HCF4538BEY datasheet(2/10 Pages) STMICROELECTRONICS

2 / 10 page

HCF4538B

2/10

from either edge of an input pulse. An unused +TR

input should be tied to VSS. An unused -TR input

should be tied to VDD . A RESET (on low level) is

provided for immediate termination of the output

pulse or to prevent output pulses when power is

turned on. An unused RESET input should be tied

to VDD . However, if an entire section of the

HCF4538B is not used, its inputs must be tied to

either VDD or VSS (see table 1). In normal

operation the circuit triggers (extends the output

pulse one period) on the application of each new

trigger pulse. For operation in the non-retiggerable

mode, Q is connected to -TR when leading edge

triggering (+TR) is used or Q is connected to +TR

when trailing edge triggering (-TR) is used. The

time period (T) for this multivibrator can be

calculated by : T = RX CX. The min. value of

external resistance, RX, is 4KΩ. The max. and

min. values of external capacitance, CX, are 100

µF and 5nF, respectively.

IINPUT EQUIVALENT CIRCUIT

PIN DESCRIPTION

Terminals 1, 8, 15 are electrically connected internally

FUNCTIONAL DIAGRAM

PIN No

SYMBOL

NAME AND FUNCTION

4, 12

+TR

Trigger Inputs (Low to

High, Edge-Triggered)

5, 11

-TR

Trigger Inputs (High to

Low, Edge-Triggered)

3, 13

RESET

Direct Reset Inputs

(Active Low)

1, 15

CX1, CX2

External Capacitor Con-

nections

2, 14

RXCX1

RXCX2

External Resistor/Capaci-

tor Connections

6, 10

Q1, Q2

Pulse Outputs

7, 9

Q1, Q2

Complementary Pulse

Outputs

VSS

Negative Supply Voltage

VDD

Positive Supply Voltage

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