PM6670S View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'PM6670S' PDF : 53 Pages View PDF
PM6670S
Device description
No-audible pulse-skip mode
Some audio-noise sensitive applications cannot accept the switching frequency to enter the
audible range as is possible in pulse-skip mode with very light loads. For this reason, the
PM6670S implements an additional feature to maintain a minimum switching frequency of
33 kHz despite a slight efficiency loss. At very light load conditions, if any switching cycle
has taken place within 30 μs (typ.) since the last one (because the output voltage is still
higher than the reference), a no-audible pulse-skip cycle begins. The low-side MOSFET is
turned on and the output is driven to fall until the reference has been crossed. Then, the
high-side switch is turned on for a TON period and, once it has expired, the synchronous
rectifier is enabled until the inductor current reaches the zero-crossing threshold (see
Figure 34).
Figure 34. Inductor current and output voltage at light load with non-audible pulse-skip
Inductor
current
VDDQ
Output
Vreg
TMAX
TON TOFF
TIDLE
t
For frequencies higher than 33 kHz (due to heavier loads) the device works in the same way
as in pulse-skip mode. It is important to notice that in both pulse-skip and no-audible pulse-
skip modes the switching frequency changes not only with the load but also with the input
voltage.
Doc ID 14432 Rev 4
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