AD7175-8 : settling time of ADC core in alternate synchronization mode

Question

Hello , 
 
 I have a question from our customer as followings. 
 Does AD7175-8 have any settling time in Alternate Synchronization Mode ? 
 
 AD7175-8 has a settling time when we use single conversion mode. 
 https://ez.analog.com/data_converters/precision_adcs/f/q-a/102922/ad7175-8-settling-time-of-single-conversion-mode/305594#305594 
 This is caused by entering sleep condition after conversion complete. 
 In Alternate Synchronization mode, AD7175-8 waits the next /SYNC signal to start conversion. 
 But I think that the AD7175-8 does not enter sleep mode in waiting next /SYNC. 
 So I think no settling time will not be occurred. 
 Does it true ? 
 If AD7175-8 have some settling time, what seconds will be needed ? 
 
 Best regards, 
 y-suzuki

JellenieR · Accepted Answer

Hi, 
 If you are encountering some issues with the timing, I would recommend to see this timing diagram on our Virtual Eval | Analog Devices Tool or Eval+ Software. 
 If you open a Virtual Eval Tool, you will observed that when converting on the AD717x, the very first conversion (Tsettle, first conversion in VE) is longer than subsequent conversions. If you enable multiple channels, check the time for Tsettle, first conversion and Tsettle, subsequent conversions, you will see that the first conversion is again longer. When the sequencer is being used with the ADC controlling everything (SYNC not being used), the ADC performs some parallel processing, processing the conversion on one channel while setting up the next channel. For the very first conversion, it cannot perform this parallel processing, hence the longer time. 
 When SYNC is being used, again, the part cannot perform any parallel processing. So, the time for every conversion after a SYNC pulse with be Tsettle, first conversion. 
 The SYNC input allows the user to reset the modulator and digital filter without affecting the setup conditions. This also allows the user to control the start of conversion from a known point, the rising edge of the SYNC input. 
 In normal SYNC mode, SYNC input can be use as a start conversion for a single channel. Thus, if you have multiple channels enabled and you want to control the start conversion of each channel an alternate synchronization mode can be used. However, like I mentioned above there will be a delay of 68MCLKs cycles after each release of SYNC pulse. Since in Alternate SYNC mode we used the SYNC pin for each channel your conversion time for each channel will be Tsettle, first conversion. 
 AD7175-8 will only enter standby mode after a single conversion mode and performing calibration modes. It will not go to standby mode if you set it up with continuous conversion mode. 
 Thanks, 
 Jellenie

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AD7175-8 : settling time of ADC core in alternate synchronization mode

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