L7986TA STMicroelectronics, L7986TA Datasheet - Page 25

• Manufacturer Part Number: L7986TA
• Description: 3A step-down switching regulator
• Manufacturer: STMicroelectronics

Specifications of L7986TA

• Low Dropout Operation: 100% duty cycle

L7986TA
Figure 13. 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.
2.
Equation 28
Where f
Equation 29
and Vs is the sawtooth amplitude. The voltage feed forward keeps the ratio Vs/Vin constant.
3.
Equation 30
4.
Choose a value for R
and C5 not comparable with parasitic capacitance of the board.
Choose a gain (R
Calculate C
Then calculate C
(BW):
ESR
is the ESR zero:
4
by placing the zero one decade below the output filter double pole:
3
4
in order to place the second pole at four times the system bandwidth
/R
1
1
) in order to have the required bandwidth (BW), that means:
, usually between 1 kΩ and 5 kΩ, in order to have values of C4
Doc ID 022098 Rev 1
R
4
f
ESR
=
C
⎛
⎝
f
----------- -
4
ESR
f
=
LC
=
------------------------------------------- -
2π ESR C
⎞
⎠
------------------------------ -
2π R
2
⋅
⋅
⋅
----------- -
f
BW
ESR
10
4
1
⋅
⋅
⋅
f
LC
-------- - R
V
V
OUT
IN
S
⋅
1
Application informations
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