chronous step-down slave controller. It enables high cur-
rent, multiphase applications when paired with a companion
master controller by extending the phase count. Compat-
ible master controllers include the LTC3884-1, LTC3774,
LTC3875, LTC3877 and LTC3866. The LTC3874-1 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 LTC3874-1
supports all the programmable features as well as fault
protection.
L,
LT, LTC, LTM, Linear Technology, the Linear logo, PolyPhase and µModule 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, 6144194, 6177787,
6580258, 5408150.
n
n
n
n
n
n
n
n
n
n
n
Phase Extender for High Phase Count Voltage Rails
Operates with Power Blocks, DrMOS or External
Gate Drivers and MOSFETs
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: 4.5 to 38V
V
OUT
Range : Up to 3.5V (LOWDCR Pin High)
Up to 5.5V (LOWDCR Pin Low)
Proprietary Current Mode Control Loop
Programmable CCM/DCM Operation
Programmable Phase Shift Control
24-Lead (4mm
×
4mm) QFN Package
applicaTions
n
n
n
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
V
IN
DrMOS
LTC3874-1
PWM0
PWM1
DrMOS
(0.29m DCR)
0.215µH
649
(0.29m DCR)
0.215µH
649
0.22µF
I
SENSE0+
I
SENSE0–
LTC3884-1
RUN0
RUN1
FAULT0
FAULT1
PGOOD0
PGOOD1
I
TH0
I
TH1
SYNC
RUN0
RUN1
FAULT0
FAULT1
MODE0
MODE1
I
TH0
I
TH1
SYNC
I
SENSE1+
I
SENSE1–
INTV
CC
V
CC0
V
CC1
PHASMD
LDWDCR
ILIM
FREQ
GND
100k
EFFICIENCY (%)
V
OUT
1.8V
120A
100µF
×3
4-Phase Efficiency and Power
Loss vs Output Current, Sub-
Milliohm DCR vs Traditional
DCR
100
V
IN
= 12V
V
OUT
= 1.8V
95 f
SW
= 425kHz
CCM
90
85
80
75
70
0
POWER LOSS
EFFICIENCY
20
17
14
11
8
POWER LOSS (W)
+
470µF
×2
100µF
×3
0.22µF
+
470µF
×2
4.7µF
1.8V
V
SENSE0+
V
SENSE1+
38741 TA01a
0.29mΩ
1.5mΩ 5
0.29mΩ
1.5mΩ
2
10 20 30 40 50 60 70 80 90 100 110 120
LOAD CURRENT (A)
38741 TA01b
REFER TO LTC3884-1 DATA SHEET
FOR MASTER SETUP
PIN NOT USED IN THIS CIRCUIT: EXTV
CC
38741f
For more information
www.linear/LTC3874-1
1
LTC3874-1
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
LOWDCR
FAULT0
FAULT1
MODE0
PWM0
18 V
CC0
17 V
IN
25
GND
16 INTV
CC
15 EXTV
CC
14 V
CC1
13 PWM1
7
MODE1
8
I
TH1
9 10 11 12
PHASMD
SYNC
FREQ
ILIM
I
TH0
V
IN
............................................................. −0.3V to 40V
V
CC0
, V
CC1
.................................................... −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
24 23 22 21 20 19
I
SENSE0+
1
I
SENSE0–
2
RUN0 3
RUN1 4
I
SENSE1
I
SENSE1
–
+
5
6
UF PACKAGE
24-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 46.9°C/W,
θ
JC_BOT
= 4.5°C/W
EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LTC3874EUF-1#PBF
LTC3874IUF-1#PBF
TAPE AND REEL
LTC3874EUF-1#TRPBF
LTC3874IUF-1#TRPBF
http://www.linear.com/product/LTC3874-1#orderinfo
PART MARKING*
38741
38741
PACKAGE DESCRIPTION
24-Lead (4mm
×
4mm) Plastic QFN
24-Lead (4mm
×
4mm) 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
38741f
For more information
www.linear.com/LTC3874-1
LTC3874-1
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
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
PWM Outputs
PWM
PWM Output High Voltage
PWM Output Low Voltage
PWM Output Current in Hi-Z State
Minimum On-Time
Internal V
CC
Voltage No Load
INTV
CC
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Voltage Drop
EXTV
CC
Hysteresis
PLL SYNC Range
Nominal Frequency
Frequency Setting Current
SYNC to Ch0 Phase Relationship Based on
the Falling Edge of SYNC and Rising Edge of
PWM0
SYNC to Ch1 Phase Relationship Based on
the Falling Edge of SYNC and Rising Edge of
PWM1
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
l
l
elecTrical characTerisTics
PARAMETER
Input Voltage Range
Output Voltage Range
Input DC Supply Current
Normal Operation
Shutdown
Undervoltage Lockout Threshold
CONDITIONS
LOWDCR = INTV
CC
(Note 3)
LOWDCR = 0V
V
RUN0,1
= 3.3V
V
RUN0,1
= 0V
V
INTVCC
Falling
V
INTVCC
Rising
MIN
4.5
TYP
MAX
38
3.5
5.5
UNITS
V
V
V
mA
mA
V
V
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
l
l
l
l
I
LOAD
= 500µA
I
LOAD
= –500µA
(Note 4)
6V < V
IN
< 38V
I
CC
= 0mA to 20mA
V
EXTVCC
Ramping Positive (Note 5)
I
CC
= 20mA, V
EXTVCC
= 5V
l
l
V
CC
– 0.2
–5
60
5.25
5.5
0.5
4.7
50
300
250
500
9
10
180
60
120
90
0
300
240
270
0.2
5
V
V
µA
ns
t
ON(MIN)
V
INTVCC
V
LDO
INT
V
EXTVCC
V
LDO
EXT
V
LDOHYS
f
RANGE
f
NOM
I
FREQ
θ
SYNC-
θ
0
INTV
CC
Regulator
5.75
2
100
V
%
V
mV
mV
1000
11
kHz
kHz
µA
Deg
Deg
Deg
Deg
Deg
Deg
Deg
Deg
2.0
1.4
V
V
38741f
l
4.5
Oscillator and Phase-Locked Loop
V
FREQ
= 0.9V
θ
SYNC-
θ
1
Digital Inputs RUN0, RUN1, MODE0, MODE1,
FAULT0, FAULT1,
LOWDCR
V
IH
V
IL
Input High Threshold Voltage
Input Low Threshold Voltage
For more information
www.linear/LTC3874-1
3
LTC3874-1
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 LTC3874-1 is tested under pulsed load conditions such
that T
J
≈ T
A
. The LTC3874E-1 is guaranteed to meet specifications
from 0°C to 85°C junction temperature. Specifications over the –40°Ç
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3874I-1 is guaranteed over the –40°C to 125°C operating junction
temperature range. Note that the maximum ambient temperature
consistent with these specifications is determined by specific operating
conditions in conjunction with board layout, the related package thermal
impedance and other environmental factors. The junction temperature T
J
is calculated from the ambient temperature T
A
and power dissipation PD
according to the following formula: T
J
= T
A
+ (PD
•
46.9°C/W)
Note 3:
Output voltage is set and controlled by master controller in
multiphase operations.
Note 4:
The minimum on-time condition corresponds to an inductor
peak-to-peak ripple current ≥40% of I
MAX
(see Minimum On-Time
Considerations in the Applications Information section).
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