Datasheet
7
LTC1569-6
Using the equation in Figure 1, the approximate filter
cutoff frequency is f
CUTOFF
= 64kHz • (10k/20k)
• (1/16) = 2kHz.
For a more precise f
CUTOFF
estimate, use Table 1 to get
a value of f
CUTOFF
when R
EXT
= 20k and use the graph
in Figure 6 to find the correct divide ratio when V
S
= 3V
and R
EXT
= 20k. Based on Table 1 and Figure 6, f
CUTOFF
= 32kHz • (20.18k/20k) • (1/16.02) = 2.01kHz.
From Table 1, the part-to-part variation of f
CUTOFF
will
be ±2%. From the graph in Figure 7, the 0°C to 70°C
drift of f
CUTOFF
will be –0.2% to 0.2%.
Example 2: LTC1569-6, R
EXT
= 10k, V
S
= 5V, divide-by-1
mode, DIV/CLK (Pin␣ 5) connected to V
–
(Pin 4), T
A
= 25°C.
APPLICATIONS INFORMATION
WUU
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Using the equation in Figure 1, the approximate filter
cutoff frequency is f
CUTOFF
= 64kHz • (10k/10k)
• (1/1) = 64kHz.
For a more precise f
CUTOFF
estimate, use Figure 2 to
correct for the supply voltage when V
S
= 5V. From
Table␣ 1 and Figure 2, f
CUTOFF
= 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 R
X
and avoid routing noisy signals near R
X
(Pin 6). Use
Figure 4. Typical Divide Ratio in the
Divide-by-4 Mode, T
A
= 25°C
Figure 5. Filter Cutoff vs Temperature,
Divide-by-4 Mode, R
EXT
= 10k
Figure 3. Filter Cutoff vs Temperature,
Divide-by-1 Mode, R
EXT
= 10k
Figure 2. Filter Cutoff vs V
SUPPLY
,
Divide-by-1 Mode, T
A
= 25°C
V
SUPPLY
(V)
2
DIVIDE RATIO
1569-6 F04
4.08
4.04
4.00
3.96
4 6 810
R
EXT
= 5k
R
EXT
= 10k
R
EXT
= 20k
R
EXT
= 40k
TEMPERATURE (°C)
–50
NORMALIZED FILTER CUTOFF
1569-6 F05
1.010
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
0.990
–25
0 25 50 75 100
V
S
= 3V
V
S
= 5V
V
S
= 10V
V
SUPPLY
(V)
2
NORMALIZED FILTER CUTOFF
1569-6 F02
1.04
1.03
1.02
1.01
1.00
0.99
0.98
0.97
0.96
4 6 810
R
EXT
= 5k
R
EXT
= 10k
R
EXT
= 20k
R
EXT
= 40k
TEMPERATURE (°C)
–50
NORMALIZED FILTER CUTOFF
1569-6 F03
1.010
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
0.990
–25
0 25 50 75 100
V
S
= 3V
V
S
= 5V
V
S
= 10V