hx711_english (1229859)
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HX71124-Bit Analog-to-Digital Converter (ADC) for Weigh ScalesDESCRIPTIONFEATURESBased on Avia Semiconductor’s patentedtechnology, HX711 is a precision 24-bit analogto-digital converter (ADC) designed for weighscales and industrial control applications tointerface directly with a bridge sensor.The input multiplexer selects either Channel Aor B differential input to the low-noiseprogrammable gain amplifier (PGA).
Channel Acan be programmed with a gain of 128 or 64,corresponding to a full-scale differential inputvoltage of ±20mV or ±40mV respectively, whena 5V supply is connected to AVDD analog powersupply pin. Channel B has a fixed gain of 32. Onchip power supply regulator eliminates the needfor an external supply regulator to provide analogpower for the ADC and the sensor. Clock input isflexible. It can be from an external clock source, acrystal, or the on-chip oscillator that does notrequire any external component. On-chip poweron-reset circuitry simplifies digital interfaceinitialization.There is no programming needed for theinternal registers.
All controls to the HX711 arethrough the pins.VAVDD10uF• Two selectable differential input channels• On-chip active low noise PGA with selectable gainof 32, 64 and 128• On-chip power supply regulator for load-cell andADC analog power supply• On-chip oscillator requiring no externalcomponent with optional external crystal• On-chip power-on-reset• Simple digital control and serial interface:pin-driven controls, no programming needed• Selectable 10SPS or 80SPS output data rate• Simultaneous 50 and 60Hz supply rejection• Current consumption including on-chip analogpower supply regulator:normal operation < 1.5mA, power down < 1uA• Operation supply voltage range: 2.6 ~ 5.5V• Operation temperature range: -40 ~ +85℃• 16 pin SOP-16 packageAPPLICATIONS• Weigh Scales• Industrial Process ControlVSUPS8550R22.7~5.5VR1VFBLoad cellBASEVSUPDVDDAVDDINA+Analog Supply RegulatorDOUTINA-INB+INB-InputMUXDigitalInterface24-bit Σ∆ADCPD_SCKPGAGain = 32, 64, 128VBGBandgap ReferenceTo/FromMCURATEInternalOscillatorHX7110.1uFAGNDXIXOFig.
1 Typical weigh scale application block diagramTEL: (592) 252-9530 (P. R. China)EMAIL: market@aviaic.comAVIA SEMICONDUCTORHX711Pin DescriptionRegulator PowerVSUP116DVDDDigital PowerRegulator Control OutputBASE215RATEOutput Data Rate Control InputAnalog PowerAVDD314XICrystal I/O and External Clock InputCrystal I/OSerial Data OutputRegulator Control InputVFB413XOAnalog GroundAGND512DOUTReference BypassVBG611PD_SCK Power Down and Serial Clock InputCh.
A Negative InputINNA710INPBCh. B Positive InputCh. A Positive InputINPA89INNBCh. B Negative InputSOP-16L PackagePin #NameFunction12345678910111213141516VSUPBASEAVDDVFBAGNDVBGINAINA+INBINB+PD_SCKDOUTXOXIRATEDVDDPowerAnalog OutputPowerAnalog InputGroundAnalog OutputAnalog InputAnalog InputAnalog InputAnalog InputDigital InputDigital OutputDigital I/ODigital InputDigital InputPowerDescriptionRegulator supply: 2.7 ~ 5.5VRegulator control output（NC when not used）Analog supply: 2.6 ~ 5.5VRegulator control input（connect to AGND when not used）Analog GroundReference bypass outputChannel A negative inputChannel A positive inputChannel B negative inputChannel B positive inputPower down control (high active) and serial clock inputSerial data outputCrystal I/O (NC when not used）Crystal I/O or external clock input, 0: use on-chip oscillatorOutput data rate control, 0: 10Hz; 1: 80HzDigital supply: 2.6 ~ 5.5VTable 1 Pin DescriptionAVIA SEMICONDUCTOR2HX711KEY ELECTRICAL CHARACTERISTICSParameterFull