down switching regulator controller for high current
distributed power systems, digital signal processors, and
other telecom and industrial DC/DC power supplies. It uses
a constant-frequency voltage mode architecture combined
with very low offset, high bandwidth error amplifiers and a
remote output sense differential amplifier per channel for
excellent transient response and output regulation.
The controller incorporates lossless inductor DCR current
sensing to maintain current balance between phases and to
provide overcurrent protection. The chip operates from a
V
CC
supply between 3V and 5.5V and is designed for step-
down conversion from V
IN
between 3V and 24V to output
voltages between 0.6V and V
CC
– 0.5V.
The TRACK/SS pins provide programmable soft-start or
tracking functions. Inductor current reversal is disabled
during soft-start to safely power prebiased loads. The
constant operating frequency can be synchronized to an
external clock or linearly programmed from 250kHz to
2.25MHz. Up to six LTC3861 controllers can operate in
parallel for 1-, 2-, 3-, 4-, 6- or 12-phase operation.
The LTC3861 is available in a 36-pin 5mm
×
6mm QFN pack-
age. LTC3861-1 is a 32-pin QFN version of the LTC3861,
which has a single differential remote output voltage sense
amplifier.
n
n
n
n
n
n
n
n
n
n
n
n
n
Operates with Power Blocks, DrMOS or External
Gate Drivers and MOSFETs
Constant-Frequency Voltage Mode Control with
Accurate Current Sharing
±0.75% 0.6V Voltage Reference
Dual Differential Output Voltage Sense Amplifiers
Multiphase Capability—Up to 12-Phase Operation
Programmable Current Limit
Safely Powers a Prebiased Load
Programmable or PLL-Synchronizable Switching
Frequency Up to 2.25MHz
Lossless Current Sensing Using Inductor DCR or
Precision Current Sensing with Sense Resistor
V
CC
Range: 3V to 5.5V
V
IN
Range: 3V to 24V
Power Good Output Voltage Monitor
Output Voltage Tracking Capability
Programmable Soft-Start
Available in a 36-Pin 5mm
×
6mm QFN Package
applicaTions
n
n
n
n
High Current Distributed Power Systems
DSP, FPGA and ASIC Supplies
Datacom and Telecom Systems
Industrial Power Supplies
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 6144194, 5055767
Typical applicaTion
V
IN
V
CC
1µF
28k
V
CC
V
CC
FREQ
FB2
I
LIM2
VINSNS
LTC3861
PWM1
RUN1,2
I
LIM1
ISNS1P
ISNS1N
ISNS2N
ISNS2P
59k
0.22µF
0.22µF
V
IN
, 7V TO 14V
LTC4449
IN
GND
V
LOGIC
TG
V
CC
TS
BOOST
BG
0.22µF
TG1
SW1
BG1
0.47µH
2.87k
V
OUT
1.2V
60A
180µF
V
OUT
10k
3.3nF
10k
280
4.7nF
10k
VSNSOUT1
VSNSP1
VSNSN1
VSNSOUT2
VSNSP2
VSNSN2
CONFIG
FB1
V
IN
LTC4449
IN
GND
V
LOGIC
TG
V
CC
TS
BOOST
BG
0.22µF
TG2
SW2
BG2
330µF
×
6
2.87k
0.47µH
3861 TA01
100µF
×
4
PWM2
I
AVG
COMP1,2 SS1,2 SGND CLKIN
5.9k 100pF
0.1µF
V
CC
100pF
3861fb
For more information
www.linear.com/LTC3861
1
LTC3861
absoluTe maximum raTings
(Note 1)
pin conFiguraTion
TRACKK/SS1
TOP VIEW
V
CC
Voltage .................................................. –0.3V to 6V
VINSNS Voltage ......................................... –0.3V to 30V
RUN1, RUN2 Voltage........................–0.3V to V
CC
+ 0.3V
ISNS1P , ISNS1N,
ISNS2P , ISNS2N ........................... –0.3V to (V
CC
+ 0.1V)
All Other Pins ................................–0.3V to (V
CC
+ 0.3V)
Operating Junction Temperature Range
(Notes 2, 3) ............................................ –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
PWMEN1
PWMEN2
PGOOD1
VINSNS
CONFIG
36 35 34 33 32 31 30 29
FB1
1
COMP1
2
VSNSP1
3
VSNSN1
4
VSNSOUT1
5
VSNSOUT2
6
VSNSN2
7
VSNSP2
8
COMP2
9
FB2
10
PWM1
28
RUN1
27
I
LIM1
26
SGND
25
ISNS1P
24
ISNS1N
23
ISNS2N
22
ISNS2P
21
SGND
20
I
LIM2
19
RUN2
37
SGND
11 12 13 14 15 16 17 18
FREQ
I
AVG
V
CC
PGOOD2
CLKOUT
UHE PACKAGE
36-LEAD (5mm
×
6mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 37) IS SGND, MUST BE SOLDERED TO PCB
orDer inFormaTion
LEAD FREE FINISH
LTC3861EUHE#PBF
LTC3861IUHE#PBF
TAPE AND REEL
LTC3861EUHE#TRPBF
LTC3861IUHE#TRPBF
PART MARKING*
3861
3861
PACKAGE DESCRIPTION
36-Lead (5mm × 6mm) Plastic QFN
36-Lead (5mm × 6mm) 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.
