參數(shù)資料
型號: L7981ATR
廠商: STMICROELECTRONICS
元件分類: 穩(wěn)壓器
英文描述: SWITCHING REGULATOR, DSO8
封裝: 3 X 3 MM, 1.08 MM HEIGHT, ROHS COMPLIANT, HSOP-8
文件頁數(shù): 15/44頁
文件大小: 1315K
代理商: L7981ATR
Application informations
L7981
22/44
Doc ID 15182 Rev 3
Equation 21
where K is the feed forward constant and 1/K is equals to 9.
3.
Calculate C4 by placing the zero at 50% of the output filter double pole frequency (fLC):
Equation 22
4.
Calculate C5 by placing the second pole at four times the system bandwidth (BW):
Equation 23
5.
Set also the first pole at four times the system bandwidth and also the second zero at
the output filter double pole:
Equation 24
The suggested maximum system bandwidth is equals to the switching frequency divided by
3.5 (FSW/3.5), anyway lower than 100 kHz if the FSW is set higher than 500 kHz.
For example with VOUT=5 V, VIN=24 V, IO=3 A, L=18 μH, COUT=22 μF, ESR<1 mΩ, the type
III compensation network is:
In Figure 12 is shown the module and phase of the open loop gain. The bandwidth is about
58 kHz and the phase margin is 50°.
R
4
BW
f
LC
---------- KR
1
=
C
4
1
π R
4
f
LC
---------------------------
=
C
5
C
4
2
π R
4
C
4
4BW
1
--------------------------------------------------------------
=
R
3
R
1
4BW
f
LC
-----------------
1
---------------------------
=
C
3
1
2
π R
3
4BW
-----------------------------------------
=
,
R
1
4.99k
Ω
=
R
2
680
Ω
=
R
3
200
Ω
=
R
4
3.3k
Ω
=
C
3
3.3nF
=
C
4
22nF
=
C
5
220pF
=
,,
,
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