HEF4047B データシートの表示（PDF） - NXP Semiconductors.
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HEF4047B Datasheet PDF : 20 Pages
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NXP Semiconductors
HEF4047B
Monostable/astable multivibrator
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Fig 11. Implementation of external counter option.
11.2.3 Timing component limitations
The capacitor used in the circuit should be non-polarized and have low leakage (that is
the parallel resistance of the capacitor should be an order of magnitude greater than the
external resistor used). There is no upper or lower limit for either Rt or Ct value to maintain
oscillation. However, for accuracy, Ct must be much larger than the inherent stray
capacitance in the system (unless this capacitance can be measured and taken into
account). Rt must be much larger than the LOCMOS ‘ON’ resistance in series with it,
which typically is hundreds of ohms.
The recommended values for Rt and Ct to comply with previously calculated formulae
without trimming should be:
– Ct 100 pF, up to any practical value
– 10 k Rt 1 M
11.2.4 Power consumption
In the standby mode (monostable or astable), power dissipation is a function of leakage
current in the circuit. For dynamic operation, the power required to charge the external
timing capacitor Ct is shown in the following formulae:
Astable mode:
P = 2 Ct V2 f
f at output pin 13
(8)
P = 4 Ct V2 f
f at output pins 10 and 11
(9)
Monostable mode:
P = ---2---.--9-----C----t---V-----2-------d---u---t--y----c---y---c---l-e----
f at output pins 10 and 11
(10)
T
Because the power dissipation does not depend on Rt, a design for minimum power
dissipation would be a small value of Ct. The value of R would depend on the desired
period (within the limitations discussed previously). Typical power consumption in astable
mode is shown in Figure 12, Figure 13 and Figure 14.
HEF4047B
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 5 — 16 December 2015
© NXP Semiconductors N.V. 2015. All rights reserved.
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