A5975AD Datasheet, PDF (26/50 Pages) STMicroelectronics – Voltage feed-forward

Application information
A5975AD
Equation 21
I_PK
=
I_O
+
Δ_-----I
2
and it can be observed that if the inductor value decreases, the peak current (which must be
lower than the current limit of the device) increases. So, when the peak current is fixed, a
higher inductor value allows a higher value for the output current. In Table 8, some inductor
manufacturers are listed.
Table 8. Inductor selection
Manufacturer
Series
Coilcraft
DO3316T
Coilcraft
MSS1260T
Wurth Elektronik
WE-PD L
Inductor value (µH)
5.6 to 12
5.6 to 15
4.7 to 27
Saturation current (A)
3.5 to 4.7
3.5 to 8
3.55 to 6
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. A layout
example is provided in Figure 13 below.
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.
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