WEIGH SCALE SYSTEM
differential gain stage noise and reduce mechanical vibration
noise from the load cell. The cutoff frequency of the low-pass
filter should be as low as possible to minimize the overall
system noise. The reference voltage is typically generated by
dividing down the supply voltage (RVR1, RVR2). Use a bypass
capacitor located as close to VREFP as possible.
Figure 19 shows an example of a weigh scale system. OPA1,
OPA2, RG, and RF form a differential gain stage to amplify the
load cell output. The gain is equal to (1 + 2 RF/RG). Depend-
ing on the load cell, the typical gain setting is from 100 to 250.
RI and CI form a single-pole low-pass filter to band-limit the
5V
1.8V ~ 3.6V
EMI Filter
1µF
0.1µF
0.1µF
1µF
0.1µF
RVR1
AVDD
DVDD
DVCC
AVCC
0.1µF
RVR2
VREFP
EMI Filter
OPA1(1)
AINP
RI
ADS1244
MSP430Fx41x
RF
Load Cell
SCLK
P1.2/TA1
P1.0/TA0
XIN
XOUT/TCLK
CI
32.768kHz
RG
DRDY/ DOUT
RF
EMI Filter
OPA2(1)
AINN
RI
P1.1/TA0/MCLK
AVSS DVSS
CLK
VREFN
GND
EMI Filter
NOTE: (1) OPA2335 or OPA2277 recommended.
FIGURE 19. Weigh Scale System.
ADS1244
15
SBAS273
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