74HC4060 Datasheet, PDF (15/25 Pages) NXP Semiconductors – 14-stage binary ripple counter with oscillator

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 R_tC_t, provided R2 ≈ 2R_t and
R2C2 << R_tC_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 Ω at V_CC = 2.0 V, 130 Ω at V_CC = 4.5 V and 100 Ω at V_CC = 6.0 V.
MR (from logic)
11 RS
74HC4060
74HCT4060
C2 R2
RTC
10
Rt
CTC
9
Ct
001aai121
Typical formula for oscillator frequency: f _osc = ₂---_.--₅----_×-----_R-¹---_t---_×-----_C----_t
Fig 12. Example of a RC oscillator
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 kΩ < R_t < 1 MΩ.
In order to avoid start-up problems, R_t ≥ 1 kΩ.
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 kΩ.
74HC_HCT4060_3
Product data sheet
Rev. 03 — 14 July 2008
© NXP B.V. 2008. All rights reserved.
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