LTC1174-3.3 Linear Technology, LTC1174-3.3 Datasheet - Page 10

• Manufacturer Part Number: LTC1174-3.3
• Description: High Efficiency Step-Down and Inverting DC/DC Converter
• Manufacturer: Linear Technology

LTC1174
LTC1174-3.3/LTC1174-5
DESIGN EXAMPLE
As a design example, assume V
5V, and I
for this application, with I
minmum value of L is determined by assuming the
LTC1174-5 is operating in continuous mode.
With I
0.1A.The peak-to-peak ripple inductor current, I
0.5A and is also equal to:
Solving for L in the above equation and with V
L = 44.8 H. The next higher standard value of L is 50 H
10
A
PPLICATI
I
RIPPLE
OUT
OUT
= 350mA and I
Figure 7. Continuous Inductor Current
4 10
= 350mA maximum. The LTC1174-5 is used
O
U
6
TIME
S
V
OUTPUT DIVIDER
REQUIRED WITH
OUT
VERSION ONLY
PGM
ADJUSTABLE
I FOR ATIO
PEAK
L
U
(pin 7) connected to V
V
Figure 6. LTC1174 Layout Diagram (See Board Layout Checklist)
= 0.6A (I
IN
D
= 9V (nominal), V
I
AVG CURRENT = I
I
PEAK
V
W
R2
A
P P
PGM
=
= 350mA
= V
R1
I
OUT
PEAK
D
RIPPLE
U
2
IN
= 0.6V,
1174 F07
+ I
IN
), I
OUT
V
. The
1
2
3
4
V
, is
GND
V
(V
LB
LB
OUT
=
=
BOLD LINES INDICATE
FB
HIGH CURRENT PATH
OUT
IN
)
LTC1174
(example: Coiltronics CTX50-4). The operating frequency,
neglecting voltage across diode V
With the value of L determined, the requirements for C
and C
should be at least:
For C
Now allow V
the operating frequency will decrease. The new frequency
is 42kHz.
SHUTDOWN
I
I
f
RMS
RMS
I
PGM
OUT
SW
V
OUT
111
IN
2 5 10 1
.
8
7
6
5
, the RMS current rating should be at least:
are calculated. For C
174
300
I
kHz
PEAK
I
OUT
IN
2
D
mA
mA
0.1 F
to drop to 6V. At this minimum input voltage
5
V
OUT
A
C
RMS
V
OUT
C
V
OUT
V
IN
V
+
IN
IN
IN
L
V
1174 F06
OUT
V
V
IN
IN
OUT
, its RMS current rating
D
is:
1 2
/
A
RMS
IN