SGS Thomson Microelectronics M74HC4538 Datasheet

M54HC4538
M74HC4538

DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATOR

.HIGH SPEED

tPD= 25 ns(TYP.) AT VCC=5V

.LOWPOWERDISSIPATION

STANDBYSTATEICC=4µA(MAX.)ATTA=25°C
ACTIVESTATE ICC=200µA (TYP.)ATVCC=5V

.HIGH NOISEIMMUNITY

V

NIH=VNIL

.OUTPUT DRIVE CAPABILITY

10 LSTTL LOADS

=28%VCC(MIN.)

B1R

(PlasticPackage)

(CeramicPackage)

.BALANCEDPROPAGATION DELAYS

t

PLH=tPHL

.WIDE OUTPUT PULSE WIDTHRANGE

t

=120ns ~ 60 sOVER ATVCC=4.5V

WOUT

.OUTPUT PULSE WIDTH INDEPENDENT

FROM TRIGGERINPUT PULSE WIDTH

.PIN ANDFUNCTION COMPATIBLE

WITH 4538B

M1R

(MicroPackage)

ORDER CODES :

M54HC 4538F1R M74H C4538M1R
M74HC 4538B1R M74HC4 538C1R

(Chip Carrier)

F1R

C1R

DESCRIPTION

The M54/74HC4538 is a high speed CMOS DUAL
MONOSTABLEMULTIVIBRATOR fabricatedinsili­con gate C2MOStechnology. It has the same high
speed performance of LSTTL combined with true
CMOS low power consumption. Eachmultivibrator
featuresboth a negative, A, and a positive, B, edge
triggered input, either ofwhichcanbeused asanin­hibit input. Also included is a clear input that when
taken low resets the one shot. The monostable
multivibrators areretriggerable. Thatis,theymay be
triggered reapeatedly while theiroutputsare gener­atinga pulseand thepulse will beextended. Pulse
widthstability overa widerange of temperature and
supply is achieved using linear CMOS techniques.
The output pulse equation is simply :
PW = 0.7 (R)(C) where PW is in seconds, R in
Ohms, andC is in Farads.

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

PIN CONNECTIONS(top view)

NC =
No Internal
Connection

October 1993

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M54/M74HC4538

SYSTEM DIAGRAM

TIMING CHART

2/14

BLOCK DIAGRAM

M54/M74HC4538

Notes : 1. Cx, Rx, Dx areexternal components.

2. Dx isa clamping diode.

3. The external capacitor is chargedto VCCinthe stand-by state, i.e. no trigger.When the supply voltage is turned off Cx is discharged
mainlythrough aninternalparasitic diode(seefigures). IfCxissufficiently largeandVCCdecreases rapidy, therewillbesomepossibility
of damaging theI.C.witha surgecurrentor latch-up. If the voltagesupplyfiltercapacitor is large enough andVCCdecrease slowly,
thesurgecurrent is automatically limitedand damage the I.C.is avoided.Themaximumforward currentof the parasitic diodeis ap­proximately 20mA.In cases whereCx is largethe time takenfor the supply voltage to fallto 0.4VCCcan be calculated as follows :
tf≥ (VCC–0.7) ⋅ Cx/20mA
In cases where tfistooshortan externalchamping diode is requiredto protectthe I.C. from the surgecurrent.

FUNCTIONAL DESCRIPTION

STAND-BY STATE
The external capacitor, Cx, is fully charged to V

CC

inthe stand-bystate.Hence, beforetriggering, tran­sistorQp andQn (connected totheRx/Cxnode)are
bothturnedoff.Thetwo comparatorsthatcontrolthe
timing and the two reference voltage sources stop
operating. The total supply current is therefore only
leakage current.

TRIGGEROPERATION
Triggering occurs when :
1 st)A is ”low” and B has a falling edge ;
2 nd) B is ”high” and A has a risingedge;
After the multivibrator has been retriggered com-

paratorC1 and C2 start operating and Qn isturned
on. Cx then discharges throughQn.The voltage at
the node Rx/Cx external falls.

Whenit reaches V

theoutputof comparator C1

REFL

becomeslow. Thisin turn resets theflip-flop andQn
is turnedoff.

At this point C1 stops functioning but C2 continues
tooperate.ThevoltageatR/Cexternalbeginstorise
witha timeconstant setbytheexternal components
Rx, Cx.

