LTC3819 Datasheet, PDF (1/32 Pages) Linear Technology – 2-Phase, High Efficiency, Step-Down Controller for Sun Server CPUs

LTC3819
2-Phase, High Efficiency,
Step-Down Controller for
Sun Server CPUs
FEATURES
■ _{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 COUT}
■ _{Three Operational Modes: PWM, Burst and Cycle Skip}
■ _{Programmable Fixed Frequency: 150kHz to 300kHz}
■ _{Wide VIN 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-LUead Narrow (0.209) SSOP Package}
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.
DESCRIPTIO
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.
TYPICAL APPLICATIO
0.1µF
220pF
3.3k
5 VID BITS
FCB
V_IN
TG1
RUN/SS
BOOST1
SW1
LTC3819
I_TH
BG1
SGND
PGND
PGOOD
VID0–VID4
SENSE1⁺
SENSE1^–
TG2
EAIN
BOOST2
ATTENOUT
SW2
ATTENIN
BG2
V_DIFFOUT
V_OS–
V_OS+
INTV_CC
SENSE2⁺
SENSE2^–
0.47µF
0.47µF
10µF
10µF
35V
×6
1µH
D1
0.002Ω
1µH
D2
0.002Ω
Figure 1. High Current Dual Phase Step-Down Converter
V_IN
5V TO 28V
V_DD__CORE
1.025V TO 1.4125V
45A
+ ^COUT
270µF
2V
×4
3716 F01
3819f
1