LT1937
W U U
U
APPLICATIO S I FOR ATIO
D1
IIN
100mA/DIV
2.2nF
FB
100mV/DIV
R2
1k
D2
LT1937
FB
C
OUT
SHDN
2V/DIV
R1
6.34Ω
5k
VIN = 3.6V
THREE LEDs
15mA
50µs/DIV
1937 F11b
D2: MMBT
1937 F11a
(11a) Recommended Soft-Startup Circuit
(11b) Soft-Startup Waveforms
Figure 11. Recommended Soft-Startup Circuit and Waveforms
area of all traces connected to the SW pin and always use
a ground plane under the switching regulator to minimize
interplanecoupling.Inaddition,thegroundconnectionfor
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.
Board Layout Consideration
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
Tomaximizeefficiency, switchriseandfalltimesaremade
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
L
L
V
IN
V
IN
D
D
C
C
IN
1
2
3
6
5
4
C
C
IN
1
2
3
5
4
O
O
GND
GND
SHDN
SHDN
R2
R2
R1
R1
1937 F12b
1937 F12a
DIMMING
CONTROL
DIMMING
CONTROL
R3
R3
(SOT-23 Package)
(SC70 Package)
Figure 12. Recommended Component Placement
1937f
8
Linear [ Linear ]
