ADAS3022 datasheet(26/40 Pages) AD

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ADAS3022

Data Sheet

Rev. A | Page 26 of 40

Fully Differential, Antiphase Signals with a

Nonzero Common Mode

For a pair of 5.12 V p-p differential antiphase signals with a

nonzero common mode (dc common-mode voltage of 7 V in

this example), the maximum differential voltage across the

inputs is ±5.12 V (dc common-mode voltage is rejected), and

the PGIA gain configuration should be set to 010.

ADAS3022

INx+

5.12V p-p

INx–

VCM = 7V

VCM

Figure 57. Differential, Antiphase Inputs with a Nonzero Common Mode

Differential, Nonantiphase Signals with a

Zero Common Mode

For a pair of 10.24 V p-p differential nonantiphase signals with

a zero common mode, the maximum differential voltage across

the inputs is ±10.24 V, and the PGIA gain configuration should

be set to 001.

ADAS3022

INx+

+5.12V

10.24V p-p

INx–

–5.12V

10.24V p-p

INx+

INx–

Figure 58. Differential, Nonantiphase Inputs with a Zero Common Mode

Single-Ended Signals with a Nonzero DC Offset

(Asymmetrical)

When a 12 V p-p signal with a 6 V dc level-shift is connected to

one input (INx+) and the dc ground sense of the signal is

connected to INx− or COM, the PGIA gain configuration is set

to 000 for the ±24.576 V range because the maximum differential

voltage across the inputs is 12 V p-p and only half the codes

available for the transfer function are used.

ADAS3022

INx+

+12V

12V p-p

VOFF

INx–

Figure 59. Typical Single-Ended Unipolar Input—Uses Only Half the Codes

Single-Ended Signals with a 0 V DC Offset (Symmetrical)

Compared with the example in the Single-Ended Signals with a

Nonzero DC Offset (Asymmetrical) section, a better solution

for single-ended signals, if possible, is to remove as much dc

offset as possible between INx+ and INx− to produce a bipolar

input voltage that is symmetric around the ground sense. In this

example, the differential voltage across the inputs is never greater

than ±0.64 V, and the PGIA gain configuration is set to 101 for

the 1.28 V p-p range. This scenario uses all of the codes

available for the transfer function, making full use of the

allowable differential input range.

ADAS3022

INx+

+0.64V

1.28V p-p

–0.64V

INx–

Figure 60. Better Single-Ended Configuration—Uses All Codes

Notice that the voltages in this example are not integer values

due to the 4.096 V reference and the PGIA scaling ratios.

Multiplexer

The ADAS3022 uses a high voltage, high performance, low

charge injection multiplexer and a total of nine inputs (IN[7:0]

and COM). Using the INx and COM bits of the configuration

between any of the eight input channels (IN[7:0]) and COM or

for up to four input pairs. Figure 61 shows various methods for

configuring the analog inputs for the type of channel (single or

paired). Refer to the Configuration Register section for more

information.

The analog inputs can be configured as follows:

•

Figure 61A: IN[7:0] referenced to a system ground.

•

Figure 61B: IN[7:0] with a common reference point.

•

Figure 61C: IN[7:0] differential pairs. For pairs, COM = 0.

The positive channel is configured with INx. If INx is even,

then IN0, IN2, IN4, and IN6 are used. If INx is odd, then

IN1, IN3, IN5, and IN7 are used, as indicated by the channels

with parentheses in Figure 61C. For example, for the IN0/IN1

pair with the positive channel on IN0, INx = 0002. For the

IN4/IN5 pair with the positive channel on IN5, INx = 1012.

Note that when the channel sequencer is used, as detailed in

the Channel Sequencer Details section, the positive channels

are always IN0, IN2, IN4, and IN6.

•

Figure 61D: inputs configured in a combination of any of

the preceding configurations (showing that the ADAS3022

can be configured dynamically).

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