LTC1773EMS データシートの表示（PDF） - Linear Technology
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LTC1773EMS Datasheet PDF : 20 Pages
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FEATURES
■ High Efficiency: Up to 95%
■ Constant Frequency 550kHz Operation
■ VIN from 2.65V to 8.5V
■ VOUT from 0.8V to VIN
■ OPTI-LOOP® Compensation Minimizes COUT
■ Synchronizable up to 750kHz
■ Selectable Burst Mode Operation
■ Low Quiescent Current: 80µA
■ Low Dropout Operation: 100% Duty Cycle
■ Secondary Winding Regulation
■ Soft-Start
■ Current Mode Operation for Excellent Line and
Load Transient Response
■ Low Shutdown IQ = 10µA
■ ±1.5% Reference Accuracy
■ Precision 2.5V Undervoltage Lockout
■ Available in 10-Lead MSOP
U
APPLICATIO S
■ Cellular Telephones
■ RF PA Supplies
■ Portable Instruments
■ Wireless MODEMS
■ Distributed Power Systems
■ Notebook and Palm Top Computers, PDAs
■ Single and Dual Cell Lithium-Ion Powered Devices
LTC1773
Synchronous Step-Down
DC/DC Controller
DESCRIPTIO
The LTC®1773 is a current mode synchronous buck regu-
lator controller that drives external complementary power
MOSFETs using a fixed frequency architecture. The oper-
ating supply range is from 2.65V to 8.5V, making it
suitable for 1- or 2-cell lithium-ion battery powered appli-
cations. Burst Mode® operation provides high efficiency at
low load currents. 100% duty cycle provides low dropout
operation which extends operating time in battery-oper-
ated systems.
The operating frequency is internally set at 550kHz, allow-
ing the use of small surface mount inductors. For switch-
ing-noise sensitive applications, it can be synchronized up
to 750kHz. Peak current limit is user programmable with
an external high side sense resistor. A SYNC/FCB control
pin guarantees regulation of secondary windings regard-
less of load on the main output by forcing continuous
operation. Burst Mode operation is inhibited during syn-
chronization or when the SYNC/FCB pin is pulled low to
reduce noise and RF interference. Soft-start is provided by
an external capacitor.
Synchronous rectification increases efficiency and elimi-
nates the need for a Schottky diode, saving components
and board space. The LTC1773 comes in a 10-lead MSOP
package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
OPTI-LOOP and Burst Mode are registered trademarks of Linear Technology Corporation.
Protected by U.S. Patents, including 5481178, 6580258, 6304066, 6127815.
TYPICAL APPLICATIO
VIN
2.65V TO 8.5V
SYNC/FCB VIN
RUN/SS SENSE–
0.1µF
ITH
TG
47pF
30k
LTC1773
SW
220pF
VFB GND BG
80.6k
RSENSE
0.025Ω
L1
3µH
Si9801DY
169k
Figure 1. Step-Down Converter
+
CIN
68µF
VOUT
2.5V
+ COUT
180µF
1773 F01
100
95
90
85
80
75
70
65
60
55
1
High Efficiency
VIN = 3.3V
VIN = 5V
VIN = 8V
L = SUMIDA CDRH6D28-3R0
10
100
1000 5000
OUTPUT CURRENT (mA)
1773 F1b
1773fb
1
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