LTC1265/LTC1265-3.3/LTC1265-5
1.2A, High Efficiency
Step-Down DC/DC Converter
FEATURES
DESCRIPTIO
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High Efficiency: Up to 95% The LTC 1265 is a monolithic step-down current mode
TM
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DC/DC converter featuring Burst Mode operation at low
Current Mode Operation for Excellent Line and Load
output current. The LTC1265 incorporates a 0.3W switch
Transient Response
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Internal 0.3W Power Switch (V = 10V) (V =10V) allowing up to 1.2A of output current.
IN
IN
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Short-Circuit Protection
Under no load condition, the converter draws only 160m A.
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Low Dropout Operation: 100% Duty Cycle
In shutdown it typically draws a mere 5m A making this
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Low-Battery Detector
converter ideal for current sensitive applications. In drop-
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Low 160m A Standby Current at Light Loads
out the internal P-channel MOSFET switch is turned on
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Active-High Micropower Shutdown: I < 15m A
Q
continuously maximizing the life of the battery source. The
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Peak Inductor Current Independent of Inductor Value
LTC1265 incorporates automatic power saving Burst Mode
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Available in 14-pin SO Package
operation to reduce gate charge losses when the load
U
currents drop below the level required for continuous
APPLICATIO S
operation.
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5V to 3.3V Conversion
The inductor current is user-programmable via an external
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Distributed Power Systems
current sense resistor. Operation up to 700kHz permits
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Step-Down Converters
the use of small surface mount inductors and capacitors.
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Inverting Converters
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
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Memory Backup Supply
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Portable Instruments
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Battery-Powered Equipment
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Cellular Telephones
TYPICAL APPLICATIO
V
IN
5.4V TO LTC1265-5 Efficiency
12V + C
IN
100
68m F
0.1m F
L1*
R **
V
PWR V SENSE
IN IN
20V
33m H
V
0.1W
OUT
V = 6V
IN
SW
SHDN 5V
95
1A
V = 9V
IN
LTC1265-5
D1
1k
+ C
OUT 90
I
TH
220m F
PGND V = 12V
IN
10V
3900pF 85
+
C
T SENSE
130pF
1000pF 80
L = 33m H
SENSE V = 5V
OUT
75
R = 0.1W
* COILTRONICS CTX33-4 SENSE
SGND
C = 130pF
** IRC LRC2010-01-R100-J T
MBRS130LT3
70
AVX TPSE227K010
0.01 0.10 1.00
AVX TPSE686K020
LOAD CURRENT (A)
LTC1265-FO1
LTC1265 TA01
Figure 1. High Efficiency Step-Down Converter
1
EFFICIENCY (%)
U
ULTC1265/LTC1265-3.3/LTC1265-5
UUW
ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO
(Voltages Refer to GND Pin) (Note 1)
TOP VIEW ORDER PART
Input Supply Voltage (Pins 1, 2, 13) ..........0.3V to 13V
NUMBER
PWR V 1 14 SW
IN
DC Switch Current (Pin 14) .................................... 1.2A
V 2 13 PWR V
IN IN
Peak Switch Current (Pin 14) ................................. 1.6A LTC1265CS
LB 3 12 PGND
OUT
Switch Voltage (Pin 14) .................................. V 13.0 LTC1265CS-5
IN
LB 4 11 SGND
IN
Operating Temperature Range
LTC1265CS-3.3
C 5 10 SHDN
T
LTC1265C ............................................... 0 to 70 C
LTC1265IS
I 6 9 N/C (V *)
TH FB
LTC1265I ........................................ 40 C to 85 C
+
SENSE 7 8 SENSE
Junction Temperature (Note 2)............................. 125 C
S PACKAGE
Storage Temperature Range ....................65 to 150 C
14-LEAD PLASTIC SO
Lead Temperature (Soldering, 10 sec).................. 300 C
*ADJUSTABLE OUTPUT VERSION
T = 125C, q = 110C/W
JMAX JA
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25 C. V = 10V, V = 0V, unless otherwise specified.
A IN SHDN
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I Feedback Current into Pin 9 LTC1265 0.2 1 m A
FB
V Feedback Voltage LTC1265C l 1.22 1.25 1.28 V
FB
= 9V, LTC1265I l 1.20 1.25 1.30 V
V
IN
V Regulator Output Voltage LTC1265-3.3: I = 800mA l 3.22 3.3 3.40 V
OUT LOAD
LTC1265-5: I = 800mA l 4.9 5 5.2 V
LOAD
D V Output Voltage Line Regulation V = 6.5V to 10V, I = 800mA 40 0 40 mV
OUT IN LOAD
Output Voltage Load Regulation LTC1265-3.3: 10mA < I < 800mA 40 65 mV
LOAD
< 800mA 60 100 mV
LTC1265-5: 10mA < I
LOAD
Burst Mode Operation Output Ripple I = 0mA 50 mV
LOAD P-P
I Input DC Supply Current (Note 3) Active Mode: 3.5V < V < 10V 1.8 2.4 mA
Q IN
Sleep Mode: 3.5V < V < 10V 160 230 m A
IN
Sleep Mode: 5V < V < 10V (LTC1265-5) 160 230 m A
IN
Shutdown: V = V , 3.5V < V < 10V 5 15 m A
SHDN IN IN
V Low-Battery Trip Point 1.15 1.25 1.35 V
LBTRIP
I Current into Pin 4 0.5 m A
LBIN
I Current Sunk by Pin 3 V = 0.4V, V = 0V 0.5 1.0 1.5 mA
LBOUT LBOUT LBIN
V = 5V, V = 10V 1.0 m A
LBOUT LBIN
V V Current Sense Threshold Voltage LTC1265: V = 5V, V = V /4 + 25mV (Forced) 25 mV
8 7 SENSE 9 OUT
V = 5V, V = V /4 25mV (Forced) 130 150 180 mV
SENSE 9 OUT
LTC1265-3.3: V = V + 100mV (Forced) 25 mV
SENSE OUT
V = V 100mV (Forced) 130 150 180 mV
SENSE OUT
LTC1265-5: V = V + 100mV (Forced) 25 mV
SENSE OUT
V = V 100mV (Forced) 130 150 180 mV
SENSE OUT
R ON Resistance of Switch LTC1265C l 0.3 0.60 W
ON
LTC1265I 0.3 0.70 W
I C Pin Discharge Current V in Regulation, V = V 40 60 100 m A
5 T OUT SENSE OUT
V = 0V 2 10 m A
OUT
t Switch Off Time (Note 4) C = 390pF, I = 800mA (LTC1265C) l 456 m s
OFF T LOAD
C = 390pF, I = 800mA (LTC1265I) l 3.5 5 7 m s
T LOAD
2
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