L7986 STMicroelectronics, L7986 Datasheet - Page 29

• Manufacturer Part Number: L7986
• Description: 3A step-down switching regulator
• Manufacturer: STMicroelectronics

Specifications of L7986

• Low Dropout Operation: 100% duty cycle

L7986
6.6
of heat. The Rth
paragraph, is about 60 °C/W for the VFQFPN package and about 40 °C/W for the HSOP
package.
Figure 16. Switching losses
Layout considerations
The PC board layout of the switching the DC/DC regulator is very important to minimize the
noise injected in high impedance nodes and interference generated by the high switching
current loops.
In a step-down converter the input loop (including the input capacitor, the power MOSFET
and the freewheeling diode) is the most critical one. This is due to the fact that the high
value pulsed currents are flowing through it. In order to minimize the EMI, this loop must be
as short as possible.
The feedback pin (FB) connection to the external resistor divider is a high impedance node,
so the interference can be minimized by placing the routing of the feedback node as far as
possible from the high current paths. To reduce the pick-up noise, the resistor divider must
be placed very close to the device.
To filter the high frequency noise, a small bypass capacitor (220 nF - 1 µF) 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.
JA
, measured on the demonstration board described in the following
Doc ID 022450 Rev 1
Application information
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