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/
TRACK/SS2
PHSMD
PWM2
CLKIN
2
3861fb
For more information
www.linear.com/LTC3861
LTC3861
elecTrical characTerisTics
SYMBOL
V
IN
V
CC
I
Q
PARAMETER
V
IN
Range
V
CC
Voltage Range
Input Voltage Supply Current
Normal Operation
Shutdown Mode
UVLO
RUN Input Threshold
RUN Input Pull-Up Current
Undervoltage Lockout Threshold
Soft-Start Pin Output Current
Internal Soft-Start Time
Regulated Feedback Voltage
–40°C to 85°C
–40°C to 125°C
V
ILIM
= 0.8V
V
FB
Falling
V
FB
Rising
V
FB
Falling
V
FB
Rising
V
PGOOD
= 5V
V
PGOOD
High to Low
V
FB
= 600mV
Sourcing
Sinking
–100
1
5
75
45
(Note 4)
Measured in a Servo Loop with EA in Loop
–40°C to 125°C
V
SNSP
= 600mV
(Note 4)
DIFFOUT = 600mV
DIFFOUT = 600mV
40
30
100
l
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
J
= 25°C (Note 3). V
CC
= 5V, V
RUN1,2
= 5V, V
FREQ
= V
CLKIN
= 0V,
V
FB
= 0.6V, f
OSC
= 0.6MHz, unless otherwise specified.
CONDITIONS
V
CC
= 5V
l
l
MIN
3
3
TYP
MAX
24
5.5
UNITS
V
V
mA
µA
mA
V
mV
µA
V
mV
µA
ms
V
RUN1,2
= 5V
V
RUN1,2
= 0V
V
CC
< V
UVLO
V
RUN
Rising
V
RUN
Hysteresis
V
RUN1,2
= 2.4V
V
CC
Rising
V
CC
Hysteresis
V
SS
= 0V
595.5
594
19
l
30
8
1.95
2.25
250
1.5
100
2.5
1.5
600
600
0.05
20
645
660
540
555
15
50
2.45
V
RUN
I
RUN
V
UVLO
I
SS
t
SS(INTERNAL)
V
FB
∆V
FB
/∆V
CC
I
LIMIT
Power Good
V
FB(OV)
V
FB(UV)
V
PGOOD(ON)
I
PGOOD(OFF)
t
PGOOD
Error Amplifier
I
FB
I
OUT
A
V(OL)
SR
f
0dB
V
DA
I
DIFF +
f
0dB
I
OUT(SINK)
I
OUT(SOURCE)
V
SNSOUT(MAX)
V
ISENSE(MAX)
A
V(ISENSE)
3.0
604.5
606
0.2
22
mV
mV
%/V
µA
mV
mV
mV
mV
Ω
µA
µs
nA
mA
mA
dB
V/µs
MHz
Regulated Feedback Voltage Line Dependence 3.0V < V
CC
< 5.5V
I
LIM
Pin Output Current
PGOOD/V
FB
Overvoltage Threshold
PGOOD/V
FB
Undervoltage Threshold
PGOOD Pull-Down Resistance
PGOOD Leakage Current
PGOOD Delay
FB Pin Input Current
COMP Pin Output Current
Open-Loop Voltage Gain
Slew Rate
COMP Unity-Gain Bandwidth
V
SNSP
Accuracy
Input Bias Current
DA Unity-Gain Crossover Frequency
Maximum Sinking Current
Maximum Sourcing Current
Maximum Output Voltage
Maximum Differential Current Sense Voltage
(V
ISNSP
-V
ISNSN
)
Voltage Gain
650
530
670
550
60
2
Differential Amplifier
l
592
–100
600
40
100
500
3.3
50
18.5
608
100
mV
nA
MHz
µA
µA
V
mV
V/V
3861fb
Current Sense Amplifier
For more information
www.linear.com/LTC3861
3
LTC3861
elecTrical characTerisTics
