LTC3858_15 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 ≤ 24V}
n _{Wide VIN Range: 4V to 38V}
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-850kHz)}
n _{Programmable Fixed Frequency (50kHz-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 Latch-Off 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 5mm × 5mm QFN Package}
APPLICATIONS
n _{Automotive Systems}
n _{Battery Operated Digital Devices}
n _{Distributed DC Power Systems}
LTC3858
Low I_Q, Dual
2-Phase Synchronous
Step-Down Controller
DESCRIPTION
The LTC^®3858 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
LTC3858 features a precision 0.8V reference and a power
good output indicator. A wide 4V to 38V 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. The output latch-off feature
protects the circuit in short-circuit conditions.
For a leaded 28-lead SSOP package with a fixed current
limit and one PGOOD output, without phase modulation
or a clock output, see the LTC3858-1 data sheet.
L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, μModule, PolyPhase, 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
V_OUT1
3.3V
5A
High Efficiency Dual 8.5V/3.3V Step-Down Converter
3.3μH
0.1μF
V_IN
TG1
BOOST1
SW1
INTV_CC
TG2
BOOST2
SW2
4.7μF
V_IN
22μF ^{9V TO 38V}
50V
0.1μF
7.2μH
BG1
BG2
LTC3858
PGND
SENSE1⁺
SENSE2⁺
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
3858 TA01
Efficiency and Power Loss
vs Load Current
100
10000
90
80
EFFICIENCY
70
1000
60
100
POWER LOSS
50
40
10
30
20
10
0
0.0001
0.001 0.01
1
V_IN = 12V
V_OUT = 3.3V
FIGURE 12 CIRCUIT
0.1
0.1
1
10
OUTPUT CURRENT (A)
3858 TA01b
3858fc
1