LTC3708_15 Datasheet, PDF (1/32 Pages) Linear Technology – Fast 2-Phase, No RSENSE Buck Controller with Output Tracking

FEATURES
n _{Very Low Duty Factor Operation (tON(MIN) < 85ns)}
n _{No RSENSE™ Option for Maximum Efficiency}
n _{Very Fast Transient Response}
n _{Programmable Output Voltage Up/Down Tracking}
n _{2-Phase Operation Reduces Input Capacitance}
n _{0.6V ±1% Output Voltage Reference}
n _{External Frequency Synchronization}
n _{Monotonic Soft-Start}
n _{Onboard High Current MOSFET Drivers}
n _{Wide VIN Range: Up to 36V}
n _{Adjustable Cycle-by-Cycle Current Limit}
n _{Instant Output Overvoltage Protection}
n _{Optional Short-Circuit Shutdown Timer}
n _{Power Good Output with 100μs Masking}
n _{Available in 5mm × 5mm QFN Package}
APPLICATIONS
n _{Digital Signal Processors}
n _{Network Servers}
LTC3708
Fast 2-Phase, No R_SENSE
Buck Controller with
Output Tracking
DESCRIPTION
The LTC^®3708 is a dual, 2-phase synchronous step-down
switching regulator with output voltage up/down tracking
capability. The IC allows either coincident or ratiometric
tracking. Multiple LTC3708s can be daisy-chained in ap-
plications requiring more than two voltages to be tracked.
Power supply sequencing is accomplished using an
external soft-start timing capacitor.
The LTC3708 uses a constant on-time, valley current mode
control architecture to deliver very low duty factors without
requiring a sense resistor. Operating frequency is selected
by an external resistor and is compensated for variations in
input supply voltage. An internal phase-locked loop allows
the IC to be synchronized to an external clock.
Fault protection is provided by an output overvoltage
comparator and an optional short-circuit shutdown timer.
The regulator current limit level is user programmable. A
wide supply range allows voltages as high as 36V to be
stepped down to 0.6V output.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
No R_SENSE is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
High Efficiency Dual Output Step-Down Converter
5V
10μF
50V
10Ω 1μF
4.7μF 100k
s4
V_IN
3.3V TO 28V
V_OUT1
2.5V
15A
POSCAP +
330μF
4V
s2
12.1k
6.04k
L1
1.4μH
B340A
19.1k
V_IN
1.5M
6.04k
0.01μF
M1
0.22μF
M3
33k
10k
0.01μF
180pF _0.1μF
V_CC DRV_CC PGOOD
TG1
TG2
BOOST1
BOOST2
SW1
SENSE1⁺
SW2
SENSE2⁺
M2
0.22μF
BG1 LTC3708 BG2
M4
SENSE1^–
PGND1
SENSE2^–
PGND2
V_FB1
TRACK2
I_ON1
I_TH1
INTLPF
RUN/SS
SGND
V_RNG1
V_FB2
FCB
I_ON2
I_TH2
EXTLPF
TRACK1
V_RNG2
f_IN
1k
100k
33k
0.1μF
25k
5V ^180pF
L1: PANASONIC ETQP3HIR4BF
L2: PANASONIC ETQP2HIR2BF
M1, M2: RENESAS HAT2168
M3, M4: RENESAS HAT2165
L2
1.2μH
B340A
V_OUT2
+
1.8V
POSCAP 15A
470μF
2.5V
s2
12.1k
1M
V_IN
0.01μF
6.04k
3708 TA01
100
95
90
85
80
75
70
0.01
V_OUT1 (0.5V/DIV)
V_OUT2 (0.5V/DIV)
2ms/DIV
3708 TA01b
9.0
7.5
6.0
4.5
20V_IN TO 2.5VOUT
5V_IN TO 2.5VOUT
20V_IN TO 1.8VOUT
3.0
5V_IN TO 1.8VOUT
1.5
0.1
1
LOAD CURRENT (A)
0
10
3708 TA01c
3708fb
1