LTC1569CS8-6 データシートの表示（PDF） - Linear Technology
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LTC1569CS8-6 Datasheet PDF : 12 Pages
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LTC1569-6
APPLICATIONS INFORMATION
Using the equation in Figure 1, the approximate filter
cutoff frequency is fCUTOFF = 64kHz • (10k/20k)
• (1/16) = 2kHz.
For a more precise fCUTOFF estimate, use Table 1 to get
a value of fCUTOFF when REXT = 20k and use the graph
in Figure 6 to find the correct divide ratio when VS = 3V
and REXT = 20k. Based on Table 1 and Figure 6, fCUTOFF
= 32kHz • (20.18k/20k) • (1/16.02) = 2.01kHz.
From Table 1, the part-to-part variation of fCUTOFF will
be ±2%. From the graph in Figure 7, the 0°C to 70°C
drift of fCUTOFF will be – 0.2% to 0.2%.
Example 2: LTC1569-6, REXT = 10k, VS = 5V, divide-by-1
mode, DIV/CLK (Pin␣ 5) connected to V – (Pin 4), TA = 25°C.
Using the equation in Figure 1, the approximate filter
cutoff frequency is fCUTOFF = 64kHz • (10k/10k)
• (1/1) = 64kHz.
For a more precise fCUTOFF estimate, use Figure 2 to
correct for the supply voltage when VS = 5V. From
Table␣ 1 and Figure 2, fCUTOFF = 64k • (10k/10k) • 0.970
= 62.1kHz.
The oscillator is sensitive to transients on the positive
supply. The IC should be soldered to the PC board and the
PCB layout should include a 1µF ceramic capacitor be-
tween V + (Pin 7) and V – (Pin 4) , as close as possible to
the IC to minimize inductance. Avoid parasitic capacitance
on RX and avoid routing noisy signals near RX (Pin 6). Use
1.04
1.03
REXT = 5k
REXT = 10k
1.02
REXT = 20k
REXT = 40k
1.01
1.00
0.99
0.98
0.97
0.96
2
4
6
8
10
VSUPPLY (V)
1569-6 F02
Figure 2. Filter Cutoff vs VSUPPLY,
Divide-by-1 Mode, TA = 25°C
1.010
1.008
1.006
1.004
VS = 3V
VS = 5V
VS = 10V
1.002
1.000
0.998
0.996
0.994
0.992
0.990
–50 –25 0
25 50 75 100
TEMPERATURE (°C)
1569-6 F03
Figure 3. Filter Cutoff vs Temperature,
Divide-by-1 Mode, REXT = 10k
4.08
REXT = 5k
REXT = 10k
REXT = 20k
REXT = 40k
4.04
4.00
3.96
2
4
6
8
10
VSUPPLY (V)
1569-6 F04
Figure 4. Typical Divide Ratio in the
Divide-by-4 Mode, TA = 25°C
1.010
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
0.990
–50
VS = 3V
VS = 5V
VS = 10V
–25 0 25 50
TEMPERATURE (°C)
75 100
1569-6 F05
Figure 5. Filter Cutoff vs Temperature,
Divide-by-4 Mode, REXT = 10k
7
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