LT3570
17
3570fb
will be enabled again going through a soft-start cycle.
Note: Overtemperature protection is intended to protect the
device during momentary overload conditions. Continuous
operation above the specifi ed maximum operating junction
temperature may result in device degradation or failure.
PCB Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board (PCB) layout. Figure 6
shows the high current paths in the step-down regulator
circuit. Note that in the step-down regulator, large switched
currents fl ow in the power switch, the catch diode and the
input capacitor.
Figure 7 shows the high current paths in the step-up
regulator. In the boost regulator, large switched currents
fl ow through the power switch, the switching diode, and
the output capacitor.
The loop formed by these large switched current com-
ponents should be as small as possible. Place these
components on the same side of the circuit board and
connect them on that layer. Place a local, unbroken ground
plane below these components and tie this ground plane
APPLICATIONS INFORMATION
Figure 6. Buck High Speed Switching Path
Figure 7. Boost High Speed Switching Path
to system ground at one location. Addi tionally, keep
the SW and BOOST nodes as small as possible. This is
implemented in the suggested layout of Figure 8 for the
QFN package which shows the topside metal from the
DC1106A demonstration board.
Thermal Considerations
To deliver the power that the LT3570 is capable of, it
is imperative that a good thermal path be provided to
dissipate the heat generated within the package. This can
be accomplished by taking advantage of the large ther-
mal pad on the underside of the IC. It is recommended
that multiple vias in the printed circuit board be used to
conduct heat away from the IC and into a copper plane
with as much area as possible.
Related Linear Technology Publications
Application notes 19, 35, 44, 76 and 88 contain more
detailed descriptions and design information for buck
regulators and other switching regulators. The LT1375 data
sheet has a more extensive discussion of output ripple,
loop compensation, and stability testing.
Figure 8. Suggested Layout
3570 F06
L2
D1 C
OUT
HIGH
FREQUENCY
CIRCULATING
PATH
C
IN
LOAD
LT3570
3750 F07
L2
LT3570
D1
C
OUT
C
IN
HIGH
FREQUENCY
SWITCHING
PATH
LOAD
