Datasheet
LTC1063
9
1063fa
CLOCK FREQUENCY (MHz)
0.5
K
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
2.5
1063 F06
1.0
1.5
2.0
3.0
f
CLK
= K/RC
C = 10pF
T
A
= 25°C
V
S
= ±7.5V
V
S
= ±2.5V
V
S
= ±5V
CLOCK FREQUENCY (kHz)
0
f
CLK
CHANGE NORMALIZED
TO ITS 25°C VALUE (%)
4
3
2
1
0
–1
–2
–3
–4
400
1063 F05
100
200
300
500
C = 200pF
T
A
= –40°C
T
A
= 85°C
V
S
= ±2.5V
V
S
= ±5V
V
S
= ±7.5V
V
S
= ±7.5V
V
S
= ±5V
V
S
= ±2.5V
INTERNAL CLOCK FREQUENCY (kHz)
K
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
V
S
= ±7.5V
V
S
= ±2.5V
F
CLK
= K/RC
C = 200pF
T
A
= 25°C
V
S
= ±5V
200
400
V
IN
R
V
OUT
1063 F04a
C
V
–
V
+
1
2
3
4
8
7
6
5
LTC1063
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:
f
CLK
= K/RC
For clock frequencies (f
CLK
) 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, (f
CLK
< 500kHz), then through
Figure 4b pick the right value of K, set C = 200pF and solve
for R.
Example 1: f
CUTOFF
= 2kHz, f
CLK
= 200kHz, V
S
= ±5V,
T
A
= 25°C, K = 1.0, C = 200pF
then, R = (1.0)/(200kHz × 204pF) = 24.5k.
Figure 4b. f
CLK
vs K
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.
Figure 5. f
CLK
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% (V
S
= ±5V), and ±1.25% for V
S
= ±2.5V.
Example 2: f
CUTOFF
= 20kHz, f
CLK
= 2MHz, V
S
= ±7.5V,
T
A
= 25°C, C = 10pF
from Figure 6, K = 0.575,
and, R = (0.575)/(2MHz × 14pF) = 20.5k.
Figure 6. f
CLK
vs K
Figure 4a.
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