LTC3736-2 Datasheet, PDF (1/28 Pages) Linear Technology – Dual 2-Phase, No RSENSE 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}
■ _{0.6V ±1% Voltage Reference}
■ _{High Current Limit}
■ _{Constant Frequency Current Mode Operation}
■ _{Low Dropout Operation: 100% Duty Cycle}
■ _{True PLL for Frequency Locking or Adjustment}
■ _{Selectable Pulse-Skipping/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}
LTC3736-2
Dual 2-Phase, No R_SENSE^TM,
Synchronous Controller
with Output Tracking
DESCRIPTIO
The LTC^®3736-2 is a 2-phase dual synchronous step-down
switching regulator controller with tracking that drives ex-
ternal complementary power MOSFETs using few external
components. The constant frequency current mode archi-
tecture 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 mini-
mized by operating the two controllers out of phase.
Pulse-skipping 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 LTC3736-2
switching frequency can be externally synchronized from
250kHz to 850kHz. An internal soft-start, which can be
lengthened externally, smoothly ramps the output voltage
during start-up.
The LTC3736-2 is available in the tiny thermally enhanced
(4mm × 4mm) QFN and 24-lead narrow SSOP packages.
, LTC and LT are registered trademarks 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_OUT1
2.5V
2.2µH
187k
47µF
220pF
59k
V_IN
SENSE1⁺ SENSE2⁺
TG1
TG2
SW1
SW2
LTC3736-2
BG1
BG2
PGND
PGND
V_FB1
V_FB2
I_TH1
I_TH2
SGND
15k
10µF
×2
V_IN
2.75V TO 9.8V
2.2µH
118k
220pF
15k
59k
V_OUT2
1.8V
47µF
37362 TA01a
Efficiency and Power Loss
vs Load Current (Figure 15 Circuit)
100
10
V_OUT = 2.5V
95
90
EFFICIENCY
1
85
80
75
0.1
POWER LOSS
70
65
0.01
60
55
50
0.001
1
10
100
1000 10000
LOAD CURRENT (mA)
37362 TA01b
37362fa
1