LTC3736
Dual 2-Phase, No R
SENSE
TM
,
Synchronous Controller
with Output Tracking
FEATURES
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DESCRIPTIO
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No Current Sense Resistors Required
Out-of-Phase Controllers Reduce Required
Input Capacitance
Tracking Function
Wide V
IN
Range: 2.75V to 9.8V
Constant Frequency Current Mode Operation
0.6V
±1.5%
Voltage Reference
Low Dropout Operation: 100% Duty Cycle
True PLL for Frequency Locking or Adjustment
Selectable Burst Mode
®
/Forced Continuous Operation
Auxiliary Winding Regulation
Internal Soft-Start Circuitry
Power Good Output Voltage Monitor
Output Overvoltage Protection
Micropower Shutdown: I
Q
= 9µA
Tiny Low Profile (4mm
×
4mm) QFN and Narrow
SSOP Packages
The LTC
®
3736 is a 2-phase dual synchronous step-down
switching regulator controller with tracking that drives
external complementary power MOSFETs using few exter-
nal components. The constant frequency current mode
architecture with MOSFET V
DS
sensing eliminates the
need for sense resistors and improves efficiency. Power
loss and noise due to the ESR of the input capacitance are
minimized by operating the two controllers out of phase.
Burst Mode operation provides high efficiency at light loads.
100% duty cycle capability provides low dropout operation,
extending operating time in battery-powered systems.
The switching frequency can be programmed up to 750kHz,
allowing the use of small surface mount inductors and ca-
pacitors. For noise sensitive applications, the LTC3736
switching frequency can be externally synchronized from
250kHz to 850kHz. Burst Mode operation is inhibited dur-
ing synchronization or when the SYNC/FCB pin is pulled low
in order to reduce noise and RF interference. Automatic soft-
start is internally controlled.
The LTC3736 is available in the tiny thermally enhanced
(4mm
×
4mm) QFN package or 24-lead SSOP narrow
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
No R
SENSE
is a trademark of Linear Technology Corporation.
APPLICATIO S
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One or Two Lithium-Ion Powered Devices
Notebook and Palmtop Computers, PDAs
Portable Instruments
Distributed DC Power Systems
TYPICAL APPLICATIO
High Efficiency, 2-Phase, Dual Synchronous DC/DC Step-Down Converter
V
IN
2.75V TO 9.8V
V
IN
SENSE1
+
SENSE2
+
TG1
2.2µH
SW1
LTC3736
BG1
V
OUT1
2.5V
187k
PGND
V
FB1
BG2
PGND
V
FB2
I
TH2
SGND
15k
220pF
15k
59k
3736 TA01a
10µF
×2
EFFICIENCY (%)
TG2
SW2
2.2µH
118k
V
OUT2
1.8V
+
47µF
220pF
59k
I
TH1
+
47µF
U
Efficiency vs Load Current
100
95
90
85
80
75
70
65
60
55
50
1
FIGURE 16 CIRCUIT
V
OUT
= 2.5V
10
100
1000
LOAD CURRENT (mA)
10000
3736 TA01b
U
U
V
IN
= 3.3V
V
IN
= 4.2V
V
IN
= 5V
3736f
1