LTC3733/LTC3733-1
3-Phase, Buck
Controllers for AMD CPUs
FEATURES
s
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DESCRIPTIO
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3-Phase Controller with Onboard MOSFET Drivers
Current Mode Control Ensures Current Sharing
Differential Amplifier Accurately Senses V
OUT
±5%
Output Current Matching Optimizes Thermal
Performance and Size of Inductors and MOSFETs
Reduced Input and Output Capacitance
Supports Active Voltage Positioning
VID Programmable Output Voltage from 0.8V to 1.55V
(AMD Opteron
TM
CPU)
6-Phase, 90A to 120A Operation
Output Power Good Indicator with Adaptive Blanking
210kHz to 530kHz Per Phase, PLL, Fixed Frequency
Synchronizable (LTC3733-1)
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
No_CPU Detection
36-Lead 0.209" SSOP and 38-Lead (5mm
×
7mm) QFN
The LTC
®
3733 family are PolyPhase
®
synchronous step-
down switching regulator controllers that drive all
N-channel external power MOSFET stages in a phase-
lockable, fixed frequency architecture. The 3-phase con-
troller drives its output stages with 120° phase separation
at frequencies of up to 530kHz per phase to minimize the
RMS current dissipated by the ESR of both the input and
output filter capacitors. The 3-phase technique effectively
triples the fundamental frequency, improving transient
response while operating each phase at an optimal fre-
quency for efficiency and ease of thermal design. Light
load efficiency is optimized 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 sides 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. An all-“1” VID
detector turns off the regulator after 1µs timeout.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode, OPTI-LOOP and PolyPhase are registered trademarks of Linear Technology
Corporation. AMD Opteron is a trademark of Advanced Micro Devices, Inc.
APPLICATIO S
s
s
High Performance Notebook Computers
Servers, Desktop Computers and Workstations
TYPICAL APPLICATIO
5V
V
CC
10µF
LTC3733-1
BOOST1
BOOST2
BOOST3
0.1µF
TG1
SW1
BG1
SENSE1
+
SENSE1
–
TG2
SW2
BG2
PGND
SENSE2
+
SENSE2
–
TG3
SW3
BG3
SENSE3
+
SENSE3
–
V
IN
V
IN
L1 0.8µH
D1
0.002Ω
SW3 SW2 SW1
POWER GOOD INDICATOR
OPTIONAL SYN IN
PGOOD
PLLIN
PLLFLTR
L2 0.8µH
D2
0.002Ω
5 VID BITS
ON/OFF
680pF
VID0-VID4
RUN
I
TH
L3 0.8µH
D3
5k
0.1µF
SS
SGND
EAIN
IN
–
IN
+
0.002Ω
100pF
Figure 1. High Current Triple Phase Step-Down Converter
3733f
U
+
22µF
35V
×2
V
IN
5V TO 28V
V
OUT
0.8V TO 1.55V
65A
U
U
+
C
OUT
470µF
4V
×4
3733 F01
1
LTC3733/LTC3733-1
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 Voltages ................................................ 7V to –0.3V
PLLIN, RUN, SS,
PLLFLTR, FCB Voltages ............................. V
CC
to –0.3V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
VID1
RUN
PLLFLTR
FCB
IN
+
IN
–
DIFFOUT
EAIN
SGND
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
BOOST1
PGOOD
PLLIN
VID1
VID0
ORDER PART
NUMBER
LTC3733CG
PLLFLTR 1
FCB 2
IN
+
3
IN
–
4
RUN
TG1
SENSE1
+
10
SENSE1
–
11
SENSE2
+
12
13
14
SENSE2
–
SENSE3
–
SENSE3
+
15
SS 16
I
TH
17
VID2 18
VID2
VID3
VID4
G PACKAGE
36-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 95°C/W
UHF PACKAGE
38-LEAD (7mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD IS SGND (PIN 39) MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
REGULATED
V
SENSEMAX
I
MATCH
PARAMETER
Regulated Voltage at IN
+
Maximum Current Sense Threshold
Current Match
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
= V
SS
= 5V unless otherwise noted.
