1
LTC1709-8/LTC1709-9
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATION
U
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP is a trademark of Linear Technology Corporation.
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 from 150kHz 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.
Figure 1. High Current 2-Phase Step-Down Converter
■
Workstations
■
Internet Servers
■
Large Memory Arrays
■
DC Power Distribution Systems
■
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 Narrow SSOP Package
17097 F01
TG1
BOOST1
SW1
BG1
PGND
SENSE1
+
SENSE1
–
TG2
BOOST2
SW2
BG2
INTV
CC
SENSE2
+
SENSE2
–
V
IN
RUN/SS
V
DIFFOUT
I
TH
ATTENIN
ATTENOUT
EAIN
VID0–VID4
V
OS
–
V
OS
+
LTC1709-8
SGND
PGOOD
0.1µF
220pF
5 VID BITS
S
S
3.3k
+
10µF
35V
×4
+
+
C
OUT
1000µF
4V
×2
V
OUT
1.3V TO 3.5V
40A
1µH
0.002Ω
0.002Ω
V
IN
5V TO 28V
1µH
0.47µF
0.47µF
10µF
2-Phase, 5-Bit VID,
Current Mode, High Efficiency,
Synchronous Step-Down Switching Regulators