SYMBOL
V
CM(ISENSE)
I
ISENSE
V
OS
f
OSC
PARAMETER
Input Common Mode Range
SENSE Pin Input Current
Current Sense Input Referred Offset
Oscillator Frequency
V
CM
= 1.5V
–40°C to 125°C
V
CLKIN
= 0V
V
FREQ
= 0V
V
FREQ
= 5V
V
CLKIN
= 5V
R
FREQ
< 24.9k
R
FREQ
= 36.5k
R
FREQ
= 48.7k
R
FREQ
= 64.9k
R
FREQ
= 88.7k
Maximum Frequency
Minimum Frequency
I
FREQ
t
CLKIN(HI)
t
CLKIN(LO)
R
CLKIN
V
CLKIN
V
FREQ
V
OL(CLKOUT)
V
OH(CLKOUT)
θ
2
-θ
1
θ
CLKOUT
-θ
1
FREQ Pin Output Current
CLKIN Pulse Width High
CLKIN Pulse Width Low
CLKIN Pull-Up Resistance
CLKIN Input Threshold
FREQ Input Threshold
V
CLKIN
Falling
V
CLKIN
Rising
V
CLKIN
= 0V
V
FREQ
Falling
V
FREQ
Rising
I
LOAD
= –500µA
I
LOAD
= 500µA
V
PHSMD
= 0V
V
PHSMD
= Float
V
PHSMD
= V
CC
V
PHSMD
= 0V
V
PHSMD
= Float
V
PHSMD
= V
CC
I
LOAD
= 500µA
I
LOAD
= –500µA
l
l
l
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
J
= 25°C (Note 3). V
CC
= 5V, V
RUN1,2
= 5V, V
FREQ
= V
CLKIN
= 0V,
V
FB
= 0.6V, f
OSC
= 0.6MHz, unless otherwise specified.
CONDITIONS
MIN
–0.3
100
–1.25
1.25
TYP
MAX
V
CC
– 0.5
UNITS
V
nA
mV
Oscillator and Phase-Locked Loop
l
l
540
0.9
600
1
200
600
1
1.45
2.1
660
1.15
kHz
MHz
kHz
kHz
MHz
MHz
MHz
3
18.5
100
100
13
1.2
2
1.5
2.5
0.2
V
CC
– 0.2
180
180
120
60
90
240
4.5
20
0.25
21.5
MHz
MHz
µA
ns
ns
kΩ
V
V
V
V
V
V
Deg
Deg
Deg
Deg
Deg
Deg
V
V
FREQ
= 0.8V
V
CLKIN
= 0V to 5V
V
CLKIN
= 0V to 5V
CLKOUT Low Output Voltage
CLKOUT High Output Voltage
Channel 1-to-Channel 2 Phase Relationship
CLKOUT-to-Channel 1 Phase Relationship
PWM/PWMEN Outputs
PWM
PWM Output High Voltage
PWM Output Low Voltage
PWM Output Current in Hi-Z State
PWM Maximum Duty Cycle
PWMEN
PWMEN Output High Voltage
I
LOAD
= 1mA
l
0.5
±5
91.5
4.5
V
µA
%
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:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
•
34°C/W)
Note 3:
The LTC3861 is tested under pulsed load conditions such that
T
J
≈
T
A
.
The LTC3861E is guaranteed to meet performance specifications
from 0°C to 85°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3861I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The maximum ambient temperature consistent with
these specifications is determined by specific operating conditions in
conjunction with board layout, the rated package thermal resistors and
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