LED6000PHTR datasheet(29/49 Pages) STMICROELECTRONICS

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LED6000

Application notes - step-down conversion

As shown in Equation 16, fz depends on the output capacitor parasitic resistance and on the

LEDs dynamic resistance. Following the considerations summarized in Section 5.2 on

page 25, in the typical application the programmed control loop bandwidth (BW) might be

higher than fz, so this zero helps stabilize the loop. If this assumption is verified, a type II

compensation network is required for loop stabilization.

In Figure 17 the type II compensation network is shown.

Figure 17. Type II compensation network

The type II compensation network transfer function, from VSNS to COMP, is computed in

Equation 19.

Equation 19

Equation 20

The following suggestions can be followed for a quite common compensation strategy,

assuming that CP << CF.



Starting from Equation 18, the control loop gain module at s = 2

* FBW allows to fix the

RF/RU ratio:

Equation 21

After choosing the regulator bandwidth (typically FBW < 0.2 * FSW) and a value for RU,

usually between 1 k

 and 50 k, in order to achieve CF and CP not comparable with



;



















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