The smaller the value the slower will be the output voltage rise and the LLC tank current.
The suggestion is to start with the minimum value (usually OK for most applications) and increase it in case a
faster Vout rise time is required.
3.4.6
Minimum time shift
Size: 4 bits
Sets the minimum value for the time shift during the normal operation.
Available values are:
•
125 ns
•
158.3 ns
•
191.7 ns
•
225 ns
•
258.3 ns
•
291.7 ns
•
325 ns
•
358.3 ns
•
391.7 ns
•
425 ns
•
458.3 ns
•
491.7 ns
•
525 ns
•
558.3 ns
•
591.7 ns
•
625 ns
Use
The minimum time shift value is used to set the maximum LLC switching frequency. The
relationship between the time shift and switching period is complex. Anyway, for this limit
condition, a good approximation can be found (see
).
Figure 2.
LLC operation at f
SW
>> f
RES
When the operating frequency is much higher than the resonance frequency, the resonant tank current I
LLC
becomes a triangular waveform, because the current provided to the secondary side becomes negligible with
respect to the magnetizing current.
Approximating the current triangular and neglecting the dead times, the time shift value (i.e. the time between
zero crossing and MOS turn-off) becomes half of each MOSFET on-time.
Therefore:
UM3002
LLC parameters
UM3002
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Rev 1
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