FeaTures
n
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LTC3731H
3-Phase, 600kHz,
Synchronous Buck Switching
Regulator Controller
DescripTion
The LTC
®
3731H is a PolyPhase
®
synchronous step-down
switching regulator controller that drives all N-channel
external power MOSFET stages in a phase-lockable fixed
frequency architecture. The LTC3731H is rated for operation
up to 140°C junction temperature. The 3-phase controller
drives its output stages with 120° phase separation at
frequencies up to 680kHz per phase to minimize the RMS
current losses in both the input and output filter capacitors.
The 3-phase technique effectively triples the fundamental
frequency, improving transient response while operating
each controller at an optimal frequency for efficiency and
ease of thermal design. Light load efficiency is optimized
by using a choice of output Stage Shedding or Burst Mode
operation.
The precision reference supports output voltages from
0.6V to 6V. Current foldback provides protection for the
external MOSFETs under short-circuit or overload condi-
tions. Please refer to the LTC3731 data sheet for 0°C to
70°C and –40°C to 85°C rated versions.
L,
LT, LTC, LTM, Linear Technology, the Linear logo, Burst Mode, OPTI-LOOP and PolyPhase
are registered trademarks and Stage Shedding is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents
including 5481178, 5929620, 6177787, 6144194, 6100678, 5408150, 6580258, 6462525,
6304066, 5705919.
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3-Phase Current Mode Controller with Onboard
MOSFET Drivers
±5% Output Current Matching Optimizes Thermal
Performance and Size of Inductors and MOSFETs
±2% V
REF
Accuracy Over Temperature Up to 140°C
Reduced Power Supply Induced Noise
±10% Power Good Output Indicator
225kHz to 680kHz Per Phase, PLL, Fixed Frequency
PWM, Stage Shedding™ or Burst Mode
®
Operation
OPTI-LOOP
®
Compensation Minimizes C
OUT
Adjustable Soft-Start Current Ramping
Short-Circuit Shutdown Timer with Defeat Option
Overvoltage Soft Latch
Adjustable Undervoltage Lockout Threshold
Selectable Phase Output for Up to 12-Phase
Operation
Available in 36-Pin Narrow (0.209") SSOP and
5mm
×
5mm QFN Packages
applicaTions
n
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Automotive and Industrial Power Supplies
High Output Current DC/DC Power Supplies
Typical applicaTion
V
CC
4.5V TO 7V
V
CC
10µF
LTC3731H
TG1
SW1
BG1
SENSE1
+
SENSE1
–
TG2
SW2
BG2
PGND
UVADJ
680pF
I
TH
5k
0.01µF
100pF
RUN/SS
SGND
EAIN
SENSE2
+
SENSE2
–
TG3
SW3
BG3
SENSE3
+
SENSE3
–
0.8µH
0.003
+
V
IN
5V TO 28V
22µF
35V
100
90 V
FCB
= OPEN
80 V
FCB
= 5V
V
FCB
= 0V
70
60
50
40
30
0.1µF
SW3 SW2 SW1
POWER GOOD INDICATOR
OPTIONAL SYNC IN
36k
12k
BOOST1
BOOST2
BOOST3
Efficiency vs I
OUT
V
IN
0.8µH
EFFICIENCY (%)
0.003
V
OUT
1.35V
55A
PGOOD
PLLIN
PLLFLTR
V
IN
V
IN
0.8µH
0.003
20
10
0
0.1
1
10
V
IN
= 8V
V
OUT
= 1.5V
100
3731H F01b
7.5k
6.04k
LOAD CURRENT (A)
+
C
OUT
470µF
4V
3731H F01
Figure 1. High Current Triple Phase Step-Down Converter
3731Hfb
LTC3731H
absoluTe MaxiMuM raTings
(Note 1)
Topside Driver Voltages (BOOST
N
) ............ 38V to –0.3V
