Datasheet

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
V
S
KV
IN
⋅=
G
PW0
V
IN
V
s
---------
1
K
---- 18===
FB
COMP
V
REF
E/A
PWM
V
S
OUT
V
CC
C
OUT
ESR
L
G
PW0
G
LC
FB
COMP
V
REF
E/A
PWM
V
S
OUT
V
CC
C
OUT
ESR
L
G
PW0
G
LC
G
LC
s()
1
s
2π f
zESR
⋅
--------------------------+
1
s
2π Qf⋅
LC
⋅
----------------------------
s
2π f
LC
⋅
-------------------


2
++
-------------------------------------------------------------------------=
f
LC
1
2π LC
OUT
⋅ 1
ESR
R
OUT
---------------+⋅⋅
------------------------------------------------------------------------= f
zESR
1
2π ESR C
OUT
⋅⋅
--------------------------------------------=,