LTC3736-1 Datasheet, PDF (1/28 Pages) Linear Technology – Dual 2-Phase, No RSENSE Synchronous Controller with Spread Spectrum

LTC3736-1
Dual 2-Phase, No R_SENSE^TM,
Synchronous Controller with
Spread Spectrum
FEATURES
■ _{Spread Spectrum Operation}
■ _{Tracking Function}
■ _{No Current Sense Resistors Required}
■ _{Out-of-Phase Controllers Reduce Required}
Input Capacitance
■ _{Wide VIN Range: 2.75V to 9.8V}
■ _{Current Mode Operation}
■ _{0.6V ±1.5% Voltage Reference}
■ _{Low Dropout Operation: 100% Duty Cycle}
■ _{Pulse Skipping Operation at Light Loads}
■ _{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}
, LTC and LT are registered trademarks of Linear Technology Corporation.
No R_SENSE is a trademark of Linear Technology Corporation.
Protected by U.S. Patents including 5481178, 5929620, 6144194, 6580258, 6304066,
6611131, 6498466.
DESCRIPTIO
The LTC^®3736-1 is a 2-phase dual synchronous step-
down switching regulator controller with tracking that
drives external complementary power MOSFETs using
few external 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 capaci-
tance are minimized by operating the two controllers out
of phase.
A unique spread spectrum architecture randomly varies
the LTC3736-1’s switching frequency from 450kHz to
580kHz, significantly reducing the peak radiated and con-
ducted noise on both the input and output supplies,
making it easier to comply with electromagnetic interfer-
ence (EMI) standards.
Pulse skipping operation provides high efficiency at light
loads. 100% duty cycle capability provides low dropout op-
eration, extending operating time in battery-powered sys-
tems. The high switching frequencies allow for the use of
small surface mount inductors and capacitors.
The LTC3736-1 is available in the low profile (0.75mm)
24-pin thermally enhanced (4mm × 4mm) QFN package
and 24-lead narrow SSOP packages.
TYPICAL APPLICATIO
Low Noise, 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
LTC3736-1
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
37361 TA01a
Output Voltage Frequency
Spectrum
–10
FIGURE 13 CIRCUIT _{SPREAD SPECTRUM}
–20 V_OUT = 2.5V
DISABLED
–30 ^{RBW = 30Hz}
SPREAD SPECTRUM
–40
ENABLED
–50
–60
–70
–80
–90
–100
–110
410k 450k 490k 530k 570k 610k
FREQUENCY (Hz)
37361 TA01b
37361f
1