CONDITIONS
(Note 3); VID Code = 10011, V
ITH
= 1.2V
q
SENSE3
+
BOOST3
I
TH
SS
V
EAIN
= 0.5V, V
ITH
Open,
V
SENSE1
–
,
V
SENSE2
–
,
V
SENSE3
– = 0.8V, 1.55V
Worst-Case Error at V
SENSE(MAX)
2
U
U
W
W W
U
W
(Note 1)
I
TH
Voltage ................................................ 2.4V to –0.3V
Operating Ambient Temperature Range ....... 0°C to 70°C
Junction Temperature (Note 2) ............................. 125°C
Storage Temperature Range
LTC3733CG .......................................–65°C to 150°C
LTC3733CUHF-1 ...............................–65°C to 125°C
Lead Temperature (LTC3733CG)
(Soldering, 10 sec) ............................................... 300°C
TOP VIEW
ORDER PART
NUMBER
LTC3733CUHF-1
31 SW1
30 BOOST2
29 TG2
28 SW2
27 V
CC
38 37 36 35 34 33 32
DIFFOUT 5
EAIN 6
SGND 7
SENSE1
SENSE1
+
–
39
26 DRV
CC
25 BG1
24 PGND
23 BG2
22 BG3
21 SW3
20 TG3
8
9
SENSE2
+
10
SENSE2
–
UHF PART
MARKING
37331
11
SENSE3
–
12
13 14 15 16 17 18 19
MIN
1.067
1.064
65
62
–5
TYP
1.075
1.075
75
75
MAX
1.083
1.086
85
88
5
UNITS
V
V
mV
mV
%
3733f
q
LTC3733/LTC3733-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
LOADREG
PARAMETER
Output Voltage Load Regulation
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
= V
SS
= 5V unless otherwise noted.
CONDITIONS
(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
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
q
MIN
TYP
0.1
–0.1
0.03
MAX
0.5
–0.5
3.6
0.62
0.7
4.5
UNITS
%
%
%/V
mmho
MHz
V
µA
V
V
mA
µA
V
µA
V
V
µA
V
REFLNREG
g
m
g
mOL
V
FCB
I
FCB
V
BINHIBIT
UVR
I
Q
Output Voltage Line Regulation
Transconductance Amplifier g
m
Transconductance Amplifier GBW
Forced Continuous Threshold
FCB Bias Current
Burst Inhibit Threshold
Undervoltage SS Reset
Input DC Supply Current
Normal Mode
Shutdown
RUN Pin ON Threshold
Soft-Start Charge Current
SS Pin Arming Threshold
SS Pin Latch-Off Threshold
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
2.5
0.58
3.05
1.5
0.60
0.2
V
FCB
= 0.65V
Measured at FCB pin
V
CC
Lowered Until the SS Pin is Pulled Low
(Note 4)
V
CC
= 5V
V
RUN
= 0V, VID0 to VID4 Open
V
RUN
, Ramping Positive
V
SS
= 1.9V
V
SS
, Ramping Positive Until Short-Circuit
Latch-Off is Armed
V
SS
, Ramping Negative
Soft-Short Condition V
EAIN
= 0.375V, V
SS
= 4.5V
V
EAIN
= 0.375V, V
SS
= 4.5V
SENSE1
+
, SENSE1
–
, SENSE2
+
, SENSE2
–
,
SENSE3
+
, SENSE3
–
All Equal 1.2V; Current at Each Pin
In Dropout
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
95
–5
1
–0.8
3.3
V
CC
– 1.5 V
CC
– 0.7 V
CC
– 0.3
3.8
2.5
20
1.5
–1.5
3.8
3.3
–1.5
1.5
13
98.5
30
40
30
20
60
60
120
0.8
2
150
90
90
90
90
5
20
100
1.9
–2.5
4.5
V
RUN
I
SS
V
SSARM
V
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
t
PGBLNK
µA
µA
%
ns
ns
ns
ns
ns
ns
ns
V
V
kΩ
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
Resistance
VID0 to VID4
PGOOD Voltage Output Low
PGOOD Output Leakage
PGOOD Trip Thesholds
V
DIFFOUT
Ramping Negative
V
DIFFOUT
Ramping Positive
Power Good Blanking
(Note 6)
