LT1375 Linear Technology, LT1375 Datasheet - Page 16

• Manufacturer Part Number: LT1375
• Description: 1.5A/ 500kHz Step-Down Switching Regulators
• Manufacturer: Linear Technology

LT1375/LT1376
APPLICATIONS
16
(magnetic) radiation is minimized by keeping catch diode,
switch pin, and input bypass capacitor leads as short as
possible. E field radiation is kept low by minimizing the
length and area of all traces connected to the switch pin
and BOOST pin. A ground plane should always be used
under the switcher circuitry to prevent interplane cou-
pling. A suggested layout for the critical components is
shown in Figure 5. Note that the feedback resistors and
compensation components are kept as far as possible
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
AND CATCH DIODE CLOSE
KEEP INPUT CAPACITOR
(NORMALLY EXISTS AS
CONNECTIONS TO THE
TO REGULATOR AND
GROUND RING NEED
NOT BE AS SHOWN.
SWITCH NODE AND
MINIMIZE AREA OF
TERMINATE THEM
INTERNAL PLANE)
TO SAME POINT
BOOST NODE
U
INFORMATION
U
CONNECT OUTPUT CAPACITOR
DIRECTLY TO HEAVY GROUND
W
L1
C3
D1
Figure 5. Suggested Layout
U
C2
INPUT
C1
BOOST
IN
SW
BIAS
D2
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 LT1376, get your resumé in order. The
other paths contain only some combination of DC and
500kHz triwave, so are much less critical.
SHDN
GND
TAKE OUTPUT DIRECTLY FROM END OF OUTPUT
CAPACITOR TO AVOID PARASITIC RESISTANCE
AND INDUCTANCE (KELVIN CONNECTION)
V
FB
C
OUTPUT
V
IN
R1
Figure 6. High Speed Switching Path
C
C
SHUTDOWN
CIRCULATING
R2
FREQUENCY
SWITCH NODE
HIGH
PATH
R
C
L1
MINIMIZE SIZE OF
FEEDBACK PIN
CONNECTIONS TO
AVOID PICKUP
TERMINATE
FEEDBACK RESISTORS
AND COMPENSATION
COMPONENTS
DIRECTLY TO SWITCHER
GROUND PIN
LOAD
1375/76 F06
1375/76 F05
5V
13756fd