LTC1265 LINER [Linear Technology], LTC1265 Datasheet - Page 12

• Manufacturer Part Number: LTC1265
• Description: 1.2A, High Efficiency Step-Down DC/DC Converter
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
LTC1265/LTC1265-3.3/LTC1265-5
Design Example
As a design example, assume V
= 0.8A and f = 250kHz. With this information we can easily
calculate all the important components.
From (1),
From (2) and assuming V
Using (3), the value of the inductor is:
For the catch diode, a MBRS130LT3 or 1N5818 will be
sufficient in this application.
C
temperature, and C
The inductor ripple current is given by:
At light loads the peak inductor current is at:
Therefore, at load current less than 0.1A the LTC1265 will
be in Burst Mode operation. Figure 8 shows the complete
circuit and Figure 9 shows the efficiency curve with the
above calculated component values.
12
IN
I
RIPPLE
R
C
L 5.2(10
ESR
I
will require an RMS current rating of at least 0.4A at
PEAK
T
SENSE
COUT
100pF
= 25mV/0.125 = 0.2A
= 100mV/0.8 = 0.125
< 0.25
5
V
)(0.125)(100pF)3.3V = 22 H
OUT
L
U
OUT
+ V
D
will require an ESR of (from 5):
INFORMATION
U
D
t
OFF
= 0.4V,
IN
= 0.22A
= 5V, V
W
OUT
= 3.3V, I
U
MAX
+
3900pF
C
IN
V
5V
IN
100pF
Figure 9. Design Example Efficiency Curve
100
0.1 F
1k
90
70
95
85
80
75
0.01
Figure 8. Design Example Circuit
L = DALE LPT4545-220 (22 H)
V
C
OUT
T
PWR V
SHDN
I
C
= 100pF
TH
T
= 3.3V
LTC1265-3.3
SGND
IN
LOAD CURRENT (mA)
SENSE
SENSE
PGND
V
IN
SW
0.1
+
–
D1
22 H
1000pF
1265 G11
0.125
1.0
LTC1265 F08
+
C
V
3.3V
0.8A
OUT
OUT