FEATURES
s
s
LTC3729
550kHz, PolyPhase,
High Efficiency, Synchronous
Step-Down Switching Regulator
DESCRIPTIO
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 multi-
plies the fundamental frequency by the number of chan-
nels 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
sensing 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 compensa-
tion 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.
s
s
s
s
s
s
s
s
s
s
s
s
s
s
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
TM
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
APPLICATIO S
s
s
s
Desktop Computers/Servers
Large Memory Arrays
DC Power Distribution Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a registered trademark of Linear Technology Corporation.
PolyPhase is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
0.1µF
S
V
IN
LTC3729
10Ω
TG1
SW1
S
M1
0.47µF
S
0.1µF
RUN/SS
PGOOD
I
TH
3.3k
S
BOOST1
BG1
PGND
SENSE1
+
SENSE1
–
TG2
SGND
BOOST2
SW2
V
DIFFOUT
BG2
EAIN
V
OS –
V
OS
+
S
0.002Ω
M2
×2
L1
D1 0.8µH
1000pF
M3
S
0.47µF
S
0.002Ω
M4
×2
L2
0.8µH
16k
S
D2
+
INTV
CC
SENSE2
+
SENSE2
–
S
10µF
16k
C
OUT
: T510E108K004AS
D1, D2: UP5840
L1, L2: CEPH149-IROMC
M1, M3: IRF7811W
M2, M4: IRF7822
Figure 1. High Current Dual Phase Step-Down Converter
U
U
U
10µF
35V
CERAMIC
×4
V
IN
5V TO 28V
V
OUT
1.6V/40A
+
C
OUT
1000µF
×2
4V
3729 TA01
sn3729 3729fas
1
LTC3729
ABSOLUTE
AXI U RATI GS
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
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN/SS
SENSE1
+
SENSE1
–
EAIN
PLLFLTR
PLLIN
PHASMD
I
TH
SGND
1
2
3
4
5
6
7
8
9
28 CLKOUT
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
SENSE1
–
SENSE1
+
CLKOUT
RUN/SS
ORDER PART
NUMBER
NC
SW1
TG1
NC
LTC3729EG
EAIN 1
PLLFLTR 2
PLLIN 3
PHASMD 4
I
TH
5
SGND 6
V
DIFFOUT
7
V
OS
–
V
DIFFOUT
10
V
OS –
11
V
OS +
12
SENSE2
–
13
SENSE2
+
14
SENSE2
–
SENSE2
+
PGOOD
TG2
SW2
NC
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 SGND
(MUST BE SOLDERED TO PCB)
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
EAIN
V
SENSEMAX
I
INEAIN
V
LOADREG
PARAMETER
Regulated Feedback Voltage
Maximum Current Sense Threshold
Feedback Current
Output Voltage Load Regulation
Main Control Loop
The
q
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
(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
q
q
q
q
V
OS+
NC
2
U
U
W
W W
U
W
(Note 1)
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
TOP VIEW
ORDER PART
NUMBER
LTC3729EUH
24 BOOST1
23 V
IN
22 BG1
21 EXTV
CC
20 INTV
CC
19 PGND
18 BG2
17 BOOST2
32 31 30 29 28 27 26 25
8
9 10 11 12 13 14 15 16
UH PART
MARKING
3729
MIN
0.792
62
65
TYP
0.800
75
75
–5
0.1
– 0.1
MAX
0.808
88
85
– 50
0.5
– 0.5
UNITS
V
mV
mV
nA
%
%
sn3729 3729fas
LTC3729
ELECTRICAL CHARACTERISTICS
SYMBOL
V
REFLNREG
V
OVL
UVLO
g
m
g
mOL
I
Q
PARAMETER
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
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay
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
Phase Detector Output Current
Sinking Capability
Sourcing Capability
Controller 2-Controller 1 Phase
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
V
PHASMD
= 0V, Open
V
PHASMD
= 5V
The
q
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
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
