Final Electrical Specifications
LTC1771
Low Quiescent Current
High Efficiency Step-Down
DC/DC Controller
February 2000
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FEATURES
DESCRIPTIO
The LTC®1771 is a high efficiency current mode step-
down DC/DC controller that draws as little as 10µA DC
supply current to regulate the output at no load while
maintaining high efficiency for loads up to several amps.
■
Very Low Standby Current: 10µA
■
Available in Space-Saving 8-Lead MSOP Package
■
High Output Currents
■
Wide VIN Range: 2.8V to 20V Operation
■
VOUT Range: 1.23V to 18V
TheLTC1771drivesanexternalP-channelpowerMOSFET
using a current mode, constant off-time architecture. An
external sense resistor is used to program the operating
current level. Current mode control provides short-circuit
protection, excellent transient response and controlled
start-up behavior. Burst Mode operation enables the
LTC1771 to maintain high efficiency down to extremely
low currents. Shutdown mode further reduces the supply
current to a mere 2µA. For low noise applications, Burst
Mode operation can be easily disabled with the MODE pin.
■
High Efficiency: Over 93% Possible
■
±2% Output Accuracy
■
Very Low Dropout Operation: 100% Duty Cycle
■
Current Mode Operation for Excellent Line and
Load Transient Response
Defeatable Burst ModeTM Operation
■
■
Short-Circuit Protected
Optional Programmable Soft-Start
■
■
Micropower Shutdown: IQ = 2µA
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Wide input supply range of 2.8V to 18V (20V maximum)
and 100% duty cycle operation for low dropout make the
LTC1771 ideal for a wide variety of battery-powered appli-
cations where maximizing battery life is important.
APPLICATIO S
■
Cellular Telephones and Wireless Modems
■
1- to 4-Cell Lithium-Ion-Powered Applications
■
Portable Instruments
The LTC1771’s availability in both 8-lead MSOP and SO
packages provides for a minimum area solution.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
■
Battery-Powered Equipment
■
Battery Chargers
■
Scanners
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TYPICAL APPLICATIO
V
IN
4.5V TO 18V
LTC1771 Efficiency
100
10µF
25V
CER
R
SENSE
0.05Ω
V
IN
= 5V
90
80
70
60
50
40
V
= 10V
IN
M1
V
SENSE
PGATE
IN
RUN/SS
Si6447DQ
L1
V
IN
= 15V
15µH
V
3.3V
2A
OUT
C
SS
0.01µF
LTC1771
I
TH
R
C
V
V
MODE
UPS5817
+
FB
IN
C
OUT
10k
GND
150µF
R2
1.64M
1%
C
C
6.3V
22OpF
R1
V
= 3.3V
SENSE
OUT
1M
1%
R
= 0.05Ω
5pF
0.1
1
10
100
1000
10000
1771 F01
LOAD CURRENT (mA)
1771 F01b
Figure 1. High Efficiency Step-Down Converter
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
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