LTC3375
8-Channel Programmable,
Parallelable 1A Buck DC/DCs
FeaTures
n
n
DescripTion
The
LTC
®
3375
is a digitally programmable high efficiency
multioutput power supply IC. The DC/DCs consist of eight
synchronous buck converters (I
OUT
up to 1A each) all
powered from independent 2.25V to 5.5V input supplies.
DC/DC enables, output voltages, operating modes, and
phasing may all be independently programmed over I
2
C
or used in standalone mode via simple I/O with power-up
defaults. The DC/DCs may be used independently or in
parallel to achieve higher output currents of up to 4A per
output with a shared inductor. Alarm levels for high die
temperature may also be programmed via I
2
C with a mask-
able
IRQ
output for monitoring DC/DC and system faults.
Pushbutton ON/OFF/RESET control, power-on reset, and
a watchdog timer provide flexible and reliable power-up
sequencing and system monitoring. The LTC3375 is avail-
able in a low profile 48-lead 7mm
×
7mm 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.
n
n
n
n
n
n
n
n
8-Channel Independent Step-Down DC/DCs
Master-Slave Configurable for Up to 4A Per Output
Channel with a Single Inductor
Independent V
IN
Supply for Each DC/DC
(2.25V to 5.5V)
All DC/DCs Have 0.425V to V
IN
Output Voltage Range
Precision Enable Pin Thresholds for Autonomous
Sequencing (or I
2
C Control)
1MHz to 3MHz Programmable/Synchronizable
Oscillator Frequency (2MHz Default)
I
2
C Selectable Phasing (90° Steps) Per Channel
Programmable Power-On Reset/Watch Dog/
Pushbutton Timing
Die Temperature Monitor Output
48-Lead (7mm
×
7mm) QFN Package
applicaTions
n
n
General Purpose Multichannel Power Supplies
Industrial/Automotive/Communications
Typical applicaTion
8-Channel 1A Multioutput Buck Regulator
4V TO 40V
V
IN1
SW1
FB1
2.2µH
10µF
LTC3375
MASTER
2.2µH
V
SHNT
ALWAYS-ON
LDO
V
CC
FBV
CC
ON
KILL
PB
PB
EN1
EN2
EN3
EN4
EN5
EN6
EN7
EN8
RST
TEMP
WDI
WD0
IRQ
I
2
C
SYNC
RT
0.425V TO V
IN1
UP TO 1A
Buck Efficiency vs Load
100
90
80
1A BUCK
2A BUCK
3A BUCK
4A BUCK
10µF
FB2
MASTER
V
IN7
SW7
FB7
2.2µH
•
•
•
SLAVE
10µF
MASTER
2.2µH
0.425V TO V
IN2
UP TO 1A
EFFICIENCY (%)
V
IN2
SW2
SLAVE
70
60
50
40
30
20
10
0.425V TO V
IN7
UP TO 1A
0
Burst Mode OPERATION
V
IN
= 3.3V
V
OUT
= 1.8V
f
OSC
= 2MHz
L = 2.2µH
1
100
1000
10
LOAD CURRENT (mA)
3375 TA01b
2
V
IN8
SW8
FB8
CT
SLAVE
10µF
0.425V TO V
IN8
UP TO 1A
3375 TA01a
3375fd
For more information
www.linear.com/3375
1
LTC3375
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 ................... 7
Pin Functions .............................................. 12
Block Diagram............................................. 15
Operation................................................... 16
Buck Switching Regulators ..................................... 16
Buck Regulators with Combined Power Stages ...... 16
Pushbutton Interface .............................................. 17
Power-Up and Power-Down Via Pushbutton ........... 17
Power-Up and Power-Down Via Enable Pin or I
2
C .. 19
I
2
C Interface ...........................................................20
I
2
C Bus Speed.........................................................20
I
2
C Start and Stop Conditions.................................20
I
2
C Byte Format ......................................................20
I
2
C Acknowledge ....................................................20
I
2
C Slave Address ................................................... 21
I
2
C Sub-Addressed Writing.....................................22
I
2
C Bus Write Operation .........................................22
I
2
C Bus Read Operation ..........................................22
Error Condition Reporting Via
RST
and
IRQ
Pins....22
Temperature Monitoring and
Overtemperature Protection ...................................23
RESET_ALL Functionality ....................................... 24
Programming the Operating Frequency .................. 24
