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LTC1779 250mA Current Mode Step-Down DC/DC Converter in ThinSOT
FEATURES
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DESCRIPTIO
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High Efficiency: Up to 94% 250mA Output Current Wide VIN Range: 2.5V to 9.8V 550kHz Constant Frequency Operation Burst ModeTM Operation at Light Load Low Dropout: 100% Duty Cycle 0.8V Reference Allows Low Output Voltages ± 2.5% Reference Accuracy Current Mode Operation for Excellent Line and Load Transient Response Low Quiescent Current: 135µA Shutdown Mode Draws Only 8µA Supply Current Low Profile (1mm) ThinSOTTM Package
The LTC®1779 is a constant frequency current mode stepdown DC/DC converter in a 6-lead ThinSOT package. The part operates with a 2.5V to 9.8V input and can provide up to 250mA of output current. Current mode control provides excellent AC and DC load and line regulation. The device incorporates an accurate undervoltage lockout feature that shuts down the LTC1779 when the input voltage falls below 2V. The LTC1779 boasts a ± 2.5% output voltage accuracy and consumes only 135µA of quiescent current. For applications where efficiency is a prime consideration, the LTC1779 is configured for Burst Mode operation, which enhances efficiency at low output current. To further maximize the life of a battery source, the internal P-channel MOSFET is turned on continuously in dropout (100% duty cycle). In shutdown, the device draws a mere 8µA. High constant operating frequency of 550kHz allows the use of a small external inductor. The LTC1779 is available in a low profile (1mm) ThinSOT package.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode and ThinSOT are trademarks of Linear Technology Corporation.
U APPLICATIO S
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1- or 2-Cell Lithium-Ion-Powered Applications Cellular Telephones Wireless Modems Portable Computers Distributed 3.3V, 2.5V or 1.8V Power Systems Scanners
TYPICAL APPLICA TIO
C3 0.1µF 1 20k 100pF 3 VFB SENSE – 4 ITH/RUN LTC1779 GND VIN SW 6 D1 R1 10Ω
L1 22µH
C1 10µF 16V
VIN 2.5V TO 9.8V VOUT 2.5V 100mA
100 90 VIN = 3.3V 80
EFFICIENCY (%)
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5
2
C2 47µF 6V
169k
70 VIN = 9.8V 60 50 40 30 0.1 VOUT = 2.5V RSENSE = 10Ω 1 10 100 LOAD CURRENT (mA) 1000
1779 F01b
78.7k
1779 F01a
C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT C2: SANYO POSCAP 6TPA47M D1: IR10BQ015 L1: COILTRONICS UP1B220
Figure 1. LTC1779 High Efficiency 2.5V/100mA Step-Down Converter
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Efficiency vs Load Current
VIN = 6V
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http://www.Datasheet4U.com
LTC1779
ABSOLUTE
(Note 1)
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TOP VIEW ITH/RUN 1 GND 2 VFB 3 6 SW 5 VIN 4 SENSE
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Input Supply Voltage (VIN).........................– 0.3V to 10V SENSE –, SW Voltages .................. – 0.3V to (VIN + 0.3V) VFB, ITH/RUN Voltages ..............................– 0.3V to 2.4V SW Peak Output Current (< 10µs) .......................... 0.5A Storage Ambient Temperature Range ... – 65°C to 150°C Operating Temperature Range (Note 2) ...–40°C to 85°C Junction Temperature (Note 3) ............................. 150°C .