lt1303-5 Linear Technology Corporation, lt1303-5 Datasheet - Page 8

• Manufacturer Part Number: lt1303-5
• Description: Micropower High Efficiency Dc/dc Converters With Low-battery Detector Adjustable And Fixed 5v
• Manufacturer: Linear Technology Corporation

LT1303/LT1303-5
APPLICATIONS
Diode Selection
The LT1303’s high switching speed demands a high speed
rectifier. Schottky diodes are preferred for their low for-
ward drop and fast recovery. Suitable choices include the
1N5817, MBRS120LT3, and MBR0520LT1. Do not use
signal diodes such as 1N4148. They cannot carry 1A
current. Also avoid “general-purpose” diodes such as
1N4001. These are far too slow and are unsuitable for any
switching regulator application. For high temperature
applications a silicon diode such as the MUR105 will have
less leakage.
8
Figure 8. This Inductor Saturates at I
Figure 9. Slight Exponential Shape to Inductor Current
Waveform Indicates Excessive DC Resistance
U
INFORMATION
U
W
L
1A. A Poor Choice
LT1303 F09
LT1303 F08
U
Capacitor Selection
Input and output capacitors should have low ESR for best
efficiency. Recommended capacitors include AVX TPS
series, Sprague 595D series, and Sanyo OS-CON. The
output capacitor’s ESR determines the high frequency
ripple amplitude. A 100 F capacitor is the minimum rec-
ommended for a 5V output. Higher output voltages can use
lower capacitance values. For example, a 12V output can
use a 33 F or 47 F capacitor. The V
should be decoupled with a 47 F or 100 F capacitor at the
pin. When driving a transformer, an additional decoupling
network of 10 and 0.1 F ceramic is recommended as
shown in Figure 10.
Table 2. Recommended Capacitors
VENDOR
AVX
Sanyo
Panasonic
Sprague
Figure 10. 10 -1 F Network to LT1303 V
Additional Decoupling. Recommended When Driving
Transformers.
V
IN
+
SERIES
TPS
OS-CON
HFQ
595D
47 F
0.1 F
CERAMIC
TYPE
Surface Mount
Through-Hole
Through-Hole
Surface Mount
GND
V
IN
10
LT1303
IN
pin of the LT1303
PGND
IN
SW
Pin Provides
PHONE
NUMBERS
[phone]
[phone]
[phone]
[phone]
• • •
LT1303 F10