LTC3708
Fast 2-Phase, No R
SENSE
Buck Controller with
Output Tracking
FEATURES
DESCRIPTION
The LTC®3708 is a dOal, 2-phase synchronoOs step-down
switching regOlator with oOtpOt voltage Op/down tracking
capability. The IC allows either coincident or ratiometric
tracking. MOltiple LTC3708s can be daisy-chained in ap-
plications reqOiring more than two voltages to be tracked.
Power sOpply seqOencing is accomplished Osing an
external soft-start timing capacitor.
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Very Low Duty Factor Operation (t
< 85ns)
ON(MIN)
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No R
™ Option for Maximum Efficiency
SENSE
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Very Fast Transient Response
Programmable Output Voltage Up/Down Tracking
2-Phase Operation Reduces Input Capacitance
0.6V ±±1 ꢀOtpOt Voltage Reference
External FreqOency Synchronization
Monotonic Soft-Start
TheLTC3708Osesaconstanton-time,valleycOrrentmode
controlarchitectOretodeliververylowdOtyfactorswithoOt
reqOiring a sense resistor. ꢀperating freqOency is selected
byanexternalresistorandiscompensatedforvariationsin
inpOtsOpplyvoltage. Aninternalphase-lockedloopallows
the IC to be synchronized to an external clock.
ꢀnboard High COrrent MꢀSFET Drivers
Wide V Range: Up to 36V
IN
AdjOstable Cycle-by-Cycle COrrent Limit
Instant ꢀOtpOt ꢀvervoltage Protection
ꢀptional Short-CircOit ShOtdown Timer
Power Good ꢀOtpOt with ±00μs Masking
Available in 5mm × 5mm QFN Package
FaOlt protection is provided by an oOtpOt overvoltage
comparator and an optional short-circOit shOtdown timer.
The regOlator cOrrent limit level is Oser programmable. A
wide sOpply range allows voltages as high as 36V to be
stepped down to 0.6V oOtpOt.
APPLICATIONS
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Digital Signal Processors
Network Servers
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L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
No R
is a trademark of Linear Technology Corporation.
SENSE
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
High Efficiency Dual Output Step-Down Converter
V
V
(0.5V/DIV)
(0.5V/DIV)
ꢀUT±
V
IN
3.3V Tꢀ 28V
ꢀUT2
5V
±0μF
50V
s4
±μF
4.7μF
±0Ω
±00k
+
V
TG±
DRV
CC
PGꢀꢀD
TG2
CC
M±
M3
M2
M4
L±
L2
±.2μH
3708 TA0±b
2ms/DIV
BꢀꢀST±
BꢀꢀST2
±.4μH
V
V
±.8V
±5A
0.22μF
0.22μF
ꢀUT±
2.5V
±5A
ꢀUT2
SW±
SENSE±
SW2
+
+
+
+
PꢀSCAP
330μF
4V
PꢀSCAP
470μF
2.5V
SENSE2
±00
95
90
85
80
75
70
9.0
7.5
6.0
4.5
3.0
±.5
0
B340A
B340A
LTC3708
BG±
BG2
s2
s2
–
–
SENSE2
SENSE±
PGND±
±2.±k
±2.±k
±9.±k
PGND2
V
V
FB2
FCB
I
ꢀN2
I
TH2
EXTLPF
TRACK±
V
RNG2
FB±
TRACK2
f
±M
IN
V
IN
V
I
IN
ꢀN±
20V Tꢀ 2.5V
IN ꢀUT
±.5M
I
TH±
5V Tꢀ 2.5V
IN
ꢀUT
INTLPF
RUN/SS
SGND
20V Tꢀ ±.8V
IN
ꢀUT
5V Tꢀ ±.8V
IN
ꢀUT
6.04k
6.04k
0.0±μF
33k
6.04k
±0k
0.0±μF
±k
33k
V
RNG±
±00k
0.±μF
0.0±μF
25k
±80pF
±80pF
0.±μF
0.0±
0.±
±
±0
5V
LꢀAD CURRENT (A)
3708 TA0±
L±: PANASꢀNIC ETQP3HIR4BF
L2: PANASꢀNIC ETQP2HIR2BF
M±, M2: RENESAS HAT2±68
M3, M4: RENESAS HAT2±65
3708 TA0±c
3708fb
1