MCP3909-ESLASHSS datasheet(22/44 Pages) MICROCHIP

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MCP3909

DS22025C-page 22

 2006-2012 Microchip Technology Inc.

4.8

Active Power 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 fre-

quencies are quite low in order to allow superior inte-

gration time (see Section 4.7 “Active Power 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

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

equivalent. For a given AC input signal with amplitude

of V, the equivalent RMS value is V/ sqrt(2), assuming

purely sinusoidal signals. Note that since the real

power is the product of two RMS inputs, the output fre-

quencies of AC signals are half of the DC inputs ones,

again assuming purely sinusoidal AC signals. The

constant FC depends on the FOUT0 and FOUT1 digital

settings. Table 4-2 shows FOUT0/1 output frequencies

for the different logic settings.

The high-frequency output HFOUT has lower integra-

tion times and, thus, higher frequencies. The output fre-

quency value can be calculated with the following

equation:

FOUT Hz



8.06 V0



GFC



VREF



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

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

TABLE 4-2:

ACTIVE POWER OUTPUT FREQUENCY CONSTANT FC FOR FOUT0/1 (VREF =2.4V)

FC (Hz)

(MCLK = 3.58 MHz)

FOUT Frequency (Hz)

with Full-Scale

DC Inputs

FOUT Frequency (Hz)

with Full-Scale

AC Inputs

MCLK/221

1.71

0.74

0.37

MCLK/220

3.41

1.48

0.74

MCLK/219

6.83

2.96

1.48

MCLK/218

13.66

5.93

2.96

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