CS5480 Datasheet, PDF (26/70 Pages) Cirrus Logic – Three Channel Energy Measurement IC

CS5480
After reset, all three energy pulse generation blocks are
disabled (DOxMODE[3:0] = Hi-Z). To output a desired
energy pulse to a DOx pin, follow the steps below:
1. Write to register PulseWidth (page 0, address 8) to
select the energy pulse width and pulse frequency
range.
2. Write to register PulseRate (page 18, address 28) to
select the energy pulse rate.
3. Write to register PulseCtrl (page 0, address 9) to
select the input to each energy pulse generation
block.
4. Write ‘1’ to bit EPGx_ON of register Config1 (page 0,
address 1) to enable the appropriate energy pulse
generation blocks.
5. Wait at least 0.1s.
6. Write bits DOxMODE[3:0] of register Config1 to
select DOx to output pulses from the appropriate
energy pulse generation block.
7. Send DSP instruction (0xD5) to begin continuous
conversion.
5.7.1 Pulse Rate
Before configuring the PulseRate register, the full-scale
pulse rate needs to be calculated and the frequency
range needs to be specified through FREQ_RNG[3:0]
bits in the PulseWidth register. Refer to section 6.6.6
Pulse Output Width (PulseWidth) – Page 0, Address 8
on page 43. The FREQ_RNG[3:0] bits should be set to
b[0110]. For example, if a meter has the meter constant
of 1000imp/ kWh, a maximum voltage (U_MAX) of 240V,
and a maximum current (I_MAX) of 100A, the maximum
pulse rate is:
[1000x(240x100/1000)] / 3600 = 6.6667Hz.
Assume the meter is calibrated with U_MAX and I_MAX,
and the Scale register contains the default value of 0.6.
After gain calibration, the power register value will be
0.36, which represents 240x100 = 24kW or 6.6667Hz
pulse output rate. The full-scale pulse rate is:
F_out = 6.6667/0.36 = 18.5185Hz.
The CS5480 pulse generation block behaves as
follows:
• The pulse rate generated by full-scale (1.0decimal)
power register:
F_OUT = (PulseRatex2000)/2^FREQ_RNG
• The PulseRate register value is:
PulseRate = (F_OUTx2^FREQ_RNG)/2000
= (18.5186x64)/2000
= 0.5925952
= 0x4BDA29
5.7.2 Pulse Width
The PulseWidth register defines the Active-low time of
each energy pulse:
Active-low = 250µs+(PulseWidth/64000).
By default, the PulseWidth register value is 1, and the
Active-low time of each energy pulse is 265.6µs. Note
that the pulse width should never exceed the pulse
period.
5.8 Voltage Sag, Voltage Swell, and
Overcurrent Detection
Voltage sag detection is used to determine when the
voltage falls below a predetermined level for a specified
interval of time (duration). Voltage swell and overcurrent
detection determines when the voltage or current rises
above a predetermined level for a specified interval of
time.
The duration is set by the value in the V1Sag_DUR
(V2Sag_DUR), V1Swell_DUR (V2Swell_DUR), and
I1Over_DUR (I2Over_DUR) registers. Setting any of these
to zero (default) disables the detect feature for the given
channel. The value is in output word rate (OWR)
samples. The predetermined level is set by the values
in the V1Sag_LEVEL (V2Sag_LEVEL), V1Swell_LEVEL
(V2Swell_LEVEL), and I1Over_LEVEL (I2Over_LEVEL)
registers.
For each enabled input channel, the measured value is
rectified and compared to the associated level register.
Over the duration window, the number of samples
above and below the level are counted. If the number of
samples below the level exceeds the number of
samples above, a Status0 register bit V1SAG (V2SAG)
is set, indicating a sag condition. If the number of
samples above the level exceeds the number of
samples below, a Status0 register bit V1SWELL
(V2SWELL) or I1OVER (I2OVER) is set, indicating a
swell or overcurrent condition (see Figure 17).
Level
D u ratio n
Figure 17. Sag, Swell, and Overcurrent Detect
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DS980F2