Document
LTC3874-1
PolyPhase Step-Down Synchronous Slave Controller with
Sub-Milliohm DCR Sensing
Features
n Phase Extender for High Phase Count Voltage Rails n Operates with Power Blocks, DrMOS or External
Gate Drivers and MOSFETs n Accurate Phase-to-Phase Current Sharing n Sub-Milliohm DCR Current Sensing n Phase-Lockable Fixed Frequency 250kHz to 1MHz n Immediate Response to Master IC's Fault n Up to 12-Phase Operation n Wide VIN Range: 4.5 to 38V n VOUT Range : Up to 3.5V (LOWDCR Pin High)
Up to 5.5V (LOWDCR Pin Low) n Proprietary Current Mode Control Loop n Programmable CCM/DCM Operation n Programmable Phase Shift Control n 24-Lead (4mm × 4mm) QFN Package
Applications
n High Current Distributed Power Systems n Telecom, Datacom and Storage Systems n Intelligent Energy Efficient Power Regulation
Description
The LTC®3874-1 is a dual PolyPhase® current mode synchronous step-down slave controller. It enables high current, multiphase applications when paired with a companion master controller by extending the phase count. Compatible 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 submilliohm 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.
Typical Application
VIN 7V TO 14V
High Efficiency, 4-Phase 1.8V/120A Step-Down Supply
470µF
+ ×2
(0.29mΩ DCR) 0.215µH
100µF ×3
649Ω 0.22µF
DrMOS
LTC3884-1
1.8V
VSENSE0+ VSENSE1+
RUN0
RUN1
FAULT0
FAULT1 PGOOD0 PGOOD1
ITH0 ITH1 SYNC
VIN
LTC3874-1
PWM0
PWM1
DrMOS
ISENSE0+ ISENSE0–
ISENSE1+ ISENSE1–
RUN0 RUN1
FAULT0
FAULT1 MODE0 MODE1 ITH0 ITH1 SYNC
INTVCC VCC0 VCC1
PHASMD LDWDCR
ILIM
FREQ GND
100k
4.7µF
(0.29mΩ DCR) 0.215µH
649Ω 0.22µF
100µF ×3
REFER TO LTC3884-1 DATA SHEET FOR MASTER SETUP
PIN NOT USED IN THIS CIRCUIT: EXTVCC
38741 TA01a
For more information www.linear/LTC3874-1
+
VOUT 1.8V 120A
470µF ×2
EFFICIENCY (%)
POWER LOSS (W)
4-Phase Efficiency and Power Loss vs Output Current, SubMilliohm DCR vs Traditional
DCR
100
20
VIN = 12V
VOUT = 1.8V
95 fSW = 425kHz
17
CCM
90
EFFICIENCY
14
85
11
80
POWER LOSS
8
0.29mΩ
75
1.5mΩ 5
0.29mΩ
1.5mΩ
70
2
0 10 20 30 40 50 60 70 80 90 100 110 120
LOAD CURRENT (A)
38741 TA01b
38741f
1
LTC3874-1
Absolute Maximum Ratings
(Note 1)
VIN.............................................................. −0.3V to 40V VCC0, VCC1..................................................... −0.3V to 6V ISENSE0+, ISENSE0–, ISENSE1+, ISENSE1–..... −0.3V to INTVCC EXTVCC, INTVCC, RUN0, RUN1..................... −0.3V to 6V MODE0, MODE1, ILIM, LOWDCR, PHASMD, FREQ..................................... −0.3V to INTVcc SYNC, FAULT0, FAULT1, ITH0, ITH1.......... −0.3V to INTVcc INTVCC Peak Output Current.................................100mA Operating Junction Temperature Range (Note 2)................................................... −40°C to 125°C Storage Temperature Range................... −65°C to 150°C
Pin Configuration
TOP VIEW
MODE0 ITH0 LOWDCR FAULT0 FAULT1 PWM0
ISENSE0+ 1 ISENSE0– 2
RUN0 3
RUN1 4 ISENSE1– 5 ISENSE1+ 6
24 23 22 21 20 19
18 VCC0
17 VIN
25
16 INTVCC
GND
15 EXTVCC
14 VCC1
13 PWM1
7 8 9 10 11 12
MODE1 ITH1
FREQ ILIM SYNC PHASMD
UF PACKAGE 24-LEAD (4mm × 4mm) PLASTIC QFN
TJMAX = 125°C, θJA = 46.9°C/W, θJC_BOT = 4.5°C/W EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
Order Information http://www.linear.com/product/LTC3874-1#orderinfo
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3874EUF-1#PBF
LTC3874EUF-1#TRPBF 38741
24-Lead (4mm × 4mm) Plastic QFN
–40°C to 125°C
LTC3874IUF-1#PBF
LTC3874IUF-1#TRPBF 38741
24-Lead (4mm × 4mm) Plastic QFN
–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.
38741f
2
For more information www.linear.com/LTC3874-1
LTC3874-1
Electrical Characteristics The l denotes the specifications which apply o.