UG-1098 ADE9000 Technical Reference Manual
Rev. 0 | Page 22 of 86
Digital to Frequency Conversion—CF Output
Many electricity meters are required to provide a pulse output
that is proportional to the energy being accumulated, with a
given pulse per kWh meter constant.
The ADE9000 includes four pulse outputs that are proportional
to the energy accumulation, in the CF1 through CF4 output pins.
Energy and Phase Selection
The CFxSEL[2:0] bits in the CFMODE register select which
type of energy to output on the CFx pin, including total or
fundamental watt, VA R , and VA. Then, the TERMSELx bits in
the COMPMODE register select which phase energies to
include in the CF output.
For example, with the CFMODE register, CF1SEL[2:0] bits = 000
and the COMPMODE register, TERMSEL1[2:0] bits = 111, CF1
indicates the total watt output of Phase A, Phase B, and Phase C.
To calibrate the Phase A, Phase B, and Phase C total watt
accumulation at the same time, using CF1 for total AWAT T,
CF2 for total BWAT T, and CF3 for total C WAT T, configure the
CFMODE register, the CF1SEL, CF2SEL, and CF3SEL bits = 000;
the COMPMODE register, TERMSEL0[2:0] bits = 001; the
COMPMODE register, TERMSEL1[2:0] bits = 010; and the
COMPMODE register, TERMSEL2[2:0] bits = 100
Configuring the Maximum CF Pulse Output Frequency
It is recommended to write xTHR = 0x0010_0000. CFxDEN
can range from 2 to 65535. Configure CFxDEN to tune the CF
frequency output. The relationship between the xTHR, CFxDEN,
and AWATT values is given in the following equation:
××
×
=
CFxDENxTHR
AWATTf
CF
DTOF
512
)Hz(
Then, the maximum recommended CF pulse output frequency
is 78.862 kHz.
kHz9.78
25120000_0010x0
066,694,2010096.4
)Hz(_
6
=
××
××
=
CFMAXIMUM
where:
f
DTOF
is 4.096MHz.
AWAT T is the value at full scale, 20,694,066.
xTHR is 0x0010_0000.
CFDEN is 2.
The default CF pulse output using power-on reset values of
xTHR and CFxDEN with full-scale inputs is
Hz5.
38
xFFFF0
512FFFF_
0000x0
066,694
,2010
096.4
)Hz(_
6
=
×
×
×
×
=
CFMAXIMUM
Configuring the CF Pulse Width
The pulse width is determined by the CFx_LT bit in the
CF_LCFG register and the CF_LTMR register value.
With CFx_LT equal to zero, the active low pulse width is set at
80 ms for frequencies lower than 1/(2 × 80 ms) = 6.25 Hz. For
higher frequencies, the duty cycle is 50% if CFxDEN is even, or
(1 + 1/CFxDEN) × 50% if CFxDEN is odd.
If CFx_LT is set to 1, the CF active low pulse width is
CF_LTMR × 6/CLKIN. The maximum CF_LTMR is 327680 =
0x0005_0000, which results in a 327680/(6/CLKIN) = 80 ms
pulse. CF_LTMR must be greater than zero.
Table 16. CF Active Low Pulse Width and Duty Cycle based on CFx_LT and CF_LTMR
CFx_LT
Active Low Pulse Width
for Low Frequencies (ms)
Active Low Pulse Width for
High Frequencies when
CFxDEN is Even
Active Low Pulse Width for
High Frequencies when
CFxDEN is Odd
Behavior when
Entering No-Load
0 80 50% (1 + 1/CFxDEN) × 50% If CFx is low, finish current pulse,
then return high.
1 CF_LTMR × 6/CLKIN × 1000 50% (1 + 1/CFxDEN) × 50% If CFx is low, keep CFx low until
no-load state is finished.
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