Datasheet

9
LT1932
1932f
APPLICATIO S I FOR ATIO
WUUU
Figure 10. Recommended Component Placement
Board Layout Considerations
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To maximize efficiency, switch rise and fall times are made
as short as possible. To prevent radiation and high fre-
quency resonance problems, proper layout of the high
frequency switching path is essential. Minimize the length
and area of all traces connected to the SW pin and always
use a ground plane under the switching regulator to
minimize interplane coupling. The signal path including
the switch, output diode D1 and output capacitor C2,
contains nanosecond rise and fall times and should be
kept as short as possible. In addition, the ground connec-
tion for the R
SET
resistor should be tied directly to the GND
pin and not be shared with any other component, ensuring
a clean, noise-free connection. Recommended compo-
nent placement is shown in Figure 10.
V
IN
SW
D1
SOFT-START
CIRCUIT
1932 F07
L1
6.8µH
V
IN
I
IN
V
OUT
LT1932
SHDN
61
4
R
SET
1.50k
C1
4.7µF
C2
1µF
2
35
LED
Q1
2N3904
R
SET
GND
C3
0.047µF
R1
1.5k
Figure 7. Soft-Start Circuit for the LT1932
V
OUT
5V/DIV
I
IN
200mA/DIV
100µs/DIV 1932 F08
Figure 8. Input Current at Start-Up Without Soft-Start
V
OUT
5V/DIV
I
IN
200mA/DIV
100µs/DIV 1932 F09
Figure 9. Input Current at Start-Up with Soft-Start
C1
L1
D1
GND
C2
R
SET
1932 F10
1
2
3
6
5
4
DIMMING
CONTROL
SHDN
V
IN