L6714 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
L6714
STMicroelectronics
'L6714' PDF : 70 Pages View PDF
L6714
System control loop compensation
Compensation network can be simply designed placing ωF=ωLC and imposing the cross-over
frequency ωT as desired obtaining (always considering that ωT might be not higher than
1/10th of the switching frequency FSW):
RF
=
R-----F---B-----⋅------∆----V----O----S---C--
VIN
⋅
5--
4
⋅
ωT ⋅
N------⋅------(---R----D----R----O-L---O----P----+-----E----S-----R-----)
CF
=
-----C----O-----⋅------N--L----
RF
21.1
Compensation network guidelines
The Compensation Network design assures to having system response according to the
cross-over frequency selected and to the output filter considered: it is anyway possible to
further fine-tune the compensation network modifying the bandwidth in order to get the best
response of the system as follow (See Figure 24):
● Increase RF to increase the system bandwidth accordingly;
● Decrease RF to decrease the system bandwidth accordingly;
● Increase CF to move ωF to low frequencies increasing as a consequence the system
phase margin.
Having the fastest compensation network gives not the confidence to satisfy the
requirements of the load: the inductor still limits the maximum dI/dt that the system can
afford. In fact, when a load transient is applied, the best that the controller can do is to
“saturate” the duty cycle to its maximum (dMAX) or minimum (0) value. The output voltage
dV/dt is then limited by the inductor charge / discharge time and by the output capacitance.
In particular, the most limiting transition corresponds to the load removal since the inductor
results being discharged only by VOUT (while it is charged by dMAXVIN-VOUT during a load
appliance).
Referring to Figure 24-left, further tuning the Compensation network cannot give any
improvements unless the output filter changes: only modifying the main inductors ot the
output capacitance improves the system response.
Figure 24. RF-CF impact on bandwidth.
dB
CF
GLOOP(s)
K
RF[dB]
ZF(s)
RF
ωLC = ωF
ωESR
ωT ω
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