MC14490 Datasheet, PDF (5/9 Pages) ON Semiconductor – Hex Contact Bounce Eliminator

+VDD
PULLUP RESISTOR
1 ^Ain
“FORM A”
CONTACT
(INTERNAL)
OSCin 7
OSCILLATOR
AND
φ1
Cext ₉
TWO–PHASE
OSCout
CLOCK GENERATOR
φ2
DATA
4–BIT STATIC SHIFT REGISTER
SHIFT LOAD
φ1 φ2
1/2 BIT
DELAY
φ1 φ2
Figure 4. Typical “Form A” Contact Debounce Circuit
(Only One Debouncer Shown)
15
Aout
OPERATING CHARACTERISTICS
The single most important characteristic of the MC14490
is that it works with a single signal lead as an input, making
it directly compatible with mechanical contacts (Form A
and B).
The circuit has a built–in pullup resistor on each input. The
worst case value of the pullup resistor (determined from the
Electrical Characteristics table) is used to calculate the con-
tact wetting current. If more contact current is required, an
external resistor may be connected between VDD and the
input.
Because of the built–in pullup resistors, the inputs cannot
be driven with a single standard CMOS gate when VDD is be-
low 5 V. At this voltage, the input should be driven with paral-
leled standard gates or by the MC14049 or MC14050
buffers.
The clock input circuit (pin 7) has Schmitt trigger shaping
such that proper clocking will occur even with very slow clock
edges, eliminating any need for clock preshaping. In addi-
tion, other MC14490 oscillator inputs can be driven from a
single oscillator output buffered by an MC14050 (see Fig-
ure 5). Up to six MC14490s may be driven by a single buffer.
The MC14490 is TTL compatible on both the inputs and
the outputs. When VDD is at 4.5 V, the buffered outputs can
sink 1.6 mA at 0.4 V. The inputs can be driven with TTL as a
result of the internal input pullup resistors.
Cext
1/6 MC14050
OSCin 7 9 OSCout
OSCin 7
NO CONNECTION
9 OSCout
FROM
CONTACTS
MC14490
TO SYSTEM
LOGIC
FROM CONTACTS
MC14490
TO SYSTEM
LOGIC
OSCin 7
NO CONNECTION
9 OSCout
FROM CONTACTS
MC14490
TO SYSTEM
LOGIC
Figure 5. Typical Single Oscillator Debounce System
MOTOROLA CMOS LOGIC DATA
MC14490
301