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參數(shù)資料
| 型號(hào)： | LT1432CS8 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 5V High Efficiency Step-Down Switching Regulator Controller |
| 中文描述： | SWITCHING CONTROLLER, PDSO8 |
| 封裝： | PLASTIC, SO-8 |
| 文件頁數(shù)： | 11/28頁 |
| 文件大小： | 611K |
| 代理商： | LT1432CS8 |
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LT1432
U
S
A
O
PPLICATI
U
U
50mV/DIV
1A/DIV
0
0
0.5A/DIV
0.2A RMS. Theoretically the output capacitor size would
be minimized by using one which just met this ripple
current, but in practice, this would yield such high output
ripple voltage that an additional output filter would have to
be added. A better solution in the case of buck converters
is usually just to increase the size of the output capacitor
to meet output ripple voltage requirements.
Figure 8 shows output ripple voltage at the top and switch
current below. Peak-to-peak ripple voltage is 80mV. This
implies an output capacitor effective series resistance
(ESR) of 80mV/0.7A = 0.11
. Capacitor ESR varies sig-
nificantly with temperature, increasing at low tempera-
tures, so be sure to check ESR ratings at the lowest
expected operating temperature. Ripple voltage can be
reduced by increasing the inductor value, but this has
rapidly diminishing returns because of typical size re-
straints.
Figure 9 shows diode current under normal load condi-
tions of 2A, and with the output shorted. Current limit has
been set at 3A. Average diode current at I
OUT
= 2A is only
about 1A because of duty cycle considerations. Under
short circuit conditions, duty cycle is nearly 100% for the
diode (switch duty cycle is near zero), and diode average
current is nearly 3A. Designs which must tolerate continu-
ous short circuit conditions should be checked carefully
for diode heating. Foldback current limiting can be used if
necessary.
Figure 10 shows inductor current (0.5A/DIV) with a 2A and
100mA load. Average inductor current is always equal to
output current, but it is obvious that with 100mA load,
inductor current drops to zero for part of the switching
cycle, indicating dicontinuous mode. When selecting an
inductor, keep in mind that RMS current determines
copper losses, peak-to-peak current determines core loss,
and peak current must be calculated to avoid core satura-
tion. Also, remember that during short circuit conditions,
inductor current will increase to the full current limit value.
Inductor failure is normally caused by overheating of the
winding insulation with resultant turn-to-turn shorts.
Foldback current limiting will be helpful.
0
1A/DIV
1A/DIV
0
Figure 8. Output Ripple Current
5
μ
s/DIV
Figure 9. Diode Current
5
μ
s/DIV
5
μ
s/DIV
Figure 10. Inductor Current
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