AD7280ABSTZ datasheet(14/48 Pages) AD

14 / 48 page

AD7280A

Rev. 0 | Page 14 of 48

TERMINOLOGY

Differential Nonlinearity (DNL)

DNL is the difference between the measured and the ideal

1 LSB change between any two adjacent codes in the ADC.

Integral Nonlinearity (INL)

INL is the maximum deviation from a straight line passing

through the endpoints of the ADC transfer function. The

endpoints of the transfer function are zero scale (a point 1 LSB

below the first code transition) and full scale (a point 1 LSB

above the last code transition).

Offset Error

Offset error applies to straight binary output coding. It is the

deviation of the first code transition (000 ... 000) to (000 ... 001)

from the ideal, that is, AGND + 1 LSB for AUX1 to AUX6 and

1 V + AGND + 1 LSB for VIN0 to VIN6.

Offset Error Match

Offset error match is the difference in zero code error across all

six channels.

Gain Error

Gain error applies to straight binary output coding. It is the

deviation of the last code transition (111 ... 110) to (111 ... 111)

from the ideal (that is, 2 × VREF − 1 LSB) after adjusting for the

offset error.

Gain Error Match

Gain error match is the difference in gain error across all six

channels.

ADC Unadjusted Error

ADC unadjusted error includes the INL error and the offset and

gain errors of the ADC and measurement channel.

Total Unadjusted Error (TUE)

TUE is the maximum deviation of the output code from the ideal.

Total unadjusted error includes the INL error, the offset and gain

errors, and the reference errors. Reference errors include the

difference between the actual and ideal reference voltage (that

is, 2.5 V) and the reference voltage temperature coefficient.

Reference Voltage Temperature Coefficient

The reference voltage temperature coefficient is derived from

the maximum and minimum reference output voltage (VREF)

measured between TMIN and TMAX. It is expressed in ppm/°C

using the following equation:

)

(

)

(

)

(

(ppm/

⎟

⎠

⎞

⎜

⎝

⎛

−

MIN

MAX

REF

Min

Max

TCV

where:

VREF(Max) is the maximum VREF between TMIN and TMAX.

VREF(Min) is the minimum VREF between TMIN and TMAX.

TMAX = +85°C or +105°C.

TMIN = −40°C.

Output Voltage Hysteresis

Output voltage hysteresis, or thermal hysteresis, is defined as

the absolute maximum change of reference output voltage after

the device is cycled through temperature from either T_HYS+

or T_HYS−, where:

T_HYS+ = +25°C to TMAX to +25°C

T_HYS− = +25°C to TMIN to +25°C

Output voltage hysteresis is expressed in ppm using the follow-

ing equation:

(

)

(

(ppm)

⎟

⎠

⎞

⎜

⎝

⎛

−

REF

HYS

T_HYS

where:

VREF(25°C) = VREF at 25°C.

VREF(T_HYS) is the maximum change of VREF at T_HYS+ or

T_HYS−.

Static Leakage Current

Static leakage current is the current measured on the cell voltage

and/or the auxiliary ADC inputs when the device is static, that

is, not converting.

Dynamic Leakage Current

Dynamic leakage current is the current measured on the cell

voltage and/or the auxiliary ADC inputs when the device is

converting, with the static leakage current subtracted. Dynamic

leakage current is specified with a convert start pulse frequency

of 10 Hz, that is, every 100 ms. The dynamic leakage current for

a different conversion rate can be calculated using the following

equation:

⎟

⎠

⎞

⎜

⎝

⎛

)

(

)

(

CNVST

DYN(A)

DYN(B)

where:

IDYN(A) is the dynamic leakage current at the convert start

frequency, fCNVST(A) (see Table 1).

IDYN(B) is the dynamic leakage current at the desired convert

start frequency, fCNVST(B).

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