LTC1709-8/LTC1709-9
2-Phase, 5-Bit VID,
Current Mode, High Efficiency,
Synchronous Step-Down Switching Regulators
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FEATURES
DESCRIPTIO
The LTC®1709-8/LTC1709-9 are 2-phase, VID program-
mable, synchronous step-down switching regulator con-
trollersthatdrivetwoallN-channelexternalpowerMOSFET
stages in a fixed frequency architecture. The 2-phase
controller drives its two output stages out of phase at
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Single Controller Operates Two Output Stages
Antiphase Reducing Required Input Capacitance
and Power Supply Induced Noise
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Two 5-Bit Desktop VID Codes:
LTC1709-8 For VRM8.4 (VOUT from 1.3V to 3.5V)
LTC1709-9 For VRM9.0 (VOUT from 1.1V to 1.85V) frequencies from 150kHz to 300kHz to minimize the RMS
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Current Mode Control Ensures Best Current Sharing
True Remote Sensing Differential Amplifier
Power Good Output Indicator
ripple currents in both input and output capacitors. The 2-
phase technique effectively multiplies the fundamental
frequency by two, improving transient response while
operating each channel at an optimum frequency for
efficiency. Thermal design is also simplified.
OPTI-LOOPTM Compensation Minimizes COUT
Programmable Fixed Frequency: 150kHz to 300kHz
±1% Output Voltage Accuracy
An internal differential amplifier provides true remote
sensing of the regulated supply’s positive and negative
output terminals as required for high current applications.
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
Low Shutdown Current: 20µA
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 compensa-
tion allows the transient response to be optimized for a
wide range of output capacitors and ESR values. The
LTC1709-8/LTC1709-9 implement two different VID
tables compliant with VRM8.4 and VRM9.0 respectively.
Available in 36-LUead Narrow SSOP Package
APPLICATIO S
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Workstations
Internet Servers
Large Memory Arrays
DC Power Distribution Systems
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, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a trademark of Linear Technology Corporation.
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TYPICAL APPLICATION
V
IN
5V TO 28V
+
10µF
35V
×4
0.1µF
V
IN
TG1
BOOST1
SW1
S
0.002Ω
RUN/SS
0.47µF
220pF
1µH
3.3k
S
LTC1709-8
I
BG1
TH
SGND
PGND
+
SENSE1
SENSE1
PGOOD
–
5 VID BITS VID0–VID4
TG2
BOOST2
SW2
0.002Ω
V
OUT
1.3V TO 3.5V
40A
EAIN
0.47µF
1µH
ATTENOUT
ATTENIN
BG2
V
V
V
INTV
DIFFOUT
CC
+
10µF
C
OUT
+
–
SENSE2
SENSE2
OS
1000µF
4V
+
–
OS
×2
17097 F01
Figure 1. High Current 2-Phase Step-Down Converter
1