74HC_HCT4060

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© NXP Semiconductors N.V. 2016. All rights reserved.

Product data sheet

Rev. 4 — 10 February 2016

15 of 25

NXP Semiconductors

74HC4060; 74HCT4060

14-stage binary ripple counter with oscillator

13. RC oscillator

13.1 Timing component limitations

The oscillator frequency is mainly determined by RtCt, provided R2  2Rt and

R2C2 << RtCt. 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, Ct must be larger than the

inherent stray capacitance. Rt must be larger than the ON resistance in series with it,

which typically is 280

 at V

CC = 2.0 V, 130  at VCC = 4.5 V and 100  at VCC = 6.0 V.

The recommended values for these components to maintain agreement with the typical

oscillation formula are:

Ct > 50 pF, up to any practical value and 10 k <Rt <1 M.

In order to avoid start-up problems, Rt  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 should not be too large. A practical value

for R2 is 2.2 k

.

Typical formula for oscillator frequency:

Fig 12. Example of a RC oscillator

f

osc

1

2.5

R

t



C

t



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=