LTC3859_15 Datasheet, PDF (1/42 Pages) Linear Technology – Low IQ, Triple Output, Buck/Buck/Boost Synchronous Controller

FEATURES
n _{Dual Buck Plus Single Boost Synchronous Controllers}
n _{Outputs Remain in Regulation Through Cold Crank}
Down to 2.5V
n _{Low Operating IQ: 55μA (One Channel On)}
n _{Wide Bias Input Voltage Range: 4.5V to 38V}
n _{Buck Output Voltage Range: 0.8V ≤ VOUT ≤ 24V}
n _{Boost Output Voltage Up to 60V}
n _{RSENSE or DCR Current Sensing}
n _{100% Duty Cycle for Boost Synchronous MOSFET}
n _{Phase-Lockable Frequency (75kHz to 850kHz)}
n _{Programmable Fixed Frequency (50kHz to 900kHz)}
n _{Selectable Continuous, Pulse-Skipping or Low Ripple}
Burst Mode^® Operation at Light Loads
n _{Very Low Buck Dropout Operation: 99% Duty Cycle}
n _{Adjustable Output Voltage Soft-Start or Tracking}
n _{Low Shutdown IQ: 14μA}
n _{Small 38-Pin 5mm ¥ 7mm QFN and TSSOP Packages}
APPLICATIONS
n _{Automotive Always-On and Start-Stop Systems}
n _{Battery Operated Digital Devices}
n _{Distributed DC Power Systems}
LTC3859
Low I_Q, Triple Output,
Buck/Buck/Boost
Synchronous Controller
DESCRIPTION
The LTC^®3859 is a high performance triple output (buck/
buck/boost) synchronous DC/DC switching regulator
controller that drives all N-channel power MOSFET stages.
Constant frequency current mode architecture allows a
phase-lockable switching frequency of up to 850kHz. The
LTC3859 operates from a wide 4.5V to 38V input supply
range. When biased from the output of the boost converter
or another auxiliary supply, the LTC3859 can operate from
an input supply as low as 2.5V after start-up.
The 55μA no-load quiescent current extends operating runtime
in battery powered systems. OPTI-LOOP compensation allows
the transient response to be optimized over a wide range of
output capacitance and ESR values. The LTC3859 features a
precision 0.8V reference for the bucks, 1.2V reference for the
boost and a power good output indicator.
Independent TRACK/SS pins for each controller ramp the output
voltages during start-up. Current foldback limits MOSFET heat
dissipation during short-circuit conditions. The PLLIN/MODE
pin selects among Burst Mode operation, pulse-skipping mode,
or continuous inductor current mode at light loads.
L, LT, LTC, LTM, Burst Mode, OPTI-LOOP and μModule are registered trademarks and
No R_SENSE is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents including 5481178, 5705919,
5929620, 6144194, 6177787, 6580258.
TYPICAL APPLICATION
V_OUT3
REGULATED AT 10V WHEN V_IN < 10V
FOLLOWS V_IN WHEN V_IN > 10V
220μF
1μF
499k
V_FB3
V_BIAS
68.1k
TG1
V_IN
2.5V TO 38V
(START-UP ABOVE 5V)
2mΩ 1.2μH
220μF
4.7μF
SW1, 2, 3
TG3
SW1
SW3 _LTC3859
BG1
BG3
SENSE3^–
SENSE3⁺
INTV_CC
BOOST1, 2, 3
0.1μF
I_{TH1, 2, 3}
SENSE1⁺
SENSE1^–
V_FB1
RUN1, 2, 3
EXTV_CC
TG2
SW2
BG2
0.1μF
SENSE2+
TRACK/SS1, 2
SENSE2–
SS3
V_FB2
PGND SGND
3859 TA01
4.9μH _6mΩ
V_OUT1
5V
5A
68.1k ^357k
220μF
6.5μH _8mΩ
V_OUT2
8.5V
3A
68.1k ^649k
68μF
Efficiency vs Input Voltage
100
95
V_OUT2 = 8.5V
90
V_OUT1 = 5V
85
80
75
70
65
60
55 ^{FIGURE 12 CIRCUIT}
I_LOAD = 2A
50
0 5 10 15 20 25 30
INPUT VOLTAGE (V)
35 40
3859 TA01b
3859fa
1