A7986ATR datasheet(19/42 Pages) STMICROELECTRONICS

19 / 42 page

DocID022801 Rev 5

19/42

A7986A

Application information

Equation 17

In this way the PWM modulator gain results constant and equal to:

Equation 18

The synchronization of the device with an external clock provided trough the SYNCH pin

can modify the PWM modulator gain (see Section 5.1 to understand how this gain changes

and how to keep it constant in spite of the external synchronization).

Figure 9. The error amplifier, the PWM modulation and the LC output filter

The transfer function on the LC filter is given by:

Equation 19

where:

Equation 20

⋅

PW0

---------

----

COMP

REF

E/A

PWM

OUT

ESR

PW0

COMP

REF

E/A

PWM

OUT

ESR

PW0

LC s

()

π f

zE SR

⋅

--------------------------

π Qf

⋅

----------------------------

π f

⋅

-------------------



 2

-------------------------------------------------------------------------

OUT

⋅

ESR

OUT

---------------

⋅⋅

------------------------------------------------------------------------

zESR

π ESR C

OUT

⋅⋅

--------------------------------------------

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