Datasheet

MAX71020
Single-Chip Electricity Meter AFE
20Maxim Integrated
Host Controller Interface
Register Map
Table 7. Register Map
Crystal Oscillator
The oscillator drives an AT cut microprocessor crystal at
a frequency of 9.8304MHz. Board layouts with minimum
capacitance from XIN to XOUT require less current.
Good layouts have XIN and XOUT shielded from each
other and from digital signals.
Since the oscillator is self-biasing, an external
resistor must not be connected across the
crystal.
Meter Calibration
Once the MAX71020 energy meter device has been
installed in a meter system, it must be calibrated. A com-
plete calibration includes the following:
●
Establishment of the reference temperature (e.g., typi-
cally 22NC).
● Calibration of the metrology section, i.e., calibration
for tolerances of the current sensors, voltage-dividers,
and signal conditioning components as well as of the
internal reference voltage (VREF) at the reference
temperature (e.g., typically 22NC).
The metrology section can be calibrated using the gain
and phase adjustment factors accessible to the CE. The
gain adjust ment is used to compensate for tolerances of
components used for signal conditioning, especially the
resistive components. Phase adjustment is provided to
compensate for phase shifts introduced by the current
sensors or by the effects of reactive power supplies.
The MAX71020 supports common industry-standard cali-
bration techniques, such as single-point (energy-only)
and multipoint (energy, V
RMS
, I
RMS
).
The load engine seeds some CE and hardware control
registers with default values required for proper opera-
tion of the CE code, but not the calibration registers
(CAL_IA, CAL_VA, etc., and PHADJ_A and PHADJ_B)
and a variety of other registers that need to change
dynamically. The default values shown in Table 7 apply
to ideal sensors and an ideal trim value of VREF.
Calibration yields non-default values for the calibration
registers. Storage of the calibration registers should be
implemented in the host, and on power-up or after reset,
the host must write the stored values into the calibra-
tion registers of the MAX71020. If the meter constant or
any other of the parameters listed in Table 7 had been
changed from default, the host must also update these
values on power-up and after reset.
Table 7 lists in the column LOADED BY the source that
is used to seed the value. Host means that the host
controller is responsible for loading the value into the CE
RAM upon reset or power-up. The host must ensure that
the registers labeled “Host” are maintained, preserved,
and checked whenever the MAX71020 reports a reset
or supply power event in its M_STAT register. LE means
that the Load Engine provides the data for the register.
The registers labeled R in the R/W column need not be
seeded with values ( — in LOADED BY column).
NAME
BYTE
ADDRESS
R/W
DEFAULT
VALUE
DESCRIPTION
LOADED
BY
CAL_I0 0x010 R/W 0x0000 4000
Calibration coefficient for current channel A. Default =
unity gain
Host
CAL_V0 0x011 R/W 0x0000 4000 Calibration coefficient for voltage channel A. Host
PHADJ_0 0x012 R/W 0x0000 0000
Phase adjust coefficient for channel A. Default = no
phase adjust.
Host
CAL_I1 0x013 R/W 0x0000 4000 Calibration coefficient for current channel B. Host
CAL_V1 0x014 R/W 0x0000 4000 Calibration coefficient for voltage channel B. Host
PHADJ_1 0x015 R/W 0x0000 0000 Phase adjust coefficient for channel B. Host
DEGSCALE 0x01A R/W 0x0000 6A8F Internal constant LE