Datasheet

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
0
A
1
A
2
2
8
A
0
A
1
A
2
MPC508A
8
2
6-Bit Channel
Address Generator
A
0
A
1
A
2
In 1
In 2
In 3
In 8
In 1
In 8
MPC508A
En
En
Out
En
+V
+V
+V
4LSBs 4MSBs
8 Analog Inputs (CH57 to 64) 8 Analog Inputs (CH1 to 8)
Settling Time to
±0.01% is 20µs
with R
S
= 100Ω
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
tie it to +V
SUPPLY
.
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
Channel Address inputs A
0
and A
1
and the 3MSBs of the
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 A
0
and A
1
inputs of the four first-tier multiplexers and the
2MSBs of the counter are applied to the A
0
and A
1
inputs of
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
8 Analog Inputs8 Analog Inputs
Out
Group 1
Group 4
Out
Enable
Enable
2
0
2
1
2
2
2
3
2
4
Settling Time to 0.01% for R
S
< 100Ω
—Two MPC508A units in parallels: 10µs
—Four MPC509 A units in parallels: 12
µ
s
Direct
Multiplexer
Output
Buffered
OPA602
1/4 OPA404
5-Bit
Binary
Counter
To
Group
2
To
Group
3
1 of 4
Decoder
In 1
In 2
In 3
In 8
A
2
A
1
A
0
2
8
A
2
A
1
A
0
MPC
508A
Group 1
Ch1-8
2
8
In 1
In 2
In 3
In 8
Group 4
Ch25-42