74HC4538 Просмотр технического описания (PDF) - NXP Semiconductors.

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производитель

74HC4538

Dual retriggerable precision monostable multivibrator

NXP Semiconductors. 

NXP Semiconductors

74HC4538; 74HCT4538

Dual retriggerable precision monostable multivibrator

12. Application information

12.1 Power-down considerations

A large capacitor (CEXT) may cause problems when powering-down the monostable due

to energy stored in this capacitor. When a system containing this device is powered-down

or rapid decrease of VCC to zero occurs, the monostable may sustain damage, due to the

capacitor discharging through the input protection diodes. To avoid this possibility, use a

damping diode (DEXT) preferably a germanium or Schottky type diode able to withstand

large current surges and connect as shown in Figure 10

DEXT

GND

CEXT

REXT

VCC

nCEXT

nREXT/CEXT

001aak193

Fig 10. Power-down protection circuit

12.2 Graphs

1.6

normalized

K factor

(K)

1.2

1.0

0.8

0.6

10−10

10−9

1 kΩ

2 kΩ

5.6 kΩ

51 kΩ

1 MΩ

10−8

10−7

10−6

VCC = 4.5 V; Tamb = 25 °C.

Fig 11. Typical pulse width accuracy versus external capacitance

001aak196 1.12

REXT ×

CEXT

(tW)

0.84

0.70

0.56

10−5

0.42

10−4

CEXT (F)

74HC_HCT4538_3

Product data sheet

Rev. 03 — 8 June 2009

© NXP B.V. 2009. All rights reserved.

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