74HC_HCT4060_Q100 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 2 — 10 April 2013 15 of 25
NXP Semiconductors
74HC4060-Q100; 74HCT4060-Q100
14-stage binary ripple counter with oscillator
13. RC oscillator
13.1 Timing component limitations
The oscillator frequency is mainly determined by R
t
C
t
, provided R2 2R
t
and
R2C2 << R
t
C
t
. The function of R2 is to minimize the influence of the forward voltage
across the input protection diodes on the frequency. The stray capacitance C2 should be
kept as small as possible. In consideration of accuracy, C
t
must be larger than the
inherent stray capacitance. R
t
must be larger than the ON resistance in series with it,
which typically is 280 at V
CC
= 2.0 V, 130 at V
CC
= 4.5 V and 100 at V
CC
= 6.0 V.
The recommended values for these components to maintain agreement with the typical
oscillation formula are:
C
t
> 50 pF, up to any practical value and 10 k <R
t
<1 M.
In order to avoid start-up problems, R
t
1 k.
13.2 Typical crystal oscillator circuit
In Figure 13, R2 is the power limiting resistor. For starting and maintaining oscillation, a
minimum transconductance is necessary, so R2 must not be too large. A practical value
for R2 is 2.2 k.
Typical formula for oscillator frequency:
Fig 12. Example of an RC oscillator
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& 5 5
W
57&
56
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W
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f
osc
1
2.5 R
t
C
t
------------------------------
=
