LTC3719
2-Phase, High Efficiency,
Step-Down Controller for
AMD Opteron™ CPUs
FEATURES
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DESCRIPTIO
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Output Stages Operate Antiphase Reducing Input
and Output Capacitance Requirements and Power
Supply Induced Noise
Dual Input Supply Capability for Load Sharing
5-Bit AMD CPU VID Code:
V
OUT
= 0.8V to 1.55V
±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
®
3719 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
s
Servers and Workstations
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP and Burst Mode are registered trademarks of Linear Technology Corporation.
AMD Opteron is a trademark of Advanced Micro Devices, Inc.
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
LTC3719
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
0.8V TO 1.55V
45A
Figure 1. High Current Dual Phase Step-Down Converter
sn3719 3719fs
+
INTV
CC
10µF
U
V
IN
5V TO 28V
U
U
+
C
OUT
270µF
2V
×4
3716 F01
1
LINER [ LINEAR TECHNOLOGY ]
