MCP3905A Datasheet, PDF (16/26 Pages) Microchip Technology – Energy Metering ICs with Active Real Power Pulse Output

MCP3905A/05L/06A
The high-frequency output HF_OUT has lower
integration times and, thus, higher frequencies. The
output frequency value can be calculated with the
following equation:
EQUATION 4-2: HF_OUT FREQUENCY
OUTPUT EQUATION
HF_OUT(Hz)
=
8---.--0---6-----×_----V_----0----×_-----V_----1----×_----G_------×_-----H_-----F_----C-
(V_REF)²
Where:
V₀ is the RMS differential voltage on channel 0
V₁ is the RMS differential voltage on channel 1
G is the PGA gain on channel 0 (current channel)
HF_C is the frequency constant selected
V_REF is the voltage reference
The constant HF_C depends on the F_OUT0 and F_OUT1
digital settings with the Table 4-4.
The detailed timings of the output pulses are described
in the Timing Characteristics table (see Section 1.0
“Electrical Characteristics” and Figure 1-1).
MINIMAL OUTPUT FREQUENCY FOR
NO-LOAD THRESHOLD
The MCP3905A/05L/06A devices also include, on
each output frequency, a no-load threshold circuit that
will eliminate any creep effects in the meter. The
outputs will not show any pulse if the output frequency
falls below the no-load threshold. The minimum output
frequency on F_OUT0/1 and HF_OUT is equal to 0.0015%
of the maximum output frequency (respectively F_C and
HF_C) for each of the F2, F1 and F0 selections (see
Table 4-3 and Table 4-4); except when F2, F1,
F0 = 011. In this last configuration, the no-load
threshold feature is disabled. The selection of F_C will
determine the start-up current load. In order to respect
the IEC standards requirements, the meter will have to
be designed to allow start-up currents compatible with
the standards by choosing the FC value matching
these requirements. For additional applications
information on no-load threshold, startup current and
other meter design points, refer to AN994, "IEC
Compliant Active Energy Meter Design Using The
MCP3905/6”, (DS00994).
TABLE 4-3: MCP3905L OUTPUT FREQUENCY SETTINGS
F2 F1 F0
HF_C
HF_C (Hz)
0
0
0
64XF_C MCLK/2¹⁵
0
0
1
32XF_C MCLK/2¹⁵
0
1
0
16XF_C MCLK/2¹⁵
0
1
1 2048XF_C MCLK/2⁷
1
0
0
8XF_C
MCLK/2¹⁶
1
0
1
64XF_C MCLK/2¹⁶
1
1
0
32XF_C MCLK/2¹⁶
1
1
1
16XF_C MCLK/2¹⁶
HF_C (Hz),
MCLK=
3.58 MHz
109.25
109.25
109.25
27968.75
54.62
54.62
54.62
54.62
HF_OUT (Hz), w/
full scale AC
inputs
23.71
23.71
23.71
6070.12
11.85
11.85
11.85
11.85
TABLE 4-4: MCP3905A/06A OUTPUT FREQUENCY SETTINGS
F2 F1 F0
HF_C
HF_C (Hz)
0
0
0
64XF_C MCLK/2¹⁵
0
0
1
32XF_C MCLK/2¹⁵
0
1
0
16XF_C MCLK/2¹⁵
0
1
1 2048XF_C MCLK/2⁷
1
0
0 128XF_C MCLK/2¹⁴
1
0
1
64XF_C MCLK/2¹⁴
1
1
0
32XF_C MCLK/2¹⁴
1
1
1
16XF_C MCLK/2¹⁴
HF_C (Hz),
MCLK=
3.58 MHz
109.25
109.25
109.25
27968.75
219.51
219.51
219.51
219.51
HF_OUT (Hz), w/
full scale AC
inputs
23.71
23.71
23.71
6070.12
47.42
47.42
47.42
47.42
F_C (Hz)
MCLK/2²¹
MCLK/2²⁰
MCLK/2¹⁹
MCLK/2¹⁸
MCLK/2¹⁹
MCLK/2²²
MCLK/2²¹
MCLK/2²⁰
F_C (Hz)
MCLK/2²¹
MCLK/2²⁰
MCLK/2¹⁹
MCLK/2¹⁸
MCLK/2²¹
MCLK/2²⁰
MCLK/2¹⁹
MCLK/2¹⁸
F_C (Hz),
MCLK=
3.58 MHz
1.71
3.41
6.83
13.66
6.83
0.85
1.71
3.41
F_C (Hz),
MCLK=
3.58 MHz
1.71
3.41
6.83
13.66
1.71
3.41
6.83
13.66
DS22011A-page 16
© 2006 Microchip Technology Inc.