Datasheet

78M6612 Data Sheet DS_6612_001
22 Rev 2
3.2 Connecting 5 V Devices
All digital input pins of the 78M6612 are compatible with external 5 V devices. I/O pins configured as
inputs do not require current-limiting resistors when they are connected to external 5 V devices.
3.3 Temperature Measurement
Measurement of absolute temperature uses the on-chip temperature sensor and applying the following
formula:
n
n
n
T
S
NTN
T +
−
=
))((
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.
3.4 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
2
, respectively).
Since TC1 and TC2 are given in
µ
V/°C and
µ
V/°C
2
, respectively, the value of the VREF voltage
(1.195V) has to be taken into account when transitioning to PPM/°C and PPM/°C
2
. 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 GAIN_ADJ (address 0x12). In this formula TEMP_X is the deviation from
nominal or calibration temperature expressed in multiples of 0.1°C:
23
2
14
2
2_
2
_
16385_
PPMCXTEMPPPMCXTEMP
ADJGAIN
⋅
+
⋅
+=
In a power and energy measurement unit, the 78M6612 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)
.