FEATURES
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LTC3738
3-Phase Buck Controller
for Intel VRM9/VRM10 with
Active Voltage Positioning
DESCRIPTIO
The LTC
®
3738 is a 3-phase synchronous step-down switch-
ing regulator controller that drives all N-channel external
power MOSFET stages in a phase-lockable, fixed fre-
quency architecture. 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 Pulse Skip mode technology.
The LTC3738 also allows users to program load slope via
a resistor for AVP control. Both external and internal
thermal sensing are available from the on-chip thermal
detector and comparator.
A differential amplifier provides sensing of both the high
and low sides of the output voltage.
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 a 1µs timeout.
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a registered trademark of Linear Technology Corporation.
Stage Shedding is a trademark of Linear Technology Corporation.
3-Phase Controller with Onboard MOSFET Drivers
Programmable Active Voltage Positioning (AVP)
with True Current Sensing
Programmable External Thermal Detection or
Internal Thermal Sensing
Precise Output Current Matching Optimizes
Thermal Performance and Solution Size
Supports Starting into Precharged V
OUTS
Differential Amplifier Accurately Senses V
OUT
PWM, Pulse Skip and Stage Shedding
TM
Operation
Synchronizable
210kHz to 530kHz Per Phase, Fixed Frequency
Output Power Good Indicator with Adaptive Blanking
Adjustable Soft-Start Current Ramping
Short-Circuit Shutdown Timer with Defeat Option
OPTI-LOOP
®
Compensation Minimizes C
OUT
38-Lead (5mm
×
7mm) QFN Package
APPLICATIO S
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High Performance Notebook Computers
Servers, Desktop Computers and Workstations
U.S. Patent Numbers: 5481178, 5994885, 5929620, 6177787, 6144194, 6580258, 6462525,
6593724, 6674274, 6100678 pending on AVP technique.
TYPICAL APPLICATIO
5V
VRM10 Step-Down Controller
V
CC
10µF
LTC3738
BOOST1
BOOST2
BOOST3
0.1µF
SW3 SW2 SW1
POWER GOOD INDICATOR
MODE SELECTION/SYNC IN
PGOOD
FCB/SYNC
PLLFLTR
THERMAL INPUT
VR HOT INDICATOR
ON/OFF
680pF
I
TH
5k
0.1µF
SS
SGND
EAIN
AVP
IN
+
IN
–
TSNS
VR_HOTB
OUTEN
TG1
SW1
BG1
SENSE1
+
SENSE1
–
TG2
SW2
BG2
PGND
SENSE2
+
SENSE2
–
TG3
SW3
BG3
SENSE3
+
SENSE3
–
VID0-VID5
6 VID BITS
V
IN
0.8µH
0.002Ω
V
IN
0.8µH
0.002Ω
V
OUT
0.8375V TO 1.6000V
0.8µH
0.002Ω
100pF
U
+
U
U
+
V
IN
5V TO 28V
22µF
×2
470µF
×4
3738 TA01
3738f
1
LTC3738
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
BOOST1
TOP VIEW
PGOOD
OUTEN
VID2
VID1
VID0
VID5
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, VR_HOTB
Pin Voltages ................................................ 7V to –0.3V
OUTEN, SS, PLLFLTR,
FCB/SYNC Voltages ................................... V
CC
to –0.3V
I
TH
Voltage ................................................ 2.4V to –0.3V
IN
+
, IN
–
, VID0-VID5, TSNS .............................. 5V to 0V
AVP, SENSE
+
, SENSE
–
.................................. 1.9V to 0V
Operating Ambient Temperature Range ....... 0°C to 85°C
Junction Temperature (Note 2) ............................. 125°C
Storage Temperature Range ..................–65°C to 125°C
38 37 36 35 34 33 32
FCB/SYNC 1
PLLFLTR 2
IN
–
31 TG1
30 SW1
29 BOOST2
28 TG2
27 SW2
39
26 V
CC
25 BG1
24 PGND
23 BG2
22 BG3
21 SW3
20 TG3
13 14 15 16 17 18 19
I
TH
TSNS
VR_HOTB
VID3
VID4
BOOST3
SS
3
4
IN
+
AVP 5
EAIN 6
SENSE1
+
SENSE1
–
7
8
9
SENSE2
+
SENSE3
–
SENSE3
+
SENSE2
–
10
11
12
UHF PACKAGE
38-LEAD (7mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 39) IS SGND MUST BE SOLDERED TO PCB
ORDER PART
NUMBER
LTC3738CUHF
UHF PART
MARKING
3738
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
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
OUTEN
= V
SS
= 5V unless otherwise noted.
