Linear Technology No Rsense LTC3736 Datasheet

FEATURES
■ No Current Sense Resistors Required
■ Out-of-Phase Controllers Reduce Required
Input Capacitance
■ Tracking Function
■ Wide V Range: 2.75V to 9.8V
IN
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
■ Auxiliary Winding Regulation
■ Internal Soft-Start Circuitry
■ Power Good Output Voltage Monitor
■ Output Overvoltage Protection
■ Micropower Shutdown: I
■ Tiny Low Profile (4mm × 4mm) QFN and Narrow
SSOP Packages
U
APPLICATIO S
■
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
2.2µH
187k
V
OUT1
2.5V
220pF
47µF
59k
®
/Forced Continuous Operation
= 9µA
Q
V
IN
+ +
SENSE1 SENSE2
TG1 TG2
SW1 SW2
LTC3736
BG1 BG2
PGND PGND
V V
FB1 FB2
I I
TH1 TH2
220pF
SGND
15k 15k
Dual 2-Phase, No R
Synchronous Controller
DESCRIPTIO
®
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
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
Linear Technology Corporation. All other trademarks are the property of their respective
owners. Protected by U.S. Patents including 5481178, 5929620, 6144194, 6580258,
6304066, 6611131, 6498466.
V
IN
2.75V TO 9.8V
10µF
×2
2.2µH
118k
V
OUT2
1.8V
47µF
59k
3736 TA01a
LTC3736
with Output Tracking
sensing eliminates the
DS
SENSE
Efficiency vs Load Current
100
95
V = 3.3V
IN
90
85
V = 4.2V
IN
80
V = 5V
IN
75
70
65
60
FIGURE 16 CIRCUIT
55
V = 2.5V
OUT
50
1 10 100 1000
LOAD CURRENT (mA)
TM
,
SENSE
is a trademark of
10000
3736 TA01b
3736fa
1