MPC506A, MPC507A

7

SBFS018A

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Common-Mode Rejection (MPC507A Only)

The matching properties of the load, multiplexer and source

affect the common-mode rejection (CMR) capability of a

differentially multiplexed system. CMR is the ability of the

multiplexer and input amplifier to reject signals that are

common to both inputs, and to pass on only the signal

difference to the output. For the MPC507A, protection is

provided for common-mode signals of

±20V above the

power supply voltages with no damage to the analog switches.

The CMR of the MPC507A and Burr-Brown's INA110

instrumentation amplifier (G = 100) is 110dB at DC to 10Hz

with a 6dB/octave roll-off to 70dB at 1000Hz. This measure-

ment of CMR is shown in the Typical Performance Curves

and is made with a Burr-Brown INA110 instrumentation

amplifier connected for gains of 500, 100, and 10.

Factors which will degrade multiplexer and system DC

CMR are:

• Amplifier bias current and differential impedance mis-

match

• Load impedance mismatch

• Multiplexer impedance and leakage current mismatch

• Load and source common-mode impedance

AC CMR roll-off is determined by the amount of common-

mode capacitances (absolute and mismatch) from each

signal line to ground. Larger capacitances will limit CMR

at higher frequencies; thus, if good CMR is desired at

higher frequencies, the common-mode capacitances and

unbalance of signal lines and multiplexer to amplifier wiring

must be minimized. Use twisted-shielded pair signal lines

wherever possible.

SWITCHING WAVEFORMS

Typical at +25

°C, unless otherwise noted.

100ns/Div

1 On

16 On

V

2V/Div

Output

0.5V/Div

V

Address Drive

(V

Output

50%

50%

t

OPEN

0V

GND

In 2 Thru In 15

In 1

In 16

Out

A

3

A

2

A

1

A

0

En

1k

Ω

50

Ω

+5V

+4.0V

12.5pF

V

A

V

OUT

NOTE: (1) Similar connection for MPC507A.

BREAK-BEFORE-MAKE DELAY (t

ENABLE DELAY (t

100ns/Div

In 1 Thru

In 16 Off

Output

2V/Div

1 On

GND

In 2 Thru In 16

In 1

Out

A

3

A

2

A

1

A

0

En

1k

Ω

+10V

12.5pF

NOTE: (1) Similar connection for MPC507A.

50

Ω

V

A

Enable Drive

V

50%

90%

90%

0V

Output

t

t