lt3470a Linear Technology Corporation, lt3470a Datasheet - Page 14

• Manufacturer Part Number: lt3470a
• Description: Micropower Buck Regulator With Integrated Boost And Catch Diodes
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
LT3470A
PCB Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Note that large,
switched currents fl ow in the power switch, the internal
catch diode and the input capacitor. The loop formed by
these components should be as small as possible. Further-
more, the system ground should be tied to the regulator
ground in only one place; this prevents the switched cur-
rent from injecting noise into the system ground. These
components, along with the inductor and output capacitor,
should be placed on the same side of the circuit board,
and their connections should be made on that layer. Place
a local, unbroken ground plane below these components,
and tie this ground plane to system ground at one location,
14
Figure 5. A Good PCB Layout Ensures Proper, Low EMI Operation
V
OUT
ideally at the ground terminal of the output capacitor C2.
Additionally, the SW and BOOST nodes should be kept as
small as possible. Unshielded inductors can induce noise
in the feedback path resulting in instability and increased
output ripple. To avoid this problem, use vias to route the
V
(as shown in Figure 5). Finally, keep the FB node as small
as possible so that the ground pin and ground traces will
shield it from the SW and BOOST nodes. Figure 5 shows
component placement with trace, ground plane and via
locations. Include vias near the GND pin, or pad, of the
LT3470A to help remove heat from the LT3470A to the
ground plane.
OUT
trace under the ground plane to the feedback divider
3470a F05
SHDN
V
GND
IN
3470af