AD7715: Debugging the output

Question We have an AD converter, it's the AD7715. We don't manage to have the right output. If we put on the input pin 0.0 Volts, the converter indicate that we are on the level 65535. We don't understand. Answer 65535 corresponds to the full-scale (all ones) output of the ADC. I suspect that something fairly simple has gone wrong in your circuit. First check connections at all pins, look for power, reference, ground and analog input. After power on, the default state of the AD7715 is output a conversion every 0.0166seconds (60Hz update rate). With nothing else connected to the interface, place a scope on the /DRDY pin and you should see it toggling at a frequency of 60Hz. After confirming operation of the AD7715, next test out the interface. Try to read the default values from the status register. After power up the status register should return 28Hex. If you don't get this value, you need to look in details at the hardware interface. When using the digital interface of the AD7715, it is critical that you provide the correct number of clock cycles when reading from or writing to the control registers. If you provide one extra clock cycle and then write to the part, you will put the part into an unexpected state. Similarly if you are reading from a 24bit register and you only provide 20 clock cycles, the interface will be out of synchronisation. One possible cause is spurious clocks on the SCLK line. The interface expects the first bit of any write to be a zero. If the first bit is a one, it will ignore all writes until it sees a zero. If after performing a read, you leave DIN low, any spurious clocks on the SCLK line will clock a bit into the Communications register. The next time you write eight bits to the Communications register, only the first seven bits will be loaded and the eighth bit will be interpreted as the first bit of a subsequent write. You can avoid this problem by pulling DIN high after each write.

The problem is that they give a step on the PT100 and the digital filter has a certain settling time.

Q The problem is that they give a step on the PT100 and the digital filter has a certain settling time. So each time they change the channel, they will have to wait for 3-4 samples to read out correct values, cycles depending if they synchronize a filter reset with the step given to the sensor Would you confirm this? A When a step change occurs on the AD7715, the filter will require 3 conversion cycles to settle. If DRDY is high before the channel change, DRDY will stay high for 3 conversion cycles after the channel change. When DRDY goes low, a valid conversion will be available. However, with the AD7715, if DRDY is low before the channel change (i.e. another conversion has been completed before the channel change occurs), the DRDY line stays low following the channel change - it is not reset high. In this case, a dummy read is required. The dummy read of the data register is needed before correct data gets loaded into the data register. So, in summary, one invalid reading may be received due to the dummy read. However, if sufficient settling time is allowed after the channel change, the second reading (after the dummy read) should be valid.

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The AD7715 is a complete analog front end for low frequency measurement applications. The part can accept low level input signals directly from a transducer...
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Table of Contents

