ST M74HC221 User Manual

M74HC221

DUAL MONOSTABLE MULTIVIBRATOR

■ HIGH SPEED :

t

= 24 ns (TYP.) at VCC = 6V

PD

■ LOW POWER DISSIPATION:

STAND BY STATE :
I

=4µA (MAX.) at TA=25°C

CC

ACTIVE STATE :
I

=700µA (MAX.) at V

CC

■ HIGH NOISE IMMUNITY:

V

= V

NIH

■ SYMMETRICAL OUTPUT IMPEDANCE:

|I

| = IOL = 4mA (MIN)

OH

■ BALANCED PROPAGATION DELAYS:

t

≅ t

PLH

■ WIDE OPERATING VOLTAGE RANGE:

V

(OPR) = 2V to 6V

CC

■ WIDE OUTPUT PULSE WIDTH RANGE :

t

WOUT

■ PIN AND FUNCTION COMPATIBLE WITH

= 28 % VCC (MIN.)

NIL

PHL

= 150 ns ~ 60 s OVER AT V

CC

= 5V

CC

= 4.5 V

74 SERIES 221

DESCRIPTION

The M74HC221 is an high speed CMOS
MONOSTABLE MULTIVIBRATOR fabricated with
silicon gate C
There are two trigger inputs, A

2

MOS technology.

INPUT (negative
edge) and B INPUT (positive edge).
Triggering on the B input occurs at a particular
voltage threshold and is not related to rise and fall
time of the applied pulse. The device may also be
trigger by using the CLR

input (positive edge)

because of the Schimtt-trigger input; after

TSSOPDIP SOP

ORDER CODES

PACKAGE TUBE T & R

DIP M74HC221B1R

SOP M74HC221M1R M74HC221RM13TR

TSSOP M74HC221TTR

triggering the output maintains the
MONOSTABLE STATE for the time period
determined by the external resistor Rx and
capacitor Cx. Taking CLR

low breaks this
MONOSTABLE STATE. If the next trigger pulse
occurs during the MONOSTABL E period it makes
the MONOSTABLE period longer.
Limit for values of Cx and Rx :
Cx : NO LIMIT
Rx : V
V
K

< 3.0V 5KΩ to 1MΩ

cc

> 3.0V 1KΩ to 1MΩ

cc

≅ 0.7

All inputs are equipped with protection circuits
against static discharge and transient excess
voltage.

PIN CONNECTION AND IEC LOGIC SYMBOLS

1/14July 2001

M74HC221

INPUT AND OUTPUT EQUIVALENT CIRCUIT PIN DESCRIPTION

PIN No SYMBOL NAME AND FUNCTION

1,9 1A

2, 10 1B, 2B

3, 11

4, 12 1Q

7

13, 5 1Q, 2Q Outputs (Active High)
14, 6

15

8 GND Ground (0V)

16 Vcc Positive Supply Voltage

TRUTH TABLE

, 2A

1 CLR
2 CLR

, 2Q Outputs (Active Low)

2R

X/CX

1C

X

2C

X

1R

X/CX

Trigger Inputs (Negative
Edge Triggered)

Trigger Inputs (Positive
Edge Triggered)

Direct Reset LOW and
trigger Action at Positive
Edge

External Resistor
Capacitor Connection

External Capacitor
Connection

External Resistor
Capacitor Connection

INPUTS OUTPUTS

A

BCLRQQ

H H OUTPUT ENABLE

X L H L(*) H(*) INHIBIT
H X H L(*) H(*) INHIBIT

L H OUTPUT ENABLE
L H OUTPUT ENABLE

X X L L H INHIBIT

X : Don’t Care
(*) : Exce pt for monostable period

NOTE

2/14

SYSTEM DIAGRAM

M74HC221

This log i c diagram has not be used to estim at e propagation delays

TIMING CHART

3/14

M74HC221

BLOCK DIAGRAM

(1) Cx, Rx , Dx are extern al components.
(2) Dx is a clamping diode.
The external capacitor is charged to Vcc in the stand-by-stat e, i.e. no trigger. When the supply vol tage is turned off Cx is discharged mainly
trough an internal parasitic diode(see figures). If Cx is sufficiently large and Vcc decreases rapidly, there will be some possibility of damaging
the I.C. with a surge current or latch-up. If the volta ge supply filter capacitor is la rge enough and Vcc decrease s l owly, the surge cu rr ent is
automatically limited and damage to the I.C. is avoided. The maximum forward current of the parasitic diode is approximately 20 mA. In cases
where Cx is large the time taken for the supply voltage to fall to 0.4 Vcc can be calculated as follows :
t

