STMicroelectronics Evaluation board for A5970AD EVALA5970AD EVALA5970AD Fiche De Données
Codes de produits
EVALA5970AD
Application information
A5970AD
24/42
DocID14661 Rev 5
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.
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
interference, so they should be as far as possible from the high current paths. An layout
example is provided in
.
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.
problems. The feedback pin connections to the external divider are very close to the device
to avoid pick-up noise.
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
the ratio between V
OUT
and V
IN
, but in practice it is substantially higher than this value to
compensate for the losses in the overall application. For this reason, the switching losses
related to the R
related to the R
DSON
increases compared to an ideal case.
A5970AD
P
ON
R
DSON
I
OUT
2
D
=