LTC3858-2
Low I , Dual
Q
2-Phase Synchronous
Step-Down Controller
FEATURES
DESCRIPTION
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Low Operating I : 170μA (One Channel On)
The LTC®3858-2 is a high performance dual step-down
switching regulator controller that drives all N-channel
synchronouspowerMOSFETstages.Aconstantfrequency
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.
Q
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Wide Output Voltage Range: 0.8V ≤ V
≤ 24V
OUT
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Wide V Range: 4V to 38V
IN
R
or DCR Current Sensing
SENSE
Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
OPTI-LOOP® Compensation Minimizes C
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OUT
Phase-Lockable Frequency (75kHz-850kHz)
Programmable Fixed Frequency (50kHz-900kHz)
Selectable Continuous, Pulse-Skipping or
Burst Mode® Operation at Light Loads
The 170ꢀA 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
LTC3858-2differsfromtheLTC3858byhavingtheovervolt-
ageprotectioncrowbarandshort-circuitlatchoffdisabled.
A wide 4V to 38V input supply range encompasses a wide
rangeofintermediatebusvoltagesandbatterychemistries.
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Very Low Dropout Operation: 99% Duty Cycle
Adjustable Output Voltage Soft-Start or Tracking
Power Good Output Voltage Monitor
Low Shutdown I : 8μA
Q
Internal LDO Powers Gate Drive from V or EXTV
No Current Foldback During Start-Up
5mm × 5mm QFN Package
IN
CC
Independent soft-start pins for each controller ramp the
output voltages during start-up. Current foldback limits
MOSFET heat dissipation during short-circuit conditions.
L,LT,LTC,LTM,BurstMode,OPTI-LOOP,μModule,PolyPhase,LinearTechnologyandtheLinear
APPLICATIONS
logoareregisteredtrademarksandNoR
andUltraFastaretrademarksofLinearTechnology
SENSE
Corporation.Allothertrademarksarethepropertyoftheirrespectiveowners.ProtectedbyU.S.
Patents,including5481178,5705919,5929620,6100678,6144194,6177787,6304066,6580258.
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Automotive Systems
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Battery Operated Digital Devices
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Distributed DC Power Systems
TYPICAL APPLICATION
High Efficiency Dual 8.5V/3.3V Step-Down Converter
Efficiency and Power Loss
vs Load Current
V
IN
9V TO 38V
22μF
50V
100
90
10000
1000
100
10
4.7μF
V
INTV
CC
IN
TG1
TG2
80
0.1μF
0.1μF
EFFICIENCY
BOOST1
SW1
BOOST2
SW2
3.3μH
7.2μH
70
60
50
POWER LOSS
BG1
BG2
LTC3858-2
PGND
40
30
20
10
0
+
+
SENSE1
SENSE2
1
0.01Ω
193k
0.007Ω
V
V
= 12V
OUT
FIGURE 13 CIRCUIT
IN
–
= 3.3V
–
V
SENSE2
OUT2
SENSE1
FB1
V
OUT1
3.3V
5A
8.5V
3.5A
V
V
FB2
0.1
62.5k
150μF
0.0001 0.001
0.01
0.1
1
10
I
I
TH2
TH1
SS1
680pF
15k
680pF
15k
OUTPUT CURRENT (A)
150μF
SGND
SS2
20k
38582 TA01b
20k
0.1μF
0.1μF
38582 TA01a
38582f
1