7

LTC1569-6

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.

APPLICATIONS INFORMATION

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 1

µF 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

Figure 4. Typical Divide Ratio in the

Divide-by-4 Mode, TA = 25°C

Figure 5. Filter Cutoff vs Temperature,

Divide-by-4 Mode, REXT = 10k

Figure 3. Filter Cutoff vs Temperature,

Divide-by-1 Mode, REXT = 10k

Figure 2. Filter Cutoff vs VSUPPLY,

Divide-by-1 Mode, TA = 25°C

VSUPPLY (V)

2

1569-6 F04

4.08

4.04

4.00

3.96

4

6

810

REXT = 5k

REXT = 10k

REXT = 20k

REXT = 40k

TEMPERATURE (

°C)

–50

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

VS = 3V

VS = 5V

VS = 10V

VSUPPLY (V)

2

1569-6 F02

1.04

1.03

1.02

1.01

1.00

0.99

0.98

0.97

0.96

4

6

810

REXT = 5k

REXT = 10k

REXT = 20k

REXT = 40k

TEMPERATURE (

°C)

–50

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

VS = 3V

VS = 5V

VS = 10V