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參數(shù)資料
| 型號(hào)： | LM2682MWC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHED CAPACITOR CONVERTER, 15 kHz SWITCHING FREQ-MAX, UUC |
| 封裝： | WAFER |
| 文件頁(yè)數(shù)： | 4/9頁(yè) |
| 文件大?。?/td> | 178K |
| 代理商： | LM2682MWC |
Basic Application Circuits
Application Information
Voltage Doubling Inverter
The main application of the LM2682 is to generate a nega-
tive voltage that is twice the positive input voltage. This cir-
cuit requires only three external capacitors and is connected
as shown in
Figure 1. It is important to keep in mind that the
efficiency of the circuit is determined by the output resis-
tance. A derivation of the output resistance is shown below:
R
OUT =
2(R
SW1+RSW2+ESRC1+RSW3+RSW4+ESRC2)+
2(R
SW1+RSW2+ESRC1+RSW3+RSW4+ESRC2)+
1/(f
OSCxC1) + 1/(fOSCxC2) + ESRC3
Using the assumption that all four switches have the same
ON resistance our equation becomes:
R
OUT =
16R
SW + 4ESRC1 + 4ESRC2 + ESRC3 +
1/(f
OSCxC1) + 1/(fOSCxC2)
Output resistance is typically 90
with an input voltage of
+5V, an operating temperature of 25C, and using low ESR
3.3 F capacitors. This equation shows the importance of
capacitor selection. Large value, low ESR capacitors will re-
duce the output resistance significantly but will also require a
larger overall circuit. Smaller capacitors will take up less
space but can lower efficiency greatly if the ESR is large.
Also to be considered is that C1 must be rated at 6 VDC or
greater while C2 and C3 must be rated at 12 VDC or greater.
The amount of output voltage ripple is determined by the out-
put capacitor C3 and the output current as shown in this
equation:
V
RIPPLE P-P = IOUT x (2xESRC3 + 1/[2x(fOSCxC3)])
Once again a larger capacitor with smaller ESR will give bet-
ter results.
DS100997-3
FIGURE 1. Doubling Voltage Inverter
DS100997-4
FIGURE 2. +5V to 5V Regulated Voltage Converter
LM2682
www.national.com
4
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