DS_6613_018
78M6613 Data Sheet
3.2
Temperature Measurement
Measurement of absolute temperature uses the on-chip temperature sensor while applying the following
formula:
T
=
(
N
(
T
)
−
N
n
)
+
T
n
S
n
In the above formula,
T
is the temperature in °C, N(T) is the ADC count at temperature T, N
n
is the ADC
count at 25°C, S
n
is the sensitivity in LSB/°C and T
n
is +25°C.
Example:
At 25°C a temperature sensor value of 518,203,584 (N
n
) is read by the ADC by a 78M6613 in
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
n
and N(T) by 512 to account for the 9-bit
shift of the ADC value and then inserting the results into the above formula, using –2220 for LSB/°C:
T
=
449,648,000 - 518,203,584
+
25
C
=
85.3
°
C
512
⋅
(
−
2220)
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
2
behavior (in
µV/°C
and
µV/°C
, respectively).
Since TC1 and TC2 are given in
µV/°C
and
µV/°C
2
, respectively, the value of the VREF voltage
2
(1.195V) has to be taken into account when transitioning to PPM/°C and PPM/°C . This means
that PPMC = 26.84*TC1/1.195, and PPMC2 = 1374*TC2/1.195).
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:
TEMP
_
X
⋅
PPMC TEMP
_
X
2
⋅
PPMC
2
GAIN
_
ADJ
=
16385
+
+
14
2
2
23
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).
Rev. 1.1
15
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
