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Data Sheet

ADAS3022

Rev. A | Page 25 of 40

ANALOG INPUTS

Input Structure

The ADAS3022 uses a differential input structure between

IN[7:0] and COM or between IN[7:0]+ and IN[7:0]− of a

channel pair. The COM input is sampled identically such that

the same voltages can be present on inputs IN[7:0]. Therefore,

the selection of paired channels or all channels referenced to

one common point is available. Because all inputs are sampled

differentially, the ADAS3022 offers true high common-mode

rejection, whereas a discrete system would require the use of

additional instrumentation or a difference amplifier.

Figure 55 shows an equivalent circuit of the analog inputs. The

internal diodes provide ESD protection for the analog inputs

(IN[7:0] and COM) from the high voltage supplies (VDDH and

VSSH). Care must be taken to ensure that the analog input

signal does not exceed the supply rails by more than 0.3 V

because this can cause the diodes to become forward-biased and

to start conducting current. Note that if the auxiliary input pair

(AUX±) is used, the diodes provide ESD protection from only the

lower voltage AVDD (5 V) supply and the system analog ground

because these inputs are connected directly to the internal SAR

ADC circuitry.

CPIN

IN[7:0]

OR COM

VSSH

AUX+

OR AUX–

AGND

VDDH

AVDD

MUX

PGIA

Figure 55. Equivalent Analog Input Circuit

Voltages beyond the absolute maximum ratings may cause

permanent damage to the ADAS3022 (see Table 4).

Programmable Gain

The ADAS3022 incorporates a programmable gain instru-

mentation amplifier with seven selectable ranges (±0.64 V,

±1.28 V, ±2.56 V, ±5.12 V, ±10.24 V, ±20.48 V, and ±24.576 V),

enabling the use of almost any direct sensor interface. The PGIA

settings are specified in terms of the maximum absolute differential

input voltage across a pair of inputs (for example, INx+ to INx−

or INx+ to COM). The power-on and default conditions are

preset to the ±20.48 V (PGIA = 111) input range.

Note that because the ADAS3022 can use any input type, such

as bipolar differential (antiphase or nonantiphase), bipolar single

ended, or pseudo bipolar, setting the PGIA is important to

make full use of the allowable input span.

Table 7 describes each differential input range and the

corresponding LSB size, PGIA bits settings, and PGIA gain.

Table 7. Differential Input Ranges, LSB Size, and PGIA

Settings

Differential Input Ranges,

INx+ − INx− (V)

LSB (μV)

PGIA Bits

PGIA Gain

(V/V)

±24.576

781.25

000

0.16

±20.48

625

111

0.2

±10.24

312.5

001

0.4

±5.12

156.3

010

0.8

±2.56

78.13

011

1.6

±1.28

39.06

100

3.2

±0.64

19.53

101

6.4

Common-Mode Operating Range

The differential input common-mode voltage (VCM) range

changes according to the maximum input range selected and

the high voltage power supplies (VDDH and VSSH). Note that

the specified operating input voltage of any input pin (see the

Specifications section) requires 2.5 V of headroom from the

VDDH and VSSH supplies; therefore,

(VSSH + 2.5 V) ≤ INx/COM ≤ (VDDH − 2.5 V)

This section provides some examples of setting the PGIA for

various input signals. Note that the ADAS3022 always calculates

the difference between the IN+ and IN− signals.

Fully Differential, Antiphase Signals with a

Zero Common Mode

For a pair of 20.48 V p-p differential antiphase signals with a

zero common mode, the maximum differential voltage across

the inputs is 20.48 V, and the PGIA gain configuration should

be set to 111.

ADAS3022

INx+

+10.24V

20.48V p-p

–10.24V

INx–

Figure 56. Differential, Antiphase Inputs with a Zero Common Mode

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