Datasheet

L7986TA Application information
Doc ID 022098 Rev 3 19/43
Equation 16
where V
S
is the sawtooth amplitude. As seen in Section 5.1, the voltage feed-forward
generates a sawtooth amplitude directly proportional to the input voltage, that is:
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 8. The error amplifier, the PWM modulator, and the LC output filter
The transfer function on the LC filter is given by:
Equation 19
where:
G
PW0
V
IN
V
s
---------=
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
++
-----------------------------------------------------------------------------------=