> (Vcc - 0.7) x Cx/20mA

f

In cases where t

is too short an ext ernal clamping diode is required to prot ect the I.C. from t he surge current.

f

FUNCTIONAL DESCRIPTION

STAND-BY STATE
The external capacit or,Cx, is f ully charged t o Vcc
in the stand-by state. Hence, before triggering,
transistor Qp and Qn (connected to the Rx/Cx
node) are both turned-off. The two comparators
that control the timing and the two reference
voltage sources stop operating. The t otal supply
current is therefore only leakage current.
TRIGGER OPERATION
Triggering occurs when :
1 st) A is "LOW" and B has a falling edge;
2 nd) B is "HIGH" and A has a rising edge;
3 rd) A is "LOW" and B is HIGH and C1 has a
rising edge;
After the multivibrator has been retriggered
comparator C1 and C2 start operating and Q n is
turned on. Cx then discharges through Qn. The
voltage at the node R/C external falls.
When it reaches V

the output of comparat or

REFL

C1 becomes low. This in turn reset the flip-flop
and Qn is turned off.
At this point C1 stops functioning but C2 continues
to operate.

The voltage at R/C external begins to rise with a
time constant set by the external com ponents Rx,
Cx.
Triggering the multivibrator causes Q to go high
after internal delay due to the flip-flop and the
gate. Q remains high until the voltage at R/C
external rises again to V

. At this point C2

REFH

output goes low and O goes low. C2 stop
operating. That means that a fter triggering when
the voltage R/C external returns to V

REFH

the
multivibrator has returned to its MONOSTABLE
STATE. In the case where Rx · Cx are large

enough and the discharge time of the capacitor
and the delay time in the I.C. can be ignored, t he
width of the output pulse tw (out) is as follows :

tW(OUT) = 0.70 Cx · Rx
RESET OPERATION
CL is normally high. If CL is low, the trigger is not
effective because Q output goes low and trigger
control f lip -f lo p is res et .
Also transistor Op is turned on and Cx is charged
quickly to Vcc. This means if CL input goes low the
IC becomes waiting state both in operating and
non operating state.

4/14

M74HC221

ABSOLUTE MAXIMUM RATINGS

Symbol Parameter Value Unit

V

V

V

I

I

OK

I

I

or I

CC

P

T

T

Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these conditions is
not implied
(*) 500mW at 65

RECOMMENDED OPERATING CONDITIONS

Symbol Parameter Value Unit

V

V

V

T

t

r

Cx External Capacitor > 100 (*) pF
Rx

(*) The Maximum allowable values of Cx and Rx are a function of leakage of capacitor Cx, the leakage of device and leakage due to the board
layout and surface resistance. Susceptibility to externally induced noise may occur for Rx > 1MΩ

Supply Voltage

CC

DC Input Voltage -0.5 to VCC + 0.5

I

DC Output Voltage -0.5 to VCC + 0.5

O

DC Input Diode Current

IK

DC Output Diode Current
DC Output Current

O

DC VCC or Ground Current

GND

Power Dissipation

D

Storage Temperature

stg

Lead Temperature (10 sec)

L

°C; derate to 300mW by 10 m W/°C from 65 °C to 85°C

Supply Voltage

CC

Input Voltage 0 to V

I

Output Voltage 0 to V

O

Operating Temperature

op

Input Rise and Fall Time (CLR and A only) VCC = 2.0V

, t

f

V
V

CC
CC

= 4.5V
= 6.0V

External Resistor Vcc < 3V 5K to 1M (*)

Vcc > 3V 1K to 1M (*)

-0.5 to +7 V

± 20 mA
± 20 mA
± 25 mA
± 50 mA

500(*) mW

-65 to +150 °C

300 °C

2 to 6 V

CC
CC

-55 to 125 °C
0 to 1000 ns

0 to 500 ns
0 to 400 ns

Ω

V
V

V
V

5/14