LTC3736_15 Datasheet, PDF (1/28 Pages) Linear Technology – Dual 2-Phase, No RSENSE, Synchronous Controller with Output Tracking

LTC3736
Dual 2-Phase, No R_SENSE^TM,
Synchronous Controller
with Output Tracking
FEATURES
■ _{No Current Sense Resistors Required}
■ _{Out-of-Phase Controllers Reduce Required}
Input Capacitance
■ _{Tracking Function}
■ _{Wide VIN 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: IQ = 9µA}
■ _{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}
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_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. All other trademarks are the property of their respective
owners. Protected by U.S. Patents including 5481178, 5929620, 6144194, 6580258,
6304066, 6611131, 6498466.
TYPICAL APPLICATIO
High Efficiency, 2-Phase, Dual Synchronous DC/DC Step-Down Converter
V_IN
SENSE1⁺ SENSE2⁺
10µF
×2
V_IN
2.75V TO 9.8V
2.2µH
TG1
TG2
SW1
SW2
LTC3736
BG1
BG2
2.2µH
V_OUT1
2.5V
187k
47µF
220pF
59k
PGND
PGND
V_FB1
V_FB2
I_TH1
I_TH2
SGND
15k
220pF
15k
118k
59k
V_OUT2
1.8V
47µF
3736 TA01a
Efficiency vs Load Current
100
95
V_IN = 3.3V
90
85
V_IN = 4.2V
80
75
V_IN = 5V
70
65
60
55
FIGURE 16 CIRCUIT
50
V_OUT = 2.5V
1
10
100
1000 10000
LOAD CURRENT (mA)
3736 TA01b
3736fa
1