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
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
q
q
MIN
0.84
3
TYP
0.002
0.86
3.5
3
1.5
580
20
MAX
0.02
0.88
4
UNITS
%/V
V
V
mmho
V/mV
µA
µA
µA
V
V
µA
µA
µA
%
40
1.9
4.5
4
5
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
I
PLLFLTR
– 0.5
1.0
0.5
– 85
98
– 1.2
1.5
3.8
2
1.6
– 60
99.5
30
40
30
20
90
90
100
90
90
90
90
ns
ns
ns
ns
ns
ns
ns
Internal V
CC
Regulator
4.8
5.0
0.2
80
4.5
4.7
0.2
400
260
550
50
– 15
15
180
240
440
290
590
5.2
1.0
160
V
%
mV
V
V
kHz
kHz
kHz
kΩ
µA
µA
Deg
Deg
Oscillator and Phase-Locked Loop
R
RELPHS
sn3729 3729fas
3
LTC3729
ELECTRICAL CHARACTERISTICS
SYMBOL
CLKOUT
PARAMETER
Phase (Relative to Controller 1)
The
q
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
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
0.995
0V < V
CM
< 5V
Measured at V
OS
+ Input
46
– 7.5
7.5
1
55
80
0.1
0.3
±1
– 9.5
9.5
1.005
MIN
TYP
60
90
120
MAX
UNITS
Deg
Deg
Deg
V
V
V
µA
%
%
V/V
dB
kΩ
CLK
HIGH
CLK
LOW
V
PGL
I
PGOOD
V
PG
Clock High Output Voltage
Clock Low Output Voltage
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level, Either Controller
PGOOD Output
Differential Amplifier
A
DA
CMRR
DA
R
IN
Gain
Common Mode Rejection Ratio
Input Resistance
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.
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Output Current
(Figure 12)
100
100
V
EXTVCC
= 5V
80
V
IN
= 5V
EFFICIENCY (%)
EFFICIENCY (%)
60
V
IN
= 12V
V
IN
= 20V
80
40
V
OUT
= 3.3V
V
EXTVCC
= 5V
I
OUT
= 20A
f = 250kHz
0.1
1
10
OUTPUT CURRENT (A)
100
3729
G01
70
EFFICIENCY (%)
V
IN
= 8V
20
0
4
U W
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
90
90
V
EXTVCC
= 0V
80
60
V
OUT
= 3.3V
f = 250kHz
1
10
OUTPUT CURRENT (A)
100
3729
G02
50
70
5
10
V
IN
(V)
3729
G03
15
20
sn3729 3729fas
LTC3729
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Input Voltage
and Mode
1000
250
INTV
CC
AND EXTV
CC
SWITCH VOLTAGE (V)
EXTV
CC
VOLTAGE DROP (mV)
800
SUPPLY CURRENT (µA)
600
ON
400
200
SHUTDOWN
0
0
5
20
15
10
25
INPUT VOLTAGE (V)
30
35
Internal 5V LDO Line Reg
5.1
5.0
I
LOAD
= 1mA
INTV
CC
VOLTAGE (V)
4.9
V
SENSE
(mV)
4.8
4.7
4.6
4.5
4.4
0
5
20
15
25
10
INPUT VOLTAGE (V)
30
35
3729
G07
V
SENSE
(mV)
Maximum Current Sense Threshold
vs V
RUN/SS
(Soft-Start)
80
V
SENSE(CM)
= 1.6V
80
60
V
SENSE
(mV)
V
SENSE
(mV)
72
V
SENSE
(mV)
40
20
64
0
0
1
2
3
V
RUN/SS
(V)
3729
G10
4
U W
3729
G04
EXTV
CC
Voltage Drop
5.05
5.00
4.95
4.90
4.85
4.80
4.75
INTV
CC
and EXTV
CC
Switch
Voltage vs Temperature
INTV
CC
VOLTAGE
200
150
100
50
EXTV
CC
SWITCHOVER THRESHOLD
0
0
10
30
20
CURRENT (mA)
40
50
3729
G05
4.70
– 50 – 25
50
25
75
0
TEMPERATURE (°C)
100
125
3729
G06
Maximum Current Sense Threshold
vs Duty Factor
75
80
70
60
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
50
50
40
30
20
10
25
0
0
20
40
60
DUTY FACTOR (%)
80
100
3729
G08
0
50
100
0
25
75
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
3729
G09
Maximum Current Sense Threshold
vs Sense Common Mode Voltage
90
80
76
70
60
50
40
30
20
10
0
–10
–20
60
–30
Current Sense Threshold
vs I
TH
Voltage
68
5
6
0
1
3
4
2
COMMON MODE VOLTAGE (V)
5
3729
G11
0
0.5
1
1.5
V
ITH
(V)
2
2.5
sn3729
3729
G12
3729fas
5
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