LTC1709-85 Datasheet, PDF (1/28 Pages) Linear Technology – 2-Phase, 5-Bit VID,Current Mode, High Efficiency,Synchronous Step-Down Switching Regulator

LTC1709-85
2-Phase, 5-Bit VID,
Current Mode, High Efficiency,
Synchronous Step-Down Switching Regulator
FEATURES
DESCRIPTIO
s _{Output Stages Operate Antiphase Reducing Input}
Capacitance Requirements and Power Supply
Induced Noise
s _{Dual Input Supply Capability for Load Sharing}
s _{5-Bit VID Code (VRM 8.5): VOUT = 1.05V to 1.825V}
s _{True Remote Sensing Differential Amplifier}
s _{Power Good Output Indicator}
s _{±1% Output Voltage Accuracy}
s _{Active Voltage Positioning Capable}
s _{Current Mode Control Ensures Current Sharing}
s _OPTI-LOOP^® _{Compensation Minimizes COUT}
s _{Three Operational Modes: PWM, Burst and Cycle Skip}
s _{Programmable Fixed Frequency: 150kHz to 300kHz}
s _{Wide VIN Range: 4V to 36V Operation}
s _{Adjustable Soft-Start Current Ramping}
s _{Internal Current Foldback and Short-Circuit Shutdown}
s _{Overvoltage Soft Latch Eliminates Nuisance Trips}
s _{Available in 36-Lead Narrow SSOP Package}
U
APPLICATIO S
s _{Server/Desktop Computers}
s _{Internet Servers}
s _{Large Memory Arrays}
s _{DC Power Distribution Systems}
The LTC^®1709-85 is a 2-phase, VID programmable, syn-
chronous step-down switching regulator controller that
drives 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 effec-
tively multiplies the fundamental frequency by two, im-
proving transient response while operating each channel
at an optimum frequency 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP and Burst Mode are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
0.1µF
220pF
3.3k
5 VID BITS
FCB
V_IN
TG1
RUN/SS
BOOST1
SW1
LTC1709-85
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
×4
1µH
0.002Ω
0.002Ω
1µH
Figure 1. High Current Dual Phase Step-Down Converter
V_IN
5V TO 28V
V_OUT
1.05V TO 1.825V
40A
+ ^COUT
1000µF
4V
×2
170985 F01
170985f
1