Is there any risk of permanent damage from using an incorrect bias resistor from pin 17 of AD7760 to AGND?

Answer: Yes, there is a high risk of damage due to the incorrect bias resistor. Excessive current will cause overheating, improper operation and could potentially lead to damage. We recommend using the correct resistor to ensure proper operation of the device - 100kOhms for 2.5V reference, and 160kOhms for 4.096V reference.

AD7760 EVB & EVAL-CED1Z Contunuous Sampling at 2.5 MSPS

Question I want to log a analog signal, and save it in a file on a computer. What is the maximum time the AD7760 EVB & EVAL-CED1Z can record at 2.5 MSPS? Answer The AD7760 EVB & EVAL-CED1Z can take a sample set of continuous data that is 500k samples in length. After this there is a bottleneck in the USB transfer beyond this buffer size. The file will save (with each sample – represented as the decimal value of the ADC output code) for whatever the last batch was sampled at – so it can be done for 2.5Msps. Note it is only for a batch and won’t do a stream beyond the 500k samples I mention.

Absolute maximum ratings of AD7760

Question Inquiry Description:Is it possible to feed nevative signals, relative to ground to the input of the on chip differential amplifier namely VINA+, VINA? .Or it is only possible to feed positive signals. I would need to input symmetrical signals relative to ground as a sinewave of +2V and -2V.In the datasheet absolute max ratings (table 4 and note1) it says -0.3 to +6.0V , but in datasheet it shows also to feed an input sinusoid of +/- 2.5 (fig,50, 52) Answer The details mentioned in the data sheet are correct.Please note that the values mentioned in the data sheet are the differential voltages(Vdiff=(V+)-(V-)). The inputs to the amplifier cannot exceedVdiff. (Vdiff is the supply going to the differential amplifier block=AVDD3) The testing of the amplifier pins was done by shorting the inputs of the differential amplifier with the feedback components populated and the devicefully powered up. Vdiff was raised to 5.7V. There are input clamps which turn on at 3.2V internally and the circuitry involved internally are 5Vdevices and therefore 6V ratng is correct. You could also connect one input to ground and the other to 5V. In general, as long as the AD7760 is fully powered with all the 5V and the 2.5Vsupplies then the absolute maximum ratings are correct.

Datasheet error of AD7760 (Figure 55 Decoupling recommendations))

Question Please see the following picture from Rev A of Datasheet of AD7760 (Figure 55 Decoupling recommendations)) of figure-55. It seems that the PIN5 in the red window should be PIN6. Answer Yes, it is a mistake, it should read Pin 6

AD7760: Bypass Digital Filters

Q Can all filters be bypassed? A Yes all can be bypassed. It’s described as “Modulator Output Mode” in the datasheet.

AD7760 at 5Msps output datarate

Q I am trying to run AD7760 at 5Msps output rate, and are confused by the timing parameters in the datasheet. I run the converter at MCLK=ICLK=20MHz, How do I configure the timing? A With regard to this mode. We have to look at the timing involved in taking data out at this rate. The mode that you are enquiring about is one which takes the data from the ADC at 5MHz. This means the data is not fully filtered by the digital filter path and bypasses the final stage in the filter which is the longest filter. This mode is not covered by our specifications listing which is run at 2.5MHz for fully filtered data. The interface timing is similiarly tested relative to operation at 2.5MHZ output data rate, this is why there are contradictions. The fastest rate of use of the AD7760 is with the modulator output. This runs at 20MHz rate and only the first 16 bits of the data output are required (due to quantization noise). We did not specify the number of bits for the 5MHz rate, so it would also be confined to 16 only or not. If so then the second part of the read cycle after each DRDY falling edge would not be necessary and so the timing requirements would be loosened.

Do you have any information on current consumption calculations for AD766x parts?

Q Do you have any information on current consumption calculations for AD766x parts? A There is only a negligible difference in the current consumption on these parts for differing input frequencies. In order to calculate the current consumption, you first need to know what configuration you are going to use, that is what modes you are going to use and at what decimation rate. You can then add up the power requirements for each item from the datasheet. For example for the AD7760, when using the whole lot i.e. Modulator + General + Diff Amp + Ref Buffer then the currents AIDD1-4 (provided in the datasheet power requirement specs on page 4) must be multiplied by their relevant voltage supplies and then the digital DIDD*DVDD must also be added to give the full power consumption for the mode. This would be the max power for the part, when it's using all the features and operating at the highest throughput rate 2.5MSPs. Any deviation from this (i.e. not using the ref buffer or diff amp) will then reduce the power used. There is also a power saving issue in the choice of decimation rate. The digital current is all that's affected from decimation rate to decimation rate. For the AD7760 over the full change from max throughput rate 2.5Mhz (dec x 8) to 78Khz (dec x256) there is a circa 50% reduction in DIDD for the part. The reduction in this current would not be as drastic for the AD7762/3 as the range of decimation rates is smaller, but there would be some reduction. Over the range of decimation rates the modulator and general currents will remain as is. So once you know the mode and the decimation rate that you are going to use, you can easily calculate the power requirements using the specs provided in the AD776X datasheets.

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