FEATURES
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LTC3729
550kHz, PolyPhase,
High Efficiency, Synchronous
Step-Down Switching Regulator
DESCRIPTION
The LTC
®
3729 is a multiple phase, synchronous
step‑down current mode switching regulator controller
that drives N‑channel external power MOSFET stages in a
phase‑lockable fixed frequency architecture. The PolyPhase
controller drives its two output stages out of phase at
frequencies up to 550kHz to minimize the RMS ripple
currents in both input and output capacitors. The output
clock signal allows expansion for up to 12 evenly phased
controllers for systems requiring 15A to 200A of output
current. The multiple phase technique effectively multiplies
the fundamental frequency by the number of channels
used, improving transient response while operating each
channel at an optimum frequency for efficiency. Thermal
design is also simplified.
An internal differential amplifier provides true remote sens‑
ing of the regulated supply’s positive and negative output
terminals as required for high current applications.
A RUN/SS pin provides both soft‑start and optional timed,
short‑circuit shutdown. Current foldback limits MOSFET
dissipation during short‑circuit conditions when the
overcurrent latchoff is disabled. OPTI‑LOOP compensation
allows the transient response to be optimized over a wide
range of output capacitance and ESR values. The LTC3729
includes a power good output pin that indicates when the
output is within
±7.5%
of the designed set point.
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Wide V
IN
Range: 4V to 36V Operation
Reduces Required Input Capacitance and Power
Supply Induced Noise
±1%
Output Voltage Accuracy
Phase-Lockable Fixed Frequency: 250kHz to 550kHz
True Remote Sensing Differential Amplifier
PolyPhase
®
Extends from Two to Twelve Phases
Reduces the Size and Value of Inductors
Current Mode Control Ensures Current Sharing
1.1MHz Effective Switching Frequency (2‑Phase)
OPTI‑LOOP
®
Compensation Reduces C
OUT
Power Good Output Voltage Indicator
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Soft‑Start Current Ramping
Internal Current Foldback Plus Shutdown Timer
Overvoltage Soft‑Latch Eliminates Nuisance Trips
Available in 5mm
×
5mm QFN
and 28‑Lead SSOP Packages
Desktop Computers/Servers
Large Memory Arrays
DC Power Distribution Systems
APPLICATIONS
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L,
LT, LTC, LTM, PolyPhase, OPTI‑LOOP Linear Technology and the Linear logo are registered
,
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
TYPICAL APPLICATION
0.1µF
S
V
IN
LTC3729
TG1
SW1
BG1
PGND
10
S
M1
0.47µF
S
0.1µF
RUN/SS
PGOOD
I
TH
3.3k
S
BOOST1
0.002
M2
×2
L1
D1 0.8µH
10µF
35V
CERAMIC
×4
V
IN
5V TO 28V
SENSE1
+
SENSE1
–
1000pF
SGND
16k
V
DIFFOUT
S
TG2
BOOST2
SW2
BG2
EAIN
INTV
CC
S
S
M3
0.47µF
S
0.002
M4
×2
L2
0.8µH
V
OUT
1.6V/40A
+
S
D2
16k
V
OS–
V
OS+
SENSE2
+
SENSE2
–
10µF
+
C
OUT
1000µF
×2
4V
C
OUT
: T510E108K004AS
D1, D2: UP5840
L1, L2: CEPH149-IROMC
M1, M3: IRF7811W
M2, M4: IRF7822
3729 TA01
Figure 1. High Current Dual Phase Step-Down Converter
3729fb
1
LTC3729
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (V
IN
) ......................... 36V to –0.3V
Topside Driver Voltages (BOOST1,2) ......... 42V to –0.3V
Switch Voltage (SW1, 2) .............................. 36V to –5 V
SENSE1
+
, SENSE2
+
, SENSE1
–
,
SENSE2
–
Voltages .........................(1.1)INTV
CC
to –0.3V
EAIN, V
OS+
, V
OS–
, EXTV
CC
, INTV
CC
,
RUN/SS, PGOOD Voltages .......................... 7V to –0.3V
Boosted Driver Voltage (BOOST‑SW) ........... 7V to –0.3V
PLLFLTR, PLLIN, CLKOUT, PHASMD,
V
DIFFOUT
Voltages ..............INTV
CC
to –0.3V for V
IN
≥ 7V
V
DIFFOUT
