FEATURES
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LTC3732
3-Phase, 5-Bit VID,
600kHz, Synchronous Buck
Switching Regulator Controller
DESCRIPTIO
The LTC
®
3732 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 3-phase controller drives its
output stages with 120° phase separation at frequencies
of up to 600kHz per phase to minimize the RMS current
losses in both the input and output filter capacitors. The 3-
phase technique effectively triples the fundamental fre-
quency, improving transient response while operating
each controller at an optimal frequency for high efficiency
and ease of thermal design. Light load efficiency is opti-
mized by using a choice of output Stage Shedding or Burst
Mode technology.
A differential amplifier provides true remote sensing of both
the high and low side of the output voltage at load points.
Soft-start and a defeatable, timed short-circuit shutdown
protect the MOSFETs and the load. A foldback current
circuit also provides protection for the external MOSFETs
under short-circuit or overload conditions.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode, OPTI-LOOP and PolyPhase are registered trademarks of Linear Technology
Corporation. Stage Shedding is a trademark of Linear Technology Corporation
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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
4.5V
≤
V
CC
≤
7V; 4.5V
≤
V
IN
≤
32V
Differential Amplifier Accurately Senses V
OUT
Reduced Input and Output Capacitance
Reduced Power Supply Induced Noise
VID DAC Programmable from 1.1V to 1.85V
(VRM9.0/9.1)
±10%
Power Good Output Indicator
250kHz to 600kHz Per Phase, PLL, Fixed Frequency
PWM, Stage Shedding
TM
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
Small 36-Lead Narrow (0.209") SSOP Package
QFN 5mm
×
7mm 38-Lead Package
Desktop Computers
High Performance Notebook Computers
High Output Current DC/DC Power Supplies
APPLICATIO S
s
s
s
TYPICAL APPLICATIO
V
CC
4.5V TO 7V
V
CC
10µF
LTC3732
BOOST1
BOOST2
BOOST3
0.1µF
SW3 SW2 SW1
TG1
SW1
BG1
SENSE1
+
SENSE1
–
TG2
SW2
BG2
PGND
SENSE2
+
SENSE2
–
TG3
SW3
BG3
SENSE3
+
SENSE3
–
V
IN
V
IN
1µH
0.003Ω
POWER GOOD INDICATOR
OPTIONAL SYNC IN
PGOOD
PLLIN
PLLFLTR
1µH
0.003Ω
5 VID BITS
680pF
VID0-VID4
I
TH
5k
0.1µF
RUN/SS
SGND
EAIN
IN
–
IN
+
1µH
0.003Ω
100pF
Figure 1. High Current Triple Phase Step-Down Converter
3732f
U
U
U
+
V
IN
5V TO 28V
22µF
35V
V
OUT
1.1V TO 1.85V
55A
+
C
OUT
470µF
4V
3732 F01
1
LTC3732
ABSOLUTE
AXI U
RATI GS
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 Voltage (V
CC
), PGOOD
Pin Voltage .................................................. 7V to –0.3V
RUN/SS, PLLFLTR, PLLIN, FCB Voltages .. V
CC
to –0.3V
I
TH
Voltage ................................................ 2.4V to –0.3V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
VID1
PLLIN
PLLFLTR
FCB
IN
+
IN
–
PLLFLTR
PLLIN
1
2
3
4
5
6
7
8
9
36 VID0
35 PGOOD
34 BOOST1
33 TG1
32 SW1
31 BOOST2
30 TG2
29 SW2
28 V
CC
27 BG1
26 PGND
25 BG2
24 BG3
23 SW3
22 TG3
21 BOOST3
20 VID4
19 VID3
LTC3732CG
BOOST1
PGOOD
VID1
VID0
FCB
ORDER PART
NUMBER
IN
+
1
IN
–
2
DIFFOUT 3
EAIN 4
PADDLE 5
SGND 6
SENSE1
+
DIFFOUT
EAIN
SGND
SENSE1
+
10
SENSE1
–
11
SENSE2
+
12
SENSE2
–
13
SENSE3
–
14
SENSE3
+
15
RUN/SS 16
I
TH
17
VID2 18
VID2
VID3
VID4
BOOST3
G PACKAGE
36-LEAD PLASTIC SSOP
UHF PACKAGE
38-LEAD (7mm
×
