
During the burst mode, if the load is decreased and the distance between two bursts reaches the value defined
by this parameter, the system decreases the number of switching cycles by one. The lower limit for the switching
cycles is defined by the “Min number of burst pulses” parameter.
Please note that this parameter is defined as a positive delta with respect to the “Min time between burst seq”
parameter, so the total maximum time between burst sequences is
Equation 17
"Max time between burst seq"
(17)
= "Min time between burst seq" + "Max time between burst seq delta "
3.5.12
Minimum period to exit burst
Size:4 bits
Sets the minimum time between two consecutive burst sequences to exit the burst mode.
Available values are:
•
66.7 μs
•
100 μs
•
133 μs
•
167 μs
•
200 μs
•
233 μs
•
267 μs
•
300 μs
•
333 μs
•
367 μs
•
400 μs
•
433 μs
•
467 μs
•
500 μs
•
533 μs
•
567 μs
When the system is in the burst mode and the load increases, the time between two burst sequences is reduced.
If the time distance between two consecutive burst sequences reaches the time threshold set by this parameter,
the system will exit the burst mode.
Therefore, the lower the value for this parameter the higher the load for exiting the burst mode.
Please note that this mechanism is not used with the pure external burst mode.
Use
To tune this parameter, initially set it to a very low value. Bring the system in the burst mode and then increase the
load to the desired burst exit point. Measure the distance between two consecutive burst sequences and program
that value in the parameter.
3.5.13
No-burst window width
Size: 1 bit
Sets the minimum time that avoids burst re-entering.
Available values are:
•
90 μs
•
7.5 ms
If the system exits the burst mode, the burst mode re-entering is forbidden for a minimum time defined to this
parameter.
Use
The suggested value is 7.5 ms to avoid burst mode re-entering at low load in case the feedback voltage
undershoot at the burst mode exit.
Please note that the no-burst window does not apply for the “BM enter for minimum TS”.
UM3002
Burst mode parameters
UM3002
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Rev 1
page 32/42