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AN501

The DG535/536 Wideband Multiplexers Suit a Wide Variety of Applications

Vishay Semiconductors 

AN501

Vishay Siliconix

Logic Input Switching Threshold

vs. Supply Voltage (V+)

13

GND = 0 V

11

TA = 25_C

9

7

5

3

8

10

12

14

16

18

V+ – Positive Supply Voltage (V)

FIGURE 9. Logic Input Switching Threshold

vs. Supply Voltage

V+

+5 V

TTL 4-Bit

Binary Address

Bus

VCC VDD

MC14504

V+

DG535/536

ST

EN

A3

A2

A1

A0

V–

FIGURE 10. Using the MC14504 for Address Logic

Level Shifting

In applications involving reduced supply voltages and offset

conditions, the input switching threshold (VT) may be reduced

below the CMOS logic “0”. This may cause the address inputs

to appear permanently as logic “1” regardless of the control

logic states. Therefore, control logic level shifting may be

needed.

TTL to CMOS level shifting can be easily accomplished using

inexpensive CMOS level shifters such as the MC14504 or

CD40109.

Crosspoint Switching

Many analog and digital systems, such as a central router used

in a video studio console (Figure 8), require crosspoint

switching functions. In this application, many channels route

signals to many different outputs. Due to its small outline PLCC

package and low power consumption, the DG536 leads itself

easily to multi-channel crosspoint functions.

Figure 11 illustrates how the DIS (disable) pin can be used to

indicate which output is selected. When logic 1 is applied to

output select, device 1 is enabled and device 2 is disabled.

With device 1 enabled, the DIS pin is connected to signal

ground, thus turning LED 1 on. With device 2 disabled (due to

CS being 1), its DIS pin represents a high impedance to ground

and LED 2 is off.

Any one of sixteen inputs can be connected to either output. This

is achieved by applying the appropriate CMOS logic address to

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the address inputs (A0 to A3) and applying the appropriate logic

level to output select simultaneously.

The circuit in Figure 11 also illustrates how the chip select

inputs can be used. As shown in Figure 12, a 32-channel

single-ended multiplexer can be configured without external

chip select circuits. This circuit makes use of the CS and CS

inputs which allow device selection from a single control line.

The basic circuit shown in Figure 11 can be extended and

elaborated to give a 16 x 16 matrix for video crosspoint

applications such as central routers used in video studios. This

circuit, shown in Figure 13, allows source (or video input) to be

connected to any video output (or any number of outputs). The

strobe input (ST) on each device is used to latch the

appropriate address into that particular device. By strobing the

required address into each device sequentially, any crosspoint

connection can be made.

The DG535/536 makes an excellent digital switch due to its

low channel-to-channel crosstalk, high off-isolation, and wide

bandwidth specifications. In digital data transmission systems,

the DG535/536 can easily handle data rates in excess of

100 Mb/s.

The circuit shown in Figure 13 can be used as a digital

cross-point to replace expensive, power consuming ECL

crosspoint ICs. Besides handling raw digital data, the

DG535/536 can also be used for other forms of data

transmission, such as FSK and PCM systems.

Document Number: 70608

03-Aug-99

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