5mm) PLASTIC QFN
PADDLE IS SGND
(MUST BE CONNECTED TO PCB AND SGND PIN)
T
JMAX
= 125°C,
θ
JA
= 95°C/W
T
JMAX
= 125°C,
θ
JA
= 34°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
REGULATED
V
SENSEMAX
I
MATCH
V
LOADREG
PARAMETER
Regulated Voltage at IN
+
Maximum Current Sense Threshold
Current Match
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
CC
= V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
(Note 3); VID Code = 11111, V
ITH
= 1.2V
q
RUN/SS
TG3
I
TH
V
EAIN
= 0.5V, V
ITH
Open,
V
SENSE1
–
,
V
SENSE2
–
,
V
SENSE3
– = 0.6V, 1.8V
Worst-Case Error at V
SENSE MAX
(Note 3)
Measured in Servo Loop,
∆I
TH
Voltage = 1.2V to 0.7V
Measured in Servo Loop,
∆I
TH
Voltage = 1.2V to 2V
V
CC
= 4.5V to 7V
V
REFLNREG
Output Voltage Line Regulation
2
U
U
W
W W
U
W
(Note 1)
Operating Ambient Temperature Range ....... 0°C to 70°C
Junction Temperature (Notes 2, 3, 7) ................... 125°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec)
SSOP Package .................................................. 300°C
Reflow Peak Body Temperature
QFN Package .................................................... 240°C
TOP VIEW
ORDER PART
NUMBER
31 TG1
30 SW1
29 BOOST2
28 TG2
27 SW2
38 37 36 35 34 33 32
LTC3732CUHF
7
UNDERSIDE
PADDLE
IS SGND
26 V
CC
25 DRV
CC
24 BG1
23 PGND
22 BG2
21 BG3
20 SW3
SENSE1
–
8
SENSE2
+
9
SENSE2 10
SENSE3
–
11
SENSE3
+
12
13 14 15 16 17 18 19
–
MIN
1.067
1.064
65
62
–5
q
q
TYP
1.075
1.075
75
75
MAX
1.083
1.086
85
88
5
UNITS
V
V
mV
mV
%
%
%
%/V
3732f
q
0.1
–0.1
0.03
0.5
–0.5
LTC3732
ELECTRICAL CHARACTERISTICS
SYMBOL
g
m
g
mOL
V
FCB
I
FCB
V
BINHIBIT
UVR
I
Q
PARAMETER
Transconductance Amplifier g
m
Transconductance Amplifier GBW
Forced Continuous Threshold
FCB Bias Current
Burst Inhibit Threshold
Undervoltage RUN/SS Reset
Input DC Supply Current
Normal Mode
Shutdown
Soft-Start Charge Current
RUN/SS Pin ON Threshold
RUN/SS Pin Arming Threshold
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
V
FCB
= 0.65V
Measured at FCB pin
V
CC
Lowered Until the RUN/SS Pin is Pulled Low
(Note 4)
V
CC
= 5V
V
RUN/SS
= 0V, VID0 to VID4 Open
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
The
q
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
I
TH
= 1.2V, Sink/Source 25µA (Note 3)
I
TH
= 1.2V, (g
m
• Z
L
, Z
L
= Series 1k-100kΩ-1nF)
q
q
MIN
3.6
0.58
TYP
5
3
0.60
0.2
MAX
6.6
0.62
0.7
UNITS
mmho
MHz
V
µA
V
V
mA
µA
µA
V
V
V
µA
V
CC
– 1.5 V
CC
– 0.7 V
CC
– 0.3
3.3
3.8
4.5
2.2
25
–1.5
1.5
3.8
3.2
–1.5
1.5
13
98.5
30
40
30
20
50
60
110
0.4
2
3
q
3.5
100
–2.5
1.9
4.5
I
RUN/SS
V
RUN/SS
V
RUN/SSARM
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)
VID
IL
VID
IH
VID
PULLUP
ATTEN
ERR
V
PGL
I
PGOOD
V
PGTHNEG
V
PGTHPOS
V
PGDLY
5
20
µA
µA
%
90
90
90
90
ns
ns
ns
ns
ns
ns
ns
V
V
µA
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
Maximum Low Level Input Voltage
Minimum High Level Input Voltage
VID0 to VID4 Internal Pull-Up Current V
VID
= 0V
VID0 to VID4
PGOOD Voltage Output Low
PGOOD Output Leakage
PGOOD Trip Thesholds
V
DIFFOUT
Ramping Negative
V
DIFFOUT
Ramping Positive
Power Good Fault Report Delay
(Note 6)
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
DIFFOUT
with Respect to Set Output Voltage,
VID Code = 11111,
PGOOD Goes Low After V
UVDLY
Delay
After V
EAIN
is Forced Outside the PGOOD Thresholds
–7
7
–0.25
Tested with a Square Wave (Note 5)
