MCP3909 datasheet(15/40 Pages) MICROCHIP

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DS22025A-page 15

MCP3909

3.15

Ground Connection (DGND)

DGND is the ground connection to internal digital

circuitry (SINC filters, multiplier, HPF, LPF, digital-to-

frequency converter and oscillator). To ensure

accuracy and noise cancellation, DGND must be

connected to the same ground as AGND, preferably

with a star connection. If a digital ground plane is

available, it is recommended that this device be tied to

this plane of the Printed Circuit Board (PCB). This

plane should also reference all other digital circuitry in

the system.

3.16

High-Frequency Output (HFOUT)

HFOUT is the high-frequency output of the device and

supplies the instantaneous real-power information. The

output is a periodic pulse output, with its period propor-

tional to the measured real power, and to the HFC

constant defined by F0, F1 and F2 pin logic states. This

output is the preferred output for calibration due to

faster output frequencies, giving smaller calibration

times. Since this output gives instantaneous real

power, the 2

ω ripple on the output should be noted.

However, the average period will show minimal drift.

3.17

Frequency Output (FOUT0, FOUT1)

FOUT0 and FOUT1 are the frequency outputs of the

device that supply the average real-power information.

The outputs are periodic pulse outputs, with its period

proportional to the measured real power, and to the FC

constant, defined by F0 and F1 pin logic states. These

pins include high-output drive capability for direct use

of electromechanical counters and 2-phase stepper

motors. Since this output supplies average real power,

any 2

ω ripple on the output pulse period is minimal.

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