LT1946 LINER [Linear Technology], LT1946 Datasheet - Page 8

• Manufacturer Part Number: LT1946
• Description: 1.2MHz Boost DC/DC Converter with 1.5A Switch and Soft-Start
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LT1946
Figure 6. Recommended Component Placement for Boost Converter. Note Direct High Current Paths Using Wide PC Traces. Minimize
Trace Area at Pin 1 (V
Introducing Switching Currents Into the Ground Plane
8
–100
–180
–200
100
–50
50
Figure 5. Bode Plot of Figure 1’s Circuit
0
0
100
100
C
U
) and Pin 2 (FB). Use Multiple Vias to Tie Pin 4 Copper to Ground Plane. Use Vias at One Location Only to Avoid
1k
1k
FREQUENCY (Hz)
FREQUENCY (Hz)
U
10k 25k
10k 25k
60
GROUND PLANE
100k
100k
W
SHUTDOWN
MULTIPLE
R1
1946 F05a
1946 F05b
VIAs
1M
1M
R2
GND
U
R
C
C
C
1
2
3
4
LT1946
C2
C
SS
Diode Selection
A Schottky diode is recommended for use with the LT1946.
The Microsemi UPS120 is a very good choice. Where the
input to output voltage differential exceeds 20V, use the
UPS140 (a 40V diode). These diodes are rated to handle an
average forward current of 1A. For applications where the
average forward current of the diode is less than 0.5A, an
ON Semiconductor MBR0520 diode can be used
Setting Output Voltage
To set the output voltage, select the values of R1 and R2
(see Figure 1) according to the following equation:
A good range for R2 is from 5k to 30k.
Layout Hints
The high speed operation of the LT1946 demands careful
attention to board layout. You will not get advertised
performance with careless layout. Figure 6 shows the
recommended component placement for a boost
converter.
8
7
6
5
R
V
C1
OUT
1
+
R
2
1 25
V
.
OUT
V
L1
V
IN
–
1
1946 F06
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