FEATURES
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LTC3811
High Speed Dual,
Multiphase Step-Down DC/DC
Controller
DESCRIPTION
The LTC
®
3811 is a dual, PolyPhase
®
synchronous step-
down switching regulator controller optimized for output
voltages up to 3.3V. The LTC3811 includes high bandwidth
error amplifiers as well as a high speed differential remote
sense amplifier. The sense voltage range is programmable
from 24mV to 85mV, allowing the use of either the inductor
DCR or a discrete sense resistor. Multiphase operation is
made possible using the MODE/SYNC input, the CLKOUT
output and the PHASEMODE control pin, allowing 1-, 2-,
3-, 4-, 6- or 12-phase operation.
Large internal gate drivers minimize switching losses and
allow the use of multiple power MOSFETs connected in
parallel for high current applications.
The operating frequency of the LTC3811 can be programmed
from 250kHz to 750kHz and can also be synchronized to
an external clock using the internal PLL.
Tracking and sequencing are possible with the LTC3811,
and soft-start is programmed with an external capacitor.
Shutdown reduces supply current to 20μA.
, LT LTC, LTM and PolyPhase are registered trademarks of Linear Technology
,
Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5481178, 6304066, 5929620, 6177787, 6144194,
6580258, 5705919.
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Fixed Frequency, Peak Current Mode Control
±0.5% Output Accuracy Over Temperature
Optimized for Low V
OUT
Applications (Up to 3.3V)
Dual or Single Output, Multiphase Operation
Wide V
IN
Range: 4.5V to 30V Operation
High Speed Differential Remote Sense Amplifier
Inductor DCR or Sense Resistor Capable
Adjustable Peak Current Sense Voltage:
24mV to 85mV
Very Low Duty Cycle Operation: t
ON(MIN)
= 65ns (Typ)
Powerful Internal Gate Drivers
Output Voltage Soft-Start, Tracking and Sequencing
Programmable Load Line for Reduced C
OUT
Clock Input and Output for Up to 12-Phase Operation
Fixed Frequency Operation from 250kHz to 750kHz
PLL Synchronization from 150kHz Up to 900kHz
Selectable CCM or DCM Operation
Available in 5mm × 7mm QFN and G36 Packages
APPLICATIONS
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Network Servers
High Current ASIC Supplies
Low Voltage Power Distribution
TYPICAL APPLICATION
Dual Output, 2-Phase Tracking Core and I/O Supply
V
IN
4.5V TO 14V
V
IN
TG1
BOOST1
SW1
BG1
RUN1
RUN2
SENSE1
+
SENSE1
–
RNG1
V
OUT1
2V
15A
RNG2
FB1
LTC3811
SENSE2
+
SENSE2
–
DIFF/IN
+
DIFF/IN
–
DIFF/OUT
FB2
INTV
CC
DRV
CC
TG2
BOOST2
SW2
BG2
PGND
Load Step
V
OUT
100mV/DIV
I
L
5A/DIV
COMP1
COMP2
SS/TRACK1 SGND SS/TRACK2
V
OUT2
1.5V
15A
V
IN
= 12V
V
OUT
= 2V
I
OUT
= 0A to 12.5A
20μs/DIV
3811 TA01b
3811 TA01a
3811f
1
LTC3811
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (V
IN
) ......................... –0.3V to 30V
Topside Driver Voltages
(BOOST1, BOOST2) ............................... –0.3V to 37V
Switch Voltage (SW1, SW2) ......................... –5V to 30V
