User manual

MCP3421 Weight Scale Demo Board User’s Guide
DS51918A-page 10  2010 Microchip Technology Inc.
1.2 ANALOG INPUT CONFIGURATION OPTIONS
The MCP3421 Weight Scale Demo Board has an MCP6V07 auto-zeroed op amp, to
investigate different signal conditioning configuration.
As shown in Figure 1-2, the user can configure the input signal chain with the following
three options, combining the jumpers:
a) Bypassing the MCP6V07: the MCP3421 input pins are directly connected to the
sensor output. In this case, the PGA of the MCP3421 is set to a gain of 8. The
jumpers must be set as follows: J4 and J5 are on the left position. J10 and J13
are ON, while J8, J9, J11 and J12 are OFF (see Figure 1-3a).
b) Extra gain is added by the low-noise, auto-zeroed op amp MCP6V07, before the
ADC. The added gain is 50x, and the ADC’s PGA is 2x. For this option the jump-
ers must be set as follows: J4 and J5 are on the right position; J9, J11 and J12
are ON, while J8, J10 and J13 are OFF (see Figure 1-3b).
c) PGA = 1x, but uses the MCP6V07 to add high gain. Extra gain is added by the
low-noise, auto-zeroed op amp MCP6V07, before the ADC. The added gain is
250x, and the ADC’s PGA is 1x. For this option the jumpers must be set as fol-
lows: J4 and J5 are on the right position; J8, J11 and J12 are ON, while J9, J10
and J13 are OFF (see Figure 1-3c).
d) Table 1-1 shows the jumper positions and their results.
FIGURE 1-2: Signal Conditioning and ADC on the MCP3421 Weight Scale Demo Board.