LT1959 Datasheet, PDF (15/24 Pages) Linear Technology – 4.5A, 500kHz Step-Down Switching Regulator

LT1959
APPLICATIONS INFORMATION
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 LT1959, get your resumé in order. The
other paths contain only some combination of DC and
500kHz triwave, so are much less critical.
MINIMIZE LT1959 C3, D1 LOOP
CONNECT TO
GROUND PLANE
V_IN
C3
D1
C5
GND
C6
1
GND
U1
L1
V_OUT
TAKE OUTPUT
DIRECTLY FROM
END OF OUTPUT
CAPACITOR
C1 R3
CONNECT TO
PLACE FEEDTHROUGHS
GROUND PLANE AROUND GND PIN FOR GOOD
THERMAL CONDUCTIVITY
R2
KEEP FB AND V_C COMPONENTS
AWAY FROM HIGH FREQUENCY,
HIGH CURRENT COMPONENTS
D2
C4
Figure 5. Suggested Layout (Topside Only Shown)
KELVIN SENSE
V_OUT
1959 F05
SWITCH NODE
L1
5V
HIGH
FREQUENCY
V_IN
CIRCULATING
PATH
LOAD
1959 F06
Figure 6. High Speed Switching Path
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