78M6613-IM/F/P MAXIM [Maxim Integrated Products], 78M6613-IM/F/P Datasheet - Page 15

• Manufacturer Part Number: 78M6613-IM/F/P
• Description: Single-Phase AC Power Measurement IC
• Manufacturer: MAXIM [Maxim Integrated Products]

DS_6613_018
3.2 Temperature Measurement
Measurement of absolute temperature uses the on-chip temperature sensor while applying the following
formula:
In the above formula, T is the temperature in °C, N(T) is the ADC count at temperature T, N
count at 25°C, S
Example: At 25°C a temperature sensor value of 518,203,584 (N
the 32-pin QFN package. At an unknown temperature T the value 449,648,000 is read at (N(T)). The
absolute temperature is then determined by dividing both N
shift of the ADC value and then inserting the results into the above formula, using –2220 for LSB/°C:
3.3 Temperature Compensation
Temperature Coefficients: The internal voltage reference is calibrated during device manufacture.
The temperature coefficients TC1 and TC2 are given as constants that represent typical component
behavior (in µV/°C and µV/°C
Temperature Compensation: The CE provides the bandgap temperature to the MPU, which then may
digitally compensate the power outputs for the temperature dependence of VREF.
The MPU, not the CE, is entirely in charge of providing temperature compensation. The MPU applies
the following formula to determine any gain adjustments. In this formula TEMP_X is the deviation from
nominal or calibration temperature expressed in multiples of 0.1°C:
Rev 2
Since TC1 and TC2 are given in µV/°C and µV/°C
(1.195V) has to be taken into account when transitioning to PPM/°C and PPM/°C
that PPMC = 26.84*TC1/1.195, and PPMC2 = 1374*TC2/1.195).
In a power and energy measurement unit, the 78M6613 is not the only component contributing to
temperature dependency. A whole range of components (e.g. current transformers, resistor
dividers, power sources, filter capacitors) will contribute temperature effects. Since the output of
the on-chip temperature sensor is accessible to the MPU, temperature-compensation
mechanisms with great flexibility are possible (e.g. system-wide temperature correction over the
entire unit rather than local to the chip).
GAIN
n
is the sensitivity in LSB/°C and T
_
ADJ
T
2
, respectively).
=
=
16385
449,648,00
512
+
T
TEMP
=
⋅
- 0
(
−
(
N
2220
518,203,58
(
_
T
2
n
S
)
X
14
)
is +25°C.
n
−
⋅
N
PPMC
n
2
, respectively, the value of the VREF voltage
)
4
n
+
+
and N(T) by 512 to account for the 9-bit
T
25
n
+
C
TEMP
n
) is read by the ADC by a 78M6613 in
=
85
3 .
_
°
C
X
2
23
2
⋅
PPMC
78M6613 Data Sheet
2
2
. This means
n
is the ADC
15