ADE7854AACPZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'ADE7854AACPZ' PDF : 96 Pages View PDF
Data Sheet
ADE7854A/ADE7858A/ADE7868A/ADE7878A
REFERENCE CIRCUIT
The nominal reference voltage at the REFIN/OUT pin is 1.2 V.
This is the reference voltage for the ADCs in the ADE7854A/
ADE7858A/ADE7868A/ADE7878A. Use a typical external
reference voltage of 1.2 V to overdrive the REFIN/OUT pin. The
temperature coefficient of the internal voltage reference is
calculated based on the endpoint method. To calculate the drift
over temperature, the values of the voltage reference at
endpoints (−40°C and +85°C) are measured and compared to
the reference value at 25°C, which in turn provides the slope of
the temperature coefficient curve. Figure 58 is a typical
representation of the drift over temperature. It contains two
curves: Curve X and Curve Y, which are typical representations
of two possible curvatures that are observed over the entire
specified temperature range.
–40°C
A'
A
–40°C
CURVE Y
CURVE X
+25°C
B
+85°C
C'
C
+85°C
TEMPERATURE (°C)
Figure 58. Internal Voltage Reference Temperature Drift
Figure 58 shows that independent consideration of two regions
is necessary for accurate analysis of the drift over temperature,
as follows:
Considering the region between Point A and Point B in
Curve X, the reference value increases with an increase in
temperature; thus, the curve has a positive slope from A to
B. This results in a positive temperature coefficient in this
region.
Considering the region between Point B and Point C in
Curve X, the slope of the curve is negative because the
voltage reference decreases with an increase in tempera-
ture; thus, this region of the curve has a negative
temperature coefficient.
Based on similar logic, Curve Y has a negative temperature
coefficient between Point Aʹ and Point B and a positive
temperature coefficient between Point B and Point Cʹ.
The drift curve on any particular IC can be matched with either
of these sample curves. The general relationship between the
absolute value of the voltage reference at a particular endpoint
temperature and the temperature coefficient for that region of
the curve is explained by the following two equations:
VREF
(−40°C)
=
VREF
(+25°C)
×
1
c
40C
106
25C
VREF (85°C)
=
VREF
(25°C)
×
1
h
85C
10
6
25C
where αc and αh are cold and hot temperature coefficients,
respectively, calculated by
VREF (40C) VREF (25C)
αc
VREF (25C)
40C 25C
× 106 ppm/°C
VREF (85C) VREF (25C)
αh
VREF (25C)
85C 25C
× 106 ppm/°C
As the sign of cold and hot temperature coefficients can vary
from one IC to another, the typical drift is specified for the
whole range with a plus or minus sign (±). To find the typical,
minimum, and maximum temperature coefficients, as listed in
the Specifications section, data based on the endpoint method is
collected on ICs spread across different lots. The minimum and
maximum temperature coefficients denote that the drift of any
particular IC is within those limits, over the specified
temperature range, with reference to 25°C. See Figure 59 and
Figure 60 for the device to device variation of the drift.
–50 –40 –30 –20 –10 0 10 20 30 40 50
COLD TEMPERATURE COEFFICIENT (ppm/°C)
Figure 59. Histogram of the Reference Drift from −40°C to +25°C
Rev. C | Page 41 of 96
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