 1A regulator through
VIN/SW pair E, and Buck 4 operates as a 3A regulator
through VIN/SW pairs F, G, and H.
3370fb
For more information www.linear.com/LTC3370
LTC3370
Operation
If none of the buck switching regulators are enabled, then
the temperature monitor is also shut down to further
reduce quiescent current.
Table 1. Master Slave Program Combinations (Each Letter
Corresponds to a VIN and SW Pair)
PROGRAM
CODE
C3C2C1
BUCK 1
BUCK 2
BUCK 3
BUCK 4
000
AB
CD
EF
GH
001
ABC
D
EF
GH
010
ABC
D
E
FGH
011
ABCH
D
E
FG
100
ABC
DE
Not Used
FGH
101
ABCD
Not Used
EF
GH
110
ABCD
Not Used
E
FGH
111
ABCD
Not Used
Not Used
EFGH
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.
Power Failure Reporting Via PGOODALL Pin
Power failure conditions are reported back by the
PGOODALL pin. Each buck switching regulator has an
internal power good (PGOOD) signal. When the regulated
output voltage of an enabled switcher falls below 98% for
Buck regulator 1 or 95% for Buck regulators 2-4 of its
programmed value, the PGOOD signal is pulled low. If any
PGOOD signal stays low for greater than 100µs, then the
PGOODALL 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.
The PGOOD signal has a 0.3% hysteresis such that when
the regulated output voltage of an enabled switcher rises
above 98.3% or 95.3%, respectively, of its programmed
value, the PGOOD signal transitions high.
Temperature Monitoring and Overtemperature
Protection
To prevent thermal damage to the LTC3370 and its surrounding components, the LTC3370 incorporates an
overtemperature (OT) function. When the LTC3370 die
temperature reaches 170°C (typical) all enabled buck
switching regulators are shut down and remain in shutdown
until the die temperature falls to 160°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 – 45mV
•1°C
7mV
Programming the Operating Frequency
The operating frequency for all of the LTC3370 regulators
is determined by an external resistor that is connected
between the RT pin and ground. The operating frequency
can be calculated using the following equation:
8 •1011 • ΩHz
fOSC =
RT
(2)
While the LTC3370 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 LTC3370’s internal oscillator can be synchronized
through an internal PLL circuit to an external frequency
by applying a square wave clock signal to the PLL/MODE
pin. During synchronization, the top MOSFET turn-on of
Buck regulator 1 is phase locked to the rising edge of
the external frequency source. All other buck switching
regulators are locked to the appropriate phase of the external frequency source (see Buck Switching Regulators).
The synchronization frequency range is 1MHz to 3MHz.
A synchronization signal on the PLL/MODE pin will force
all active buck switching regulators to operate in forced
continuous mode PWM.
(1)
3370fb
For more information www.linear.com/LTC3370
15
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 1.
Typical values for R1 range from 40kΩ to 1MΩ. 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
CFF
R2
FB
R1
+
COUT
3370 F01
OPTIONAL
Figure 1. Feedback Components
Buck Regulators
All four buck regulators are designed to be used with
inductors ranging from 1µH to 3.3µH depending on the
lowest switching frequency at which the buck regulator
must operate. When operating at 1MHz a 3.3µH inductor
should be used, while at 3MHz a 1µH inductor may be
used, or a higher value inductor may be used if reduced
current ripple is desired. Table 2 shows some recommended inductors for the buck regulators. The bucks are
compensated to operate across the range of possible VIN
and VOUT voltages when the appropriate inductance is
used for the desired switching frequency.
The input supply should be decoupled with a 10µF capacitor
while the output should be decoupled with a 22µF capacitor. Refer to the Capacitor Selection section for details on
selecting a proper capacitor.
Combined Buck Power Stages
The LTC3370 has eight power stages that can handle average load currents of 1A each. These power stages may be
combined in any one of eight possible combinations, via
16
the C1, C2, and C3 pins (see Table 1). Tables 3, 4, and 5
show recommended inductors for the combined power
stage configurations.
The input supply should be decoupled with a 22µF capacitor
while the output should 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 some cases it may be beneficial to use more power
stages than needed to achieve increased efficiency of the
active regulators. In general the efficiency will improve by
adding stages for any regulator running close to what the
rated load current would be without the additional stage.
For example, if the application requires a 1A regulator that
supplies close to 1A at a high duty cycle, a 3A regulator
that only peaks at 3A but averages a lower current, and
a 2A regulator that runs at 1.5A at a high duty cycle, better efficiency may be achieved by using the 3A, 3A, 2A
configuration.
Input and Output Decoupling Capacitor Selection
The LTC3370 has individual input supply pins for each
buck power stage 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 that 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 1, 4, 5, 8, 17, 20, 21, 24 and
29 all need to be decoupled with at least 10µF capacitors. If
power stages are combined the supplies should be shorted
with as short of a trace as possible, and the decoupling
capacitor should be scaled accordingly.