+Documents
+General: FAQ
+AD1139: FAQ
+AD7091R Conversion Result Change
+AD1556: FAQ
+AD1580: FAQ
+AD1582: FAQ
+AD2S1200: FAQ
+AD2S1205: FAQ
+AD2S1210: FAQ
+AD2S75: FAQ
+AD2S80: FAQ
+AD2S80A: FAQ
+AD2S82A: FAQ
+AD2S83: FAQ
+AD2S90: FAQ
+AD2S99: FAQ
+AD4110-1: FAQ
+AD411x: FAQ
+AD5940: FAQ
+AD598: FAQ
+AD650: FAQ
+AD652: FAQ
+AD654: FAQ
+AD7091: FAQ
+AD7091R-X: FAQ
+AD711: FAQ
+AD7124-4: FAQ
+AD7124-8: FAQ
+AD7134: FAQ
+AD713: FAQ
+AD7142: FAQ
+AD7147: FAQ
+AD7148: FAQ
+AD7150: FAQ
+AD7151: FAQ
+AD7175-2: FAQ
+AD7176-2: FAQ
+AD7176: FAQ
+AD717x: FAQ
+AD7190: FAQ
+AD7192: FAQ
+AD7193: FAQ
+AD7195: FAQ
+AD719x: FAQ
+AD7265: FAQ
+AD7266: FAQ
+AD7280: FAQ
+AD7291: FAQ
+AD7298: FAQ
+AD7305: FAQ
+AD7321: FAQ
+AD7323: FAQ
+AD7328: FAQ
+AD7366-5: FAQ
+AD7367: FAQ
+AD736ARZ: FAQ
+AD737: FAQ
+AD738x : FAQ
+AD7398: FAQ
+AD7400A: FAQ
+AD7401: FAQ
+AD7403: FAQ
+AD74111: FAQ
+AD7415: FAQ
+AD7416: FAQ
+AD7417: FAQ
+AD7418: FAQ
+AD7450: FAQ
+AD7475: FAQ
+AD7484: FAQ
+AD7490: FAQ
+AD7492: FAQ
+AD75019: FAQ
+AD7503: FAQ
+AD7541A: FAQ
+AD7546: FAQ
AD7547: FAQ
+AD7568: FAQ
+AD7578: FAQ
+AD7606-4: FAQ
+AD7606: FAQ
+AD7606B: FAQ
+AD7606C: FAQ
+AD7608: FAQ
+AD7616 FAQ
+AD7616-P: FAQ
+AD7621: FAQ
+AD7625: FAQ
+AD7626: FAQ
+AD7631: FAQ
+AD7653: FAQ
+AD7654: FAQ
+AD7655: FAQ
+AD7656: FAQ
+AD7657-1: FAQ
+AD7663: FAQ
+AD7674: FAQ
+AD7675: FAQ
+AD7678: FAQ
+AD7682: FAQ
+AD7683: FAQ
+AD7684: FAQ
+AD7685: FAQ
+AD7688: FAQ
+AD7689: FAQ
+AD7690: FAQ
+AD7691: FAQ
+AD7705: FAQ
+AD7706: FAQ
+AD7707: FAQ
+AD7708: FAQ
+AD7709: FAQ
+AD7710: FAQ
+AD7711A: FAQ
+AD7712: FAQ
+AD7713: FAQ
+AD7714: FAQ
+AD7714YN: FAQ
-AD7715: FAQ
- The problem is that they give a step on the PT100 and the digital filter has a certain settling time.
- AD7715: Debugging the output
+AD7716: FAQ
+AD7718: FAQ
+AD7719: FAQ
+AD7720: FAQ
+AD7722: FAQ
+AD7725: FAQ
+AD7730: FAQ
+AD7731: FAQ
+AD7732: FAQ
+AD7738: FAQ
+AD7740: FAQ
+AD7741: FAQ
+AD7745: FAQ
+AD7746: FAQ
+AD7747: FAQ
+AD7760: FAQ
+AD7763: FAQ
+AD7766: FAQ
+AD7768: FAQ
+AD777x: FAQ
+AD7780: FAQ
+AD7785: FAQ
+AD7787: FAQ
+AD7788: FAQ
+AD7790: FAQ
+AD7792: FAQ
+AD7793: FAQ
+AD7794: FAQ
+AD7795: FAQ
+AD7798: FAQ
+AD7799: FAQ
+AD7805: FAQ
+AD7808: FAQ
+AD7809: FAQ
+AD780: FAQ
+AD7811: FAQ
+AD7812: FAQ
+AD7817: FAQ
+AD7819: FAQ
+AD7821: FAQ
+AD7825: FAQ
+AD7829: FAQ
+AD7835: FAQ
+AD7849: FAQ
+AD7851: FAQ
+AD7854: FAQ
+AD7856: FAQ
+AD7858: FAQ
+AD7859: FAQ
+AD7864: FAQ
+AD7865 : FAQ
+AD7872: FAQ