V
CC
Shunt Regulator ...............................................25
Watchdog Timer .....................................................25
Applications Information ................................ 26
Buck Switching Regulator Output Voltage and
Feedback Network ..................................................26
Buck Regulators .....................................................26
Combined Buck Regulators.....................................26
V
CC
Shunt Regulator ............................................... 28
Input and Output Decoupling Capacitor Selection ..29
Choosing the C
T
Capacitor ......................................29
Programming the Global Register...........................29
Programming the
RST
and
IRQ
Mask Registers .....29
Status Byte Read Back ...........................................29
PCB Considerations ................................................ 31
Typical Applications ...................................... 32
Package Description ..................................... 35
Typical Application ....................................... 36
Related Parts .............................................. 36
2
3375fd
For more information
www.linear.com/3375
LTC3375
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
48 EN1
47 EN2
46 SDA
45 SCL
44 TEMP
43 V
SHNT
42 FBV
CC
41 V
CC
40 WDI
39 WDO
38 EN7
37 EN8
FB1 1
V
IN1
2
SW1 3
SW2 4
V
IN2
5
FB2 6
FB3 7
V
IN3
8
SW3 9
SW4 10
V
IN4
11
FB4 12
GND
49
36 FB8
35 V
IN8
34 SW8
33 SW7
32 V
IN7
31 FB7
30 FB6
29 V
IN6
28 SW6
27 SW5
26 V
IN5
25 FB5
UK PACKAGE
48-LEAD (7mm
×
7mm) PLASTIC QFN
T
JMAX
= 150°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 49) IS GND, MUST BE SOLDERED TO PCB
V
IN1-8
, FB1-8, EN1-8, V
CC
, V
SHNT
, FBV
CC
, CT,
ON,
KILL, IRQ, RST, PB,
WDI, WDO, SYNC, RT,
SDA, SCL ..................................................... –0.3V to 6V
TEMP ...................–0.3V to Lesser of (V
CC
+ 0.3V) or 6V
I
IRQ
, I
RST
, I
WDO
, I
ON
.................................................5mA
I
VSHNT
......................................................................3mA
Operating Junction Temperature Range
(Notes 2, 3) ............................................ –40°C to 150°C
Storage Temperature Range .................. –65°C to 150°C
orDer inForMaTion
LEAD FREE FINISH
LTC3375EUK#PBF
LTC3375IUK#PBF
LTC3375HUK#PBF
TAPE AND REEL
LTC3375EUK#TRPBF
LTC3375IUK#TRPBF
LTC3375HUK#TRPBF
PART MARKING*
LTC3375UK
LTC3375UK
LTC3375UK
PACKAGE DESCRIPTION
48-Lead (7mm
×
7mm) Plastic QFN
48-Lead (7mm
×
7mm) Plastic QFN
48-Lead (7mm
×
7mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–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. Consult LTC Marketing for information on non-standard lead based finish parts.
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/
EN4 13
EN3 14
IRQ
15
RST
16
CT 17
SYNC 18
RT 19
ON 20
PB
21
KILL
22
EN6 23
EN5 24
3375fd
For more information
www.linear.com/3375
3
LTC3375
elecTrical characTerisTics
SYMBOL
V
VCC
V
VCC_UVLO
I
VCC_ALLOFF
I
VCC
f
OSC
f
SYNC
V
SYNC
V
RT
V
TEMP(ROOM)
∆V
TEMP
/°C
OT
OT_HYST
DT_WARN
PARAMETER
V
CC
Voltage Range
Undervoltage Threshold on V
CC
V
CC
Input Supply Current
V
CC
Input Supply Current
Internal Oscillator Frequency
V
CC
Voltage Falling
V
CC
Voltage Rising
All Switching Regulators in Shutdown,
PB
= HIGH
At Least 1 Buck Active, SYNC = 0V, R
T
= 400k,
V
FB_BUCK
= 0.85V
At Least 1 Buck Active, SYNC = 2MHz
V
RT
= V
CC
, SYNC = 0V
V
RT
= V
CC
, SYNC = 0V
R
RT
= 400k, SYNC = 0V
t
LOW
, t
HIGH
> 40ns
l
l
l
l
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
CC
= V
IN1-8
= 3.3V, unless otherwise specified.
CONDITIONS
l
l
l
MIN
2.7
2.35
2.45
TYP
2.45
2.55
11
50
200
MAX
5.5
2.55
2.65
25
85
325
2.2
2.25
2.2
3
0.4
UNITS
V
V
V
µA
µA
µA
MHz
MHz
MHz
MHz
V
V
mV
mV
mV/°C
°C
°C
°C
°C
°C
1.8
1.75
1.8
1
1.2
780
2
2
2
Synchronization Frequency
SYNC Level High
SYNC Level Low
RT Servo Voltage
TEMP Voltage at 25°C