BOOST1 – SW1, BOOST2 – SW2 ................. –0.3V to 7V
DRV
CC
, INTV
CC
, EXTV
CC
, RUN1, RUN2, DIFF/IN
+
,
DIFF/IN
–
, PHASEMODE, PGOOD1, PGOOD2,
MODE/SYNC Voltages .................................. –0.3V to 7V
FB1, FB2, RNG1, RNG2, SS/TRACK1, SS/TRACK2,
PLL/LPF SENSE1
+
, SENSE1
–
, SENSE2
+
,
,
SENSE2
–
Voltages................................. –0.3V to INTV
CC
DRV
CC
LDO RMS Output Current .........................100mA
OperatingTemperature Range (Note 2)..... –40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range................... –65°C to 125°C
Lead Temperature (Soldering, 10 sec)
SSOP Package .................................................. 300°C
PIN CONFIGURATION
MODE/SYNC
TOP VIEW
PGOOD1
PGOOD2
PLL/LPF
TOP VIEW
CLKOUT
PGOOD1
RUN1
RUN2
31 BOOST1
30 TG1
29 SW1
28 BG1
27 EXTV
CC
39
26 PGND
25 DRV
CC
24 V
IN
23 BG2
22 SW2
21 TG2
20 BOOST2
13 14 15 16 17 18 19
DIFF/OUT
CSOUT
PHASEMODE
RNG1
DIFF/IN
+
DIFF/IN
RNG2
–
RUN2
RUN1
1
2
3
4
5
6
7
8
9
36 PGOOD2
35 PLL/LPF
34 MODE/SYNC
33 BOOST1
32 TG1
31 SW1
30 BG1
29 EXTV
CC
28 PGND
27 DRV
CC
26 V
IN
25 BG2
24 SW2
23 TG2
22 BOOST2
21 CLKOUT
20 RNG2
19 RNG1
38 37 36 35 34 33 32
SENSE1 1
SENSE1– 2
SS/TRACK1 3
COMP1 4
FB1 5
SGND 6
INTV
CC
7
FB2 8
COMP2 9
SS/TRACK2 10
SENSE2
–
11
SENSE2
+
12
+
SENSE1
+
SENSE1
–
SS/TRACK1
COMP1
FB1
SGND
INTV
CC
10
FB2 11
COMP2 12
SS/TRACK2 13
SENSE2
–
SENSE2
+
DIFF/IN
–
DIFF/IN
+
14
15
DIFF/OUT 16
17
18
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 39) IS PGND, MUST BE SOLDERED TO PCB
G PACKAGE
36-LEAD PLASTIC SSOP WIDE
T
JMAX
= 125°C,
θ
JA
= 100°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3811EUHF#PBF
LTC3811EG#PBF
TAPE AND REEL
LTC3811EUHF#TRPBF
LTC3811EG#TRPBF
PART MARKING
3811
LTC3811EG
PACKAGE DESCRIPTION
38-Lead (5mm × 7mm) Plastic QFN
36-Lead Plastic SSOP Wide
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
3811f
2
LTC3811
ELECTRICAL CHARACTERISTICS
SYMBOL
Input Supply
V
IN
I
Q
Operating Input Voltage Range
Total Quiescent Supply Current
Continuous Mode (Note 4)
Shutdown Mode
RUN Pin Input Leakage
Low Level RUN Input Threshold
High Level RUN Input Threshold
Feedback Voltage Accuracy
Feedback Pin Input Current
Line Regulation
Load Regulation
Error Amplifier Unity Gain Crossover
Frequency
Error Amplifier Maximum Output
Voltage (Internally Clamped)
FB Voltage Threshold to Disable Error
Amplifier Output
SS/TRACK1, SS/TRACK2 Charging
Currents
SS/TRACK1, SS/TRACK2 Pull-Down
Resistance in Shutdown
Differential Mode Gain,
ΔV
DIFF/OUT
/ΔV
DIFF/IN
Output Offset Voltage,
V
DIFF/OUT
– V
DIFF/IN
+
Input Resistance
Power Supply Rejection Ratio
Maximum Differential Mode Input
Voltage
Maximum Sink Current
Maximum Source Current
Unity Gain Bandwidth
Maximum Current Sense Threshold
(V
SENSE
+ – V
SENSE
–)
(Note 6)
V
FB
= 0.575V, V
CM
= 1.25V
V
RNG
= 0V
V
RNG
= INTV
CC
V
RNG
= 2V
V
FB
= 0.625V, V
CM
= 1.25V
V
RNG
= 0V
V
RNG
= INTV
CC
V
RNG
= 2V
8
(Note 5)
●
The
●
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, MODE/SYNC = 0V, unless otherwise specified.
