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, 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 22

R4

=

⎛

⎝

f--Ef--L--S-C--R--⎠⎞

2

⋅

--B----W-----

fESR

⋅

-V-----S--

VIN

⋅

R1

Where fESR is the ESR zero:

Equation 23

fESR

=

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

2π ⋅ ESR ⋅ COUT

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 24

C4

=

-------------1---0--------------

2π ⋅ R4 ⋅ fLC

4. Then calculate C3 in order to place the second pole at four times the system bandwidth

(BW):

Equation 25

C5

=

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

2π ⋅ R4 ⋅ C4 ⋅ 4 ⋅ BW – 1

For example with VOUT=3.3V, VIN=12V, IO=1.5A, L=22µH, COUT=330µF, ESR=50mΩ, the

type II compensation network is:

R1 = 1.1kΩ, R2 = 249Ω, R4 = 10kΩ, C4 = 6.8nF, C5 = 68pF

In Figure 15 is shown the module and phase of the open loop gain. The bandwidth is about

30kHz and the phase margin is 45°.

24/37

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