Datasheet

V
DRV
V
DS
UCC28710, UCC28711
UCC28712, UCC28713
UCC28714, UCC28715
www.ti.com SLUSB86 –NOVEMBER 2012
Valley Switching
The UCC28710 family utilizes valley switching to reduce switching losses in the MOSFET, to reduce induced-
EMI, and to minimize the turn-on current spike at the sense resistor. The controller operates in valley-switching in
all load conditions unless the V
DS
ringing has diminished.
Referring to Figure 19 below, the UCC28710 family operates in a valley-skipping mode in most load conditions to
maintain an accurate voltage or current regulation point and still switch on the lowest available V
DS
voltage.
Figure 19. Valley-Skipping Mode
Start-Up Operation
The internal high-voltage start-up switch connected to the bulk capacitor voltage (V
BLK
) through the HV pin
charges the VDD capacitor. During start up there is typically 300 µA available to charge the VDD capacitor.
When VDD reaches the 21-V UVLO turn-on threshold, the controller is enabled, the converter starts switching
and the start-up switch is turned off. The initial three cycles are limited to I
PP(min)
. After the initial three cycles at
minimum I
PP(min)
, the controller responds to the condition dictated by the control law. The converter will remain in
discontinuous mode during charging of the output capacitor(s), maintaining a constant output current until the
output voltage is in regulation.
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Product Folder Links: UCC28710, UCC28711 UCC28712, UCC28713 UCC28714, UCC28715