LT3430 Linear Technology, LT3430 Datasheet - Page 17

• Manufacturer Part Number: LT3430
• Description: High Voltage/ 3A/ 200kHz Step-Down Switching Regulator
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LAYOUT CONSIDERATIONS
As with all high frequency switchers, when considering
layout, care must be taken in order to achieve optimal elec-
trical, thermal and noise performance. For maximum effi-
ciency, switch rise and fall times are typically in the nano-
second range. To prevent noise both radiated and con-
ducted, the high speed switching current path, shown in
Figure 5, must be kept as short as possible. This is imple-
mented in the suggested layout of Figure 6. Shortening
AVAILABLE SPACE UNDERNEATH
THE DEVICE BETWEEN PINS AND
SW PINS 2 AND 5 ARE ALSO
SHORTED TOGETHER (USING
ARE SHORTED TOGETHER.
V
IN
1
2
3
4
5
6 BOOST
GND PLANE)
PINS 3 AND 4
GND
SW
V
V
SW
IN
IN
LT3430
U
U
MINIMIZE LT3430
C3-D1 LOOP
GND
V
IN
W
V
IN
GROUND PINS (4 CORNERS) FOR
GOOD THERMAL CONDUCTIVITY
PLACE FEEDTHROUGH AROUND
Figure 5. High Speed Switching Path
D1
C3
C3
U
Figure 6. Suggested Layout
CIRCULATING
FREQUENCY
LT3430
PATH
HIGH
L1
1
2
3
4
5
6
7
8
GND
SW
V
V
SW
BOOST
GND
C2
IN
IN
LT3430
D2
this path will also reduce the parasitic trace inductance of
approximately 25nH/inch. At switch off, this parasitic in-
ductance produces a flyback spike across the LT3430
switch. When operating at higher currents and input volt-
ages, with poor layout, this spike can generate voltages
across the LT3430 that may exceed its absolute maximum
rating. A ground plane should always be used under the
switcher circuitry to prevent interplane coupling and over-
all noise.
BIAS
GND
GND
D1
V
FB
C
L1
16
15
14
13
12
11
10
9
C1
SHDN
SYNC
R1
LOAD
C
FB
C1
3430 F05
GROUND PLANE
R
C
CONNECT TO
C
C
R2
5V
C
F
KEEP FB AND V
AWAY FROM HIGH FREQUENCY,
HIGH CURRENT COMPONENTS
V
GND
KELVIN SENSE
OUT
V
OUT
3430 F06
SOLDER THE EXPOSED PAD
TO THE ENTIRE COPPER
GROUND PLANE UNDERNEATH
THE DEVICE. NOTE: THE BOOST
AND BIAS COPPER TRACES ARE
ON A SEPARATE LAYER FROM
THE GROUND PLANE
C
COMPONENTS
LT3430
sn3430 3430is
17