nous step-down slave controller. It enables high current,
multi-phase applications when paired with a companion
master controller by extending the phase count. Compat-
ible master controllers include the LTC3884, LTC3866,
LTC3875, LTC3877 and LTC3774. The LTC3874 employs a
unique architecture that enhances the signal-to-noise ratio
of the current sense signal, allowing the use of sub-milliohm
DC resistance power inductors to maximize efficiency while
reducing switching jitter. Its peak current mode architecture
allows for accurate phase to phase current sharing even
for dynamic loads.
Effectively working with a master controller, the LTC3874
supports all the programmable features as well as fault
protection.
L,
LT, LTC, LTM, Linear Technology, the Linear logo, PolyPhase and Burst Mode are registered
trademarks of Analog Devices, Inc. All other trademarks are the property of their respective
owners. Protected by U.S. Patents, including 5481178, 5705919, 5929620, 6100678, 6144194,
6177787, 6304066, 6580258.
n
n
n
n
n
Phase Extender for High Phase Count Voltage Rails
Accurate Phase-to-Phase Current Sharing
Sub-Milliohm DCR Current Sensing
Phase-Lockable Fixed Frequency 250kHz to 1MHz
Immediate Response to Master IC's Fault
Up to 12 Phase Operation
Wide V
IN
Range: 4.5V to 38V
V
OUT
Range: Up to 3.5V (LOWDCR Pin = INTV
CC
)
Up to 5.5V (LOWDCR Pin = OV)
Proprietary Current Mode Control Loop
Programmable CCM/DCM Operation
Programmable Phase Shift Control
Dual N-Channel MOSFET Gate Drivers
28-Lead (4mm
×
5mm) QFN Package
APPLICATIONS
n
n
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High Current Distributed Power Systems
Telecom, Datacom, and Storage Systems
Intelligent Energy Efficient Power Regulation
TYPICAL APPLICATION
High Efficiency, 4-Phase 1.8V/120A Step-Down Supply
V
IN
7V TO 14V
4.7µF
V
IN
INTV
CC
LTC3874 TG0
PHASMD BOOST0
LOWDCR
90k
EXTV
CC
FREQ
ILIM
SW0
BG0
I
SENSE0+
I
SENSE0
LTC3884
RUN0
RUN1
GPIO0
GPIO1
PGOOD0
PGOOD1
I
TH0
I
TH1
SYNC
RUN0
RUN1
FAULT0
FAULT1
MODE0
MODE1
I
TH0
I
TH1
SYNC
–
Dual Phase Efficiency and Power Loss
vs Output Current, Sub-Milliohm DCR
vs Traditional DCR
0.1µF
0.33µH
(0.32m DCR)
100
V
OUT
1.8V
120A
EFFICIENCY (%)
95
90
85
POWER LOSS
80
75
0.32m
1.5m
0.32m
1.5m
0
10
20
30
40
LOAD CURRENT (A)
50
6
4
2
0
60
V
IN
= 12V
V
OUT
= 1.8V
CCM
EFFICIENCY
14
12
10
8
POWER LOSS (W)
+
931
0.22µF
470µF
×2
TG1
BOOST1
SW1
BG1
GND
I
SENSE1+
I
SENSE1–
0.1µF
0.33µH
(0.32m DCR)
V
SENSE0+
V
SENSE1
+
+
931
0.22µF
470µF
×2
70
3874 TA01b
3874 TA02
3874fb
For more information
www.linear.com/LTC3874
1
LTC3874
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
LOWDCR
FAULT0
FAULT1
SW0
22 BOOST0
21 BG0
20 V
IN
29
GND
19 INTV
CC
18 EXTV
CC
17 BG1
16 BOOST1
15 SW1
9 10 11 12 13 14
FREQ
ILIM
SYNC
PHASMD
I
TH1
TG1
I
TH0
TG0
V
IN
............................................................. −0.3V to 40V
BOOST0, BOOST1 ...................................... −0.3V to 46V
SW0, SW1 .................................................... −5V to 40V
(BOOST0-SW0), (BOOST1-SW1) ................. −0.3V to 6V
I
SENSE0+
, I
SENSE0 –
, I
SENSE1+
, I
SENSE1–
... −0.3V to INTV
CC
EXTV
CC
, INTV
CC
, RUN0, RUN1 .................... −0.3V to 6V
MODE0, MODE1, ILIM, LOWDCR,
PHASMD, FREQ .................................... −0.3V to INTVcc
SYNC,
FAULT0, FAULT1,
I
TH0
, I
TH1
......... −0.3V to INTVcc
INTV
CC
Peak Output Current ................................100mA
Operating Junction Temperature Range
(Note 2) .................................................. −40°C to 125°C
Storage Temperature Range .................. −65°C to 150°C
28 27 26 25 24 23
MODE0 1
I
SENSE0
I
SENSE0
+
–
2
3
RUN0 4
RUN1 5
I
SENSE1–
6
I
SENSE1+
7
MODE1 8
UFD PACKAGE
28-LEAD (4mm
×
5mm) PLASTIC QFN
θ
JA
= 43°C/W,
θ
JC
= 3.4°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3874EUFD#PBF
LTC3874IUFD#PBF
TAPE AND REEL
LTC3874EUFD#TRPBF
LTC3874IUFD#TRPBF
PART MARKING*
3874
3874
PACKAGE DESCRIPTION
28-Lead (4mm
×
5mm) Plastic QFN
28-Lead (4mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°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.