PARAMETER
CONDITIONS
MIN
4.5
V
FB1,2
= 0.7V
V
RUN1,2
= 0V
V
RUN1,2
= 3.3V
●
●
TYP
MAX
30
UNITS
V
mA
μA
μA
V
V
10.5
20
–1
1.8
598
597
–100
600
20
40
1
0.3
RUN Pin ON/OFF Control
I
RUN
V
IL(RUN)
V
IH(RUN)
V
FB1
, V
FB2
I
FB1
, I
FB2
ΔV
FB
/ΔV
IN
ΔV
FB
/ΔV
COMP
f
0dB(EA)
V
OH(EA)
V
OL(EA)
V
FB(OFF)
Soft-Start/Tracking
I
SS1
, I
SS2
R
SS1
, R
SS2
V
SS/TRACK1
= V
SS/TRACK2
= 0.3V
V
RUN1
= V
RUN2
= 0V
–2.5
1
μA
kΩ
Error Amplifier Characteristics (Both Channels)
602
603
100
0.002
–0.1
–0.01
8
2.6
10
0.3
0.02
mV
mV
nA
%/V
%
MHz
V
mV
V
V
COMP
= 1.25V (Note 5)
4.5V ≤ V
IN
≤ 30V (Note 5)
ΔV
COMP
= 1.25V to 1.5V (Note 5)
(Note 6)
V
FB
= 0.54V, No Load
●
●
Error Amplifier Minimum Output Voltage V
FB
= 0.66V, No Load
V
INTVCC
– V
FB
Differential Amplifier
A
V
V
OS(DIFF)
R
IN
PSRR
DIFF
V
DM(DIFF)
I
MAX
+
I
MAX
–
f
0dB(DIFF)
Current Comparators
V
SENSE(MAX)
14
32.5
60
24
50
85
–21
–41
–67
34
67.5
110
mV
mV
mV
mV
mV
mV
3811f
ΔV
DIFF/IN
= 1V to 3.5V, I
DIFF/OUT
= –100μA
V
DIFF/IN
+ = 1.25V, V
DIFF/IN
– = 0V,
I
DIFF/OUT
= –100μA
Measured at V
DIFF/IN
+
7V ≤ V
IN
≤ 30V
V
DIFF/IN
+ – V
DIFF/IN
–, Measured at
V
DIFF/OUT
, I
DIFF/OUT
= –100μA
0.995
–6
1.000
1.005
6
V/V
mV
kΩ
dB
160
100
5.5
2
–2
V
mA
mA
MHz
V
SENSE(MIN)
Minimum Current Sense Threshold
(V
SENSE
+ – V
SENSE
–)
3
LTC3811
ELECTRICAL CHARACTERISTICS
SYMBOL
I
SENSE
V
CM(CS)
PARAMETER
Total Sense Pin Current
(V
SENSE
+ + V
SENSE
–)
V
SENSE
+, V
SENSE
– Pin Common Mode
Input Voltage Range
Voltage Position Transconductance,
ΔI
CSOUT
/ΔV
SENSE
(Note 8)
Output Offset Current, Measured at
CSOUT
Nominal Frequency
Lowest Frequency
Highest Frequency
Minimum Synchronizable Frequency
Maximum Synchronizable Frequency
Phase Detector Output Current
Sinking
Sourcing
Channel 1 to Channel 2 Phase
Relationship (Note 9)
Channel 1 to CLKOUT Phase
Relationship (Note 9)
Low Level CLKOUT Output Voltage
High Level CLKOUT Output Voltage
MODE/SYNC Input Resistance
Low Level MODE/SYNC Input Threshold
High Level MODE/SYNC Input Threshold
PGOOD Voltage Low
PGOOD Leakage Current
ΔV
FB
, PGOOD Overvoltage Threshold
ΔV
FB
, PGOOD Undervoltage Threshold
ΔV
FB
, PGOOD Comparator Hysteresis
Delay from UV/OV Condition to PGOOD
Falling
Delay from UV/OV Fault Recovery to
PGOOD Rising
Thermal Shutdown Junction
Temperature
Thermal Shutdown Junction
Temperature Hysteresis
(Note 6)
(Note 6)
I
PGOOD
