Final Electrical Specifications
LTC1709-8/LTC1709-9
2-Phase, 5-Bit VID,
Current Mode, High Efficiency,
Synchronous Step-Down Switching Regulators
May 2000
FEATURES
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DESCRIPTIO
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Single Controller Operates Two Output Stages:
Antiphase Reducing Required Input Capacitance
and Power Supply Induced Noise
Two 5-Bit Desktop VID Codes:
LTC1709-8 For VRM8.4 (V
OUT
from 1.3V to 3.5V)
LTC1709-9 For VRM9.0 (V
OUT
from 1.1V to 1.85V)
Current Mode Control Ensures Best Current Sharing
True Remote Sensing Differential Amplifier
Power Good Output Indicator
OPTI-LOOP
TM
Compensation Minimizes C
OUT
Programmable Fixed Frequency: 150kHz to 300kHz
±1%
Output Voltage Accuracy
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
Low Shutdown Current: 20µA
Available in 36-Lead SSOP Package
The LTC
®
1709-8/LTC1709-9 are 2-phase, VID program-
mable, synchronous step-down switching regulator con-
trollers that drive two all N-channel external power MOSFET
stages in a fixed frequency 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 response while operating
each channel at an optimum frequency for efficiency.
Thermal design is also simplified.
An internal differential amplifier provides true remote
sensing of the regulated supply’s positive and negative
output terminals as required for high current applications.
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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a trademark of Linear Technology Corporation.
APPLICATIO S
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Workstations
Internet Servers
Large Memory Arrays
DC Power Distribution Systems
TYPICAL APPLICATIO
0.1µF
RUN/SS
3.3k
220pF
I
TH
SGND
PGOOD
5 VID BITS
+
V
IN
TG1
BOOST1
SW1
S
S
10µF
35V
×4
1µH
0.47µF
LTC1709-8
BG1
PGND
VID0–VID4
EAIN
ATTENOUT
ATTENIN
V
DIFFOUT
V
OS –
V
OS +
SENSE1
+
SENSE1
–
TG2
BOOST2
SW2
BG2
INTV
CC
SENSE2
+
SENSE2
–
0.47µF
1µH
0.002Ω
V
OUT
1.3V TO 3.5V
40A
10µF
+
Figure 1. High Current Dual Phase Step-Down Converter
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
V
IN
5V TO 28V
0.002Ω
U
U
+
C
OUT
1000µF
4V
×2
17097 F01
1
LINER [ LINEAR TECHNOLOGY ]
