LT1937ES5 Linear Technology, LT1937ES5 Datasheet - Page 8

• Manufacturer Part Number: LT1937ES5
• Manufacturer: Linear Technology

Specifications of LT1937ES5

• Operating Supply Voltage (typ): 3.3/5/9V
• Number Of Segments: 6
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Package Type: TSOT-23
• Pin Count: 5
• Mounting: Surface Mount
• Operating Supply Voltage (min): 2.5V
• Operating Supply Voltage (max): 10V
• Lead Free Status / Rohs Status: Not Compliant

APPLICATIO S I FOR ATIO
LT1937
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
8
CONTROL
DIMMING
(11a) Recommended Soft-Startup Circuit
D2: MMBT
C
O
LT1937
R3
R2
U
D
FB
(SOT-23 Package)
D1
2.2nF
U
D2
L
1
2
3
5k
R2
1k
R1
Figure 11. Recommended Soft-Startup Circuit and Waveforms
W
R1
6.34
Figure 12. Recommended Component Placement
5
4
1937 F11a
C
OUT
1937 F12a
C
U
IN
V
GND
SHDN
IN
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.
100mA/DIV
100mV/DIV
2V/DIV
SHDN
DIMMING
CONTROL
I
FB
IN
V
THREE LEDs
15mA
IN
= 3.6V
C
O
(11b) Soft-Startup Waveforms
R3
R2
D
(SC70 Package)
50 s/DIV
L
1
2
3
R1
6
5
4
1937 F11b
1937 F12b
C
IN
V
GND
SHDN
IN
1937f