1
LTC3736
3736fa
, 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. All other trademarks are the property of their respective
owners. Protected by U.S. Patents including 5481178, 5929620, 6144194, 6580258,
6304066, 6611131, 6498466.
Dual 2-Phase, No R
SENSE
TM
,
Synchronous Controller
with Output Tracking
High Efficiency, 2-Phase, Dual Synchronous DC/DC Step-Down Converter
■
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
= 9
µ
A
■
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.
■
One or Two Lithium-Ion Powered Devices
■
Notebook and Palmtop Computers, PDAs
■
Portable Instruments
■
Distributed DC Power Systems
SENSE1
+
V
IN
LTC3736
SGND
SENSE2
+
TG1
TG2
SW1
SW2
BG1
BG2
PGND
PGND
V
FB1
V
FB2
220pF
V
OUT1
2.5V
V
OUT2
1.8V
47
µ
F
47
µ
F
15k
220pF
15k
59k
59k
187k
118k
2.2
µ
H
2.2
µ
H
I
TH1
3736 TA01a
I
TH2
10
µ
F
×
2
V
IN
2.75V TO 9.8V
LOAD CURRENT (mA)
65
EFFICIENCY (%)
95
100
60
55
90
75
85
80
70
1
100
1000
10000
3736 TA01b
50
10
V
IN
= 3.3V
FIGURE 16 CIRCUIT
V
OUT
= 2.5V
V
IN
= 5V
V
IN
= 4.2V
Efficiency vs Load Current
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
