ST M74HC221 User Manual

M74HC221

DUAL MONOSTABLE MULTIVIBRATOR

■HIGH SPEED :

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

■LOW POWER DISSIPATION:

STAND BY STATE : ICC=4μA (MAX.) at TA=25°C ACTIVE STATE :

ICC=700μA (MAX.) at VCC = 5V

■HIGH NOISE IMMUNITY: VNIH = VNIL = 28 % VCC (MIN.)

■SYMMETRICAL OUTPUT IMPEDANCE: |IOH| = IOL = 4mA (MIN)

■BALANCED PROPAGATION DELAYS: tPLH tPHL

■WIDE OPERATING VOLTAGE RANGE: VCC (OPR) = 2V to 6V

■WIDE OUTPUT PULSE WIDTH RANGE : tWOUT = 150 ns ~ 60 s OVER AT VCC = 4.5 V

■PIN AND FUNCTION COMPATIBLE WITH 74 SERIES 221

DESCRIPTION

The M74HC221 is an high speed CMOS MONOSTABLE MULTIVIBRATOR fabricated with silicon gate C2MOS technology.

There are two trigger inputs, A 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

PIN CONNECTION AND IEC LOGIC SYMBOLS

DIP		SOP	TSSOP
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 MONOSTABLE period it makes the MONOSTABLE period longer.

Limit for values of Cx and Rx : Cx : NO LIMIT

Rx : Vcc < 3.0V 5KΩ to 1MΩ Vcc > 3.0V 1KΩ to 1MΩ

K 0.7

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

July 2001

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M74HC221

INPUT AND OUTPUT EQUIVALENT CIRCUIT				PIN DESCRIPTION
				PIN No	SYMBOL	NAME AND FUNCTION
				1,9	1A, 2A	Trigger Inputs (Negative
						Edge Triggered)
				2, 10	1B, 2B	Trigger Inputs (Positive
						Edge Triggered)
					1 CLR	Direct Reset LOW and
				3, 11		trigger Action at Positive
					2 CLR
						Edge
				4, 12	1Q, 2Q	Outputs (Active Low)
				7	2RX/CX	External Resistor
						Capacitor Connection
				13, 5	1Q, 2Q	Outputs (Active High)
				14, 6	1CX	External Capacitor
					2CX	Connection
				15	1RX/CX	External Resistor
						Capacitor Connection
				8	GND	Ground (0V)
				16	Vcc	Positive Supply Voltage
TRUTH TABLE
	INPUTS		OUTPUTS			NOTE
A	B	CLR	Q	Q
	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

(*) : Except for monostable period

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M74HC221

SYSTEM DIAGRAM

This logic diagram has not be used to estimate propagation delays

TIMING CHART

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M74HC221

BLOCK DIAGRAM

(1)Cx, Rx, Dx are external components.

(2)Dx is a clamping diode.

The external capacitor is charged to Vcc in the stand-by-state, i.e. no trigger. When the supply voltage is turned off Cx is di scharged 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 voltage supply filter capacitor is large enough and Vcc decrease slowly, the surge current 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 :

tf > (Vcc - 0.7) x Cx/20mA

In cases where tf is too short an external clamping diode is required to protect the I.C. from the surge current.

FUNCTIONAL DESCRIPTION

STAND-BY STATE

The external capacitor,Cx, is fully charged to 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 total 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 Qn is turned on. Cx then discharges through Qn. The voltage at the node R/C external falls.

When it reaches VREFL the output of comparator 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 components 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 VREFH . At this point C2 output goes low and O goes low. C2 stop

operating. That means that after triggering when

the voltage R/C external returns to VREFH 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, the 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 flip-flop is reset.

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.

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			M74HC221
ABSOLUTE MAXIMUM RATINGS
Symbol	Parameter	Value		Unit
VCC	Supply Voltage	-0.5 to +7		V
VI	DC Input Voltage	-0.5 to VCC + 0.5		V
VO	DC Output Voltage	-0.5 to VCC + 0.5		V
IIK	DC Input Diode Current	± 20		mA
IOK	DC Output Diode Current	± 20		mA
IO	DC Output Current	± 25		mA
ICC or IGND	DC VCC or Ground Current	± 50		mA
PD	Power Dissipation	500(*)		mW
Tstg	Storage Temperature	-65 to +150		°C
TL	Lead Temperature (10 sec)	300		°C

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

RECOMMENDED OPERATING CONDITIONS

Symbol		Parameter					Value	Unit
VCC	Supply Voltage						2 to 6	V
VI	Input Voltage						0 to VCC	V
VO	Output Voltage						0 to VCC	V
Top	Operating Temperature						-55 to 125	°C
	Input Rise and Fall Time	(CLR	and	A	only)	VCC = 2.0V	0 to 1000	ns
tr, tf						VCC = 4.5V	0 to 500	ns
						VCC = 6.0V	0 to 400	ns
Cx	External Capacitor						> 100 (*)	pF
Rx	External Resistor					Vcc < 3V	5K to 1M (*)	Ω
						Vcc > 3V	1K to 1M (*)

(*) 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

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