+AD7874: FAQ
+AD7879: FAQ
+AD7887: FAQ
+AD7888: FAQ
+AD7891-1: FAQ
+AD7891: FAQ
+AD7893-2: FAQ
+AD7895: FAQ
+AD7896: FAQ
+AD7899: FAQ
+AD7912: FAQ
+AD7921: FAQ
+AD7924: FAQ
+AD7927: FAQ
+AD7938: FAQ
+AD7942: FAQ
+AD7949: FAQ
+AD7960: FAQ
+AD7961: FAQ
+AD797: FAQ
+AD7980: FAQ
+AD7982: FAQ
+AD7984: FAQ
+AD7986: FAQ
+AD7988-1: FAQ
+AD7993: FAQ
+AD7994: FAQ
+AD7997: FAQ
+AD7998: FAQ
+ADA2200: FAQ
+ADAS1000: FAQ
+ADAS3022: FAQ
+ADAS3023: FAQ
+ADC: FAQ
+ADVFC32: FAQ
+EVAL-AD7719-EB: FAQ
+EVAL-ADAS3022EDZ: FAQ
+RDC1740: FAQ
+AD4030-24: FAQ
+AD4114: FAQ
+AD4116: FAQ
+AD4130-8 FAQ
+AD4131-8: FAQ
+AD4134 FAQ
+AD4170: FAQ
+AD4858
+AD674BBD: FAQ
+AD7172-2: FAQ
+AD7175-8: FAQ
+AD7191: FAQ
AD73360: FAQ
+AD73360AR: FAQ
+AD73360L: FAQ
+AD7357: FAQ
+AD7386-4: FAQ
+AD738x-4: FAQ
AD7398 SPI Voltage vs VCC
+AD7457: FAQ
+AD7606C-16: FAQ
+AD7609: FAQ
+AD7656-1: FAQ
AD7660: FAQ
+AD7665: FAQ
+AD7680: FAQ
+AD7686: FAQ
+AD7764: FAQ
+AD7778: FAQ
AD7892: FAQ
+AD7980SRMZ-EP: FAQ
+AD7991: FAQ
+AD9243: FAQ
+AD9260: FAQ
+AD9261: FAQ
+AD9262: FAQ
+AD974: FAQ
+AD976A: FAQ
+AD977A: FAQ
+ADAQ4003: FAQ
+ADAQ7768-1: FAQ
+ADAQ8092 FAQ
+DC590, DC2026, QuikEval: FAQs
+EVAL-AD7768-4FMCZ: FAQ
+Legacy LTC - Sigma Delta ADCs FAQ
+LTC2408: FAQ
+LTC2497: FAQ
+MAX1028: FAQ
+MAX1036: FAQ
+MAX1037EKA+: FAQ
+MAX11040GUU+: FAQ
+MAX11043: FAQ
+MAX11045: FAQ
+MAX11046 16-BIT AD: FAQ
+MAX11048: FAQ
+MAX11100EUB+: FAQ
+MAX11101: FAQ
+MAX11103: FAQ
+MAX11108: FAQ
MAX11125: FAQ
+MAX11125ATI+: FAQ
+MAX11130: FAQ
+MAX11131ATI+: FAQ
+MAX11136ATI+: FAQ
+MAX11150EVKIT#: FAQ
+MAX11154: FAQ
MAX11156: FAQ
+MAX11156ETC+: FAQ
+MAX11158: FAQ
+MAX11163: FAQ
+MAX11168EUB+: FAQ
+MAX11169EUB+: FAQ
+MAX11190: FAQ
+MAX11190ATE+: FAQ
MAX11192: FAQ
+MAX11192EVKIT#: FAQ
+MAX11200: FAQ
+MAX11200EEE+: FAQ
+MAX11201: FAQ
+MAX11203EEE+: FAQ
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+MAX11207EEE+: FAQ
MAX11210: FAQ
+MAX11210EEE+: FAQ
+MAX11213EEE+T: FAQ
MAX11214: FAQ
MAX11214EUG+: FAQ
+MAX11214EUG+_T1: FAQ
+MAX11216: FAQ
+MAX11254ATJ+: FAQ
+MAX11254EVKIT#: FAQ
+MAX11259AWX+T: FAQ
+MAX11259PMB#: FAQ
+MAX11261BOB#: FAQ
+MAX11261ENX+: FAQ
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+MAX11625: FAQ
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+MAX11645EWC+T: FAQ
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+MAX11900: FAQ
MAX11905: FAQ
+MAX11905EVKIT#: FAQ
+MAX1202AEAP+: FAQ
+MAX1220: FAQ
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