MCP3906AT-ISLASHSS datasheet(16/26 Pages) MICROCHIP

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MCP3905A/05L/06A

DS22011A-page 16

The

high-frequency

output

HFOUT has lower

integration times and, thus, higher frequencies. The

output frequency value can be calculated with the

following equation:

EQUATION 4-2:

HFOUT FREQUENCY

OUTPUT EQUATION

The constant HFC depends on the FOUT0 and FOUT1

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 FOUT0/1 and HFOUT is equal to 0.0015%

of the maximum output frequency (respectively FC and

HFC) 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 FC 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

TABLE 4-4:

MCP3905A/06A OUTPUT FREQUENCY SETTINGS

HFOUT Hz

()

8.06 V0

V1 G

HFC

VREF

()

----------------------------------------------------------------

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)

HFC is the frequency constant selected

VREF is the voltage reference

HFC

HFC (Hz)

HFC (Hz),

MCLK=

3.58 MHz

HFOUT (Hz), w/

full scale AC

inputs

FC (Hz)

FC (Hz),

MCLK=

3.58 MHz

64XFC

MCLK/215

109.25

23.71

MCLK/221

1.71

32XFC

MCLK/215

109.25

23.71

MCLK/220

3.41

16XFC

MCLK/215

109.25

23.71

MCLK/219

6.83

2048XFC

MCLK/27

27968.75

6070.12

MCLK/218

13.66

8XFC

MCLK/216

54.62

11.85

MCLK/219

6.83

64XFC

MCLK/216

54.62

11.85

MCLK/222

0.85

32XFC

MCLK/216

54.62

11.85

MCLK/221

1.71

16XFC

MCLK/216

54.62

11.85

MCLK/220

3.41

HFC

HFC (Hz)

HFC (Hz),

MCLK=

3.58 MHz

HFOUT (Hz), w/

full scale AC

inputs

FC (Hz)

FC (Hz),

MCLK=

3.58 MHz

64XFC

MCLK/215

109.25

23.71

MCLK/221

1.71

32XFC

MCLK/215

109.25

23.71

MCLK/220

3.41

16XFC

MCLK/215

109.25

23.71

MCLK/219

6.83

2048XFC

MCLK/27

27968.75

6070.12

MCLK/218

13.66

128XFC

MCLK/214

219.51

47.42

MCLK/221

1.71

64XFC

MCLK/214

219.51

47.42

MCLK/220

3.41

32XFC

MCLK/214

219.51

47.42

MCLK/219

6.83

16XFC

MCLK/214

219.51

47.42

MCLK/218

13.66

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