Triggering themultivibratorcausesQtogohigh after
internal delay dueto the flip-flop and thegate. Qre­mains high until the voltage at R/C external rises
againto V

. Atthis pointC2outputgoeslow and

REFH

G goes low. C2 stops operating. That means that
aftertriggering whenthe voltageat R/Cexternal re­turns to V

the multivibrator has returned to its

REFH

MONOSTABLE STATE. Inthe casewhere Rx • Cx
are large enoughand thedischarge time ofthe ca­pacitorand thedelay timeintheI.C. can be ignored,
the width ofthe output pulse tw (out) is as follows:

t

W(OUT)

= 0.72 Cx • Rx

RE-TRIGGEROPERATION
When a second trigger pulse follows the first its ef-

fect will depend on the state of the multivibrator. If
the capacitor Cx is being charged the voltage level
ofRx/Cx externalfalls toV

againandQ remains

REFL

high i.e.the retrigger pulse arrivesin a time shorter
than the period Rx • Cx seconds, the capacitor
charging time constant. If the second trigger pulse
is veryclosetothe initialtrigger pulse itis ineffective
; i.e.,the second trigger must arrive inthe capacitor
discharge cycle to be ineffective.

Hence the minimum time fora secondtrigger to be
effective,trr (Min.) depends on VCCand Cx.

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M54/M74HC4538

FUNCTIONAL DESCRIPTION (continued)

RESETOPERATION
CD isnormally high. If CD is low, the trigger is not
effective because Q output goes low and trigger
controlflip-flop is reset.

Also transistor Op is turned on and Cx is charged
quickyto VCC. Thismeans if CDinput goes low,the
IC becomeswaitingstateboth in operating andnon
operating state.

TRUTH TABLE

INPUTS OUTPUTS

ABCDQQ

H H OUTPUT ENABLE
X L H L H INHIBIT
H X H L H INHIBIT

L H OUTPUT ENABLE

X X L L H INHIBIT

INPUT AND OUTPUT EQUIVALENT CIRCUIT

NOTE

PIN DESC RIPTION

PIN No SYMBOL NAME AND FUNCTION

1, 15 1T1, 2T1 External Capacitor

Connections

2, 14 1T2, 2T2 External Resistor/Capacitor

Connections

3, 13 1CD, 2CD Direct Reset Inputs (Active

LOW)

4, 12 1A, 2A Trigger Inputs (LOW to

HIGH, Edge-Triggered)

5, 11 1B, 2B Trigger Inputs (HIGH to

LOW, Edge-Triggered)

6, 10 Q1, Q2 Pulse Outputs

7, 9 Q1, Q2 Complementary Pulse Outputs

8 GND Ground (0V)

16 V

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CC

Positive Supply Voltage

IEC LOGIC SYMBOL

M54/M74HC4538

ABSOLU TE M AXIMU M R AT INGS

Symbol Parameter Value Unit

V

CC

V

V

O

I

IK

I

OK

I

O

I

or I

CC

P

D

T

stg

T

AbsoluteMaximumRatingsarethose values beyondwhichdamage tothedevice mayoccur. Functionaloperationunder these conditionisnotimplied.
(*)500 mW: ≅ 65oC derateto 300 mWby 10mW/oC: 65oCto85oC

RECO MM ENDED OPERAT I N G CO NDI TIONS

Symbol Parameter Value Unit

V

CC

V

I

V

O

T

op

t

r,tf

C

X

R

X

(*)The maximumallowable values ofCx andRx area function of leakage of capacitor Cx, the leakageof deviceand leakagedue to the board
layoutand surface resistance. Susceptibility to externallyinduced noise may occur forRx > 1MΩ

Supply Voltage -0.5 to +7 V
DC Input Voltage -0.5 to VCC+ 0.5 V

I

DC Output Voltage -0.5 to VCC+ 0.5 V
DC Input Diode Current ± 20 mA
DC Output Diode Current ± 20 mA
DC Output Source Sink Current Per Output Pin ± 25 mA
DC VCCor Ground Current ± 50 mA

GND

Power Dissipation 500 (*) mW
Storage Temperature -65 to +150
Lead Temperature (10sec) 300

L

Supply Voltage 2 to 6 V
Input Voltage 0 to V
Output Voltage 0 to V
Operating Temperature: M54HC Series

M74HC Series

CC
CC

-55 to +125

-40 to +85

Input Rise and Fall Time (CLR only) VCC= 2 V 0 to 1000

V

= 4.5 V 0 to 500

CC

V

= 6 V 0 to 400

CC

External Capacitor NO LIMITATION (*)
External Resistor VCC≤ 3 V 5K to 1M (*)

V

>3V 1Kto1M(*)

CC

o
o

o
o

ns

C
C

V
V

C
C

Ω

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