VID Parameters
0.25
0.1
0.3
1
–10
11
100
–13
13
150
%
V
µA
%
%
µs
Power Good Output Indication
3732f
3
LTC3732
ELECTRICAL CHARACTERISTICS
SYMBOL
f
NOM
f
LOW
f
HIGH
R
PLLTH
R
PLL IN
I
PLLFLTR
PARAMETER
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
Differential Gain
Input Offset Voltage
Common Mode Input Voltage Range
Common Mode Rejection Ratio
Output Current
Gain Bandwidth Product
Slew Rate
Maximum High Output Voltage
Input Resistance
I
OUT
= 1mA
R
L
= 2k
I
OUT
= 1mA
Measured at IN
+
Pin
0V < IN
+
= IN
–
< 5V, I
OUT
= 1mA, Input Referred
IN
+
= IN
–
= 1.2V, I
OUT
= 1mA,
Input Referred; Gain = 1
0
50
10
70
40
2
5
V
CC
– 1.2 V
CC
– 0.8
80
0.995
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
Oscillator and Phase-Locked Loop
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
= 2.4V
Minimum Pulse Width >100ns
360
190
600
400
225
680
1
50
20
20
120
240
1.000
0.5
1.005
5
V
CC
440
260
750
kHz
kHz
kHz
V
kΩ
µA
µA
Deg
Deg
V/V
mV
V
dB
mA
MHz
V/µs
V
kΩ
The
q
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
R
RELPHS
Differential Amplifier
A
V
V
OS
CM
CMRR
I
CL
GBP
SR
V
O(MAX)
R
IN
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired. A maximum current of 200µA is allowed to
pull-up the RUN/SS pin to prevent overcurrent shutdown.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
LTC3732CG: T
J
= T
A
+ (P
D
×
95°C/W)
LTC3732CUHF: T
J
= T
A
+ (P
D
×
34°C/W)
Note 3:
The IC is tested in a feedback loop that includes the differential
amplifier in a unity-gain configuration loaded with 100µA to ground driving
the VID DAC into the error amplifier and servoing the resultant voltage to
the midrange point for the error amplifier (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:
ATTEN
ERR
specification is in addition to the output voltage
accuracy specified at VID code = 11111.
Note 7:
This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
3732f
4
LTC3732
TYPICAL PERFOR A CE 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
3732 G01
EFFICIENCY (%)
EFFICIENCY (%)
80
75
70
65
60
55
50
0
5
I
L
= 50A
EFFICIENCY (%)
INDUCTOR CURRENT (A)
Reference Voltage vs
Temperature
610
6.0
605
MAXIMUM I
SENSE
THRESHOLD (mV)
ERROR AMPLIFIER g
m
(mmho)
REFERENCE VOLTAGE (mV)
600
595
590
–50 –30 –10
10 30 50 70
TEMPERATURE (°C)
Oscillator Frequency vs
Temperature
700
600
500
400
V
PLLFLTR
= 1.2V
300
200
100
0
–45 –30 –15
0 15 30 45 60
TEMPERATURE (°C)
75
90
V
PLLFLTR
= 0V
V
PLLFLTR
= 2.4V
V
PLLFLTR
= 5V
FREQUENCY (kHz)
FREQUENCY (kHz)
500
400
300
200
100
0
0
0.6
1.2
V
PLLFLTR
1.8
2.4
3732 G08
UNDER VOLTAGE RESET (V)
U W
90
3732 G04
3732 G07
Efficiency vs V
IN
(Figure 14)
100
95
90
85
I
L
= 20A
V
OUT
= 1.5V
f = 250kHz
100
Efficiency vs Frequency (Figure 14)
I
LOAD
= 20A
V
OUT
= 1.5V
95
V
IN
= 5V
90
V
IN
= 12V
85
V
IN
= 20V
80
V
IN
= 8V
10
15
V
IN
(V)
20
25
3732 G02
75
200
300
400
FREQUENCY (kHz)
500
600
3732 G03
Error Amplifier gm vs
Temperature
85
Maximum I
SENSE
Threshold vs
Temperature
5.5
80
V
O
= 1.8V
75
V
O
= 0.6V
70
5.0
4.5
110
4.0
–45 –30 –15
0 15 30 45 60
TEMPERATURE (°C)
75
90
65
–45 –30 –15
0 15 30 45 60
TEMPERATURE (°C)
75
90
3732 G05
3732 G06
Oscillator Frequency vs V
PLLFLTR
700
600
4
5
Undervoltage Reset Voltage vs
Temperature
3
2
1
0
–45 –30 –15
0 15 30 45 60
TEMPERATURE (°C)
75
90
3732 G09
3732f
5
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