Cirrus-logic AN31 Manuel d'utilisateur

IntroductionBridge transducers are common ininstrumentation. This application note illustratessome bridge transducer digitizer circuits whichuse the C

12.5 mV (considered the nominal value for thisparticular selection of PGA gain and VREFvoltage) can be gain calibrated for input signalsfrom 20 % less

0.005VA+ VD+VREF+VREF-AIN1+CS550420 bitsAIN1-A0VA-SCLKSDATACONVCALXIN3262346(2) LT1007432201417CSDRDY1101582mV/VTransducer46041000.0051007+10≈ 3.6V0.

includes the negative supply rail. Oneapplication for this may be for measuring atemperature compensating resistor in series withthe bridge (see inset

0.005VA+ VD+VREF+VREF-AIN1+CS550420 bitsAIN1-A0VA-SCLKSDATACONVCALXIN3262346LT1007432201417CSDRDY1101582mV/VTransducer46041000.0051007+1017.8k10k≈ 3.6

issued to the converter only after the DG303switch has been switched to one position longenough for the buffer amplifier to have settledon the signal.

VA+ VD+VREF+VREF-AIN1+CS550420 bitsAIN1-A0VA- DGNDSCLKSDATACONVCALXIN3262346LT1007432201417CSDRDY1161015872k2k1k2mV/VTransducer+1041000.0051007+10+103

the converter is flipped and a conversion isperformed on channel one of the converter. Thenegative answer for channel one is thensubtracted from the p

10k10k4.096 MHz101VA+ MDRV+MDRV-VD+BX2XINXOUT0.1 0.1TP0610+100.124+5+5-VREF-VREF+6753R1R3R27.5k5.0k7.5k-5VA-VD-10-50.1 0.1+3014.7 nFDGNDAIN+AGND1 AGND

Switched Bridge with CS5504 Using ± 5 VAnalog SuppliesThis circuit in Figure 12 is basically identical tothe previous circuit, but is configured to ru

nominal. In other words, the gain can becalibrated for an input as low as 10 mV or ashigh as 15 mV when the nominal value is set for12.5 mV. The nomin

offset drift, amplifier noise (both thermal and1/f), amplifier finite open loop gain, andparasitic thermocouples. Parasitic thermocouplesare introduce

decade divider (74HC4017) can be followed bya binary 214 divider (74HC4020) to yield a25 Hz excitation frequency. The converter willoutput conversion

excitation. In external excitation mode, the BX1pin of the converter is an input and is used todetermine the polarity of the excitation. Thephase of t

Figure 16. CS5516 or CS5520 and a 1 mV/V AC-Excited Load Cell.10k10k10k4.096 MHz101VA+ MDRV+MDRV-VD+BX2XINXOUT0.10.12N3906+100.124+5+5-1.0 mV/VVREF-

the 5 mV span at a fifty samples per secondupdate rate. The CS5520 should be used ifhigher resolution is desired at the 50 Hz updaterate. Averaging 25

100k10k10k4.096 MHz101VA+ MDRV+MDRV-VD+BX2XINXOUT0.1 0.1TP0610+10 0.124+5+5GSE 4444Floating BeamPlatform-1.9 mV/VVREF-VREF+6753R1R3R25k*6k*5k*-5VA-VD-

4003002001000-4 -3 -2 -1 0 1 2 3 41000 Conversions1 = 1.07 LSBAverage = 0.035 LSBOutput wordrate = 50/secondOUTPUT CODE (1 LSB = 34.3 nV)OCCURANCES

rate of 1/second. Averaging 50 words reducesthe noise by √50, or by a factor of 7.07. Sincethe standard deviation, or rms value of the noiseillustr

a single +5 V supply, use two 100 ohm resistorsconnected in series between +5 V and ground.Then connect the input of the digitizer circuit tothe 2.5 V

• Notes •Bridge Transducer Digitizer Circuits28 AN31REV3

elements of the amplifier stage. Note that aninstrumentation amplifier is not needed becausethe A/D input is fully differential. The dualamplifier fun

All of the converters (CS5504-09) can beoperated with a single +5 V supply. All of theconverters can also be operated with +5 Vanalog supply and +3.3

negative offset into the amplifier and the zerotrim is used to finely adjust this offset. With zeroweight on the scale, the zero trim is adjusted toyi

Figure 5 illustrates an application which uses aninstrumentation amplifier to amplify and convertthe differential bridge signal to aground-referenced

measurement is required. Figure 6 illustrates anexample circuit in which the power to the bridgetransducer is switched on only when ameasurement is de

18.7k0.0150.01518.7kVA+VREF+VREF-AIN+CS550916 bitsAIN-SCLKSDATACONVCAL10k10k3503503503503216547LT1013BP/UP-11321616151449CSDRDY87100.18X 16610100kTP06

3014.096 MHz101VA+ MDRV+MDRV-VD+BX2XINXOUT0.1 0.1+5-VREF-VREF+R1R3R27.5k5k7.5kVA- VD-10-50.10.1+3014.7 nF4.7 nFDGNDAIN+AGND1 AGND2AIN-SMODESODSIDSCLKD