Datasheet

8
LT1937
1937f
APPLICATIO S I FOR ATIO
WUUU
(11a) Recommended Soft-Startup Circuit
V
IN
= 3.6V 50µs/DIV 1937 F11b
THREE LEDs
15mA
FB
100mV/DIV
SHDN
2V/DIV
I
IN
100mA/DIV
Figure 11. Recommended Soft-Startup Circuit and Waveforms
(11b) Soft-Startup Waveforms
Board Layout Consideration
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 electromagnetic interfer-
ence (EMI) problems, proper layout of the high frequency
switching path is essential. The voltage signal of the SW
pin has sharp rise and fall edges. Minimize the length and
15
4
R1
2
3
R2
R3
DIMMING
CONTROL
C
O
C
IN
V
IN
GND
SHDN
1937 F12a
D
L
Figure 12. Recommended Component Placement
area of all traces connected to the SW pin and always use
a ground plane under the switching regulator to minimize
interplane coupling. In addition, the ground connection for
the feedback resistor R1 should be tied directly to the GND
pin and not shared with any other component, ensuring a
clean, noise-free connection. Recommended component
placement is shown in Figure 12.
(SOT-23 Package)
16
5
4
R1
2
3
R2
R3
DIMMING
CONTROL
C
O
C
IN
V
IN
GND
SHDN
1937 F12b
D
L
(SC70 Package)
R2
1k
R1
6.34Ω
5k
D2: MMBT
2.2nF
D1
D2
C
OUT
1937 F11a
LT1937
FB