LTC3870
PolyPhase Step-Down
Slave Controller for Digital
Power System Management
Description
Features
LTC3880 Family Phase Extender Supporting
LTC3880/3880-1, LTC3883/3883-1, LTC3886,
LTC3887 Master Controllers
n Cascade with Multiple Chips for Very Large Current
Applications
n Accurate PolyPhase Current Sharing
n EXTV
CC Capable of 5V to 14V Input
n Wide V Range: 4.5V to 60V
IN
n Wide Output Voltage Range : 0.5V to 14V
n Wide SYNC Frequency Range: 100kHz to 1MHz
n Pin Programmable of CCM/DCM Operation
n Pin Programmable of Phase-Shift Control
n Integrated Powerful N-Channel MOSFET Gate Drivers
n Available in a 28-Pin (4mm × 5mm) QFN Package
The LTC®3870 is a PolyPhase® step-down slave controller specially designed for multiphase operation with the
LTC3880 family digital power system management DC/DC
controllers. It provides a small and cost effective solution
for supplying very large currents by cascading it with a
master controller. A peak current mode architecture provides the LTC3870 with excellent current sharing from
phase to phase and from chip to chip.
n
Coherently working with the LTC3880 family, the LTC3870
does not require additional I2C addresses, and it supports
all programmable features as well as fault protection.
The constant switching frequency can be synchronized
to an external clock from the master controller from
100kHz to 1MHz.
Applications
L, LT, LTC, LTM, PolyPhase, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners. Protected by U.S. Patents including 5481178, 5705919, 5929620, 6144194, 6177787,
6580258, 5408150
High Power Distributed Power Systems
Telecom Systems
n Industrial Applications
n
n
Typical Application
Load Transient Response of a
2-Phase Master (3880)/Slave
(3870) Converter
VIN
4.7µF
VOUT0
30A
+
VIN
INTVCC
TG0
1.0µH
530µF
0.1µF
TG1
BOOST0
BOOST1
SW0
BG0
2.15k
BG1
PGND
0.2µF
0.1µF
SW1
1.74k
EXTVCC
LTC3880*
RUN0
3.3V
RUN1
VSENSE0+ GPIO0
GPIO1
ITH0
1.8V
VSENSE1
ITH1
SYNC
* REFER TO LTC3880 DATA SHEET
FOR MASTER SETUP
RUN0
RUN1
FAULT0
FAULT1
ITH0
ITH1
SYNC
+
530µF
0.2µF
LTC3870
ISENSE0+
ISENSE0–
VOUT1
40A
0.56µH
IL_3880(CH1)
10A/DIV
IL_3870(CH1)
10A/DIV
ISENSE1+
ISENSE1–
FREQ
PHASMD
ILIM
MODE0
MODE1
SGND
ILOAD
10A/DIV
0A TO 10A TO 0A
VOUT1
100mV/DIV
AC-COUPLED
100k
VIN = 12V
VOUT1 = 1.8V
50µs/DIV
3870 TA01b
3870 TA01a
3870fb
For more information www.linear.com/LTC3870
1
LTC3870
Absolute Maximum Ratings
Pin Configuration
(Note 1)
VIN.............................................................. –0.3V to 65V
BOOST0, BOOST1........................................–0.3V to 71V
SW0, SW1..................................................... –5V to 65V
ISENSE0+, ISENSE0−, ISENSE1+, ISENSE1–..........–0.3V to 15V
(BOOST0-SW0), (BOOST1-SW1).................. –0.3V to 6V
INTVCC, RUN0/RUN1.................................... –0.3V to 6V
EXTVCC....................................................... –0.3V to 14V
MODE0/MODE1, FREQ, PHASMD, ILIM....–0.3V to INTVCC
FAULT0/FAULT1, ITH0/ITH1, SYNC............... –0.3V to 3.6V
INTVCC, EXTVCC Peak Current (Note 9)................100mA
Operating Junction Temperature Range
........................................................... –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
SW0
TG0
FAULT1
FAULT0
FREQ
ITH0
TOP VIEW
28 27 26 25 24 23
22 BOOST0
MODE0 1
ISENSE0+ 2
21 BG0
ISENSE0– 3
20 VIN
29
SGND
RUN0 4
RUN1 5
19 PGND
18 EXTVCC
ISENSE1– 6
17 INTVCC
ISENSE1+ 7
16 BG1
MODE1 8
15 BOOST1
SW1
TG1
PHASMD
SYNC
ILIM
ITH1
9 10 11 12 13 14
UFD PACKAGE
28-LEAD (4mm × 5mm) PLASTIC QFN
TJMAX = 125°C, θJA = 43°C/W, θJC_BOT = 3.4°C/W
EXPOSED PAD (PIN 29) IS SGND, MUST BE SOLDERED TO PCB
Order Information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3870EUFD#PBF
LTC3870EUFD#TRPBF
3870
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LTC3870IUFD#PBF
LTC3870IUFD#TRPBF
3870
28-Lead (4mm × 5mm) 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.
