LTC1574-3.3 LINER [Linear Technology], LTC1574-3.3 Datasheet - Page 6

• Manufacturer Part Number: LTC1574-3.3
• Description: High Efficiency Step-Down DC/DC Converters with Internal Schottky Diode
• Manufacturer: LINER [Linear Technology]

LTC1574
LTC1574-3.3/LTC1574-5
APPLICATIONS
With I
The peak-to-peak ripple inductor current, I
and is also equal to:
6
inductor L1 is chosen for its excellent self-shielding prop-
erties. Open magnetic structures such as drum and rod
cores are to be avoided since they inject high flux levels
into their surroundings. This can become a major source
of noise in any converter circuit.
Design Example
As a design example, assume V
V
is used for this application with I
V
the LTC1574-5 is operating in continuous mode.
TYPICAL APPLICATIONS
OUT
IN
. The minimum value of L is determined by assuming
= 5V and I
OUT
= 350mA and I
Figure 6. Continuous Inductor Current
OUT
U
= 350mA maximum. The LTC1574-5
TIME
4V TO 12.5V
** AVX TPSD107K010
PEAK
* AVX TPSD226K025
†
INFORMATION
COILTRONICS CTX50-4
U
= 0.6A (I
V
IN
PGM
U
W
IN
12
11
PGM
(Pin 6) connected to
6
I
AVG CURRENT = I
I
PEAK
V
I
LB
LB
= 9V (nominal),
PGM
Low Noise, High Efficiency 3.3V Regulator
IN
OUT
= V
RIPPLE
IN
LTC1574
GND
), I
V
IN
U
=
= 350mA
5
2, 4, 13, 15
V
, is 0.5A
I
OUT
PEAK
= 0.1A.
SHDN
2
1574 • F06
+ I
V
SW
FB
V
7
10
3, 14
Solving for L in the above equation and with V
L = 44 H. The next higher standard value of L is 50 H
(example: Coiltronics CTX50-4). The operating frequency,
ignoring voltage across diode V
With the value of L determined, the requirements for C
and C
should be at least:
For C
100pF
+
50 H
I
I
I
f
RIPPLE
RMS
RMS
OUT
†
22 F*
25V
OUT
111
2 5 10 1
2
.
, the RMS current rating should be at least:
are calculated. For C
174
300mA
kHz
I
+
I
PEAK
OUT
2
4 10
mA
0.1 F
100 F**
10V
5
2
V
OUT
A
6
V
RMS
56k
33k
V
OUT
V
6.8nF
V
V
IN
IN
IN
OUT
L
V
OUT
IN
1574 TA03
V
3.3V
450mA
D
V
OUT
, its RMS current rating
D
is:
1 2
/
A
P-P
A
RMS
D
= 0.5V,
IN