Datasheet

15
LT1506
APPLICATIONS INFORMATION
WUU
U
from the switch node. Also note that the high current
ground path of the catch diode and input capacitor are kept
very short and separate from the analog ground line.
The high speed switching current path is shown schemati-
cally in Figure 6. Minimum lead length in this path is
essential to ensure clean switching and low EMI. The path
including the switch, catch diode, and input capacitor is
the only one containing nanosecond rise and fall times. If
you follow this path on the PC layout, you will see that it is
irreducibly short. If you move the diode or input capacitor
away from the LT1506, get your resumé in order. The
other paths contain only some combination of DC and
500kHz triwave, so are much less critical.
Figure 5. Suggested Layout (Topside Only Shown)
Figure 6. High Speed Switching Path
1
U1
C1
CONNECT TO
GROUND PLANE
KEEP FB AND V
C
COMPONENTS
AWAY FROM HIGH FREQUENCY,
HIGH CURRENT COMPONENTS
PLACE FEEDTHROUGHS
AROUND GND PIN FOR GOOD
THERMAL CONDUCTIVITY
R3
D2
C4
R2
L1
1506 F05
C5 C6GND
V
OUT
D1C3V
IN
GND
CONNECT TO
GROUND PLANE
MINIMIZE LT1506 C3, D1 LOOP
KELVIN SENSE
V
OUT
TAKE OUTPUT
DIRECTLY FROM
END OF OUTPUT
CAPACITOR
1506 F06
5V
L1
V
IN
HIGH
FREQUENCY
CIRCULATING
PATH
LOAD
SWITCH NODE