lt1935es5-trpbf Linear Technology Corporation, lt1935es5-trpbf Datasheet - Page 6

• Manufacturer Part Number: lt1935es5-trpbf
• Description: 1.2mhz Boost Dc/dc Converter In Thinsot With 2a Switch
• Manufacturer: Linear Technology Corporation

APPLICATIONS
Figure 5. Transient Response with a 68pF Phase-Lead Capacitor
LT1935
6
100mV/DIV
200mA/DIV
I LOAD
V OUT
V
OUT
Figure 7. Suggested Layout
5V/DIV
2V/DIV
1A/DIV
V OUT
GND
RUN
U
I IN
+
FB
D1
C2
INFORMATION
R2
84.5k
10k
U
RUN
50µs/DIV
R1
L1
68pF
Reduces the Peak Input Current During Start-Up. V
Figure 6. Adding a Resistor and Capacitor to the SHDN Pin
SHDN
W
20µs/DIV
C3
GND
C1
20µF
OUT
V
OUT
1935 F05
= 5V, C2 = 20µF, Output Load = 10Ω.
U
V
SHDN
IN
1935 F06a
1935 F03
Soft Start
The SHDN pin can be used to soft start the LT1935,
reducing the maximum input current during start up. The
SHDN pin is driven through an external RC filter to create
a ramp at this pin. Figure 6 shows the start-up waveforms
with and without the soft start circuit. Without soft start,
the input current peaks at ~3A. With soft start, the peak
current is reduced to 1A. By choosing a large RC time
constant, the peak start-up current can be reduced to the
current that is required to regulate the output, with no
overshoot. Choose the value of the resistor so that it can
supply 100µA when the SHDN pin reaches 1.8V.
Layout Hints
The high speed operation of the LT1935 demands careful
attention to board layout. You will not get advertised
performance with careless layout. Figure 7 shows the
recommended component placement. Make the ground
pin copper area large. This helps to lower the die
temperature.
5V/DIV
2V/DIV
1A/DIV
V OUT
RUN
I IN
RUN
0.22µF
10k
IN
= 3.3V,
SHDN
200µs/DIV
GND
1935 F06b
1935f