Voltages.............V
IN
– 2V to –0.3V for V
IN
< 7V
I
TH
Voltage ............................................... 2.7V to –0.3V
Peak Output Current <1µs(TGL1,2, BG1,2) .................5A
INTV
CC
RMS Output Current ................................. 50mA
Operating Ambient Temperature
Range (Note 6)......................................... –40°C to 85°C
Junction Temperature (Note 2) ............................. 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
(G Package Only) .............................................. 300°C
PIN CONFIGURATION
TOP VIEW
SENSE1
–
RUN/SS
SENSE1
+
SENSE1
–
EAIN
PLLFLTR
PLLIN
PHASMD
I
TH
SGND
1
2
3
4
5
6
7
8
9
28 CLKOUT
NC
27 TG1
26 SW1
25 BOOST1
24 V
IN
23 BG1
22 EXTV
CC
21 INTV
CC
20 PGND
19 BG2
18 BOOST2
17 SW2
16 TG2
15 PGOOD
EAIN 1
PLLFLTR 2
PLLIN 3
PHASMD 4
I
TH
5
SGND 6
V
DIFFOUT
7
V
OS
–
TOP VIEW
SENSE1
+
CLKOUT
RUN/SS
SW1
24 BOOST1
23 V
IN
22 BG1
21 EXTV
CC
20 INTV
CC
19 PGND
18 BG2
17 BOOST2
9 10 11 12 13 14 15 16
PGOOD
TG2
SW2
V
OS+
NC
SENSE2
–
SENSE2
+
NC
32 31 30 29 28 27 26 25
V
DIFFOUT
10
V
OS–
11
V
OS+
12
SENSE2
–
13
SENSE2
+
8
14
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 95°C/W
UH PACKAGE
32-LEAD 5mm
×
5mm PLASTIC QFN
θ
JA
= 34°C/W
EXPOSED PAD IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3729EG#PBF
LTC3729EUH#PBF
TAPE AND REEL
LTC3729EG#TRPBF
LTC3729EUH#TRPBF
PART MARKING
LTC3729
3729
PACKAGE DESCRIPTION
28‑Lead Plastic SSOP
32‑Lead (5mm
×
5mm)Plastic QFN
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/
TG1
NC
3729fb
2
LTC3729
ELECTRICAL CHARACTERISTICS
SYMBOL
V
EAIN
V
SENSEMAX
I
INEAIN
V
LOADREG
V
REFLNREG
V
OVL
UVLO
g
m
g
mOL
I
Q
I
RUN/SS
V
RUN/SS
V
RUN/SSLO
I
SCL
I
SDLDO
I
SENSE
DF
MAX
TG1, 2 t
r
TG1, 2 t
f
BG1, 2 t
r
BG1, 2 t
f
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
V
INTVCC
V
LDO
INT
V
LDO
EXT
V
EXTVCC
V
LDOHYS
f
NOM
f
LOW
f
HIGH
R
PLLIN
PARAMETER
Regulated Feedback Voltage
Maximum Current Sense Threshold
Feedback Current
Output Voltage Load Regulation
Main Control Loop
(Note 3); I
TH
Voltage = 1.2V
V
SENSE–
= 5V
V
SENSE1, 2
= 5V
(Note 3)
(Note 3)
Measured in Servo Loop; I
TH
Voltage = 0.7V
Measured in Servo Loop; I
TH
Voltage = 2V
V
IN
= 3.6V to 30V (Note 3)
Measured at V
EAIN
V
IN
Ramping Down
I
TH
= 1.2V; Sink/Source 5µA; (Note 3)
I
TH
= 1.2V; (g
m
xZ
L
; No Ext Load); (Note 3)
(Note 4)
EXTV
CC
Tied to V
OUT
; V
OUT
= 5V
V
RUN/SS
= 0V
V
RUN/SS
= 1.9V
V
RUN/SS
Rising
V
RUN/SS
Rising from 3V
Soft Short Condition V
EAIN
= 0.5V; V
RUN/SS
= 4.5V
V
EAIN
= 0.5V
Each Channel; V
SENSE1–, 2–
= V
SENSE1+, 2+
= 0V
In Dropout
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
–85
98
0.5
–0.5
1.0
l
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
MIN
0.792
62
65
TYP
0.800
75
75
–5
0.1
–0.1
0.002
0.84
3
0.86
3.5
3
1.5
580
20
–1.2
1.5
3.8
2
1.6
–60
99.5
30
40
30
20
90
90
100
4.8
5.0
0.2
80
l
MAX
0.808
88
85
–50
0.5
–0.5
0.02
0.88
4
UNITS
V
mV
mV
nA
%
%
%/V
V
V
mmho
V/mV
µA
µA
µA
V
V
µA
µA
µA
%
Reference Voltage Line Regulation
Output Overvoltage Threshold
Undervoltage Lockout
Transconductance Amplifier g
m
Transconductance Amplifier Gain
Input DC Supply Current
Normal Mode
Shutdown
Soft‑Start Charge Current
RUN/SS Pin ON Threshold
RUN/SS Pin Latchoff Arming
RUN/SS Discharge Current
Shutdown Latch Disable Current
Total Sense Pins Source Current
Maximum Duty Factor
Top Gate Transition Time:
Rise Time
Fall Time
Bottom Gate Transition Time:
Rise Time
Fall Time
40
1.9
4.5
4
5
90
90
90
90
ns
ns
ns
ns
ns
ns
ns
Top Gate Off to Bottom Gate On Delay
C
LOAD
= 3300pF Each Driver
Synchronous Switch‑On Delay Time
Bottom Gate Off to Top Gate On Delay
C
LOAD
= 3300pF Each Driver
Top Switch‑On Delay Time
Minimum On‑Time
Internal V
CC
Voltage
INTV
CC
Load Regulation
EXTV
CC
