LTC1779_15 Datasheet, PDF (1/12 Pages) Linear Technology – 250mA Current Mode Step-Down DC/DC Converter in ThinSOT

LTC1779
250mA Current Mode
Step-Down DC/DC Converter
in ThinSOT
FEATURES
s _{High Efficiency: Up to 94%}
s _{250mA Output Current}
s _{Wide VIN Range: 2.5V to 9.8V}
s _{550kHz Constant Frequency Operation}
s _{Burst Mode}^TM _{Operation at Light Load}
s _{Low Dropout: 100% Duty Cycle}
s _{0.8V Reference Allows Low Output Voltages}
s _{±2.5% Reference Accuracy}
s _{Current Mode Operation for Excellent Line and Load}
Transient Response
s _{Low Quiescent Current: 135µA}
s _{Shutdown Mode Draws Only 8µA Supply Current}
s _{Low Profile (1mm) ThinSOT}^TM _Package
U
APPLICATIO S
s _{1- or 2-Cell Lithium-Ion-Powered Applications}
s _{Cellular Telephones}
s _{Wireless Modems}
s _{Portable Computers}
s _{Distributed 3.3V, 2.5V or 1.8V Power Systems}
s _Scanners
DESCRIPTIO
The LTC^®1779 is a constant frequency current mode step-
down 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 pro-
vides excellent AC and DC load and line regulation. The
device incorporates an accurate undervoltage lockout fea-
ture 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 applica-
tions 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.
TYPICAL APPLICATIO
20k
100pF
1
6
I_TH/RUN SW
LTC1779
2
5
GND
V_IN
3
V_FB
SENSE^{– 4}
C3
0.1µF _L1
22µH
+
D1
R1
10Ω
C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT
C2: SANYO POSCAP 6TPA47M
D1: IR10BQ015
L1: COILTRONICS UP1B220
C1
10µF
16V
C2
47µF
6V
V_IN
2.5V
TO 9.8V
169k
V_OUT
2.5V
100mA
78.7k
1779 F01a
Figure 1. LTC1779 High Efficiency 2.5V/100mA Step-Down Converter
Efficiency vs Load Current
100
90
V_IN = 3.3V
80
70
60
V_IN = 6V
V_IN = 9.8V
50
40
30
0.1
V_OUT = 2.5V
R_SENSE = 10Ω
1
10
100
LOAD CURRENT (mA)
1000
1779 F01b
1