L7986TA STMicroelectronics, L7986TA Datasheet - Page 19

• Manufacturer Part Number: L7986TA
• Description: 3A step-down switching regulator
• Manufacturer: STMicroelectronics

Specifications of L7986TA

• Low Dropout Operation: 100% duty cycle

L7986TA
6.4
Compensation network
The compensation network has to assure stability and good dynamic performance. The loop
of the L7986TA is based on the voltage mode control. The error amplifier is a voltage
operational amplifier with high bandwidth. So selecting the compensation network the E/A
will be considered as ideal, that is, its bandwidth is much larger than the system one.
The transfer functions of PWM modulator and the output LC filter are studied (see
The transfer function of the PWM modulator, from the error amplifier output (COMP pin) to
the OUT pin, results:
Equation 16
where V
generates a sawtooth amplitude directly proportional to the input voltage, that is:
Equation 17
In this way the PWM modulator gain results constant and equals to:
Equation 18
The synchronization of the device with an external clock provided trough SYNCH pin can
modifies the PWM modulator gain (see
and how to keep it constant in spite of the external synchronization).
Figure 8.
V
V
FB
FB
REF
REF
S
is the sawtooth amplitude. As seen in
The error amplifier, the PWM modulation and the LC output filter
E/A
E/A
V
V
S
S
COMP
COMP
Doc ID 022098 Rev 1
G
G
PW0
PW0
G
PW0
PWM
PWM
Chapter 5.1
G
V
=
S
PW0
=
V
-------- -
V
IN
s
K V
=
⋅
=
Chapter
V
-------- -
V
--- -
K
IN
IN
1
s
=
to understand how this gain changes
18
V
V
5.1, the voltage feed forward
CC
CC
OUT
OUT
Application informations
G
G
LC
LC
L
L
ESR
ESR
C
C
OUT
OUT
Figure
19/43
9).