Are there any regulations for the capacitance of the capacitor attached to the output terminal of a general-purpose logic IC?

It is recommended to keep the capacitor connected to the output terminal below 500 pF.

Fig. 1 Connecting a large capacitor to an output
Fig. 1 Connecting a large capacitor to an output

If a large capacitor (capacitive load) is connected to the general-purpose logic IC, there is a possibility of malfunction due to the charge/discharge current that flows when the output mode transitions (H⇒L, L⇒H). It is recommended to keep the capacitor connected to the output pin to 500 pF or less, as there is a possibility that a current exceeding the specified value may flow through the output parasitic diode due to discharge. For loads higher than that, limit the discharge current via resistors as shown in Fig. 1 Please note that in this case, a delay occurs in the output signal.

Fig. 2 Connecting a large capacitor to an input (TC4000 and TC74HC/AC series)
Fig. 2 Connecting a large capacitor to an input (TC4000 and TC74HC/AC series)

Devices without an input-tolerant function such as the TC4000 and TC74HC/AC series should not also drive a large capacitive load because current could flow through the input protection diode if the power-off time is short.
It is recommended to keep the load capacitance connected to an input pin below 500 pF. If it is exceeded, insert a resistor as shown in Fig. 2 Note that there will also be a delay in the input signal in this case.

Related Links

The following documents also contain related information.

Product Lists

FAQs

Application Notes

Product page General Purpose Logic ICs
Products
e-Learning Basics of CMOS Logic ICs
e-Learning
e-Learning Usage Considerations of CMOS Logic ICs
e-Learning

Back to FAQs of General-Purpose Logic ICs

A new window will open