scale differentialinput rangeNotesTYPMAX±0.5(AVDD/GAIN)V(inp)-V(inn)Common mode inputOutput data rateMINAGND+1.2Internal Oscillator, RATE = 0Internal Oscillator, RATE =DVDDCrystal or external clock,RATE = 0Crystal or external clock,RATE = DVDDUNITVAVDD-1.310VHz80fclk/1,105,920fclk/138,240Output data coding2’s complementOutput settling time (1)RATE = 0400RATE = DVDD50Gain = 1280.2Gain = 640.4Gain = 128，RATE = 050Gain = 128，RATE = DVDD90Input offset（Gain = 128）±6nV/℃Gain（Gain = 128）±5ppm/℃Gain = 128，RATE = 0100dBPower supply rejection Gain = 128，RATE = 0Reference bypass（VBG）Crystal or external clockfrequency100dB1.25VInput offset driftInput noiseTemperature driftInput common moderejectionPower supply voltageAnalog supply current(including regulator)Digital supply current80000017FFFFF11.0592msmVnV(rms)20MHzVDVDD2.65.5AVDD，VSUP2.65.5Normal1400Power down0.3Normal100Power down0.2HEXµAµA（1）Settling time refers to the time from power up, reset, input channel change and gain changeto valid stable output data.Table 2 Key Electrical CharacteristicsAVIA SEMICONDUCTOR3HX711Analog InputsChannel A differential input is designed tointerface directly with a bridge sensor’sdifferential output.
It can be programmed with again of 128 or 64. The large gains are needed toaccommodate the small output signal from thesensor. When 5V supply is used at the AVDD pin,these gains correspond to a full-scale differentialinput voltage of ±20mV or ±40mV respectively.Channel B differential input has a fixed gain of32. The full-scale input voltage range is ±80mV,when 5V supply is used at the AVDD pin.Power Supply OptionsDigital power supply (DVDD) should be thesame power supply as the MCU power supply.When using internal analog supply regulator,the dropout voltage of the regulator depends onthe external transistor used. The output voltage isequal to VAVDD=VBG*(R1+R2)/ R1 (Fig.
1). Thisvoltage should be designed with a minimum of100mV below VSUP voltage.If the on-chip analog supply regulator is notused, the VSUP pin should be connected to eitherAVDD or DVDD, depending on which voltage ishigher. Pin VFB should be connected to Groundand pin BASE becomes NC. The external 0.1uFbypass capacitor shown on Fig. 1 at the VBGoutput pin is then not needed.Clock Source OptionsBy connecting pin XI to Ground, the on-chiposcillator is activated. The nominal output datarate when using the internal oscillator is 10(RATE=0) or 80SPS (RATE=1).If accurate output data rate is needed, crystal orexternal reference clock can be used. A crystalcan be directly connected across XI and XO pins.An external clock can be connected to XI pin,through a 20pF ac coupled capacitor. Thisexternal clock is not required to be a square wave.It can come directly from the crystal output pin ofthe MCU chip, with amplitude as low as 150 mV.Output Data Rate and FormatWhen using the on-chip oscillator, output datarate is typically 10 (RATE=0) or 80SPS(RATE=1).When using external clock or crystal, outputdata rate is directly proportional to the clock orcrystal frequency.
Using 11.0592MHz clock orcrystal results in an accurate 10 (RTE=0) or80SPS (RATE=1) output data rate.The output 24 bits of data is in 2’s complementformat. When input differential signal goes out ofthe 24 bit range, the output data will be saturatedat 800000h (MIN) or 7FFFFFh (MAX), until theinput signal comes back to the input range.Serial InterfacePin PD_SCK and DOUT are used for dataretrieval, input selection, gain selection and powerdown controls.When output data is not ready for retrieval,digital output pin DOUT is high. Serial clockinput PD_SCK should be low.
