LTC3819
2-Phase, High Efficiency,
Step-Down Controller for
Sun Server CPUs
FEATURES
■
DESCRIPTIO
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
Output Stages Operate Antiphase Reducing Input
and Output Capacitance Requirements and Power
Supply Induced Noise
Dual Input Supply Capability for Load Sharing
5-Bit SUN CPU VID Code:
V
OUT
= 1.025V to 1.4125V
±1%
Output Voltage Accuracy
True Remote Sensing Differential Amplifier
Power Good Output Voltage Monitor
Supports Active Voltage Positioning
Current Mode Control Ensures Current Sharing
OPTI-LOOP
®
Compensation Minimizes C
OUT
Three Operational Modes: PWM, Burst and Cycle Skip
Programmable Fixed Frequency: 150kHz to 300kHz
Wide V
IN
Range: 4V to 36V Operation
Adjustable Soft-Start Current Ramping
Internal Current Foldback and Short-Circuit Shutdown
Overvoltage Soft Latch Eliminates Nuisance Trips
Available in 36-Lead Narrow (0.209) SSOP Package
The LTC
®
3819 is a 2-phase, VID programmable, synchro-
nous step-down switching regulator controller that drives
two N-channel external power MOSFET stages in a fixed fre-
quency architecture. The 2-phase controller drives its two
output stages out of phase at frequencies up to 300kHz to
minimize the RMS ripple currents in both input and output
capacitors. The 2-phase technique effectively multiplies the
fundamental frequency by two, improving transient re-
sponse while operating each channel at an optimum fre-
quency for efficiency. Thermal design is also simplified.
An operating mode select pin (FCB) can be used to select
among three modes including Burst Mode
®
operation for
highest efficiency. An internal differential amplifier provides
true remote sensing of the regulated supply’s positive and
negative output terminals as required in high current ap-
plications.
The RUN/SS pin provides 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 compensation
allows the transient response to be optimized for a wide
range of output capacitors and ESR values.
APPLICATIO S
■
Sun™ Server CPU Supply
, LTC and LT are registered trademarks of Linear Technology Corporation. OPTI-LOOP
and Burst Mode are registered trademarks 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, 6304066, 5705919.
TYPICAL APPLICATIO
0.1µF
220pF
FCB
RUN/SS
3.3k
I
TH
SGND
PGOOD
5 VID BITS
V
IN
TG1
BOOST1
SW1
S
10µF
35V
×6
0.47µF
1µH
S
0.002Ω
LTC3819
BG1
PGND
D1
VID0–VID4
EAIN
ATTENOUT
ATTENIN
V
DIFFOUT
V
OS –
V
OS +
SENSE1
+
SENSE1
–
TG2
BOOST2
SW2
BG2
SENSE2
+
SENSE2
–
D2
0.47µF
1µH
0.002Ω
V
DD
_
CORE
1.025V TO 1.4125V
45A
Figure 1. High Current Dual Phase Step-Down Converter
3819f
+
INTV
CC
10µF
U
V
IN
5V TO 28V
U
U
+
C
OUT
270µF
2V
×4
3716 F01
1
LTC3819
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN/SS
SENSE1
+
SENSE1
–
EAIN
PLLFLTR
PLLIN
FCB
I
TH
SGND
1
2
3
4
5
6
7
8
9
36 PGOOD
35 TG1
34 SW1
33 BOOST1
32 V
IN
31 BG1
30 EXTV
CC
29 INTV
CC
28 PGND
27 BG2
26 BOOST2
25 SW2
24 TG2
23 ATTENIN
22 V
BIAS
21 VID4
20 VID3
19 VID2
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,
V
BIAS
, ATTENIN, ATTENOUT, PGOOD, NO_CPU,
VID0–VID4, Voltages ...............................7V to – 0.3V
Boosted Driver Voltage (BOOST-SW) ..........7V to – 0.3V
PLLFLTR, PLLIN, V
DIFFOUT
,
FCB Voltages ................................... INTV
CC
to – 0.3V
I
TH
Voltage ................................................2.7V to – 0.3V
Peak Output Current <1µs(TG1, 2, BG1, 2) ................ 3A
INTV
CC
RMS Output Current ................................ 50mA
Operating Ambient Temperature Range
(Note 2) .............................................. – 40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC3819EG
V
DIFFOUT
10
V
OS–
11
V
OS
+
12
SENSE2
–
13
SENSE2
+
14
ATTENOUT 15
NO_CPU 16
VID0 17
VID1 18
G PACKAGE
36-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 85°C/W
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
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
(Note 4)
Main Control Loop
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
BIAS
= 5V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
I
TH
Voltage = 1.2V; Measured at V
EAIN
(Note 4)
●
●
MIN
0.594
62
TYP
0.600
75
–5
MAX
0.606
88
– 50
0.5
– 0.5
0.02
0.63
–1
4.8
0.68
4
UNITS
V
mV
nA
%
%
%/V
V
µA
V
V
V
3819f
(Note 4)
Measured in Servo Loop,
∆I
TH
Voltage: 1.2V to 0.7V
Measured in Servo Loop,
∆I
TH
Voltage: 1.2V to 2V
V
IN
= 3.6V to 30V (Note 4)
●
●
●
0.1
– 0.1
0.002
0.57
0.6
– 0.17
4.3
V
REFLNREG
V
FCB
I
FCB
V
BINHIBIT
V
OVL
UVLO
Reference Voltage Line Regulation
Forced Continuous Threshold
Forced Continuous Current
Burst Inhibit (Constant Frequency)
Threshold
Output Overvoltage Threshold
Undervoltage Lockout
Measured at FCB pin
Measured at V
EAIN
V
IN
