74HC147 datasheet(17/23 Pages) PHILIPS

17 / 23 page

2003 Oct 30

Philips Semiconductors

Product speciﬁcation

Hex inverting Schmitt trigger

74HC14; 74HCT14

APPLICATION INFORMATION

The slow input rise and fall times cause additional power

dissipation. This can be calculated using the following

formula:

Pad =fi × (tr × ICC(AV) +tf × ICC(AV)) × VCC.

Where:

Pad = additional power dissipation (µW);

fi = input frequency (MHz);

tr = input rise time (µs); 10% to 90%;

tf = input fall time (µs); 10% to 90%;

ICC(AV) = average additional supply current (µA).

ICC(AV) differs with positive or negative input transitions, as

shown in Figs 16 and 17.

For 74HC/HCT14 used in a relaxation oscillator circuit,

see Fig.18.

Note to application information

All values given are typical unless otherwise specified.

handbook, halfpage

400

300

100

200

MNA852

ICC(AV)

(

µA)

VCC (V)

positive - going

edge

negative - going

edge

negative - going

Fig.16 Average ICC for 74HC14 Schmitt trigger

devices.

Linear change of VI between 0.1VCC to 0.9VCC

handbook, halfpage

400

300

100

200

MNA853

VCC (V)

positive - going

egde

positive - going

edge

negative - going

egde

negative - going

edge

ICC(AV)

(

µA)

Fig.17 Average ICC for HCT Schmitt trigger

devices.

Linear change of VI between 0.1VCC to 0.9VCC.

handbook, halfpage

MNA854

Fig.18 Relaxation oscillator using 74HC/HCT14.

74HC14 : f

---

0.8 RC

-------------------

≈

74HCT14 : f

---

0.67 RC

----------------------

≈

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