Voltage Drop
EXTV
CC
Switchover Voltage
EXTV
CC
Switchover Hysteresis
Nominal Frequency
Lowest Frequency
Highest Frequency
PLLIN Input Resistance
Tested with a Square Wave (Note 5)
6V < V
IN
< 30V; V
EXTVCC
= 4V
I
CC
= 0 to 20mA; V
EXTVCC
= 4V
I
CC
= 20mA; V
EXTVCC
= 5V
I
CC
= 20mA, EXTV
CC
Ramping Positive
I
CC
= 20mA, EXTV
CC
Ramping Negative
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥ 2.4V
360
230
480
4.5
Internal V
CC
Regulator
5.2
1.0
160
V
%
mV
V
V
440
290
590
kHz
kHz
kHz
kΩ
3729fb
4.7
0.2
400
260
550
50
Oscillator and Phase-Locked Loop
3
LTC3729
ELECTRICAL CHARACTERISTICS
SYMBOL
I
PLLFLTR
R
RELPHS
CLKOUT
PARAMETER
Phase Detector Output Current
Sinking Capability
Sourcing Capability
Controller 2‑Controller 1 Phase
Phase (Relative to Controller 1)
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
V
PHASMD
= 0V, Open
V
PHASMD
= 5V
V
PHASMD
= 0V
V
PHASMD
= Open
V
PHASMD
= 5V
4
0.2
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
EAIN
with Respect to Set Output Voltage
V
EAIN
Ramping Negative
V
EAIN
Ramping Positive
–6
6
–7.5
7.5
0.1
0.3
±1
–9.5
9.5
MIN
TYP
–15
15
180
240
60
90
120
MAX
UNITS
µA
µA
Deg
Deg
Deg
Deg
Deg
V
V
V
µA
%
%
CLK
HIGH
CLK
LOW
PGOOD Output
V
PGL
I
PGOOD
V
PG
Differential
Amplifier
A
DA
CMRR
DA
R
IN
Clock High Output Voltage
Clock Low Output Voltage
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level, Either Controller
Gain
Common Mode Rejection Ratio
Input Resistance
0V < V
CM
< 5V
Measured at V
OS
+
Input
0.995
46
1
55
80
1.005
V/V
dB
kΩ
Note 1:
Absolute Maximum Ratings are those values beyond which
the life of a device may be impaired.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC3729EG: T
J
= T
A
+ (P
D
• 95°C/W)
LTC3729EUH: T
J
= T
A
+ (P
D
• 34°C/W)
Note 3:
The LTC3729 is tested in a feedback loop that servos V
ITH
to a
specified voltage and measures the resultant V
EAIN
.
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 5:
The minimum on‑time condition corresponds to the on inductor
peak‑to‑peak ripple current ≥40% of I
MAX
(see Minimum On‑Time
Considerations in the Applications Information section).
Note 6:
The LTC3729E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
3729fb
4
LTC3729
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Output Current
(Figure 12)
100
100
90
EFFICIENCY (%)
V
EXTVCC
= 5V
V
EXTVCC
= 0V
80
70
90
Efficiency vs Output Current
(Figure 12)
100
Efficiency vs Input Voltage
(Figure 12)
V
OUT
= 3.3V
V
EXTVCC
= 5V
I
OUT
= 20A
f = 250kHz
80
EFFICIENCY (%)
V
IN
= 5V
V
IN
= 8V
V
IN
= 12V
V
IN
= 20V
60
40
V
OUT
= 3.3V
V
EXTVCC
= 5V
I
OUT
= 20A
f = 250kHz
0.1
1
10
OUTPUT CURRENT (A)
100
3729
G01
EFFICIENCY (%)
V
OUT
= 3.3V
f = 250kHz
80
20
60
70
0
50
1
10
OUTPUT CURRENT (A)
100
3729
G02
5
10
V
IN
(V)
15
20
3729
G03
Supply Current vs Input Voltage
and Mode
1000
250
EXTV
CC
Voltage Drop
5.05
INTV
CC
AND EXTV
CC
SWITCH VOLTAGE (V)
5.00
4.95
4.90
4.85
4.80
4.75
INTV
CC
and EXTV
CC
Switch
Voltage vs Temperature
INTV
CC
VOLTAGE
EXTV
CC
VOLTAGE DROP (mV)
800
SUPPLY CURRENT (µA)
200
600
ON
400
150
100
50
200
SHUTDOWN
0
5
20
15
10
25
INPUT VOLTAGE (V)
30
35
EXTV
CC
SWITCHOVER THRESHOLD
0
0
0
10
30
20
CURRENT (mA)
40
50
3729
G05
4.70
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3729
G04
3729
G06
Internal 5V LDO Line Reg
5.1
5.0
INTV
CC
VOLTAGE (V)
4.9
4.8
4.7
4.6
4.5
4.4
0
V
SENSE
(mV)
50
I
LOAD
= 1mA
75
Maximum Current Sense Threshold
vs Duty Factor
80
70
60
V
SENSE
(mV)
0
20
40
60
DUTY FACTOR (%)
80
100
3729
G08
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
50
40
30
20
10
25
0
5
20
15
25
10
INPUT VOLTAGE (V)
30
35
3729
G07
0
50
100
0
25
75
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
3729 G09
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