Ramping Down
●
0.64
3
0.66
3.33
2
U
W
U
U
W W
W
LTC3819
ELECTRICAL CHARACTERISTICS
SYMBOL
g
m
g
mOL
I
Q
PARAMETER
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
Operating Supply Voltage Range
Resistance Between ATTENIN
and ATTENOUT Pins
Resistive Divider Error
VID0 to VID4 Pull-Up Resistance
VID0 to VID4 Logic Threshold Low
VID0 to VID4 Logic Threshold High
VID0 to VID4 Leakage
NO_CPU Maximum Output Voltage
V
BIAS
< VID0–VID4 < 7V
I
NO_CPU
= 2mA
1.6
±1
0.4
(Note 8)
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
BIAS
= 5V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
I
TH
= 1.2V, Sink/Source 5µA (Note 4)
I
TH
= 1.2V, (g
m
• Z
L
; No Ext Load) (Note 4)
(Note 5)
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
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver (Note 6)
C
LOAD
= 3300pF Each Driver (Note 6)
Tested with a Square Wave (Note 7)
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
2.7
5
– 0.35
40
0.4
0.25
●
MIN
TYP
3
1.5
1.2
20
MAX
UNITS
mmho
V/mV
mA
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
SDLHO
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
V
BIAS
R
ATTEN
ATTEN
ERR
R
PULLUP
VID
THLOW
VID
THHIGH
VID
LEAK
V
NO_CPU
– 0.5
1.0
0.5
– 85
98
–1.2
1.5
4.1
2
1.6
– 60
99.5
30
40
30
20
90
90
180
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
5.5
5.2
1.0
160
V
%
mV
V
V
V
kΩ
%
kΩ
V
V
µA
V
VID Parameters
3819f
3
LTC3819
ELECTRICAL CHARACTERISTICS
SYMBOL
f
NOM
f
LOW
f
HIGH
R
PLLIN
I
PLLFLTR
PARAMETER
Nominal Frequency
Lowest Frequency
Highest Frequency
PLLIN Input Resistance
Phase Detector Output Current
Sinking Capability
Sourcing Capability
Controller 2-Controller 1 Phase
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level, Either Controller
Oscillator and Phase-Locked Loop
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
BIAS
= 5V, V
RUN/SS
= 5V unless otherwise noted.
CONDITIONS
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥
2.4V
MIN
190
120
280
TYP
220
140
310
50
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
– 15
15
180
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
EAIN
with Respect to Set Output Voltage
V
EAIN
Ramping Negative
V
EAIN
Ramping Positive
V
AMPMD
= 0V
0V < V
CM
< 5V; V
AMPMD
= 0V
Measured at V
OS
+ Input; V
AMPMD
= 0V
–8
8
0.995
46
– 10
10
1
55
80
0.1
0.3
±1
– 12
12
1.005
MAX
250
160
360
UNITS
kHz
kHz
kHz
kΩ
µA
µA
Deg
V
µA
%
%
V/V
dB
kΩ
R
RELPHS
V
PGL
I
PGOOD
V
PG
PGOOD Output
Differential Amplifier/Op Amp Gain Block
A
DA
CMRR
DA
R
IN
Differential Amplifier 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:
The LTC3819EG 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.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
LTC3819EG: T
J
= T
A
+ (P
D
• 85°C/W)
Note 4:
The LTC3819 is tested in a feedback loop that servos V
ITH
to a
specified voltage and measures the resultant V
EAIN
.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 6:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 7:
The minimum on-time condition corresponds to the on inductor
peak-to-peak ripple current
≥
40% I
MAX
(see Minimum On-Time
Considerations in the Applications Information section).
Note 8:
Each built-in pull-up resistor attached to the VID inputs also has a
series diode to allow input voltages higher than the VIDV
CC
supply without
damage or clamping (see the Applications Information section).
3819f
4
LTC3819
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Load Current
(3 Operating Modes) (Figure 12)
100
90
80
EFFICIENCY (%)
EFFICIENCY (%)
Burst Mode
OPERATION
80
V
IN
= 5V
60
V
IN
= 8V
V
IN
= 12V
V
IN
= 20V
40
V
OUT
= 1.4125V
V
EXTVCC
= 0V
FREQ = 200kHz
V
FCB
= 0V
0.1
1
10
LOAD CURRENT (A)
100
3819 G02
60
50
40
30
20
10
0
0.01
0.1
EFFICIENCY (%)
70
FORCED
CONTINUOUS
MODE
CONSTANT
FREQUENCY
(BURST DISABLED)
V
IN
= 5V
V
OUT
= 1.4125V
FREQ = 200kHz
10
1
LOAD CURRENT (A)
100
3819 G01
Supply Current vs Input Voltage
and Mode
1000
ON
800
INTV
CC
AND EXTV
CC
SWITCH VOLTAGE (V)
EXTV
CC
VOLTAGE DROP (mV)
SUPPLY CURRENT (µA)
600
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
4.8
4.7
4.6
4.5
4.4
0
5
20
15
25
10
INPUT VOLTAGE (V)
30
35
3819 G07
V
SENSE
(mV)
V
SENSE
(mV)
U W
3819 G04
Efficiency vs Load Current
(Figure 12)
100
100
Efficiency vs Input Voltage
(Figure 12)
I
OUT
= 20A
V
OUT
= 1.4125V
90
80
70
20
60
0
50
5
15
10
INPUT VOLTAGE (V)
20
3819 G03
EXTV
CC
Voltage Drop
250
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
3819 G05
4.70
– 50 – 25
50
25
75
0
TEMPERATURE (°C)
100
125
3819 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
3819 G08
0
50
100
0
25
75
PERCENT OF NOMINAL OUTPUT VOLTAGE (%)
3819 G09
3819f
5
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