V
TEMP
Slope
Overtemperature Shutdown
Overtemperature Hysteresis
R
RT
= 400k
l
800
150
820
Temperature Monitor
l
6.75
165
10
Inactive
140
125
110
Temperature Rising
Die Temperature Warning Threshold (Die DT[1], DT[0] = 00
Temperature that Causes
IRQ
= 0)
DT[1], DT[0] = 01
DT[1], DT[0] = 10
DT[1], DT[0] = 11
Buck Input Voltage Range
Undervoltage Threshold on V
IN
Burst Mode
®
Operation
Forced Continuous Mode Operation
Shutdown Input Current
Shutdown Input Current
PMOS Current Limit
Feedback Regulation Voltage
Feedback Regulation Voltage
Feedback Regulation Voltage
V
FB
Servo Voltage Step Size
Feedback Leakage Current
Maximum Duty Cycle
PMOS On-Resistance
NMOS On-Resistance
PMOS Leakage Current
NMOS Leakage Current
Soft-Start Time
V
FB_BUCK
= 0.85V
V
FB_BUCK
= 0V
I
SW_BUCK
= 100mA
I
SW_BUCK
= –100mA
EN_BUCK = 0
EN_BUCK = 0
Default (1, 1, 0, 0) Reference Voltage
–2
–2
l
l
l
1A Buck Regulators
V
BUCK
V
OUT
V
IN_UVLO
I
VIN_BUCK
V
IN
Voltage Falling
V
IN
Voltage Rising
V
FB_BUCK
= 0.85V (Note 4)
I
SW_BUCK
= 0µA, V
FB_BUCK
= 0V
All Switching Regulators in Shutdown
At Least One Other Buck Active
(Note 5)
Forced Continuous Mode Default (1, 1, 0, 0)
Forced Continuous Mode Full Scale (1, 1, 1, 1)
l
l
2.25
V
FB
1.95
2.05
2.05
2.15
18
400
0
1
2.0
705
780
405
–50
100
335
315
2.3
725
800
425
25
5.5
V
IN
2.15
2.25
50
550
1
2
2.7
745
820
445
50
V
V
V
V
µA
µA
µA
µA
A
mV
mV
mV
mV
nA
%
mΩ
mΩ
l
l
I
FWD
V
FB
(Default)
V
FB
(High)
V
FB
(Low)
V
LSB
I
FB
DMAX
R
PMOS
R
NMOS
I
LEAKP
I
LEAKN
R
SWPD
t
SS
Forced Continuous Mode Zero Scale (0, 0, 0, 0)
l
2
2
1
1
µA
µA
kΩ
ms
3375fd
Output Pull-Down Resistance in Shutdown EN_BUCK = 0 (I
2
C Bit Set)
4
For more information
www.linear.com/3375
LTC3375
elecTrical characTerisTics
SYMBOL
V
PGOOD(FALL)
V
PGOOD(HYS)
I
FWD2
I
FWD3
I
FWD4
V
CC
Regulator
V
FBVCC
R
REG
V
VSHNT_MAX
R
CLAMP
I
2
C Port
ADDRESS
V
IH
V
IL
I
IH
I
IL
V
OL_SDA
f
SCL
t
BUF
t
HD_SDA
t
SU_STA
t
SU_STO
t
HD_DAT(O)
t
HD_DAT(I)
t
SU_DAT
t
LOW
t
HIGH
t
f
t
r
I
OH
V
OL
V
IH
V
IL
t
WDI
t
WDO
t
WDRESET
I
2
C Address
Input High Voltage
Input Low Voltage
Input High Current
Input Low Current
SDA Output Low Voltage
Clock Operating Frequency
Bus Free Time Between Stop and Start
Condition
Hold Time After Repeated Start
Condition
Repeated Start Condition Set-Up Time
Stop Condition Set-Up Time
Data Hold Time Output
Data Hold Time Input
Data Set-Up Time
SCL Clock Low Period
SCL Clock High Period
Clock/Data Fall Time
Clock/Data Rise Time
Output High Leakage Current
Output Low Voltage
Input High Threshold
Input Low Threshold
Time From Last WDI
WDO Low Time Absent a Transition at WDI
Time From a WDI Transition Until the
WD Timer Is Reset
C
B
= Capacitance of One Bus Line (pF)
C
B
= Capacitance of One Bus Line (pF)
ON,
RST, IRQ,
WDO 5.5V at Pin
ON,
RST, IRQ,
WDO 3mA Into Pin
KILL, PB,
WDI
KILL, PB,
WDI
l
l
l
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
CC
= V
IN1-8
= 3.3V, unless otherwise specified.
PARAMETER
Falling PGOOD Threshold Voltage
PGOOD Hysteresis
PMOS Current Limit
PMOS Current Limit
PMOS Current Limit
FBV
CC
Regulation Voltage
Pull-Down Resistance for V
CC
(Regulator)
V
SHNT
Clamp Voltage
Pull-Down Resistance for V
SHNT
(Clamp)
I
SHNT
= 2mA, FBV
CC
= 0V
CONDITIONS
% of Full-Scale (1, 1, 1, 1) Reference Voltage
% of Regulated V
FB
2 Buck Converters Combined (Note 5)
3 Buck Converters Combined (Note 5)
4 Buck Converters Combined (Note 5)
1.17
MIN
TYP
92.5
1
4.6
6.9
9.2
1.2
200
6.1
200
0110100[R/WB]
1.2
0.4
50
50
0.4
400
1.3
0.6
0.6
0.6
0
0
250
1.3
0.6
20+0.1C
B
20+0.1C
B
-1
0.1
1.2
0.4
1.5
200
2
300
300
1
0.4
900
V
V
nA
nA
V
kHz
µs
µs
µs
µs
ns
ns
ns
µs
µs
ns
ns
µA
V
V
V
sec
ms
µs
1.23
MAX
UNITS
%
%
A
A
A
V
Ω
V
Ω
Buck Regulators Combined
SDA/SCL
SDA/SCL
SDA/SCL
SDA/SCL
I
SDA
= 3mA
l
l
Interface Logic Pins (ON,
KILL, RST, IRQ, PB,
WDI, WDO)
3375fd
For more information
www.linear.com/3375
5
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