Description
SN74LS390 Dual 4-bit
Decade Counter IC
The SN74LS390 is a monolithic integrated circuit from the Texas Instruments LS (Low-Power Schottky) family, designed as a dual, independent 4-bit decade counter. This single package effectively contains two separate counter units, each built with internal master-slave flip-flops and additional gating logic. Its primary function is to count electronic pulses, and it is specifically configured to count in decades, meaning each counter cycles through ten distinct states (0-9) before resetting. This dual configuration is a key design aspect, aimed at significantly increasing system density by reducing the number of individual IC packages required for counting tasks.
Each of the two internal counters within the
SN74LS390
is not a single 4-bit counter but is itself composed of two smaller counters: a divide-by-2 section and a divide-by-5 section. These sub-counters have individual clock inputs (1CKA and 1CKB for the first counter, for example), providing flexibility in how the counting sequence is configured. The outputs of these sections can be interconnected in various ways, allowing each counter to implement different division ratios, including a full divide-by-10 sequence or a bi-quinary count (2 and 5) to produce a symmetrical square wave at the final output.
The device includes a direct clear (reset) input for each 4-bit counter, allowing for the immediate and asynchronous reset of the count to zero, independent of the clock signal. All outputs are buffered, which enhances output drive capability and reduces the possibility of noise issues during signal transitions. Characterized for operation from 0°C to 70°C, it is intended for use in commercial and industrial electronic systems where reliable, medium-speed counting and frequency division are required.
Features:
Contains two fully independent 2-bit and 5-bit counters in one package.
Can be used as a divide-by-2, divide-by-5, or divide-by-10 counter.
Individual clock inputs for the divide-by-2 and divide-by-5 sections.
Direct reset for each 4-bit decade counter.
Buffered outputs for improved noise immunity.
Typical maximum clock frequency of 35 MHz.
Packaged in a 16-pin format.
Specifications:
Parameter
Condition
Min
Typ
Max
Unit
Maximum Clock Frequency:
25
35
MHz
Propagation Delay:
Clock A to QA
12
20
ns
Clock B to QB
13
21
ns
Clock B to QC
24
39
ns
Clock B to QD
26
39
ns
Power Supply Voltage:
4.75
5
5.25
V
Operating Temperature Range:
0
70
°C
Pinout Diagram:
Footprint Diagram:
Applications:
Frequency Division.
Digital Counters.
Timing Circuits.
Control Systems.
Arithmetic Circuits.
Package Contents:
1x
SN74LS390 Dual 4-bit Decade Counter IC
Datasheet
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