L5985 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L5985' PDF : 36 Pages View PDF
L5985
Figure 16. Switching losses
Application informations
5.6
Layout considerations
The PC board layout of switching DC/DC regulator is very important to minimize the noise
injected in high impedence nodes and interferences generated by the high switching current
loops.
In a step down converter the input loop (including the input capacitor, the power MOSFET
and the free wheeling diode) is the most critical one. This is due to the fact that the high
value pulsed current are flowing through it. In order to minimize the EMI, this loop has to be
as short as possible.
The feedback pin (FB) connection to external resistor divider is a high impedence node, so
the interferences can be minimized placing the routing of feedback node as far as possible
from the high current paths. To reduce the pick up noise the resistor divider has to be placed
very close to the device. To filter the high frequency noise, a small capacitor can be added
as close as possible to the input voltage pin of the device.
Thanks to the exposed pad of the device, the ground plane helps to reduce the thermal
resistance junction to ambient; so a large ground plane enhances the thermal performance
of the converter allowing high power conversion.
In Figure 17 a layout example is shown.
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