ADS7253 datasheet(32/73 Pages) TI2

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NFSC + 1

PFSC

PLC

PFSR ± 1 LSB

NFSR

Fully-Differential Analog Input

(AINP_x ± AINM_x)

1 LSB

VIN

NFSC

ADS8354, ADS7854, ADS7254

SBAS556B – OCTOBER 2013 – REVISED AUGUST 2014

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8.3.3 Transfer Function

The device output is in twos compliment format. Device resolution for a fully-differential input is calculated by

Equation 7:

1 LSB = (2 × FSR_ADC_x) / (2

where:

•

N = 16 (ADS8354), 14 (ADS7854), or 12 (ADS7254)

•

FSR_ADC_x is the full-scale input range of the ADC (refer to the Analog Input section for more details)

(7)

Table 2 shows the different input voltages and the corresponding output codes from the device.

Table 2. Transfer Characteristics

INPUT VOLTAGE

OUTPUT CODE (Hex)

INPUT

(AINP_x – AINM_x),

VOLTAGE

CODE

ADS8354

ADS7854

ADS7254

±VREF RANGE

±2 × VREF RANGE

< – VREF_x

< –2 × VREF_x

NFSC

8000

2000

800

–VREF_x + 1 LSB

–2 × VREF_x + 1 LSB

NFSR

NFSC + 1

8001

2001

801

–1 LSB

FFFF

3FFF

FFF

PLC

0000

000

> VREF_x – 1 LSB

> 2 × VREF_x – 1 LSB

PFSR – 1 LSB

PFSC

7FFF

1FFF

7FF

Figure 86 shows the ideal transfer characteristics for the device.

Figure 86. Ideal Transfer Characteristics for a Fully-Differential Analog Input

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