A7986ATR datasheet(21/42 Pages) STMICROELECTRONICS

部件名	A7986ATR

功能描述	3 A step-down switching regulator for automotive applications

PDF	42 Pages

Scroll/Zoom	100%

制造商	STMICROELECTRONICS [STMicroelectronics]

网页	http://www.st.com

标志

21 / 42 page

DocID022801 Rev 5

21/42

A7986A

Application information

Figure 10. Type III compensation network

In Figure 11, the Bode diagram of the PWM and LC filter transfer function (GPW0 · GLC(f))

and the open loop gain (GLOOP(f) = GPW0 · GLC(f) · GTYPEIII(f)) are drawn.

Figure 11. 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 follows:

Choose a value for R1, usually between 1 kΩ and 5 kΩ.

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

Equation 24

where K is the feed-forward constant and 1/K is equal to 18.

Calculate C4 by placing the zero at 50% of the output filter double pole frequency (fLC):

---------- KR

⋅⋅

A7986ATR 数据表(PDF) 21 Page - STMicroelectronics