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 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.
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
LTC3861-1 controllers can operate in parallel for 1-, 2-, 3-,
4-, 6- or 12-phase operation.
The LTC3861-1 is pin-to-pin compatible with the LTC3860.
It is available in a 32-pin 5mm × 5mm QFN package. The
LTC3861is a 36-pin QFN version of the LTC3861-1, which
has dual differential output voltage sense amplifiers.
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
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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
Differential Remote Output Voltage Sense Amplifier
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 32-Pin 5mm × 5mm QFN Package
applicaTions
n
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High Current Distributed Power Systems
DSP, FPGA and ASIC Supplies
Datacom and Telecom Systems
Industrial Power Supplies
Typical applicaTion
V
IN
, 7V TO 14V
V
CC
1µF
28.7k
V
CC
FREQ
FB2
I
LIM2
VINSNS
LTC3861-1
PWM1
RUN1,2
I
LIM1
ISNS1P
ISNS1N
ISNS2N
ISNS2P
59k
0.22µF
0.22µF
LTC4449
IN
GND
V
LOGIC
TG
V
CC
TS
BOOST
BG
0.22µF
V
CC
LTC4449
IN
GND
V
LOGIC
TG
V
CC
TS
BOOST
BG
0.22µF
V
IN
, 7V TO 14V
180µF
0.47µH
2.87k
V
OUT
1.2V
60A
V
OUT
VSNSOUT
VSNSP
VSNSN
CONFIG
1nF
20k
221
1nF
PWM2
FB1
13k 220pF
I
AVG
COMP1,2 SS1,2 SGND CLKIN
0.1µF
V
CC
100pF
V
IN
330µF
×
6
2.87k
0.47µH
38611 TA01
100µF
×
4
20k
38611fb
For more information
www.linear.com/LTC3861-1
1
LTC3861-1
absoluTe maximum raTings
(Note 1)
pin conFiguraTion
TRACK/SS1
PWMEN1
PWMEN2
TOP VIEW
PGOOD1
VINSNS
CONFIG
SGND
I
AVG
PWM1
24 RUN1
23 I
LIM1
22 ISNS1P
33
SGND
21 ISNS1N
20 ISNS2N
19 ISNS2P
18 I
LIM2
17 RUN2
9 10 11 12 13 14 15 16
CLKIN
FREQ
PHSMD
TRACK/SS2
CLKOUT
PGOOD2
PWM2
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
32 31 30 29 28 27 26 25
V
CC
1
FB1 2
COMP1 3
VSNSOUT 4
VSNSN 5
VSNSP 6
COMP2 7
FB2 8
UH PACKAGE
32-LEAD (5mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 33) IS SGND, MUST BE SOLDERED TO PCB
orDer inFormaTion
LEAD FREE FINISH
LTC3861EUH-1#PBF
LTC3861IUH-1#PBF
TAPE AND REEL
LTC3861EUH-1#TRPBF
LTC3861IUH-1#TRPBF
PART MARKING*
38611
38611
PACKAGE DESCRIPTION
32-Lead (5mm × 5mm) Plastic QFN
32-Lead (5mm × 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.
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/
2
38611fb
For more information
www.linear.com/LTC3861-1
LTC3861-1
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
(Note 4)
(Note 4)
V
VSNSN
= 0V
V
VSNSN
= 0V
(Note 4)
DIFFOUT = 1.2V
DIFFOUT = 1.2V
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
= 5V, 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
18
6
1.95
2.25
250
1.5
100
2.5
1.5
600
600
0.05
20
645
660
540
555
15
30
–100
1
5
75
45
40
1.007
–2
40
100
500
4
50
18.5
–0.3
1
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
A
V
V
OS
f
0dB
I
OUT(SINK)
I
OUT(SOURCE)
V
SNSOUT(MAX)
V
ISENSE(MAX)
A
V(ISENSE)
V
CM(ISENSE)
3.0
604.5
606
0.2
22
mV
mV
%/V
µA
mV
mV
mV
mV
Ω
µA
µs
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
Differential Amplifier Voltage Gain
Input Referred Offset
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
Input Common Mode Range
650
530
670
550
60
2
100
nA
mA
mA
dB
V/µs
MHz
Differential Amplifier
0.993
2
V/V
mV
MHz
µA
µA
V
mV
V/V
V
CC
– 0.5
V
38611fb
Current Sense Amplifier
For more information
www.linear.com/LTC3861-1
3
LTC3861-1
elecTrical characTerisTics
SYMBOL
I
ISENSE
V
OS
f
OSC
PARAMETER
SENSE Pin Input Current
Current Sense Input Referred Offset
Oscillator Frequency
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
= 5V, V
CLKIN
= 0V,
V
FB
= 0.6V, f
OSC
= 0.6MHz, unless otherwise specified.
CONDITIONS
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
3
18.5
100
100
13
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
MIN
–1.25
TYP
100
MAX
1.25
UNITS
nA
mV
Oscillator and Phase-Locked Loop
l
l
360
540
400
600
200
600
1
1.45
2.1
440
660
kHz
kHz
kHz
kHz
MHz
MHz
MHz
0.25
20
21.5
MHz
MHz
µA
ns
ns
kΩ
V
V
V
V
V
V
Deg
Deg
Deg
Deg
Deg
Deg
V
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
FREQ
= 0.8V
V
CLKIN
= 0V to 5V
V
CLKIN
= 0V to 5V
1.2
2
1.5
2.5
0.2
V
CC
– 0.2
180
180
120
60
90
240
4.5
0.5
±5
91.5
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
V
µA
%
V
4.5
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 LTC3861-1 is tested under pulsed load conditions such that
T
J
≈
T
A
. The LTC3861-1E 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 LTC3861-1I 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
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