Datasheet

8
LT1303/LT1303-5
APPLICATIONS INFORMATION
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Figure 8. This Inductor Saturates at I
L
≈1A. A Poor Choice
LT1303 F08
PHONE
VENDOR SERIES TYPE NUMBERS
AVX TPS Surface Mount [phone]
Sanyo OS-CON Through-Hole [phone]
Panasonic HFQ Through-Hole [phone]
Sprague 595D Surface Mount [phone]
Table 2. Recommended Capacitors
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 100µF 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 33µF or 47µF capacitor. The V
IN
pin of the LT1303
should be decoupled with a 47µF or 100µF capacitor at the
pin. When driving a transformer, an additional decoupling
network of 10Ω and 0.1µF ceramic is recommended as
shown in Figure 10.
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.
LT1303 F09
Figure 9. Slight Exponential Shape to Inductor Current
Waveform Indicates Excessive DC Resistance
+
47µF
0.1µF
CERAMIC
10Ω
V
IN
• • •
LT1303 F10
V
IN
SW
GND PGND
LT1303
Figure 10. 10Ω-1µF Network to LT1303 V
IN
Pin Provides
Additional Decoupling. Recommended When Driving
Transformers.