lt1310emse-trpbf Linear Technology Corporation, lt1310emse-trpbf Datasheet - Page 7

• Manufacturer Part Number: lt1310emse-trpbf
• Description: 1.5a Boost Dc/dc Converter With Phase-locked Loop
• Manufacturer: Linear Technology Corporation

OPERATIO
C
To synchronize to an external input signal, the timing
capacitor and PLL filter components must be chosen
properly. This is a simple process and can be done using
the graph in Figure 2a.
In Figure 2a, operating frequency is plotted versus timing
capacitor (C
ing to the minimum and maximum lock frequency given a
specific C
find the intersection of the desired operating frequency
and the dashed line. Then move to the corresponding C
value.
Alternately, use the following equations as a starting point:
for f
for f
T
C
C
Selection for Operating Frequency
LOCK
LOCK
T
T
0 75
0 75
100k
.
.
T
10k
100
10
1k
2MHz:
2MHz:
value. To choose the right timing capacitor,
T
Figure 2a. C
10k
) with the upper and lower lines correspond-
250 10
310 10
U
f
f
LOCK
LOCK
FREQUECY
MINIMUM
•
•
LOCK
100k
T
FREQUENCY (Hz)
–
–
vs Operating Frequency
6
6
–
–
MAXIMUM
LOCK
FREQUECY
40 10
60 10
•
•
1M
–
–
12
12
1310 F02a
10M
T
SHUTDOWN
SYNC IN
Because the lock range for the PLL is nearly 2:1, the
nearest standard value NP0 capacitor can be used. For
the application shown in Figure 1, a 1.6MHz switching
frequency corresponds to an 100pF timing capacitor.
Since the switching frequency affects inductor ripple
current, the inductor must also be scaled. Table 1 shows
recommended component values for various switching
frequencies.
Table 1. Recommended Component Values for Various Switching
Frequencies (R
SWITCHING
FREQUENCY
600kHz
1MHz
1.6MHz
2MHz
2.5MHz
3MHz
V
5V
IN
C1
4.7 F
CERAMIC
Figure 2b. Circuit Used for C
C
LP
R
LP
LP
330pF
180pF
100pF
68pF
47pF
33pF
= 3.01k)
C
T
SHDN
SYNC
PLL-LPF
V
V
IN
C
R
1500pF
1000pF
LT1310
820pF
820pF
330pF
330pF
C
C
C
C
L1
C
GND
SW
FB
C
T
2700pF
2200pF
1500pF
1500pF
1500pF
1000pF
C
LP
T
Selection
C
T
10k
10k
15k
15k
20k
20k
R
LT1310
178k
20.5k
C
sn1310 1310fs
1310 F02a
6.2 H
5.6 H
4.7 H
3.3 H
2.7 H
10 H
C2
4.7 F
CERAMIC
L1
V
12V
OUT
7