8

LTC1063

S

APPLICATI

I FOR ATIO

Self-Clocking Operation

The LTC1063 features an internal oscillator which can be

tuned via an external RC. The LTC1063’s internal oscillator

is primarily intended for generation of clock frequencies

below 500kHz. The first curve of the Typical Performance

Characteristics section shows how to quickly choose the

value of the RC for a given frequency. More precisely, the

frequency of the internal oscillator is equal to:

Figure 4b shows the variation of the parameter K versus

clock frequency and power supply. First choose the de-

Figure 4b pick the right value of K, set C = 200pF and solve

for R.

then,

R = (1.0)/(200kHz

× 204pF) = 24.5k.

Note a 4pF parasitic capacitance is assumed in parallel

with the external 200pF timing capacitor. Figure 5 shows

the clock frequency variation from – 40

°C to 85°C. The

200kHz clock of Example 1 will change by –1.75% at 85

°C.

For a very limited temperature range, the internal oscillator

of the LTC1063 can be used to generate clock frequencies

above 500kHz (Figures 6 and 7). The data of Figure 6 is

derived from several devices. For a given external (RC)

value, the observed device-to-device clock frequency varia-

tion was

Example 2:

from Figure 6, K = 0.575,

and,

R = (0.575)/(2MHz

× 14pF) = 20.5k.

CLOCK FREQUENCY (MHz)

0.5

0.80

0.75

0.70

0.65

0.60

0.55

0.50

0.45

0.40

2.5

1063 F05

1.0

1.5

2.0

3.0

C = 10pF

R

1063 F03a

C

1

2

3

4

8

7

6

5

LTC1063

Figure 4a.

INTERNAL CLOCK FREQUENCY (kHz)

1.25

1.20

1.15

1.10

1.05

1.00

0.95

0.90

0.85

0.80

0.75

1063 F04b

100

300

500

C = 200pF

200

400

CLOCK FREQUENCY (kHz)

0

4

3

2

1

0

–1

–2

–3

–4

400

1063 F05

100

200

300

500

C = 200pF