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For more information www.linear.com/LTC3370
LTC3370
Applications Information
Table 2. Recommended Inductors for 1A Buck Regulators
PART NUMBER
IHLP1212ABER1R0M-11
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)
MANUFACTURER
Vishay
Toko
CoilCraft
Toko
Vishay
CoilCraft
Vishay
Table 3. 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
Würth Elektronik
CoilCraft
Toko
Vishay
CoilCraft
Toko
Table 4. Recommended Inductors for 3A Buck Regulators
PART NUMBER
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
Vishay
74437346022
2.2
6.5
20
7.3 × 6.6 × 2.8
Würth Elektronik
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
XAL4020-102ME
MANUFACTURER
CoilCraft
Toko
CoilCraft
CoilCraft
TDK
Table 5. Recommended Inductors for 4A Buck Regulators
PART NUMBER
XAL5030-122ME
SPM6530T-1R0M120
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
MANUFACTURER
CoilCraft
TDK
CoilCraft
TDK
Vishay
CoilCraft
Toko
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For more information www.linear.com/LTC3370
17
LTC3370
Applications Information
PCB Considerations
When laying out the printed circuit board, the following
list should be followed to ensure proper operation of the
LTC3370:
1. The exposed pad of the package (Pin 33) should connect
directly to a large ground plane to minimize thermal and
electrical impedance.
2. Each of the input supply pins should 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 LTC3370.
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 multiple power stage buck regulator application
the trace length of switch nodes to the inductor must
be kept equal to ensure proper operation.
7. Care should be taken to minimize capacitance on the
TEMP pin. If the TEMP voltage must drive more than
~30pF, then the pin should be isolated with a resistor
placed close to the pin of a value between 10k and 100k.
Keep in mind that any load on the isolation resistor will
create a proportional error.
4. The switching power traces connecting SWA, SWB,
SWC, SWD, SWE, SWF, SWG, and SWH to the inductors should be minimized to reduce radiated EMI and
parasitic coupling. Due to the large voltage swing of
18
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For more information www.linear.com/LTC3370
LTC3370
Typical Applications
4 × 2A Quad Buck Application
2.25V TO 5.5V
22µF
1.2V
2A
2.2µH
47µF
232k
VINA
VINB
VING
VINH
SWA
SWB
SWG
SWH
FB1
FB4
464k
2.5V
2A
2.2µH
47µF
2.2µH
806k
665k
47µF
1.8V
2A
649k
LTC3370
2.5V TO 5.5V
22µF
2.25V TO 5.5V
22µF
VINC
VIND
VINE
VINF
SWC
SWD
SWE
SWF
FB2
FB3
3.3V TO 5.5V
22µF
2.2µH
511k
309k
47µF
3.3V
2A
162k
EN1
EN2
EN3
EN4
PLL/MODE
C1
C2
C3
MICROPROCESSOR
CONTROL
RT
402k
VCC
2.7V TO 5.5V
10µF
PGOODALL
TEMP
EXPOSED PAD
MICROPROCESSOR
CONTROL
3370 TA02
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For more information www.linear.com/LTC3370
19
LTC3370
Typical Applications
Buck Regulators with Sequenced Start-Up Driven from a High Voltage Upstream Buck Converter
VIN
5.5V TO 36V
CIN
22µF
VIN
100k
INTVCC
INTVCC
2.2µF
PGOOD
PLLIN/MODE
470pF
SENSE+
47µF
2.2µH
1.2V
4A
COUT: SANYO 10TPE330M
D1: DFLS1100
L1 COILCRAFT SER1360-802KL
MTOP, MBOT: Si7850DP
100µF
VINF
VING
SWH
SWA
SWB
SWC
FB1
232k
464k
SWF
SWG
22µF
22µF
2.2µH
806k
47µF
1.8V
2A
649k
LTC3370
2.2µH
19.1k
FB4
VIND
10µF
5V
6A
100k
SGND
VINH
VINA
VINB
VINC
COUT
330µF
1nF
–
TRACK/SS SENSE
EXTVCC
SGND
VFB
1M
RSENSE
7mΩ
MBOT
BG
ITH
0.1µF
L1
8µH
SW
FREQ
34.8k
MTOP
0.1µF
LTC3891
RUN
BOOST
TMR GND ON
2.5V
1A
D1
TG
ILIM
LTC2955TS8-1
VIN
EN
KILL
INT
PB
MICROPROCESSOR
CONTROL
PGND
VINE
SWD
SWE
FB2
FB3
10µF
2.2µH
665k
511k
309k
22µF
3.3V
1A
162k
EN1
EN2
EN3
EN4
PLL/MODE
C1
C2
C3
MICROPROCESSOR
CONTROL VCC
RT
402k
VCC
PGOODALL
TEMP
10µF
MICROPROCESSOR
CONTROL
EXPOSED PAD
3370 TA03
20
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For more information www.linear.com/LTC3370
LTC3370
Typical Applications
Combined Buck Regulators with Common Input Supply
2.7V TO 5.5V
10µF
1.2V
4A
2.2µH
100µF
324k
VINA
VINH
SWA
SWB
SWC
SWD
FB1
SWH
SWG
SWF
2.2µH
511k
511k
VINB
VING
10µF
LTC3370
10µF
10µF
VINC
VINF
VIND
VINE
SWE
10µF
2.2µH
665k
MICROPROCESSOR
CONTROL
10µF
FB4
649k
10µF
68µF
1.6V
3A
FB2
EN2
C1
FB3
C2
C3
VCC
22µF
2.5V
1A
10µF
309k
EN1
PGOODALL
EN3
TEMP
EN4
PLL/MODE
RT
EXPOSED PAD
10µF
MICROPROCESSOR
CONTROL
3370 TA04
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For more information www.linear.com/LTC3370
21
LTC3370
Package Description
Please refer to http://www.linear.com/product/LTC3370#packaging for the most recent package drawings.
