MCP3906T-I/SS(2007) View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

MCP3906T-I/SS
(Rev.:2007)

Energy-Metering ICs with Active (Real) Power Pulse Output

Microchip Technology 

MCP3905/06

4.7 FOUT0/1 and HFOUT Output

Frequencies

The thresholds for the accumulated energy are differ-

ent for FOUT0/1 and HFOUT (i.e., they have different

transfer functions). The FOUT0/1 allowed output

frequencies are quite low in order to allow superior

integration time (see Section 4.6 “Low-Pass Filter

and DTF Converter”). The FOUT0/1 output frequency

can be calculated with the following equation:

EQUATION 4-1: FOUT FREQUENCY

OUTPUT EQUATION

FOUT(Hz)

=

8---.--0---6----×-----V----0----×-----V----1----×----G------×-----F----C-

(VREF)2

Where:

V0 = the RMS differential voltage on Channel 0

V1 = the RMS differential voltage on Channel 1

G = the PGA gain on Channel 0

(current channel)

FC = the frequency constant selected

VREF = the voltage reference

For a given DC input V, the DC and RMS values are

equivalent. For a given AC input signal with peak-to-

peak amplitude of V, the equivalent RMS value is

V/sqrt(2), assuming purely sinusoidal signals. Note that

since the active (real) power is the product of two RMS

inputs, the output frequencies of an AC signal is half

that of the DC equivalent signal, again assuming purely

sinusoidal AC signals. The constant FC depends on the

FOUT0 and FOUT1 digital settings. Table 4-3 shows

FOUT0/1 output frequencies for the different logic set-

tings.

TABLE 4-3: OUTPUT FREQUENCY CONSTANT FC FOR FOUT0/1 (VREF = 2.4V)

F1

F0

FC (Hz)

FC (Hz)

(MCLK = 3.58 MHz)

FOUT Frequency (Hz)

with Full-Scale

DC Inputs

FOUT Frequency (Hz)

with Full-Scale

AC Inputs

0

0

MCLK/221

1.71

0.74

0.37

0

1

MCLK/220

3.41

1.48

0.74

1

0

MCLK/219

6.83

2.96

1.48

1

1

MCLK/218

13.66

5.93

2.96

© 2007 Microchip Technology Inc.

DS21948D-page 15

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