Datasheet

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 × V
REF
− 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 Un adju ste d 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 (V
REF
)
measured between T
MIN
and T
MAX
. It is expressed in ppm/°C
using the following equation:
6
10
)(V5.2
)()(
C)(ppm/ ×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−×
−
=°
MIN
MAX
REFREF
REF
TT
MinVMaxV
TCV
where:
V
REF
(Max) is the maximum V
REF
between T
MIN
and T
MAX
.
V
REF
(Min) is the minimum V
REF
between T
MIN
and T
MAX
.
T
MAX
= +85°C or +105°C.
T
MIN
= −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 T
MAX
to +25°C
T_HYS− = +25°C to T
MIN
to +25°C
Output voltage hysteresis is expressed in ppm using the follow-
ing equation:
6
10
C)25(
)(C)25(
(ppm) ×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
°
−°
=
REF
REFREF
HYS
V
T_HYSVV
V
where:
V
REF
(25°C) = V
REF
at 25°C.
V
REF
(T_HYS) is the maximum change of V
REF
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:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
=
)(
)(
ACNVST
BCNVST
DYN(A)
DYN(B)
f
fI
I
where:
I
DYN(A)
is the dynamic leakage current at the convert start
frequency, f
CNVST(A)
(see Table 1).
I
DYN(B)
is the dynamic leakage current at the desired convert
start frequency, f
CNVST(B)
.