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Is it OK to connect a capacitor to an output?

If a large capacitor is connected to a CMOS device, large charge and discharge currents flow for a long time, which could result in a malfunction or device damage. Additionally, because the output is short-circuited for a long time, internal wires could melt. If the power-off time is short, current could also flow through an output parasitic diode. Therefore, a large capacitive load should not be driven directly.

It is recommended to keep the capacitive load on an output pin below 500 pF. If it is exceeded, insert a resistor to limit the charge and discharge currents as shown in Figure 1.

[Figure 1: Connecting a large capacitor to an output]


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 Figure 2.

 

[Figure 2: Connecting a large capacitor to an input of the
TCTC4000 and TC74HC/AC series]

For a capacitor connect to an output, please refer to “PDFダウンロードPrecaution when Designing Circuits: Logic ICs”.

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