LT1507
500kHz Monolithic
Buck Mode Switching Regulator
FEATURES
s Constant 500kHz Switching Frequency
s Uses All Surface Mount Components
s Operates with Inputs as Low as 4V
s Saturated Switch Design (0.3Ω)
s Cycle-by-Cycle Current Limiting
s Easily Synchronizable
s Inductor Size as Low as 2µH
s Shutdown Current: 20µA
U
APPLICATIONS
s Portable Computers
s Battery-Powered Systems
s Battery Charger
s Distributed Power
DESCRIPTION
The LT®1507 is a 500kHz monolithic buck mode switching
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
with all the necessary oscillator, control and logic cir-
cuitry. High switching frequency allows a considerable
reduction in the size of external components. The topology
is current mode for fast transient response and good loop
stability. Both fixed output voltage (3.3V) and adjustable
parts are available.
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.
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-
tion and thermal shutdown are provided. Standard surface
mount external parts are used including the inductor and
capacitors.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
5V to 3.3V Volt Down Converter
D2†
1N914
5V
C3*
47µF
16V
TANTALUM
+ DEFAULT
(OPEN)
= ON
BOOST
VIN VSW
LT1507-3.3
SHDN
SENSE
GND VC
CC
3.3nF
C2
0.1µF
L1***
5µH
D1
1N5818
* AVX TPSD477M016R0150 OR SPRAGUE 593D EQUIVALENT.
RIPPLE CURRENT RATING ≥ 0.6A
** AVX TPSD108M010R0100 OR SPRAGUE 593D EQUIVALENT
*** COILTRONICS CTX5-1. SUBSTITUTION UNITS SHOULD BE RATED
AT ≥ 1.25A, USING LOW LOSS CORE MATERIAL
† SEE BOOST PIN CONSIDERATIONS IN APPLICATIONS INFORMATION
SECTION FOR ALTERNATIVE D2 CONNECTION
OUTPUT
3.3V
1.25A
+
C1**
100µF
10V
TANTALUM
5V to 3.3V Efficiency
100
VIN = 5V
VOUT = 3.3V
90
80
70
60
50
0
0.25 0.50 0.75 1.00
LOAD CURRENT (A)
1.25
LT1507 • TA02
1
