LTC3868-1 Datasheet, PDF (1/38 Pages) Linear Technology – Low IQ, Dual 2-Phase Synchronous Step-Down Controller

Features
n _{Low Operating IQ: 170µA (One Channel On)}
n _{Wide Output Voltage Range: 0.8V ≤ VOUT ≤ 14V}
n _{Wide VIN Range: 4V to 24V}
n _{RSENSE or DCR Current Sensing}
n _{Out-of-Phase Controllers Reduce Required Input}
Capacitance and Power Supply Induced Noise
n _OPTI-LOOP^® _{Compensation Minimizes COUT}
n _{Phase-Lockable Frequency (75kHz to 850kHz)}
n _{Programmable Fixed Frequency (50kHz to 900kHz)}
n _{Selectable Continuous, Pulse-Skipping or}
Burst Mode^® Operation at Light Loads
n _{Very Low Dropout Operation: 99% Duty Cycle}
n _{Adjustable Output Voltage Soft-Start}
n _{Power Good Output Voltage Monitor}
n _{Output Overvoltage Protection}
n _{Output Latchoff Protection During Short Circuit}
n _{Low Shutdown IQ: 8µA}
n _{Internal LDO Powers Gate Drive from VIN or EXTVCC}
n _{No Current Foldback During Start-Up}
n _{Small 4mm × 5mm QFN and Narrow SSOP Packages}
Applications
n _{Notebook and Palmtop Computers}
n _{Portable Instruments}
n _{Battery Operated Digital Devices}
n _{Distributed DC Power Systems}
LTC3868-1
Low I_Q, Dual
2-Phase Synchronous
Step-Down Controller
Description
The LTC^®3868-1 is a high performance dual step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant frequency
current mode architecture allows a phase-lockable fre-
quency of up to 850kHz. Power loss and noise due to the
input capacitor ESR are minimized by operating the two
controller outputs out of phase.
The 170μA no-load quiescent current extends operating
life in battery powered systems. OPTI-LOOP compensa-
tion allows the transient response to be optimized over
a wide range of output capacitance and ESR values. The
LTC3868-1 features a precision 0.8V reference and a power
good output indicator. A wide 4V to 24V input supply range
encompasses a wide range of intermediate bus voltages
and battery chemistries.
Independent soft-start pins for each controller ramp the
output voltages during start-up. Current foldback limits
MOSFET heat dissipation during short-circuit conditions.
The output short-circuit latchoff feature further protects
the circuit in short-circuit conditions.
For a leadless 32-pin QFN package with the additional fea-
tures of adjustable current limit, clock out, phase modula-
tion and two PGOOD outputs, see the LTC3868 data sheet.
L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, µModule, Linear Technology and the Linear logo
are registered trademarks and No R_SENSE and UltraFast are trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners. Protected by U.S.
Patents, including 5481178, 5705919, 5929620, 6100678, 6144194, 6177787, 6304066, 6580258.
Typical Application
High Efficiency Dual 8.5V/3.3V Step-Down Converter
3.3µH
0.1µF
V_IN
TG1
BOOST1
INTV_CC
TG2
BOOST2
4.7µF
V_IN
22µF ^{9V TO 24V}
50V
0.1µF
7.2µH
SW1
SW2
BG1
BG2
LTC3868-1
PGND
SENSE1⁺
SENSE2⁺
V_OUT1
3.3V
5A
0.007Ω
62.5k
150µF
680pF
SENSE1^–
V_FB1
I_TH1
SS1
SGND
SENSE2^–
V_FB2
I_TH2
SS2
20k 15k
0.1µF
0.1µF
680pF
15k
0.01Ω
193k
20k
V_OUT2
8.5V
3.5A
150µF
38681 TA01
Efficiency and Power Loss
vs Load Current
100
10000
90
80
1000
70
EFFICIENCY
60
100
50
POWER LOSS
40
10
30
20
10
0
0.0001
0.001 0.01
V_IN = 12V
1
V_OUT = 3.3V
FIGURE 12 CIRCUIT
0.1
0.1
1
10
OUTPUT CURRENT (A)
38681 TA01b
38681fb