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LTC1063CN8 Datasheet PDF : 12 Pages
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LTC1063
APPLICATI S 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:
fCLK = K/RC
For clock frequencies (fCLK) below 100kHz, K equals 1.07.
Figure 4b shows the variation of the parameter K versus
clock frequency and power supply. First choose the de-
sired clock frequency, (fCLK < 500kHz), then through
Figure 4b pick the right value of K, set C = 200pF and solve
for R.
Example 1: fCUTOFF = 2kHz, fCLK = 200kHz, VS = ±5V,
TA = 25°C, K = 1.0, C = 200pF
then,
R = (1.0)/(200kHz × 204pF) = 24.5k.
VIN 1
2
V– 3
4
LTC1063
8
7
VOUT
6 V+
5
R
Figure 4a.
C
1063 F03a
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.
4
C = 200pF
3
TA = –40°C
2
VS = ±2.5V
VS = ±5V
1
VS = ±7.5V
0
TA = 85°C
–1
–2
VS = ±7.5V
–3
VS = ±2.5V
VS = ±5V
–4
0
100 200 300 400 500
CLOCK FREQUENCY (kHz)
1063 F05
Figure 5. fCLK vs Temperature
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 ±1% (VS = ±5V), and ±1.25% for VS = ±2.5V.
Example 2: fCUTOFF = 20kHz, fCLK = 2MHz, VS = ±7.5V,
TA = 25°C, C = 10pF
from Figure 6, K = 0.575,
and,
R = (0.575)/(2MHz × 14pF) = 20.5k.
8
1.25
1.20
FCLK = K/RC
C = 200pF
1.15 TA = 25°C
1.10
1.05
1.00
VS = ±7.5V
VS = ±5V
0.95
0.90
0.85
VS = ±2.5V
0.80
0.75
100 200 300 400 500
INTERNAL CLOCK FREQUENCY (kHz)
Figure 4b. fCLK vs K
1063 F04b
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.5
fCLK = K/RC
C = 10pF
TA = 25°C
VS = ±7.5V
VS = ±5V
VS = ±2.5V
1.0 1.5 2.0 2.5 3.0
CLOCK FREQUENCY (MHz)
1063 F05
Figure 6. fCLK vs K
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