CONDITIONS
(Note 3); VID Code = 110101, V
ITH
= 1.2V
●
MIN
1.166
1.163
65
62
–5
●
●
TYP
1.175
1.175
75
75
MAX
1.184
1.187
85
88
5
UNITS
V
V
mV
mV
%
%
%
%/V
mmho
MHz
V
EAIN
= 0.5V, V
ITH
Open,
V
SENSE1
–
,
V
SENSE2
–
,
V
SENSE3
– = 0.8V, 1.85V
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
I
TH
= 1.2V, Sink/Source 25µA (Note 3)
I
TH
= 1.2V, (g
m
• Z
L
, Z
L
= Series 1k-100kΩ-1nF)
●
0.1
–0.1
0.03
3.05
1.5
0.5
–0.5
V
REFLNREG
g
m
g
mOL
V
FCB
I
FCB
Output Voltage Line Regulation
Transconductance Amplifier g
m
Transconductance Amplifier GBW
Forced Continuous Threshold
FCB Bias Current
●
0.58
0.60
0.2
0.62
0.7
V
FCB
= 0.65V
2
U
V
µA
3738f
W
U
U
W W
W
LTC3738
ELECTRICAL CHARACTERISTICS
SYMBOL
V
PSTH
UVR
I
Q
PARAMETER
Pulse Skip Threshold
Undervoltage SS Reset
Input DC Supply Current
Normal Mode
Shutdown
OUTEN Pin ON Threshold
Soft-Start Charge Current
SS Pin Arming Threshold
SS Pin Latch-Off Threshold
SS Discharge Current
Shutdown Latch Disable Current
Total SENSE Pins Source Current
Maximum Duty Factor
Top Gate Rise Time
Top Gate Fall Time
Bottom Gate Rise Time
Bottom Gate Fall Time
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
OUTEN
= V
SS
= 5V unless otherwise noted.
CONDITIONS
Measured at FCB pin
V
CC
Lowered Until the SS Pin is Pulled Low
(Note 4)
V
CC
= 5V
V
OUTEN
= 0V
V
OUTEN
, 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
= 0.3V, V
SS
= 4.5V
V
EAIN
= 0.3V, V
SS
= 4.5V
SENSE1
+
, SENSE1
–
, SENSE2
+
, SENSE2
–
,
SENSE3
+
, SENSE3
–
All Equal 1.2V
In Dropout
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
95
–5
0.4
–0.8
MIN
3.3
TYP
3.8
2.5
20
0.6
–1.5
3.8
3.3
–1.5
1.5
90
98.5
30
40
30
20
60
60
120
0.4
0.8
3.5
(Note 6)
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
DIFFOUT
with Respect to Set Output Voltage,
VID Code = 110101
PGOOD Goes Low After V
UVDLY
Delay
After VID Changes Outside PGOOD Window
–7
7
–10
10
100
●
MAX
4.5
UNITS
V
V
mA
µA
V
µA
V
V
µA
V
CC
– 1.5 V
CC
– 0.7 V
CC
– 0.3
100
0.8
–2.5
4.5
V
OUTEN
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
VID9/VID10
ATTEN
ERR
V
PGL
I
PGOOD
V
PGTHNEG
V
PGTHPOS
t
PGBLNK
5
120
µA
µA
%
90
90
90
90
ns
ns
ns
ns
ns
ns
ns
V
V
V
%
V
µA
%
%
µs
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
VRM9 Enable Threshold at VID5
VID0 to VID4
PGOOD Voltage Output Low
PGOOD Output Leakage
PGOOD Trip Thesholds
V
DIFFOUT
Ramping Negative
V
DIFFOUT
Ramping Positive
Power Good Blanking
Tested with a Square Wave (Note 5)
VID Parameters
V
CC
– 1
4.5
0.25
–0.25
0.1
Power Good Output Indication
0.3
±1
–14
14
3738f
3
LTC3738
ELECTRICAL CHARACTERISTICS
SYMBOL
f
NOM
f
LOW
f
HIGH
R
FCB
I
PLL LPF
PARAMETER
Nominal Frequency
Lowest Frequency
Highest Frequency
FCB Clock Input Threshold