2
3874fb
For more information
www.linear.com/LTC3874
LTC3874
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
IN
= 12V, V
RUN0,1
= 3.3V unless otherwise specified.
SYMBOL
Input Voltage
V
IN
V
OUT
I
Q
V
UVLO
Control Loop
I
ISENSE0,1
I
SENSE
Pins Bias Current
V
ISENSE0,1
< (V
INTVCC
– 3.3V)
V
ISENSE0,1
> (V
INTVCC
– 3.3V)
(Table 3)
ILIM = INTV
CC
, LOWDCR = INTV
CC
,
V
ISENSE0,1
= 1.2V, V
ITH
= 2.18V
ILIM = 0V, LOWDCR = INTV
CC
,
V
ISENSE0,1
= 1.2V, V
ITH
= 2.18V
ILIM = INTV
CC
, LOWDCR = 0V,
V
ISENSE0,1
= 1.2V, V
ITH
= 2.18V
ILIM = 0V, LOWDCR = 0V,
V
ISENSE0,1
= 1.2V, V
ITH
= 2.18V
Gate Drivers
TG R
UP
TG R
DOWN
BG R
UP
BG R
DOWN
TG0,1
t
r
t
f
BG0,1
t
r
t
f
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
V
INTVCC
V
LDO
INT
V
EXTVCC
V
LDO
EXT
V
LDOHYS
TG Pull-Up R
DS(ON)
TG Pull-Down R
DS(ON)
BG Pull-Up R
DS(ON)
BG Pull-Down R
DS(ON)
TG Transition Time:
Rise Time
Fall Time
BG Transition Time:
Rise Time
Fall Time
Top Gate Off to Bottom Gate on Delay Time
Bottom Gate Off to Top Gate On Delay Time
Minimum On-Time
Internal V
CC
Voltage No Load
INTV
CC
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Voltage Drop
EXTV
CC
Hysteresis
TG High
TG Low
BG High
BG Low
(Note 5)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 5)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver (Note 5)
C
LOAD
= 3300pF Each Driver (Note 5)
(Note 6)
6V < V
IN
< 38V
I
CC
= 0mA to 20mA
EXTV
CC
Ramping Positive (Note 7)
I
CC
= 20mA, V
EXTVCC
= 5V
l
l
l
l
l
l
l
ELECTRICAL CHARACTERISTICS
PARAMETER
Input Voltage Range
Output Voltage Range
Input DC Supply Current
Normal Operation
Shutdown
Undervoltage Lockout Threshold
CONDITIONS
MIN
4.5
TYP
MAX
38
3.5
5.5
UNITS
V
V
V
mA
mA
V
V
LOWDCR = INTV
CC
(Note 3)
LOWDCR = 0V
(Note 4)
V
RUN0,1
= 3.3V
V
RUN0,1
= 0V
V
INTVCC
Falling
V
INTVCC
Rising
4.6
1.8
3.5
3.8
±0.15
±1
26.8
14.5
65
33
28.8
16
72
40
±0.4
±3
30.8
17.5
79
47
µA
µA
mV
mV
mV
mV
V
ISENSE(MAX)
Maximum Current Sense Threshold
2.6
1.5
2.4
1.1
30
30
30
30
30
30
60
5.25
4.5
5.5
0.5
4.7
50
300
100
5.75
2
Ω
Ω
Ω
Ω
ns
ns
ns
ns
ns
ns
ns
V
%
V
mV
mV
INTV
CC
Regulator
3874fb
For more information
www.linear.com/LTC3874
3
LTC3874
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
IN
= 12V, V
RUN0,1
= 3.3V unless otherwise specified.
SYMBOL
f
RANGE
f
NOM
I
FREQ
θ
SYNC-θ0
PARAMETER
PLL SYNC Range
Nominal Frequency
Frequency Setting Current
SYNC to Ch0 Phase Relationship Based on
the Falling Edge of SYNC and Rising Edge
of TG0
SYNC to Ch1 Phase Relationship Based on
the Falling Edge of SYNC and Rising Edge
of TG1
PHASMD = 0
PHASMD = 1/3 • INTV
CC
PHASMD = 2/3 • INTV
CC
PHASMD = INTV
CC
PHASMD = 0
PHASMD = 1/3 • INTV
CC
PHASMD = 2/3 • INTV
CC
PHASMD = INTV
CC
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
l
MIN
250
TYP
MAX
1000
UNITS
kHz
kHz
µA
Deg
Deg
Deg
Deg
Deg
Deg
Deg
Deg
Oscillator and Phase-Locked Loop
V
FREQ
= 0.9V
9
500
10
180
60
120
90
0
300
240
270
2.0
1.4
11
θ
SYNC-θ1
Digital Inputs RUN0, RUN1, MODE0, MODE1,
FAULT0, FAULT1,
LOWDCR
V
IH
V
IL
Input High Threshold Voltage
Input Low Threshold Voltage
V
V
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 LTC3874 is tested under pulsed load conditions such that
T
J
≈ T
A
. The LTC3874E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3874I is guaranteed
over the –40°C to 125°C operating junction temperature range. High
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