Datasheet

Application information B5973D
26/44 DocID14117 Rev 4
8.2 Layout considerations
The layout of switching DC-DC converters is very important to minimize noise and
interference. Power-generating portions of the layout are the main cause of noise and so
high switching current loop areas should be kept as small as possible and lead lengths as
short as possible.
High impedance paths (in particular the feedback connections) are susceptible to
interference, so they should be as far as possible from the high current paths. An layout
example is provided in Figure 13.
The input and output loops are minimized to avoid radiation and high frequency resonance
problems. The feedback pin connections to the external divider are very close to the device
to avoid pick-up noise. Another important issue is the ground plane of the board. Since the
package has an exposed pad, it is very important to connect it to an extended ground plane
in order to reduce the thermal resistance junction to ambient.
Figure 13. Layout example
8.3 Thermal considerations
The dissipated power of the device is tied to three different sources:
 Conduction losses due to the not insignificant R
DSON
, which are equal to:
Equation 22
Where D is the duty cycle of the application. Note that the duty cycle is theoretically given by
the ratio between V
OUT
and V
IN
, but in practice it is substantially higher than this value to
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