UH Package
32-Lead Plastic QFN (5mm × 5mm)
(Reference LTC DWG # 05-08-1693 Rev D)
0.70 ±0.05
5.50 ±0.05
4.10 ±0.05
3.50 REF
(4 SIDES)
3.45 ±0.05
3.45 ±0.05
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
RECOMMENDED SOLDER PAD LAYOUT
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
5.00 ±0.10
(4 SIDES)
BOTTOM VIEW—EXPOSED PAD
0.75 ±0.05
R = 0.05
TYP
0.00 – 0.05
R = 0.115
TYP
PIN 1 NOTCH R = 0.30 TYP
OR 0.35 × 45° CHAMFER
31 32
0.40 ±0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
3.50 REF
(4-SIDES)
3.45 ±0.10
3.45 ±0.10
(UH32) QFN 0406 REV D
0.200 REF
NOTE:
1. DRAWING PROPOSED TO BE A JEDEC PACKAGE OUTLINE
M0-220 VARIATION WHHD-(X) (TO BE APPROVED)
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
22
0.25 ±0.05
0.50 BSC
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For more information www.linear.com/LTC3370
LTC3370
Revision History
REV
DATE
DESCRIPTION
A
03/16
Changed pin labeling on Typical Application circuit
PAGE NUMBER
1
B
09/16
Changed Pin Configuration TJMAX to 150°C
3
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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/LTC3370
23
LTC3370
Typical Application
Combined Bucks with 3MHz Switching Frequency and Sequenced Power Up
2.25V TO 5.5V
10µF
10µF
10µF
1.2V
3A
1µH
68µF
324k
VINA
VINH
VINB
VING
2.25V TO 5.5V
10µF
10µF
1µH
VINC
SWH
SWG
SWA
SWB
SWC
FB4
FB1
VINF
VIND
LTC3370
3.3V
1A
22µF
SWD
511k
VINE
FB2
SWE
SWF
10µF
1µH
MICROPROCESSOR
CONTROL
2.5V
2A
47µF
665k
FB3
309k
162k
VCC
2.5V TO 5.5V
10µF
10µF
1µH
2V
2A
432k
649k
3.3V TO 5.5V
47µF
649k
C1
C2
C3
2.7V TO 5.5V
VCC
PGOODALL
TEMP
PLL/MODE
EN1
EN2
EN3
EN4
RT
EXPOSED PAD
10µF
MICROPROCESSOR
CONTROL
267k
3370 TA05
Related Parts
PART NUMBER
DESCRIPTION
COMMENTS
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-Lead (6mm × 6mm × 0.75mm) QFN.
LTC3675
7-Channel Configurable High Power PMIC
Quad Synchronous Buck Regulators (1A, 1A, 500mA, 500mA). Buck DC/DCs Can be
Paralleled to Deliver Up to 2× Current with a Single Inductor. 1A Boost, 1A BuckBoost, 40V LED Driver. 44-Lead (4mm × 7mm × 0.75mm) QFN Package.
LTC3676
8-Channel Power Management Solution for
Application Processor
Quad Synchronous Buck Regulators (2.5A, 2.5A, 1.5A, 1.5A). Quad LDO Regulators
(300mA, 300mA, 300mA, 25mA). Pushbutton On/Off Control with System Reset.
DDR Solution with VTT and VTTR Reference. 40-Lead (6mm × 6mm × 0.75mm) QFN
Package.
LTC3375
LTC3374
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, 48-Lead (7mm × 7mm × 0.75mm) QFN Package (LTC3375)
38-Lead (5mm × 7mm × 0.75mm) QFN and TSSOP Packages (LTC3374).
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 RST Monitoring with
Windowed Watchdog Timer (CT Programmable), 38-Lead (5mm × 7mm × 0.75mm)
QFN and TSSOP Packages.
24 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTC3370
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC3370
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LT 0916 REV B • PRINTED IN USA
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