CD4051B_15 Datasheet, PDF (19/38 Pages) Texas Instruments – CMOS Single 8-Channel Analog Multiplexer/Demultiplexer

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9 Application and Implementation
CD4051B, CD4052B, CD4053B
SCHS047H – AUGUST 1998 – REVISED APRIL 2015
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 CD405xB multiplexers and demuliplexers can be used for a wide variety of applications.
9.2 Typical Application
One application of the CD4051B is to use it in conjunction with a microcontroller to poll a keypad. Figure 28
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, allowing for multiple simultaneous key-presses with very little power consumption. It also utilizes
very few pins on the microcontroller. The down side of polling is that the microcontroller must continually scan
the keys for a press and can do little else during this process.
Input
Microcontroller
Channel Select
INH
3.3 V
COM
V_DD
V_EE
V_SS
CBA
CD4051B
CBA
000
001
010
011
Ch 0
Ch 1
Ch 2
Ch 3
100
101
110
111
Ch 4
Ch 5
Ch 6
Ch 7
3.3 V
k₀
k₁
k₂
k₃
k₄
k₅
k₆
k₇
Pull-down resistors (10NŸ)
Figure 28. The CD4051B 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 should be considered to prevent ringing.
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