Switch Voltage (SW
N
) ................................... 32V to –5V
Boosted Driver Voltage (BOOST
N
– SW
N
).... 7V to –0.3V
Peak Output Current <1ms (TG
N
, BG
N
) .......................5A
Supply Voltages (V
CC
, V
DR
), PGOOD
Pin Voltage ................................................... 7V to –0.3V
RUN/SS, PLLFLTR, PLLIN, UVADJ,
FCB Voltages ..............................................V
CC
to –0.3V
SENSE
+
, SENSE
–
Voltages ........................ 5.5V to –0.3V
I
TH
Voltage ............................................... 2.4V to –0.3V
Operating Junction
Temperature Range (Note 2) .................. –40°C to 140°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature G Package (Soldering, 10sec) .. 300°C
pin conFiguraTion
TOP VIEW
V
CC
PLLIN
PLLFLTR
FCB
NC
NC
NC
EAIN
SGND
1
2
3
4
5
6
7
8
9
36 CLKOUT
35 PGOOD
34 BOOST1
33 TG1
32 SW1
31 BOOST2
30 TG2
29 SW2
28 V
DR
27 BG1
26 PGND
25 BG2
24 BG3
23 SW3
22 TG3
21 BOOST3
20 PHASMD
19 SGND
NC 1
NC 2
EAIN 3
SENSE1
+
4
SENSE1
SENSE2
–
+
TOP VIEW
PLLFLTR
CLKOUT
BOOST1
PLLIN
SW1
24 BOOST2
23 TG2
22 SW2
33
SGND
21 V
CC
20 BG1
19 PGND
18 BG2
17 BG3
9 10 11 12 13 14 15 16
PHASMD/PG
UVADJ
BOOST3
RUN/SS
SENSE3
+
SW3
TG3
I
TH
32 31 30 29 28 27 26 25
SENSE1
+
10
SENSE1
–
11
SENSE2
+
12
SENSE2
–
13
SENSE3
–
14
SENSE3
+
15
RUN/SS 16
I
TH
17
UVADJ 18
5
6
7
8
SENSE2
–
SENSE3
–
G PACKAGE
36-LEAD PLASTIC SSOP
T
JMAX
= 140°C,
θ
JA
= 70°C/W,
θ
JC
= 25°C/W
PINS 5 AND 6 CAN BE GROUNDED OR NC
PIN 7 MUST BE LEFT AS NC
UH PACKAGE
32-LEAD (5mm 5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W,
θ
JC
= 3°C/W
EXPOSED PAD (PIN 33) IS SGND, MUST BE SOLDERED TO PCB
PINS 1, 2 AND 32 MUST BE LEFT AS NC
orDer inForMaTion
LEAD FREE FINISH
LTC3731HG#PBF
LTC3731HUH#PBF
TAPE AND REEL
LTC3731HG#TRPBF
LTC3731HUH#TRPBF
PART MARKING
LTC3731HG
3731
PACKAGE DESCRIPTION
36-Lead Plastic SSOP
32-Lead (5mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 140°C
–40°C to 140°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/
3731Hfb
TG1
FCB
NC
LTC3731H
elecTrical characTerisTics
SYMBOL
PARAMETER
Main Control Loop
V
REGULATED
Regulated Voltage at EAIN
V
SENSEMAX
I
MATCH
V
LOADREG
V
REFLNREG
g
m
g
mOL
V
FCB
I
FCB
V
BINHIBIT
UVR
UVADJ
I
UVADJ
I
Q
I
RUN/SS
V
RUN/SS
Maximum Current Sense Threshold
Maximum Current Threshold Match
Output Voltage Load Regulation
V
ITH
= 1.2V (Note 3)
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
MIN
0.594
0.590
65
60
–5
0.1
–0.1
0.03
l
TYP
0.600
0.600
75
75
MAX
0.606
0.614
85
90
5
0.7
–0.7
7
0.66
0.7
4.5
1.23
50
3.5
100
–2.5
1.9
4.5
UNITS
V
V
mV
mV
%
%
%
%/V
mmho
MHz
V
µA
V
V
V
nA
mA
µA
µA
V
V
V
µA
V
EAIN
= 0.5V, V
ITH
Open,
V
SENSE1–
, V
SENSE2–
, V
SENSE3–
= 0.6V, 1.8V
Worst-Case Error at V
SENSEMAX
l
(Note 3)
Measured in Servo Loop, ∆I
TH
Voltage = 1.2V to 0.7V
l
l
Measured in Servo Loop, ∆I
TH
Voltage = 1.2V to 2V
V
CC
= 4.5V to 7V
I
TH
= 1.2V, Sink/Source 25µA (Note 3)
I
TH
= 1.2V (g
m
• Z
L
, Z
L
= Series 1k – 100kΩ – 1nF)
l
Output Voltage Line Regulation
Transconductance Amplifier g
m
Transconductance Amplifier GBW
Forced Continuous Threshold
FCB Bias Current
Burst Inhibit Threshold
