fs6611 Fortune Semiconductor Corporation, fs6611 Datasheet - Page 16

• Manufacturer Part Number: fs6611
• Description: Energy Metering Ic With Impulse Output
• Manufacturer: Fortune Semiconductor Corporation

Rev. 1.1
13.8 Transfer Function
13.8.1
The FS6611 calculates the product of two voltage
signals (on Channel 1 and Channel 2) and then low
pass filters this product to extract real power
information. This real power information is then
converted to a frequency. The frequency information
is output on F1 and F2 in the form of active low
pulses. The pulse rate at these outputs is relatively
low, e.g., 0.34Hz maximum for AC signals with S0 =
S1 = 0 (see Table III). This means that the frequency
at these outputs is generated from real power
information accumulated over a relatively long
period of time. The result is an output frequency that
is proportional to the average real power. The
averaging of the real power signal is implicit to the
power to impulse converter. The output frequency or
pulse rate is related to the input voltage signals by
the following equation.
Where:
Note:
*
will vary if the specified CLKIN frequency is altered.
Example
In this example, with AC voltages of ±470mV peak
applied to V1 and ±660mV peak applied to V2, the
F
1–4
S1
0
0
1
1
Freq =
is a binary fraction of the master clock and therefore
Freq: Output frequency on F1 and F2 (Hz)
V1: Differential rms voltage signal on
V2: Differential rms voltage signal on
Gain:1, 2, 8, or 16, depending on the PGA
V
F
Table II
1-4
REF
S0
Frequency Outputs F1 and F2
0
1
0
1
: One of four possible frequencies
: The reference voltage (2.5V ± 8%)
Channel 1 (Volts)
Channel 2 (Volts)
gain selection made using logic
inputs G0 and G1
selected by using the logic inputs S0
and S1—see Table II
. 8
F
06
1-4
13.6
1.7
3.4
6.8
(Hz)
×
F
V
1-4
1
Frequency Selection
×
V
V
2
REF
2
×
3.579545MHz/2
3.579545MHz/2
3.579545MHz/2
3.579545MHz/2
Gain
XTAL/CLKIN
×
F
1
−
4
*
21
20
19
18
expected output frequency is calculated as follows:
Note:
If the on-chip reference is used, actual output
frequencies may vary from device to device due to
reference tolerance of ±8%.
Freq =
Table Ⅲ shows a complete listing of all maximum
output frequencies.
Table Ⅲ Maximum Output Frequency on F1 and F2
13.8.2
The pulse output CF (Calibration Frequency) is
intended for use during calibration. The output pulse
rate on CF can be up to 2048 times the pulse rate on
F1 and F2. The lower the F
the higher the CF scaling (except for the high
frequency mode SCF = 0, S1 = S0 = 1). Table Ⅳ
shows how the two frequencies are related,
depending on the states of the logic inputs S0, S1,
and SCF. Because of its relatively high pulse rate,
the frequency at this logic output is proportional to
the instantaneous real power. As is the case with F1
and F2, the frequency is derived from the output of
the low-pass filter after multiplication. However,
because the output frequency is high, this real power
information is accumulated over a much shorter time.
Hence, less averaging is carried out in the digital to
frequency converter. With much less averaging of
the real power signal, the CF output is much more
responsive to power fluctuations (see Fig2, Signal
Processing Block Diagram).
S1
0
0
1
1
Gain = 1, G0 = G1 = 0
F
V1 = rms of 470mV peak ac = 0.47/
V2 = rms of 660mV peak ac = 0.66/
V
1–4
REF
. 8
Frequency Output CF
= 1.7Hz, S0 = S1 = 0
= 2.5V (nominal reference value)
06
S0
0
1
0
1
×
. 0
2
47
×
×
2
. 0
×
66
for AC Inputs (Hz)
2
Max Frequency
5 .
×
2
1
1–4
×
0.34
0.68
1.36
2.72
1
7 .
frequency selected,
= 0.34 (Hz)
2
2
FS6611
Volts
Volts
16/20