Final Electrical Specifications
LTC1878
High Efficiency
Monolithic Synchronous
Step-Down Regulator
May 2000
U
FEATURES
DESCRIPTIO
The LTC®1878 is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. Supply current during operation is
only 10µA and drops to < 1µA in shutdown. The 2.65V to
6V input voltage range makes the LTC1878 ideally suited
forsingleLi-Ionbattery-poweredapplications. 100%duty
cycle provides low dropout operation, extending battery
life in portable systems.
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High Efficiency: Up to 95%
■
Very Low Quiescent Current: Only 10µA
During Operation
■
600mA Output Current at VIN = 3.3V
■
2.65V to 6V Input Voltage Range
■
550kHz Constant Frequency Operation
Synchronizable from 400kHz to 700kHz
Selectable Burst ModeTM Operation/
Pulse Skipping Mode
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■
Switching frequency is internally set at 550kHz, allowing
the use of small surface mount inductors and capacitors.
For noise sensitive applications the LTC1878 can be
externally synchronized from 400kHz to 700kHz. Burst
Mode operation is inhibited during synchronization or
when the SYNC/MODE pin is pulled low, preventing low
frequency ripple from interfering with audio circuitry.
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■
■
■
■
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No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
0.8V Reference Allows Low Output Voltages
Shutdown Mode Draws < 1µA Supply Current
±2% Output Voltage Accuracy
Current Mode Control for Excellent Line and
Load Transient Response
Overcurrent and Overtemperature Protected
■
■
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.8V feed-
back reference voltage. The LTC1878 is available in a
space saving 8-lead MSOP package.
Available in 8-LeUad MSOP Package
APPLICATIO S
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Cellular Telephones
■
Wireless Modems
For higher input voltage (12V abs max) applications, refer
to the LTC1877 data sheet.
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Personal Information Appliances
■
Portable Instruments
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Distributed Power Systems
Burst Mode is a trademark of Linear Technology Corporation.
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Battery-Powered Equipment
U
Efficiency vs Output Load Current
TYPICAL APPLICATIO
100
V
= 3.6V
= 4.2V
95
90
85
80
75
70
IN
High Efficiency Step-Down Converter
10µH*
V
†
IN
7
6
1
2
5
V
OUT
V
SYNC
SW
2.65V
TO 6V
IN
3.3V
20pF
887k
22µF**
CER
V
IN
+
LTC1878
47µF***
V
= 6V
RUN
IN
3
I
V
FB
TH
GND
4
280k
220pF
Burst Mode OPERATION
V
= 3.3V
OUT
1878 TA01
L = 10µH
*TOKO D62CB A920CY-100M
0.1
1
10
100
1000
**TAIYO-YUDEN CERAMIC JMK325BJ226MM
***SANYO POSCAP 6TPA47M
OUTPUT CURRENT (mA)
†V
CONNECTED TO V FOR 2.65V < V < 3.3V
1878 TA02
OUT
IN IN
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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