LTC1709-7
2-Phase, 5-Bit VID,
Current Mode, High Efficiency,
Synchronous Step-Down Switching Regulator
U
FEATURES
DESCRIPTIO
■
Output Stages Operate Antiphase Reducing Input
Capacitance Requirements and Power Supply
Induced Noise
TheLTC®1709-7isa2-phase,VIDprogrammable,synchro-
nous step-down switching regulator controller that drives
twoallN-channelexternalpowerMOSFETstagesinafixed
frequencyarchitecture.The2-phasecontrollerdrivesitstwo
output stages out of phase at frequencies up to 300kHz to
minimize the RMS ripple currents in both input and output
capacitors.The2-phasetechniqueeffectivelymultipliesthe
fundamental frequency by two, improving transient re-
sponse while operating each channel at an optimum fre-
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
Dual Input Supply Capability for Load Sharing
5-Bit Mobile VID Code: VOUT = 0.925V to 2V
Current Mode Control Ensures Current Sharing
True Remote Sensing Differential Amplifier
Power Good Output Indicator
OPTI-LOOPTM Compensation Minimizes COUT
Three Operational Modes: PWM, Burst and Cycle Skip quency for efficiency. Thermal design is also simplified.
Programmable Fixed Frequency: 150kHz to 300kHz
An operating mode select pin (FCB) can be used to regu-
±1% Output Voltage Accuracy
late a secondary winding or select among three modes
Wide VIN Range: 4V to 36V Operation
includingBurstModeTM operationforhighestefficiency.An
Adjustable Soft-Start Current Ramping
internaldifferentialamplifierprovidestrueremotesensing
Internal Current Foldback and Short-Circuit Shutdown
of the regulated supply’s positive and negative output ter-
Overvoltage Soft Latch Eliminates Nuisance Trips
minals as required in high current applications.
Active Voltage Positioning Capable
Available in 36-LUead Narrow SSOP Package
The RUN/SS pin provides soft-start and optional timed,
short-circuit shutdown. Current foldback limits MOSFET
APPLICATIO S
■
dissipation during short-circuit conditions when the
overcurrentlatchoffisdisabled.OPTI-LOOPcompensation
allows the transient response to be optimized for a wide
range of output capacitors and ESR values.
Mobile/Desktop Computers
Internet Servers
Large Memory Arrays
■
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP and Burst Mode are trademarks of Linear Technology Corporation.
■
DC Power Distribution Systems
U
TYPICAL APPLICATIO
V
IN
5V TO 28V
+
10µF
35V
×4
0.1µF
V
IN
FCB
TG1
S
0.002Ω
RUN/SS
BOOST1
SW1
0.47µF
220pF
3.3k
1µH
S
LTC1709-7
I
TH
BG1
SGND
PGND
+
SENSE1
SENSE1
PGOOD
–
5 VID BITS VID0–VID4
TG2
BOOST2
SW2
0.002Ω
V
OUT
0.925V TO 2V
40A
EAIN
0.47µF
1µH
ATTENOUT
ATTENIN
BG2
V
V
V
INTV
DIFFOUT
CC
+
10µF
C
OUT
+
–
SENSE2
SENSE2
OS
1000µF
4V
+
–
OS
×2
170989 F01
Figure 1. High Current Dual Phase Step-Down Converter
1