Datasheet

LT3479
10
3479fc
APPLICATIONS INFORMATION
GND
GND
SS
V
C
FBN
FBP
V
REF
SW
SW
L
V
S
V
IN
R
T
SHDN
LT3479
R
T
R2
C
SS
R
C
R1
C
C
C
OUT
D
C
IN
C
S
L1
MINIMIZE THE AREA
OF THIS TRACE
TO V
S
TO V
IN
TO GND
TO SHDN
3479 F04
PLACE VIAS AROUND EXPOSED PAD
TO ENHANCE THERMAL PERFORMANCE
TO V
OUT
Figure 4. Suggested Board Layout
Switching Frequency
The switching frequency of the LT3479 is set by an exter-
nal resistor attached to the R
T
pin. Do not leave this pin
open. A resistor must always be connected for proper
operation. See Table 4 and Figure 7 for resistor values
and corresponding frequencies.
Table 4. Switching Frequency
SWITCHING FREQUENCY (MHz) R
T
(kΩ)
3.5 1.78
3 2.87
2.5 4.32
2 6.49
1.5 10.2
1 17.8
0.5 39.2
0.2 113
Figure 5. Start-Up with No Soft-Start Capacitor
0.2MS/DIV
I
L
2A/DIV
V
OUT
5V/DIV
3479 F05
Figure 6. Start-Up with C
SS
= 22nF
0.2ms/DIV
I
L
2A/DIV
V
OUT
5V/DIV
3479 F06