cs5461 Cirrus Logic, Inc., cs5461 Datasheet - Page 25

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

be set to a value much higher than the EOUT pulse
rate.
The FOUT pin outputs negative and positive ener-
gy, but has no energy direction indicator. The max-
imum FOUT pulse frequency is set by the value in
the PulseRateF Register.
5.4 Anti-Creep for the Pulse Outputs
Anti-Creep can be enabled/disabled for both
EOUT/EDIR and FOUT pulse output systems in
the Control Register. Anti-creep allows the elec-
tronic meter to maintain a “buffer” energy band,
defined by positive/negative energy threshold lev-
els, such that when the magnitude of the accumu-
lated energy is below this level, no energy pulses
are issued. The anti-creep feature is especially use-
ful when the meter demands that the energy pulse
outputs are set to relatively high frequency. A high-
er frequency pulse rate means that less energy reg-
istration is required to generate a pulse; and so it is
more likely that random noise present in the power
line and/or current-sense circuit can generate a
pulse that does not represent billable energy.
5.5 Design Examples
EXAMPLE #1: For a power line with maximum
rated levels of 250 V (RMS) and 20 A (RMS), the
pulse-frequency on the EOUT pin needs to be
‘IR’ = 100 pulses-per-second (100 Hz) when the
RMS-voltage and RMS-current levels on the power
line are 220 V and 15 A respectively. To meet this
requirement, the pulse-rate frequency (‘PR’) in the
Pulse-Rate Register must be set accordingly.
After calibration, the first step to finding the value
of ‘PR’ is to set the voltage and current sensor gain
constants, K
able voltage levels on the CS5461 inputs when the
power line voltage and current levels are at the
maximum values of 250 V and 20 A. K
needed to determine the appropriate ratios of the
voltage/current transformers and/or shunt resistor
DS546F2
V
and K
I
, such that there will be accept-
V
and K
I
are
values to use in the front-end voltage/current sen-
sor networks.
For a sinewave, the largest RMS value that can be
accurately measured (without over-driving the in-
puts) will register ~0.707 of the maximum DC in-
put level. Since power signals are often not
perfectly sinusoidal in real-world situations, and to
provide for some over-range capability, the RMS
Voltage Register and RMS Current Register is set
to measure 0.6 when the RMS-values of the
line-voltage and line-current levels are 250 V and
20 A. Therefore, when the RMS registers measure
0.6, the voltage level at the inputs will be
0.6 x 250 mV = 150 mV. The sensor gain con-
stants, K
that the voltage and current channel inputs should
be 150 mV RMS when the power line voltage and
current are at the maximum values of 250 V and
20 A.
K
K
These sensor gain constants are used to calculate
what the input voltage levels will be on the CS5461
inputs when the line-voltage and line-current are
220 V and 15 A. These values are V
om.
V
V
The pulse rate on EOUT will be at ‘PR’ pulses per
second (Hz) when the RMS-levels of voltage/cur-
rent inputs are at 250 mV. When the voltage/cur-
rent inputs are set at V
rate needs to be ‘IR’ = 100 pulses per second. IR
will be some percentage of PR. The percentage is
defined by the ratios of V
V
V
I
Vnom
Inom
Inom
= 150 mV / 20 A = 0.0075 Ω
= 150 mV / 250 V = 0.0006
/250 mV with the following formula:
= K
= K
PulseRate
V
I
V
and K
* 15 A = 112.5 mV
* 220 V = 132 mV
I
=
, are determined by demanding
IR
=
Vnom
PR
⋅
------------------ -
250mV
V
and V
Vnom
Vnom
⋅
Inom
/250 mV and
------------------ -
250mV
Vnom
V
CS5461
Inom
, the pulse
and V
25
In-