LT1533
Ultralow Noise
1A Switching Regulator
FEATURES
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DESCRIPTION
The LT
®
1533 is a new class of switching regulator designed
to reduce conducted and radiated electromagnetic interfer-
ence (EMI). Ultralow noise and EMI are achieved by providing
user control of the output switch slew rates. Voltage and
current slew rates can be independently programmed to
optimize switcher harmonic content versus efficiency. The
LT1533 can reduce high frequency harmonic power by as
much as 40dB with only minor losses in efficiency.
The LT1533 utilizes a dual output switch current mode
architecture optimized for low noise topologies. The IC
includes two 1A power switches along with all necessary
oscillator, control and protection circuitry. Unique error amp
circuitry can regulate both positive and negative voltages.
The internal oscillator may be synchronized to an external
clock for more accurate placement of switching harmonics.
Protection features include cycle by cycle current limit pro-
tection, undervoltage lockout and thermal shutdown.
Low minimum supply voltage and low supply current during
shutdown make the LT1533 well suited for portable applica-
tions. The part may also be forced into a 50% duty cycle mode
for unregulated applications. The LT1533 is available in the
16-pin narrow SO package.
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Greatly Reduced Conducted and Radiated EMI
(<100
µ
V
P-P
in Typical Application)
Low Switching Harmonic Content
Independent Control of Switch Voltage and
Current Slew Rates
Two 1A Current Limited Power Switches
Regulates Positive and Negative Voltages
20kHz to 250kHz Oscillator Frequency
Easily Synchronized to External Clock
Wide Input Voltage Range: 2.7V to 23V
Low Shutdown Current: 12µA Typical
Easier Layout than with Conventional Switchers
Outputs Can Be Forced to 50% Duty Cycle for
Unregulated Applications
APPLICATIONS
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Precision Instrumentation Systems
Isolated Supplies for Industrial Automation
Medical Instruments
Wireless Communications
Single Board Data Acquisition Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
Low Noise 5V to 12V Forward Push-Pull DC/DC Converter
5V
+
33µF
11
3
820pF
4
5
16.9k
6
SHDN
DUTY
SYNC
C
T
R
T
14
V
IN
COL A
COL B
PGND
LT1533
R
VSL
R
CSL
15k
10
V
C
GND
9
NFB
8
FB
2
T1
1N4148
L1
300µH
B
L2
33µH
C1
47µF
16V
A
12V
150mA
C2
33µF
20V
12V Output Noise (BW = 100MHz)
1N4148
15
Note 1
16
13
12
7
15k
15k
21.5k, 1%
+
+
A
100µV/DIV
B
2mV/DIV
1533 TA01
0.015µF
1000pF
2.49k
1%
C1: SANYO OS-CON
C2: AVX TPS TANTALUM
L1: COILTRONICS CTX300-2
L2: COILCRAFT DT1608C-333
T1: COILTRONICS CTX02-13834
NOTE 1: 25nH TRACE INDUCTANCE
OR COILCRAFT B07T
U
U
U
<100µV
P-P
2µs/DIV
1533 TA02
1
LINER [ LINEAR TECHNOLOGY ]
