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Category: Datasheet/Specs

Hello everybody,

I'm planning to use the AD4115 but I can not get a clear answer about the voltage ranges in the input (with buffer). I use AVDD=5V.

The datasheet says +/-10V (I suppose with the VRef=2.5V). now, If I take the given formula Code = 2N – 1 × ((VIN × 0.1/VREF) + 1), the input range should be +/-25V in order to have the full range. Why is it limited to +/-10V ?
On the other way, the datasheet says page 24 :" The AD4115 voltage input pins are specified for an accuracy of ±10 V" and there is the picture 26 where it is given at +/-20V, or even at +/25V with some limitations. So it is very confusing. What is happening between 10 and 20V interval ?

Now, the VRef can be external, up to AVVD. if I use an external 5V reference voltage, what happen ? What are the ranges ? Is the given formula still correct ?

My goal is to measure voltages up to +/15V.

if someone can make this less confusing...

Jerome

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• You are welcome and also thank you for taking the interest in our product. If you have more questions, feel free to post another thread and we will be glad to support you. I will be closing…

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• Hi  ,

The +/-10V is the differential input signal where the full specification is guaranteed however the device is still functional and is able to convert a differential input signal of +/-VREF * 10. Having an input beyond the +/-10V may cause the device to behave outside the specified performance.

Please do not be confused of the terms differential input voltage range and absolute pin voltage. The absolute input pin voltage(+/-20V) is the maximum voltage that the VINx pin can accept. Note that the absolute input voltage pin must not be exceed for the device to properly function. On the other hand, the differential input voltage  is the differential voltage (VIN+ - VIN-) the ADC is able to read and convert.

The formula is still applicable even if you are using an external 5V reference will have wider differential input voltage range (+/-VREF*10) but your input signal per VINx will still be limited by the absolute input pin voltage.

You will be able to measure +/-15V using just a 2.5V reference.

Hope this helps and gives you clarity.

Regards,

JC

• Hello,

I'm sorry, it is not very clear because the datasheet does not define the terms and is ambiguous.
Page 24, figure 26 :  between what and what is defined "Absolute Input Pin Voltage"? Is this similar to  a common mode voltage superposed to the +/-10V  between two pins ?
If I use single ended inputs with VINCom to ground, figure 26 is irrelevant if I understand correctly. I can only get +/-10V with full accuracy, is it correct ?

Now, if precision is degraded between 10 and 15V if I want to acquire from -15 to 15V, what is the degradation ? Why nothing is given in these zones ?

I have a reference voltage of 5V available. Is using it enhance the +/10V range to +/-20V for single ended inputs with VINCom to ground ? It should be if the diagram fig 26 is still correct for absolute values (I guess from AVss).

Jerome.

• Hi  ,

Figure 26 shows the absolute pin voltage or the voltage range allowable for the voltage input pins and achieve guaranteed accuracy for AVDD = 5V. Each voltage pins of the AD4115 can accept +/-20V. The specified accuracy is for differential input voltage (VIN+ - VIN-) of +/-10V. For single-ended, when VINCOM is connected to ground (VIN+ - VINCOM), you can only have the specified accuracy for +/-10V.

The accuracy is only specified for differential voltage +/-10V as we have only tested the part for this range. You may refer to this FAQ if you want to get an estimated value for -15V to 15V. Note that this is only an estimated value, the actual performance could be better or worse.

Using a 5V reference will only increase your functional range to -/+50V. The specified accuracy is still limited to the differential voltage range (VINx+ - VINCOM) of +/-10V when VINCOM is grounded.

Regards,

JC

• Hello,

Ok, I see.

This is the weirdest specifications I've ever came acrossi for an  ADC. I've never seen any manufacturer specifying ADCs in only 2/5 of the full scale and giving no information outside this range ("functional" does not mean anything except the part will survive). That's beyond any understanding.
As I nevertheless trust AD for the usual quality of their products (and the premium price) , I guess that it will work correctly for +/15V..

Jerome.

• Hi  ,

You are welcome and also thank you for taking the interest in our product. If you have more questions, feel free to post another thread and we will be glad to support you. I will be closing this thread.

Regards,

JC