NLVHC4538ADTR2G ON Semiconductor, NLVHC4538ADTR2G Datasheet - Page 10

• Manufacturer Part Number: NLVHC4538ADTR2G
• Manufacturer: ON Semiconductor

Specifications of NLVHC4538ADTR2G

• Logic Family: HC
• High Level Output Current: -5.2mA
• Low Level Output Current: 5.2mA
• Quiescent Current: 130nA
• Number Of Elements: 2
• Operating Temperature Classification: Military
• Operating Supply Voltage (max): 6V
• Operating Supply Voltage (typ): 3.3/5V
• Operating Temperature (min): -55
• Operating Temperature (max): 125C
• Technology: CMOS
• Abs. Propagation Delay Time: 295ns
• Operating Supply Voltage (min): 3V
• Lead Free Status / RoHS Status: Compliant

retriggerable mode. Briefly, the device operates as follows
(refer to Figure 10): In the quiescent state, the external
timing capacitor, C
occurs, the Q output goes high and C
the lower reference voltage (V
then charges, through R
voltage (V
one−shot has timed out and the Q output goes low.
operation refers to both the logic detail (Figure 9) and the
timing diagram (Figure 10).
QUIESCENT STATE
output latch is high and the reset latch is high (#1 in
Figure 10). Thus the Q output (pin 6 or 10) of the monostable
multivibrator is low (#2, Figure 10).
transistors M1, M2, and M3 are turned off. The external
timing capacitor, C
upper and lower reference circuit has a low output (#5).
is low.
LOWER REFERENCE
UPPER REFERENCE
Figure 12 shows the HC4538A configured in the
The following, more detailed description of the circuit
In the quiescent state, before an input trigger appears, the
The output of the trigger−control circuit is low (#3), and
In addition, the output of the trigger−control reset circuit
TRIGGER-CONTROL
TRIGGER INPUT A
TRIGGER INPUT B
CIRCUIT OUTPUT
RESET LATCH
RESET INPUT
(PIN 4 OR 12)
(PIN 2 OR 14)
(PIN 3 OR 13)
(PIN 6 OR 10)
(PIN 5 OR 11)
R
X
Q OUTPUT
ref
/C
CIRCUIT
CIRCUIT
X
Upper [ 2/3 V
INPUT
x
x
V
, is charged to V
, is charged to V
ref
QUIESCENT
LOWER
x
STATE
, back up to the upper reference
3
5
6
1
4
2
12
ref
CC
7
9
Lower [ 1/3 V
10
13
13
11
), at which point the
x
CC
TRIGGER CYCLE
discharges quickly to
14
15
τ
CC
16
(#4), and both the
(A INPUT)
. When a trigger
18
17
19
Figure 12. Timing Diagram
CIRCUIT OPERATION
V
ref
CC
http://onsemi.com
MC74HC4538A
UPPER
). C
8
x
10
TRIGGER CYCLE
τ
TRIGGER OPERATION
at input A (#7) or a falling−edge signal at input B (#8), with
the unused trigger input and the Reset input held at the
voltage levels shown in the Function Table. Either trigger
signal will cause the output of the trigger−control circuit to
go high (#9).
initiates two events. First, the output latch goes low, thus
taking the Q output of the HC4538A to a high state (#10).
Second, transistor M3 is turned on, which allows the
external timing capacitor, C
ground (#11). (Note that the voltage across C
input of both the upper and lower reference circuit
comparator).
reference circuit (#12), the outputs of both reference circuits
will be high (#13). The trigger−control reset circuit goes high,
resetting the trigger−control circuit flip−flop to a low state
(#14). This turns transistor M3 off again, allowing C
to charge back up toward V
(#15). Once the voltage across C
reference voltage, the lower reference circuit will go low
allowing the monostable multivibrator to be retriggered.
(B INPUT)
The HC4538A is triggered by either a rising−edge signal
The trigger−control circuit going high simultaneously
When C
x
discharges to the reference voltage of the lower
21
20
22
RESET
23
CC
x
, with a time constant t = R
, to rapidly discharge toward
x
25
charges to above the lower
t
rr
RETRIGGER
24
τ
+
t
rr
x
appears at the
x
to begin
x
C
x