LTC3827
Low I , Dual, 2-Phase
Q
Synchronous Step-Down Controller
FEATURES
DESCRIPTION
The LTC®3827 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 650kHz. Power loss and noise due to the
ESRoftheinputcapacitorESRareminimizedbyoperating
the two controller output stages out of phase.
n
Wide Output Voltage Range: 0.8V ≤ V
≤ 10V
OUT
n
Low Operating I : 80μA (One Channel On)
Out-of-Phase Controllers Reduce Required Input
Q
n
Capacitance and Power Supply Induced Noise
OPTI-LOOP® Compensation Minimizes C
n
n
n
n
n
OUT
1ꢀ Output Voltage Accuracy
Wide V Range: 4V to 36V Operation
IN
Phase-Lockable Fixed Frequency 140kHz to 650kHz
Selectable Continuous, Pulse Skipping or Low Ripple
Burst Mode® Operation at Light Loads
The 80μA 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
LTC3827 features a precision 0.8V reference and a power
goodoutputindicator. Awide4Vto36Vinputsupplyrange
encompasses all battery chemistries.
n
n
n
n
n
n
n
n
n
Dual N-Channel MOSFET Synchronous Drive
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Output Voltage Soft-Start or Tracking
Output Current Foldback Limiting
Power Good Output Voltage Monitor
Output Overvoltage Protection
Low Shutdown I : 8μA
Internal LDO Powers Gate Drive from V or V
Small 5mm × 5mm QFN Package
Independent TRACK/SS pins for each controller ramp the
output voltage during start-up. Current foldback limits
MOSFET heat dissipation during short-circuit conditions.
Q
IN
OUT
The PLLIN/MODE pin selects among Burst Mode opera-
tion, pulse skipping mode, or continuous inductor cur-
rent mode at light loads. For a leaded package version
(28-lead SSOP), see the LTC3827-1 datasheet.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents
including 5481178, 5929620, 6177787, 6144194, 5408150, 6580258, 6304066, 570919.
APPLICATIONS
n
Automotive Systems
Battery-Operated Digital Devices
Distributed DC Power Systems
n
n
TYPICAL APPLICATION
High Efficiency Dual 8.5V/3.3V Step-Down Converter
Efficiency and Power Loss
vs Load Current
V
IN
4V TO 36V
+
22μF
50V
100000
10000
1000
100
100
90
1μF
4.7μF
EFFICIENCY
V
IN
INTV
CC
V
= 12V; V
= 3.3V
IN
OUT
TG1
TG2
80
0.1μF
BOOST1
SW1
BOOST2
SW2
70
7.2μH
3.3μH
0.1μF
60
50
BG1
BG2
LTC3827
PGND
40
30
20
10
0
POWER LOSS
10
+
+
SENSE1
SENSE1
SENSE2
0.015Ω
0.015Ω
1
–
–
SENSE2
FIGURE 13 CIRCUIT
V
V
8.5V
3.5A
OUT1
3.3V
5A
OUT2
0.1
V
V
FB1
FB2
0.001 0.01 0.1
1
10 100 1000 10000
62.5k
192.5k
I
I
TH2
TH1
TRACK/SS1 SGND TRACK/SS2
0.1μF
LOAD CURRENT (mA)
220pF
15k
220pF
15k
150μF
150μF
3827 TA01b
20k
20k
0.1μF
3827 TA01
3827ff
1