AD7747_power down mode

Q Here is a customer asked about the power down mode of AD7747. In datasheet, it say we can put AD7747 into power down mode by writing the configuration register. However, there is no detail about the description of the power down mode, for example, which portion of the part is power down? I think the digital interface should be alive, because it needs to monitor the command to get out of the power down mode. And How much time does it take to go into or come back from the power down mode? So could you please help provide some information about it. A as the digital section doesn't consume much power, most of the digital, especially I2C interface remains active at all times. the analog section is however powered down fully. The wake-up time is not defined, the customer could determine the wake-up time by measuring the time between the end of the write into the config register and the start of a conversion (excitation signal starts)

Extending the capacitance input range of AD7747

Q In the AD7747 datasheet it is mentioned that the capacitance input range is ±8 pF (changing), and it can accept up to 17 pF common-mode capacitance (not changing). Can this range be extended? A There is a method of extending the capacitance range for the AD7745 and AD7746. The range extension circuit is provided in circuit note CN-0129: http://www.analog.com/static/imported-files/circuit_notes/CN0129.pdf This circuit has to ensure that the charge transfer within the sensing capacitance CSENS remains within the input range of the AD7745/AD7746. To achieve this, the excitation voltage needs to be decreased by a factor of F, so that the sensing capacitance connected to the input can be increased by a factor F. The method used of scaling the AD7745/46 excitation voltage does not work for the AD7747, unfortunately. The excitation signal is not externally available on the AD7747, it is connected internally with the modulator to one CIN pin. The only possible method is to scale the CIN capacitance by connecting a small capacitor in series with the capacitive sensor. See suggestion in the paragraph attached below. Unfortunately I don't have any data to show how successful or stable this suggested solution might be. "Connect a known fixed capacitor in series with the sensor. That would work by equation C = C1 x C2 / (C1 + C2). This method results in a non-linear relation between the sensor capacitance and the output data, but this could be corrected in the host uC software. Also, the AD774x input range might not be fully used with implication of lower signal/noise ratio, but I believe the AD774x itself has enough resolution to keep the system resolution on required level. My main concern would be how stable is the serial capacitor over temperature and temperature compensation for that."

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AD7747 Production
The AD7747 is a high-resolution, S-? capacitance-to-digital converter (CDC). The capacitance to be measured is connected directly to the device inputs...
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AD7747 on Analog.com

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
+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
- AD7747_power down mode
- Extending the capacitance input range of AD7747
+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
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+AD780: FAQ
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+AD7812: FAQ
+AD7817: FAQ
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+AD7825: FAQ
+AD7829: FAQ
+AD7835: FAQ
+AD7849: FAQ
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+AD7874: FAQ
+AD7879: FAQ
+AD7887: FAQ
+AD7888: FAQ
+AD7891-1: FAQ
+AD7891: FAQ
+AD7893-2: FAQ
+AD7895: FAQ
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+AD797: FAQ
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+AD7988-1: FAQ
+AD7993: FAQ
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+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
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+MAX11045: FAQ
+MAX11046 16-BIT AD: FAQ
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