NCL30486B
Variable Maximum On−time
Around line zero−crossing, the primary inductor slope is
too low to reach the peak current setpoint imposed by the CC
control. The DRV pulse is terminated by the max. on−time.
This creates sudden variation of the on−time and creates
an input current spike (EMI filter inductance responds to
rate of change of current).
Varying the maximum on−time with VREFX helps
decreasing this spike over the output load range. Figure 72
and Figure 73 shows the maximum on−time curve as a
function of VREFX.
T
(ms)
on,MAX
20
18
16
14
12
10
7
0.15
0.18 0.25
0.5
0.6
0.8
0.9
1
V
REFX
(V)
0.35
0.45
0.65
0.75
Figure 72. Variable Maximum On−time, 20−ms Option
T
(ms)
on,MAX
20
18
16
14
12
11
10
9
8
7
0.15
0.18 0.25 0.35
0.5
0.6
0.65
0.8
0.9
1
V
REFX
(V)
0.45
0.75
Figure 73. Variable Maximum On−time, 14−ms Option
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