CD54HC4051_15 Datasheet, PDF (23/45 Pages) Texas Instruments – High-Speed CMOS Logic Analog Multiplexers and Demultiplexers

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CD54HC4051, CD74HC4051
CD54HCT4051, CD74HCT4051, CD54HC4052, CD74HC4052, CD54HCT4052
CD74HCT4052, CD54HC4053, CD74HC4053, CD54HCT4053, CD74HCT4053
SCHS122K – NOVEMBER 1997 – REVISED SEPTEMBER 2015
9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The CDx4HCx405x line of multiplexers and demultiplexers can be used for a wide variety of applications.
9.2 Typical Application
One application of the CD74HC4051 device is use in conjunction with a microcontroller to poll a keypad.
Figure 20 shows the basic schematic for such a polling system. The microcontroller uses the channel-select pins
to cycle through the different channels while reading the input to see if a user is pressing any of the keys. This is
a very robust setup that allows for simultaneous key presses with very little power consumption. It also uses very
few pins on the microcontroller. The down side of polling is that the microcontroller must frequently scan the keys
for a press.
Microcontroller
Polling Input
Channel Select
3.3V
E
COM
V_CC
V_EE
GND
S₂ S₁ S₀
CD74HC4051
S₂S₁S₀
000
001
010
011
Ch 0
Ch 1
Ch 2
Ch 3
1 0 0 _{Ch 4}
101
Ch 5
110
1 1 1 ^{Ch 6}
Ch 7
k₀
k₁
k₂
k₃
k₄
k₅
k₆
k₇
Pull-down resistors (10NŸ)
Figure 20. CD74HC4051 Being Used to Help Read Button Presses on a Keypad
9.2.1 Design Requirements
These devices use CMOS technology and have balanced output drive. Take care to avoid bus contention
because it can drive currents that would exceed maximum limits. The high drive will also create fast edges into
light loads, so routing and load conditions must be considered to prevent ringing.
Copyright © 1997–2015, Texas Instruments Incorporated
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