Hardware Description
2015 Microchip Technology Inc.
DS50002413A-page 17
3.1
INPUT AND ANALOG FRONT END
The MCP39F521 Power Monitor Demonstration Board will operate from 90V to 230V.
At the bottom of the main board are the high-voltage line and neutral connections. The
shunt sits on the neutral side, or low side, of a two-wire system. The board comes
populated with a surface mount 2 m
Ω
shunt. If a lower value external shunt is to be
used, the wires going from the external shunt to the CP1 and CP2 connections should
twisted together.
The neutral side of the two-wire system goes into a resistor divider on the voltage
channel input, along with a DC offset added from V
DD
. Anti-aliasing low-pass filters are
included. The voltage channel uses two 499 k
Ω
resistors to achieve a divider ratio of
1000:1. For a line voltage of 220 V
RMS
, the channel 1 input signal size will be
220 mV
RMS.
FIGURE 3-3:
Analog Front-End Circuitry.
Note that all of the analog circuitry associated with this part of the circuit is connected
to the analog ground plane (A
GND
).
499 k
LINE
499 k
1 k
33 nF
A
GND
A
GND
V1+
1 k
NEUTRAL
33 nF
A
GND
I1+
1 k
NEUTRAL OUT
33 nF
A
GND
I1-
2 m
Shunt
MCP39F521
CP1
CP2
