MAX71020 Datasheet, PDF (13/37 Pages) Maxim Integrated Products – Single-Chip Electricity Meter AFE

MAX71020
Single-Chip Electricity Meter AFE
Table 3. Pulse Output Function Assignments
OUTPUT
XPULSE
YPULSE
VPULSE
WPULSE
FUNCTION
Pulse output on each zero crossing on voltage input
Pulse output when voltage sag detected
Pulse output when programmed VARh consumption has occurred
Pulse output when programmed Wh consumption has occurred
XPULSE and YPULSE
Pulses generated by the CE may be exported to the
XPULSE and YPULSE pulse output pins. Pins D2 and D3
are used for these pulses, respectively. The XPULSE and
YPULSE outputs can be updated once on each pass of
the CE code. See the CE Interface Description section
for details.
VPULSE and WPULSE
By default, WPULSE and VPULSE are negative pulses
(i.e., low level pulses, designed to sink current through
an LED). PLS_MAXWIDTH[7:0] determines the maximum
negative pulse width T_MAX in units of CK_FIR clock
cycles based on the pulse interval T_I according to the
formula:
T_MAX = (2 x PLS_MAXWIDTH[7:0] + 1) x T_I
T_I is based on an internal value that determines the pulse
interval and the ADC clock, both of which are determined
by the particular characteristics of the compute engine.
In the MAX71020, the default value for T_I is 65.772µs, but
this value changes in customized versions of this part.
If PLS_MAXWIDTH = 255 no pulse-width checking is per-
formed, and the pulses default to 50% duty cycle. T_MAX
is typically programmed to 10ms (T_MAX = 76), which
works well with most calibration systems.
The polarity of the pulses may be inverted with the control
bit PLS_INV. When PLS_INV is set, the pulses are active-
high. The default value for PLS_INV is zero, which selects
active-low pulses.
Temperature Sensor
The MAX71020 includes an on-chip temperature sen-
sor for determining the temperature of its bandgap
reference. The primary use of the temperature data is to
determine the magnitude of compensation required to
offset the thermal drift in the system for the compensation
of current, voltage, and energy measurement. See the
Metrology Temperature Compensation section.
The temperature sensor is awakened on command from
the host microcontroller by setting the TEMP_START
control bit. The host microcontroller must wait for the
TEMP_START bit to clear before reading STEMP[15:0]
and before setting the TEMP_START bit once again.
The result of the temperature measurement can be read
from the STEMP[15:0] register. The 16-bit value is in
two’s complement form and ranges from -1024 to +1023
(decimal). The sensed temperature can be computed
from the 16-bit STEMP[15:0] reading using the following
formula:
Temp (NC) = 0.325 x STEMP + 22
An additional register, VSENSE[7:0], senses the level
of supply voltage. Table 4 shows the registers used for
temperature measurement.
Digital I/O
On reset or power-up, all DIO pins are configured as
high-impedance. DIO pins can be configured indepen-
dently by the host microcontroller by manipulating the
D0, D1, D2, and D3 bit fields.
The WPULSE and VPULSE pulse generator outputs are
available on pins D0/WPULSE and D1/VPULSE, respectively.
Table 4. Temperature Measurement Registers
NAME
RST
WK
TBYTE_BUSY
0
0
DIR
DESCRIPTION
Indicates that hardware is still writing the result. Additional
R
writes to this byte are locked out while it is one. Write duration
could be as long as 6ms.
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