When DOUT goesto low, it indicates data is ready for retrieval. Byapplying 25~27 positive clock pulses at thePD_SCK pin, data is shifted out from the DOUToutput pin. Each PD_SCK pulse shifts out one bit,starting with the MSB bit first, until all 24 bits areshifted out. The 25th pulse at PD_SCK input willpull DOUT pin back to high (Fig.2).Input and gain selection is controlled by thenumber of the input PD_SCK pulses (Table 3).PD_SCK clock pulses should not be less than 25or more than 27 within one conversion period, toavoid causing serial communication error.InputPD_SCK PulsesGainchannel25A12826B3227A64Table 3 Input Channel and Gain SelectionWhen using a crystal or an external clock, theinternal oscillator is automatically powered down.AVIA SEMICONDUCTOR4HX711Next Output DataCurrent Output DataOne conversion periodMSBDOUTLSBT2T3T1PD_SCK123PD_SCK12PD_SCK12Next Conversion：CH.A, Gain:128424253424252634242526T4Next Conversion：CH.B, Gain:3227Next Conversion：CH.B, Gain:64Fig.2 Data output, input and gain selection timing and controlSymbolNoteMINT1DOUT falling edge to PD_SCK rising edge0.1T2PD_SCK rising edge to DOUT data readyT3PD_SCK high time0.21T4PD_SCK low time0.21Reset and Power-DownWhen chip is powered up, on-chip power onrest circuitry will reset the chip.Pin PD_SCK input is used to power down theHX711.
When PD_SCK Input is low, chip is innormal working mode.TYPMAXUnit µs0.1 µs50 µs µspowered down. When PD_SCK returns to low,chip will reset and enter normal operation mode.After a reset or power-down event, inputselection is default to Channel A with a gain of128.Application ExamplePower down:PD_SCK60µ sPower downNormalFig.1 is a typical weigh scale application usingHX711.
It uses on-chip oscillator (XI=0), 10Hzoutput data rate (RATE=0). A Single powersupply （2.7～5.5V） comes directly from MCUpower supply. Channel B can be used for batterylevel detection. The related circuitry is not shownon Fig. 1.Fig.3 Power down controlWhen PD_SCK pin changes from low to highand stays at high for longer than 60µs, HX711enters power down mode (Fig.3). When internalregulator is used for HX711 and the externaltransducer, both HX711 and the transducer will beAVIA SEMICONDUCTOR5HX711Reference PCB Board (Single Layer)Fig.4 Reference PCB board schematicFig.5 Reference PCB board layoutAVIA SEMICONDUCTOR6HX711Reference Driver (Assembly)/*------------------------------------------------------------------Call from ASM:LCALL ReaADCall from C:extern unsigned long ReadAD(void);..unsigned long data;data=ReadAD();..----------------------------------------------------------------------*/PUBLICReadADHX711ROMsegment codersegHX711ROMsbitADDO = P1.5;sbitADSK = P0.0;/*-------------------------------------------------OUT: R4, R5, R6, R7R7=>LSB---------------------------------------------------*/ReadAD:CLRADSK//AD Enable（PD_SCK set low）SETB ADDO//Enable 51CPU I/0JBADDO,$//AD conversion completed?MOVR4,#24ShiftOut:SETB ADSK//PD_SCK set high（positive pulse）NOPCLRADSK//PD_SCK set lowMOVC,ADDO//read on bitXCHA,R7//move dataRLCAXCHA,R7XCHA,R6RLCAXCHA,R6XCHA,R5RLCAXCHA,R5DJNZ R4,ShiftOut//moved 24BIT?SETB ADSKNOPCLRADSKRETENDAVIA SEMICONDUCTOR7HX711Reference Driver（C）//------------------------------------------------------------------sbitADDO = P1^5;sbitADSK = P0^0;unsigned long ReadCount(void){unsigned long Count;unsigned char i;ADDO=1;ADSK=0;Count=0;while(ADDO);for (i=0;i<24;i++){ADSK=1;Count=Count<<1;ADSK=0;if(ADDO) Count++;}ADSK=1;Count=Count^0x800000;ADSK=0;return(Count);}AVIA SEMICONDUCTOR8HX711Package Dimensions9.90 10.109.706.006.205.803.90 4.103.701.270.480.391.601.20MAXTypUnit: mmMINSOP-16L PackageAVIA SEMICONDUCTOR9.
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