MPC508A, MPC509A

11

SBFS019A

www.ti.com

Direct

Multiplexer

Output

Buffered

OPA602

1/4 OPA404

MPC508A

Out

Out

In 1

In 2

In 3

In 8

A

2

8

A

MPC508A

8

2

6-Bit Channel

Address Generator

A

In 1

In 2

In 3

In 8

In 1

In 8

MPC508A

En

En

Out

En

+V

+V

+V

4LSBs

4MSBs

Settling Time to

±0.01% is 20µs

with R

INSTALLATION AND

OPERATING INSTRUCTIONS

The ENABLE input, pin 2, is included for expansion of the

number of channels on a single node as illustrated in Figure

5. With ENABLE line at a logic 1, the channel is selected by

the 2-bit (MPC509A) or 3-bit (MPC508A) Channel Select

Address (shown in the Truth Tables). If ENABLE is at logic

0, all channels are turned OFF, even if the Channel Address

Lines are active. If the ENABLE line is not to be used, simply

If the +15V and/or –15V supply voltage is absent or shorted

to ground, the MPC509A and MPC508A multiplexers will

not be damaged; however, some signal feedthrough to the

output will occur. Total package power dissipation must not

be exceeded.

For best settling speed, the input wiring and interconnections

between multiplexer output and driven devices should be

kept as short as possible. When driving the digital inputs

from TTL, open collector output with pull-up resistors are

recommended

To preserve common-mode rejection of the MPC509A, use

twisted-shielded pair wire for signal lines and inter-tier

connections and/or multiplexer output lines. This will help

common-mode capacitance balance and reduce stray signal

pickup. If shields are used, all shields should be connected as

close as possible to system analog common or to the com-

mon-mode guard driver.

CHANNEL EXPANSION

Single-Ended Multiplexer (MPC508A)

Up to 32 channels (four multiplexers) can be connected to a

single node, or up to 64 channels using nine MPC508A

multiplexers on a two-tiered structure as shown in Figures 5

and 6.

FIGURE 5. 32-Channel, Single-Tier Expansion.

FIGURE 6. Channel Expansion Up to 64 Channels Using

8 x 8 Two-Tiered Expansion.

Differential Multiplexer (MPC509A)

Single or multitiered configurations can be used to expand

multiplexer channel capacity up to 32 channels using a

32 x 1 or 16 channels using a 4 x 4 configuration.

Single-Node Expansion

The 32 x 1 configuration is simply eight (MPC509A) units

tied to a single node. Programming is accomplished with a

5-bit counter, using the 2LSBs of the counter to control

counter to drive a 1-of-8 decoder. The 1-of-8 decoder then is

used to drive the ENABLE inputs (pin 2) of the MPC509A

multiplexers.

Two-Tier Expansion

Using a 4 x 4 two-tier structure for expansion to 16 channels,

the programming is simplified. A 4-bit counter output does

not require a 1-of-8 decoder. The 2LSBs of the counter drive

the second-tier multiplexer.

Single vs Multitiered Channel Expansion

In addition to reducing programming complexity, two-tier

configuration offers the added advantages over single-node

expansion of reduced OFF channel current leakage (reduced

OFFSET), better CMR, and a more reliable configuration if

a channel should fail in the ON condition (short). Should a

channel fail ON in the single-node configuration, data cannot

be taken from any channel, whereas only one channel group

is failed (4 or 8) in the multitiered configuration.

MPC

508A

Out

Group 1

Group 4

Out

Enable

Enable

Settling Time to 0.01% for R

—Two MPC508A units in parallels: 10µs

—Four MPC509 A units in parallels: 12µs

Direct

Multiplexer

Output

Buffered

OPA602

1/4 OPA404

5-Bit

Binary

Counter

To

Group

2

To

Group

3

In 1

In 2

In 3

In 8

A

2

8

A

MPC

508A

Group 1

Ch1-8

2

8

In 1

In 2

In 3

In 8

Group 4

Ch25-42