Undervoltage RUN/SS Reset
Undervoltage Lockout Threshold
Undervoltage Bias Current
Input DC Supply Current
Normal Mode
Shutdown
Soft-Start Charge Current
RUN/SS Pin ON Threshold
3
0.54
5
3
0.60
0.2
V
FCB
= 0.65V
Measured at FCB Pin
V
CC
Lowered Until the RUN/SS Pin is Pulled Low
At UVADJ Threshold
(Note 4)
V
CC
= 5V
V
RUN/SS
= 0V
V
RUN/SS
= 1.9V
V
RUN/SS
, Ramping Positive
V
RUN/SS
, Ramping Positive Until Short-Circuit
Latch-Off is Armed
V
RUN/SS
, Ramping Negative
Soft-Short Condition V
EAIN
= 0.375V, V
RUN/SS
= 4.5V
V
EAIN
= 0.375V, V
RUN/SS
= 4.5V
SENSE1
+
, SENSE1
–
, SENSE2
+
, SENSE2
–
, SENSE3
+
,
SENSE3
–
All Equal 1.2V; Current at Each Pin
In Dropout, V
SENSEMAX
≤ 30mV
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
95
–5
–0.8
1
3.3
1.13
V
CC
– 1.5 V
CC
– 0.7 V
CC
– 0.3
3.8
1.18
0.2
2.3
50
–1.5
1.5
3.8
3.2
–1.5
1.5
13
98.5
30
40
30
20
50
60
110
90
90
90
90
5
20
V
RUN/SSARM
RUN/SS Pin Arming Threshold
V
RUN/SSLO
I
SCL
I
SDLHO
I
SENSE
DF
MAX
TG t
R
, t
F
BG t
R
, t
F
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
RUN/SS Pin Latch-Off Threshold
RUN/SS Discharge Current
Shutdown Latch Disable Current
SENSE Pins Source Current
Maximum Duty Factor
Top Gate Rise Time
Top Gate Fall Time
Bottom Gate Rise Time
Bottom Gate Fall Time
µA
µA
%
ns
ns
ns
ns
ns
ns
ns
Top Gate Off to Bottom Gate On Delay All Controllers, C
LOAD
= 3300pF Each Driver
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay All Controllers, C
LOAD
= 3300pF Each Driver
Top Switch-On Delay Time
Minimum On-Time
Tested with a Square Wave (Note 5)
3731Hfb
LTC3731H
elecTrical characTerisTics
SYMBOL
V
PGL
I
PGOOD
V
PGTHNEG
V
PGTHPOS
V
PGDLY
f
NOM
f
LOW
f
HIGH
V
PLLTH
R
PLLIN
I
PLLFLTR
R
RELPHS
CLKOUT
PARAMETER
PGOOD Voltage Output Low
PGOOD Output Leakage
PGOOD Trip Thresholds
V
EAIN
Ramping Negative
V
EAIN
Ramping Positive
Power Good Fault Report Delay
Nominal Frequency
Lowest Frequency
Highest Frequency
PLLIN Input Threshold
PLLIN Input Resistance
Phase Detector Output Current
Sinking Capability
Sourcing Capability
Controller 2-Controller 1 Phase
Controller 3-Controller 1 Phase
Controller 1 TG to CLKOUT Phase
PHASMD = 0V
PHASMD = 5V
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
Power Good Output Indication
I
PGOOD
= 2mA, G Package
I
PGOOD
= 1.6mA, UH Package
V
PGOOD
= 5V
V
EAIN
with Respect to Set Output Voltage, PGOOD
Goes Low After V
UVDLY
Delay
After V
EAIN
is Forced Outside the PGOOD Thresholds
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
= 2.4V
Minimum Pulse Width > 100ns
360
190
600
–7
7
–10
10
100
400
225
680
1
50
20
20
120
240
30
60
0.1
0.5
0.3
1
1
–13
13
150
440
260
750
V
V
µA
%
%
µs
kHz
kHz
kHz
V
kΩ
µA
µA
Deg
Deg
Deg
Deg
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
Oscillator and Phase-Locked Loop
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:
The LTC3731H is guaranteed to meet specifications over the –40°C
to 140°C operating junction temperature range. Note that the maximum
ambient temperature is determined by specific operating conditions in
conjunction with board layout, the rated package thermal resistance and
other environmental factors.
