L5983 查看數據表（PDF） - STMicroelectronics

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L5983

2A step-down switching regulator

STMicroelectronics 

Application informations

L5983

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 1k and 5k.

2. Choose a gain (R4/R1) in order to have the required bandwidth (BW), that means:

Equation 18

R4

=

B-----W----

fLC

⋅

-1--

K

⋅

R1

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 19

C4

=

-------------1--------------

π ⋅ R4 ⋅ fLC

4. Calculate C5 by placing the second pole at four times the system bandwidth (BW):

Equation 20

C5

=

----------------------------C-----4----------------------------

2π ⋅ R4 ⋅ C4 ⋅ 4 ⋅ BW – 1

5. Set also the first pole at four times the system bandwidth and also the second zero at

the output filter double pole:

Equation 21

R3

=

-----------R----1----------- ,

4-----⋅---B-----W---- – 1

fLC

C3

=

-------------------1---------------------

2π ⋅ R3 ⋅ 4 ⋅ BW

The suggested maximum system bandwidth is equals to the switching frequency divided by

3.5 (FSW/3.5), anyway lower than 100kHz if the FSW is set higher than 500kHz.

For example with VOUT=3.3V, VIN=12V, IO=1.5A, L=22µH, COUT=22µF, the type III

compensation network is:

R1 = 4.99kΩ, R2 = 1.1kΩ, R3 = 120Ω, R4 = 4.99kΩ, C3 = 4.7nF, C4 = 10nF, C5 = 68pF

In Figure 12 is shown the module and phase of the open loop gain. The bandwidth is about

77kHz and the phase margin is 47°.

21/37

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