= 2mA
V
PGOOD
= 6V
V
FB(OV)
– V
FB(NOM)
in Percent
V
FB(UV)
– V
FB(NOM)
in Percent
UV or OV Comparator
7
–13
10
–10
12
145
38
1.8
0.12
0.30
1.0
13
–7
V
SENSE1
+ – V
SENSE1
– = V
SENSE2
+
– V
SENSE2
– = ±50mV, V
CM
= 1.25V,
V
CSOUT
= 1.25V
V
SENSE1
+ – V
SENSE1
– = V
SENSE2
+
– V
SENSE2
– = 1.25V, V
CSOUT
= 1.25V
V
PLL/LPF
Pin Floating, MODE/SYNC = DC
Voltage
V
PLL/LPF
= 0V, MODE/SYNC = DC Voltage
V
PLL/LPF
= INTV
CC
, MODE/SYNC = DC
Voltage
MODE/SYNC = External Clock
MODE/SYNC = External Clock
f
MODE/SYNC
< f
OSC
f
MODE/SYNC
> f
OSC
V
PHASMODE
= 0V
V
PHASMODE
= 50% INTV
CC
V
PHASMODE
= INTV
CC
V
PHASMODE
= 0V
V
PHASMODE
= 50% INTV
CC
V
PHASMODE
= INTV
CC
R
CLK
= 50k to Ground
R
CLK
= 50k to Ground
4.0
5.8
75
0.3
900
–40
The
●
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, MODE/SYNC = 0V, unless otherwise specified.
CONDITIONS
V
CM
= 1.25V
0
MIN
TYP
–1.5
3.5
MAX
UNITS
μA
V
Voltage Position Amplifier (QFN Package Only)
g
m
5.0
mS
I
OS(VP)
40
μA
Multiphase Oscillator and Phase-Lock Loop (Note 9)
f
NOM
f
LOW
f
HIGH
f
SYNC(MIN)
f
SYNC(MAX)
I
PLL/LPF
450
200
650
500
250
750
125
1000
–4.3
5.1
180
180
120
90
60
240
0.2
550
300
850
175
kHz
kHz
kHz
kHz
kHz
μA
μA
deg
deg
deg
deg
deg
deg
V
V
kΩ
V
V
V
μA
%
%
mV
μs
μs
θ1
–
θ2
θ1
–
θ
CLKOUT
V
OL(CLKOUT)
V
OH(CLKOUT)
R
MODE/SYNC
V
IL(MODE/SYNC)
V
IH(MODE/SYNC)
V
OL(PGOOD)
I
PGOOD(OFF)
ΔV
FB(OV)
ΔV
FB(UV)
ΔV
FB(HYST)
t
PG(FAULT)
t
PG(OK)
Thermal Protection
T
JSD
T
JSD(HYST)
Power Good Indicators
165
25
°C
°C
3811f
4
LTC3811
ELECTRICAL CHARACTERISTICS
SYMBOL
V
DRVCC
ΔV
DRVCC(LOAD)
ΔV
DRVCC(LINE)
V
DRVCC(UVLO)
V
DRVCC(HYST)
V
EXTVCC
V
EXTVCC(HYST)
V
EXTVCC(DROP)
Gate Drivers
t
r
(TG1, TG2)
t
f
(TG1, TG2)
t
r
(BG1, BG2)
t
f
(BG1, BG2)
R
DS(ON)(TG)
TG1, TG2
R
DS(ON)(BG)
BG1, BG2
I
PK(TG)
TG1, TG2
I
PK(BG)
BG1, BG2
t
DEAD1
t
DEAD2
t
ON(MIN)
Top Gate Rise Time
Top Gate Fall Time
Bottom Gate Rise Time
Bottom Gate Fall Time
Top Gate Pull-Down NMOS
On-Resistance
Bottom Gate Pull-Down NMOS
On-Resistance
Top Gate (TG) Peak Source Current
Bottom Gate (BG) Peak Source Current
Bottom Gate Off to Top Gate On
Deadtime
Top Gate Off to Bottom Gate On
Deadtime
Minimum On-Time
(Note 6)
(Note 6)
V
COMP
= 1.25V (Note 6, 7)
C
L
= 3300pF (Note 6)
C
L
= 3300pF (Note 6)
C
L
= 3300pF (Note 6)
C
L
= 3300pF (Note 6)
TG to SW
BG to PGND
20
10
20
10
0.9
0.9
1.0
1.0
30
30
65
ns
ns
ns
ns