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
Gain Bandwidth Product
Maximum High Output Voltage
Input Resistance
Sinking Current Ability of AVP Pin
Sourcing Current Ability of AVP Pin
Measured at IN
+
Pin
IN
+
= 1.2V
IN
+
= 1.2V
IN
+
= 1.2V, V
IN
= 60mV
0V < IN
+
= IN
–
< 5V, Input Referred
IN
+
= IN
–
= 1.2V, Input Referred
0
70
2
V
CC
– 0.8
160
0.250
1.4
180
1.67
0.21
3.4
V
CC
– 1
After All VID Bits = “1”
0.5
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
Oscillator and Phase-Locked Loop
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
= 2.4V
325
190
480
365
220
550
1.2
20
20
120
240
1
1.000
0.5
5
415
250
630
kHz
kHz
kHz
V
µA
µA
Deg
Deg
µs
V/V
mV
V
dB
MHz
V
kΩ
mA
mA
mV
V
V
V
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
OUTEN
= V
SS
= 5V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
R
RELPHS
No_CPU Detection
t
NOCPU
A
V
V
OS
CM
CMRR
GBP
V
O(MAX)
R
IN
I
SINK
I
SOURCE
Differential Amplifier
Active Voltage Positioning
V
AVP
– V
O(MAX)
Max Voltage Drops V
AVP
to VO
Thermal Detection
V
INT
V
INT_HYS
V
TH_TH
Thermal Comparator Trip Threshold
Hysteresis
Internal Detection Enable Threshold
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:
T
J
= T
A
+ (P
D
×
34°C/W)
Note 3:
The IC is tested in a feedback loop that includes the differential
amplifier 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 110101.
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.
3738f
4
LTC3738
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs I
OUT
100
90
80
EFFICIENCY (%)
V
FCB/SYNC
= 5V
92
91
I
L
= 20A
90
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
V
FCB/SYNC
= OPEN
V
FCB/SYNC
= 0V
V
IN
= 12V
V
OUT
= 1.2V
FREQUENCY = 210kHz
10
1
INDUCTOR CURRENT (A)
100
3738 G01
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)
V
PLLFLTR
= 5V
V
PLLFLTR
= 2.4V
FREQUENCY (kHz)
UNDERVOLTAGE RESET (V)
450
400
350
300
250
200
150
V
PLLFLTR
= 0V
V
PLLFLTR
= 1.2V
100
–45 –30 –15
0 15 30 45 60
TEMPERATURE (°C)
U W
75
90
3738 G04
T
A
= 25°C unless otherwise noted.
Efficiency vs Frequency
Efficiency vs V
IN
V
IN
= 12V
FREQUENCY = 210kHz
92
91
90
89
88
87
86
V
IN
= 5V
V
IN
= 10V
V
IN
= 14V
89
88
I
L
= 50A
87
86
85
4
5
6
7
8
9 10
V
IN
(V)
11 12 13 14
3733 G02
V
IN
= 12V
85 V
OUT
= 1.2V
I
LOAD
= 20A
84
250
300
200
400
350
FREQUENCY (kHz)
450
500
3738 G03
Error Amplifier g
m
vs Temperature
85
Maximum I
SENSE
Threshold
vs Temperature
80
V
O
= 1.85V
75
V
O
= 0.8V
70
3.0
2.5
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
3738 G05
3738 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
3738 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
3738 G07
3738 G09
3738f
5
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