LT1507
500kHz Monolithic
Buck Mode Switching Regulator
FEATURES
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with all the necessary oscillator, control and logic cir-
cuitry. High switching frequency allows a considerable
reductioninthesizeofexternalcomponents.Thetopology
is current mode for fast transient response and good loop
stability. Both fixed output voltage (3.3V) and adjustable
parts are available.
Constant 500kHz Switching Frequency
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Uses All Surface Mount Components
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Operates with Inputs as Low as 4V
Saturated Switch Design (0.3Ω)
Cycle-by-Cycle Current Limiting
Easily Synchronizable
Inductor Size as Low as 2µH
Shutdown Current: 20µA
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A special high speed bipolar process and new design
techniques allow this regulator to achieve high efficiency
at a high switching frequency. Efficiency is maintained
over a wide output current range by keeping quiescent
supply current to 4mA and by utilizing a supply boost
capacitor to allow the NPN power switch to saturate. A
shutdown signal will reduce supply current to 20µA. The
LT1507 can be externally synchronized from 570kHz to
1MHz with logic level inputs.
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APPLICATIONS
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Portable Computers
Battery-Powered Systems
Battery Charger
Distributed Power
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The LT1507 fits into standard 8-pin SO and PDIP pack-
ages. Temperature rise is kept to a minimum by the high
efficiency design. Full cycle-by-cycle short-circuit protec-
tionandthermalshutdownareprovided.Standardsurface
mount external parts are used including the inductor and
capacitors.
DESCRIPTION
TheLT®1507isa500kHzmonolithicbuckmodeswitching
regulator, functionally identical to the LT1375 but opti-
mized for lower input voltage applications. It will operate
over a 4V to 15V input range, compared with 5.5V to 25V
for the LT1375. A 1.5A switch is included on the die along
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
5V to 3.3V Volt Down Converter
5V to 3.3V Efficiency
100
D2†
1N914
V
IN
V
OUT
= 5V
= 3.3V
90
80
70
60
50
C2
0.1µF
BOOST
OUTPUT
3.3V
5V
V
IN
V
SW
L1***
5µH
1.25A
LT1507-3.3
C3*
47µF
16V
+
DEFAULT
(OPEN)
= ON
SHDN
GND
SENSE
TANTALUM
V
C
C1**
100µF
10V
D1
1N5818
+
C
C
3.3nF
TANTALUM
AVX TPSD477M016R0150 OR SPRAGUE 593D EQUIVALENT.
RIPPLE CURRENT RATING ≥ 0.6A
*
0
0.25
0.50
0.75
1.00
1.25
AVX TPSD108M010R0100 OR SPRAGUE 593D EQUIVALENT
COILTRONICS CTX5-1. SUBSTITUTION UNITS SHOULD BE RATED
AT ≥ 1.25A, USING LOW LOSS CORE MATERIAL
**
***
LOAD CURRENT (A)
LT1507 • TA02
†
SEE BOOST PIN CONSIDERATIONS IN APPLICATIONS INFORMATION
SECTION FOR ALTERNATIVE D2 CONNECTION
1