Junction temperature (T
J
) is calculated from the ambient temperature T
A
and power dissipation PD according to the following formula:
LTC3731HG: T
J
= T
A
+ (P
D
• 70°C/W)
LTC3731HG: T
J
= T
CASE
+ (P
D
• 25°C/W)
LTC3731HUH: T
J
= T
A
+ (P
D
• 34°C/W)
High junction temperatures degrade operating lifetimes. Operating lifetime
at junction temperatures greater than 125°C is derated to 1000 hours. The
LTC3731H is tested under pulsed load conditions such that T
J
≈ T
A
.
Note 3:
The IC is tested in a feedback loop that servoes the error amplifier
output voltage to its midrange point (V
ITH
= 1.2V).
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 an inductor
peak-to-peak ripple current of ≥40% of I
MAX
(see minimum on-time
considerations in the Applications Information Section).
Note 6:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions.
Overtemperature protection becomes active at a junction temperature
greater than the maximum operating temperature. Continuous operation
above the specified maximum operating junction temperature may impair
device reliability.
3731Hfb
LTC3731H
Typical perForMance characTerisTics
Efficiency vs I
OUT
(Figure 14)
100
90 V
FCB
= OPEN
80 V
FCB
= 5V
V
FCB
= 0V
70
60
50
40
30
20
10
0
0.1
1
10
V
IN
= 8V
V
OUT
= 1.5V
100
3731H G01
Efficiency vs V
IN
(Figure 14)
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
0
5
10
15
V
IN
(V)
20
25
3731H G02
Efficiency vs Frequency
(Figure 14)
100
I
LOAD
= 20A
V
OUT
= 1.5V
V
IN
= 5V
EFFICIENCY (%)
90
V
IN
= 12V
85
V
IN
= 20V
V
IN
= 8V
V
OUT
= 1.5V
f = 225kHz
I
L
= 15A
I
L
= 45A
95
EFFICIENCY (%)
80
75
200
300
400
FREQUENCY (kHz)
500
600
3731H G03
LOAD CURRENT (A)
Reference Voltage
vs Temperature
610
6.0
Error Amplifier g
m
vs Temperature
85
MAXIMUM I
SENSE
THRESHOLD (mV)
Maximum I
SENSE
Threshold
vs Temperature
605
ERROR AMPLIFIER g
m
(mmho)
REFERENCE VOLTAGE (mV)
5.5
80
V
O
= 1.75V
75
V
O
= 0.6V
70
600
5.0
595
4.5
590
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3731H G04
4.0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3731H G05
65
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3731H G06
Oscillator Frequency
vs Temperature
700
OPERATING FREQUENCY (kHz)
600
FREQUENCY (kHz)
500
400
300
200
100
0
–50 –25
0
25
50
75
100 125 150
3731H G07
700
V
PLLFLTR
= 2.4V
Operating Frequency vs V
PLLFLTR
5
4
Undervoltage Reset Voltage
vs Temperature
500
UNDER VOLTAGE RESET (V)
V
PLLFLTR
= 5V
600
3
V
PLLFLTR
= 1.2V
400
2
1
0
–50 –25
V
PLLFLTR
= 0V
300
200
0
TEMPERATURE (°C)
0.5
1
1.5
2
PLLFLTR PIN VOLTAGE (V)
2.5
3731H G08
0
25
50
75
100 125 150
3731H G09
TEMPERATURE (°C)
3731Hfb
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