cs5461 Cirrus Logic, Inc., cs5461 Datasheet - Page 21

• Manufacturer Part Number: cs5461
• Description: Single-phase, Bidirectional Power/energy Ic
• Manufacturer: Cirrus Logic, Inc.

new range and step size (in degrees) with respect to
the new line frequency.
To calibrate the phase delay, use a purely resistive
load and adjust the phase compensation bits until
the Average Power Register value is maximized.
4.7 Time-Base Calibration
The Time-Base Calibration Register (notated as
“TBC” in Figure 2) is used to compensate for slight
errors in the XIN frequency. External oscillators
and crystals have certain tolerances. To improve
the accuracy of the clock for energy measurements,
the Time-Base Calibration Register can be manip-
ulated to compensate for the frequency error. Note
from Figure 2 that the TBC Register only affects
the value in the Average Power Register.
As an example, if the desired XIN frequency is
4.096 MHz, but during production-level testing the
average frequency of the crystal on a particular
board is measured to be 4.091 MHz. The ratio of
the desired frequency to the actual frequency is
4.096 MHz / 4.091 MHz = ~1.00122219506. The
Time-Base Calibration Register can be set to
1.00122213364 = 0x80280C(h), which is close to
the desired ratio.
4.8 On-Chip Temperature Sensor
After a few minutes of normal-active operation in
‘continuous conversions’ data acquisition mode,
the CS5461 will stabilize to a constant steady-state
operating temperature. However, the CS5461’s op-
erating temperature may be influenced by changes
in the ambient temperature. Such ambient temper-
ature fluctuations will cause some drift in the gain
of the CS5461’s two A/D converters. The on-chip
temperature sensor provides the option to calibrate
such drift.
The output code value in the Temperature Register
is the relative temperature reading of the on-chip
temperature sensor.
DS546F2
By recording the digitized temperature readings
and comparing these readings to the fluctuations in
the A/D output codes of the Vrms and Irms Regis-
ter readings, the fluctuation of the A/D converter
can be characterized over a wide range of ambient
temperatures.
Once a temperature drift characterization of the de-
vice has been performed, a temperature compensa-
tion algorithm can be integrated into the firmware
within the on-board MCU to compensate for this
temperature drift.
4.9 Interrupt
The INT pin is used to indicate that an event has
taken place in the converter that needs attention.
These events inform the system about operation
conditions and internal error conditions. The INT
signal is created by combining the Status Register
with the Mask Register. Whenever a bit in the Sta-
tus Register becomes active, and the corresponding
bit in the Mask Register is a logic 1, the INT signal
becomes active. The interrupt condition is cleared
when the bits of the Status Register are returned to
their inactive state.
4.9.1 Typical use of the INT pin
The steps below show how interrupts can be han-
dled.
•
•
Initialization:
Step I0 - All Status bits are cleared by writing
FFFFFF (Hex) into the Status Register.
Step I1 - The conditional bits which will be
used to generate interrupts are then set to
logic 1 in the Mask Register.
Step I3 - Enable interrupts.
Interrupt Handler Routine:
Step H0 - Read the Status Register.
Step H1 - Disable all interrupts.
Step H2 - Branch to the proper interrupt service
routine.
CS5461
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