Consult LTC Marketing for information on nonstandard 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/
Electrical Characteristics
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 15V, VRUN0,VRUN1 = 3.3V, fSYNC = 350kHz
(externally driven) unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
MIN
VIN
Input Voltage Range
(Note 3)
4.5
60
V
VOUT
Output Voltage Range
(Note 4)
0.5
14
V
IQ
Input Voltage Supply Current
Normal Operation
VRUN0,VRUN1 = 0V (Note 5)
VRUN0,VRUN1 = 3.3V, No Caps on TG and BG
1.1
2.6
mA
mA
VUVLO
Undervoltage Lockout Threshold
When VIN > 4.2V
VINTVCC Falling
VINTVCC Rising
3.7
4.0
V
V
2
TYP
MAX
UNITS
3870fb
For more information www.linear.com/LTC3870
LTC3870
Electrical Characteristics
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 15V, VRUN0,VRUN1 = 3.3V, fSYNC = 350kHz
(externally driven) unless otherwise specified.
SYMBOL
PARAMETER
CONDITIONS
IISENSE0+,
IISENSE1+
Current Sense + Pin Current
VISENSE0,1+ = 3.3V
IISENSE0–,
IISENSE1–
Current Sense − Pin Current
VIILIMIT
MIN
TYP
MAX
UNITS
l
±0.1
±1
µA
VISENSE0,1– = 3.3V
l
±0.1
±1
µA
Maximum Current Sense threshold
(High Range)
VITH = 2.22V, ILIM = INTVCC
l
70
75
80
mV
Maximum Current Sense threshold
(Low Range)
VITH = 2.22V, ILIM = GND
l
45
50
55
mV
Control Loop
Gate Drivers
TG RUP
Pull-Up On-Resistance
TG High
2.5
Ω
TG RDOWN
Pull-down On-Resistance
TG Low
1.5
Ω
BG RUP
Pull-Up On-Resistance
BG High
2.4
Ω
BG RDOWN
Pull-down On-Resistance
BG Low
1.1
Ω
TG0, TG1
tr
tf
TG Transition Time:
Rise Time
Fall Time
(Note 6)
CLOAD = 3300pF
CLOAD = 3300pF
30
30
ns
ns
BG0, BG1
tr
tf
BG Transition Time:
Rise Time
Fall Time
(Note 6)
CLOAD = 3300pF
CLOAD = 3300pF
30
30
ns
ns
TG/BG t1D
Top Gate Off to Bottom Gate On Delay Time
(Note 6)
CLOAD = 3300pF Each Driver
30
ns
BG/TG t2D
Bottom Gate Off to Top Gate On Delay Time
(Note 6)
CLOAD = 3300pF Each Driver
30
ns
tON(MIN)
Minimum On-Time
(Note 7)
90
ns
INTVCC Regulator
VINTVCC_VIN
Internal VCC Voltage No Load
6.0V