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
DIFFOUT
with Respect to Set Output Voltage,
VID Code = 10011
PGOOD Goes Low After V
UVDLY
Delay
After VID Changes Outside PGOOD Window
–7
7
q
Tested with a Square Wave (Note 5)
VID Parameters
–0.25
0.1
0.25
0.3
±1
–10
10
120
–14
14
%
V
µA
%
%
µs
3733f
Power Good Output Indication
3
LTC3733/LTC3733-1
ELECTRICAL CHARACTERISTICS
SYMBOL
f
NOM
f
LOW
f
HIGH
R
PLLTH
R
PLL IN
I
PLL LPF
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
No-CPU Shutdown Latency
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
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
After All VID Bits = “1”
0.5
0.995
Oscillator and Phase-Locked Loop
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
= 2.4V
LTC3733-1 Only
LTC3733-1 Only
LTC3733-1 Only
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
310
190
470
350
210
530
1
50
20
20
120
240
1
1.000
0.5
1.005
5
5
400
250
620
kHz
kHz
kHz
V
kΩ
µA
µA
Deg
Deg
µs
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
= V
SS
= 5V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
R
RELPHS
No_CPU Detection
t
NOCPU
A
V
V
OS
CM
CMRR
I
CL
GBP
SR
V
O(MAX)
R
IN
Differential Amplifier
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 formula:
LTC3733CG: T
J
= T
A
+ (P
D
×
95°C/W)
LTC3733CUHF-1: 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 10011.
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.
3733f
4
LTC3733/LTC3733-1
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs I
OUT
100
90
80
V
FCB
= OPEN
95
90
I
L
= 50A
85
80
75
V
IN
= 8V
V
OUT
= 1.5V
0.1
10
1
INDUCTOR CURRENT (A)
100
3733 G01
EFFICIENCY (%)
EFFICIENCY (%)
60
50
40
30
20
10
0
V
FCB
= 0V
EFFICIENCY (%)
70
V
FCB
= 5V
Reference Voltage vs
Temperature
610
4.0
605
3.5
MAXIMUM I
SENSE
THRESHOLD (mV)
ERROR AMPLIFIER g
m
(mmho)
REFERENCE VOLTAGE (mV)
600
595
590
–45 –30 –15
0 15 30 45 60
TEMPERATURE (°C)
Oscillator Frequency vs
Temperature
600
550
500
FREQUENCY (kHz)
UNDERVOLTAGE RESET (V)
V
PLLFLTR
= 2.4V
FREQUENCY (kHz)
450
400
350
300
250
200
150
V
PLLFLTR
= 0V
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 5V
100
–45 –30 –15
0 15 30 45 60
TEMPERATURE (°C)
U W
75
3733 G04
Efficiency vs V
IN
100
V
OUT
= 1.5V
f = 210kHz
I
L
= 20A
100
Efficiency vs Frequency
V
OUT
= 1.5V
I
LOAD
= 20A
97
V
IN
= 8V
94
V
IN
= 5V
91
V
IN
= 12V
88
V
IN
= 20V
70
0
5
15
10
V
IN
(V)
20
25
3733 G02
85
200
250
300 350 400 450
FREQUENCY (kHz)
500
550
3733 G03
Error Amplifier g
m
vs
Temperature
85
Maximum I
SENSE
Threshold vs
Temperature
80
V
O
= 1.55V
75
V
O
= 0.8V
70
3.0
2.5
90
2.0
–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
3733 G05
3733 G06
Oscillator Frequency vs V
PLLFLTR
550
500
450
400
350
300
250
200
75
90
0
0.4
0.8
1.2
1.6
V
PLLFLTR
(V)
2.0
2.4
3733 G08
Undervoltage Reset Voltage vs
Temperature
5.0
4.5
4.0
3.5
3.0
–45 –30 –15
0 15 30 45 60
TEMPERATURE (°C)
75
90
3733 G07
3733 G09
3733f
5
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