參數(shù)資料
型號: L5987ATR
廠商: STMICROELECTRONICS
元件分類: 穩(wěn)壓器
英文描述: 4.4 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO8
封裝: ROHS COMPLIANT, HSOP-8
文件頁數(shù): 19/41頁
文件大?。?/td> 1002K
代理商: L5987ATR
Application information
L5987
26/41
Doc ID 14972 Rev 3
Figure 15.
Open loop gain: module Bode diagram
The guidelines for positioning the poles and the zeroes and for calculating the component
values can be summarized as follow:
1.
Choose a value for R1, usually between 1 kΩ and 5 kΩ, in order to have values of C4
and C5 not comparable with parasitic capacitance of the board.
2.
Choose a gain (R4/R1) in order to have the required bandwidth (BW), that means:
Equation 26
Where fESR is the ESR zero:
Equation 27
and Vs is the saw-tooth amplitude. The voltage feed forward keeps the ratio Vs/Vin constant.
3.
Calculate C4 by placing the zero one decade below the output filter double pole:
Equation 28
4.
Then calculate C3 in order to place the second pole at four times the system bandwidth
(BW):
R
4
f
ESR
f
LC
------------
2
BW
f
ESR
------------
V
S
V
IN
--------- R
1
=
f
ESR
1
2
π ESR C
OUT
--------------------------------------------
=
C
4
10
2
π R
4
f
LC
-------------------------------
=
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