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Category: Datasheet/Specs

I  am FAE in Japanese distributor.

Datasheet of AD7195 explains “The AD7195 also scales the ac excitation switching frequency

in accordance with the output data rate. “

Could you tell me the ac excitation switching frequency at ODR=100Hz?

C8 and C10 of EVAL-AD7195 are 1nF ,and R3 and R4 are 100ohm.

The Cut off frequency(Fc) is 1.6MHz.

The LPF works as Anti Arias Filter.

Could we use Fc=100Hz of LPF with ac excitation ?

Best regards

N.Kokubo

Top Replies

• Hi Kokubo,

The AC excitation switching frequency is set by the ODR. For each switching phase, the ADC will need the complete settling time to perform the conversion. If ODR is set to 100sps, time for the first conversion will be 8/ODR (4/ODR for phase 1, 4/ODR for phase 2). The 2 phase results are averaged to generate an output. After this, further conversions happen at 4/ODR as part performs running average. 4/ODR is approximate value. For More accurate values, try out  Virtual Eval with 2 channels and check timing analysis.

The LPF is needed to provide rejection at multiples of the modulator frequency. Please check weigh scales application on pg 43 of the AD7195 Data sheet

Thanks

Vikas J

• Hi Vikas san

I am checking  Virtual Eval with 2 channels.

Virtual Eval shows 25sps in the sinc4 ,chop disable, FS=48 and 4.9MHz clock.

ODR is 4.9e6/1024/48=100sps according to the formula in the datasheet

Why does Virtual Eval show 25sps?

Is Virtual Eval influenced AC excitation?

Does 1st/2nd Channel mean Phase1/2?

Best regards

N.Kokubo

• HI Vikas san

I am cheking your Virtual Eval with 2 channels.

Virtual Eval show 25sps with sin4, chop disable, FS=48 and 4.9MHz clock.

ODR is 100ps=4.92E6/1024/48 according to the formula in the datasheet.

Why does Virtual Eval show 25sps?

Is Virtual Eval influenced by AC excitation?

Best regards

N.Kokubo

• Hi Kokubo san

FS = 48 will give you ODR of 100sps for single channel, sinc4 and chop disabled.

Virtual Eval shows 25sps as the channels are multiplexed, hence if you need 100sps with AC excitation, then you would have to use FS accordingly.

In your case, FS = 12 will give ODR of approx 100sps.There is settling time involved when you enable more than 1 channel, AC excitation or chopping. Hence, you can refer to table 12 for filter word vs Output data rate when AC excitation and one channel is enabled.

Thanks

Vikas J

• Hi Vikas san

If AD7195 works with only 1 channel and AC excitation enable, AD7195 will behave like 2 channels.

AD7195 first outputs the result of ACX1=H, then output2 the result of ACX1=L.

the result of ACX1=L is averaged to the result of the previous ACX1=H.

Is my understanding correct?

Best regards

N.Kokubo

• Hi Kokubo san,

Yes,

In terms of simulation on Virtual Eval , AD7195 with AC excitation will behave like two channels enabled.

The part first outputs after 8/ODR duration. The output is running average of consecutive conversions when ACX = L and ACX = H.

Thanks

Vikas J

• Hi Vikas san

I well understand you.