Ω
Ω
A
A
ns
ns
ns
PARAMETER
LDO Regulator Output Voltage
DRV
CC
Load Regulation
DRV
CC
Line Regulation
LDO Regulator Undervoltage Threshold
LDO Regulator Undervoltage Hysteresis
EXTV
CC
Switchover Voltage
EXTV
CC
Switchover Hysteresis
EXTV
CC
Voltage Drop
I
DRVCC
= 20mA, EXTV
CC
Rising
I
DRVCC
= 20mA
I
DRVCC
= 20mA, V
EXTVCC
= 5V
DRV
CC
Linear Regulator
V
EXTVCC
= 0V
I
LOAD
= 0mA to 50mA
ΔV
IN
= 8.5V to 30V
DRV
CC
Rising
●
The
●
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, MODE/SYNC = 0V, unless otherwise specified.
CONDITIONS
MIN
5.6
–2.0
TYP
6.0
–0.5
0.01
3.7
0.56
4.5
400
100
0.2
MAX
6.4
UNITS
V
%
%/V
V
V
V
mV
mV
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. Unless otherwise specified, all voltages are relative
to SGND and all currents are positive into a pin.
Note 2:
The LTC3811E is guaranteed to meet performance specifications
from 0°C to 85°C temperature. Specifications over the –40°C to
85°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls.
Note 3:
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
• TBD°C/W)
Note 4:
The dynamic input supply current is higher due to power
MOSFET gate charging (Q
G
• f
OSC
). See Applications Information for more
information.
Note 5:
The error amplifiers are measured in a feedback loop using an
external servo operational amplifier that drives the V
FB
pin and regulates
V
COMP
to be equal to the external control voltage.
Note 6:
Guaranteed by design, not subject to test.
Note 7:
The minimum on-time condition corresponds to an inductor peak-
to-peak ripple current of 50% of I
MAX
. See Applications Information for
more details.
Note 8:
The voltage positioning amplifier operates as a transconductance
amplifier, where the input voltages are the SENSE
+
to SENSE
–
potentials
for both channels. The amplifier output current flows through an external
resistor in order to program the amount of voltage droop at full load.
Note 9:
The PHASEMODE function is only available in the QFN package.
The 36-lead GW package has a fixed channel 1-to-channel 2 phase
relationship of 180°C and a channel 1-to-CLKOUT phase relationship of
90°C. The version in the 36-lead GW package is therefore optimized for
2- and 4-phase operation.
Note 10:
Rise and fall times are measured at 10% and 90% levels.
3811f
5
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