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AD5410- HOW TO ARREST Current OutPut Constant Glitches/Fluctuation.

Question asked by agniteja@saitroniks.com on Nov 13, 2017
Latest reply on Nov 15, 2017 by rrosario

Dear ADI/ rrosarioDRicemsameratjohnson,

Question : How to arrest the Output current fluctuation or How to eliminate the glitches current output in AD5410.  

Problem Explanation :

We are using AD5410 in our application and driving it from 2-20mA current output. In the data acquisition system, in order to read 2-20mA current output , we are using a Load Resistor(RL) of 120Ohms Tol:1% (Since the Voltage Drop Across the resistor is proportional to current flowing through the resistor) . After Connecting a calibrated current meter (DMM in mA mode) to measure the current and while simultaneously reading  the voltage waveform across the RL using an DSO (Hantek 1200) , We have the following observations -  

1. The current shown in the DMM is constant and not fluctuating .

2. The voltage waveform (which is proportional to the current flown)  measured across the R has constant glitches(i.e. the voltage constantly varies from a minimum value to maximum value)  as shown in the below voltagwave form

Very important Note: DAC Data Register is written/updated only ONCE for pumping one current value.  Multiple/cyclic writes to data register for the same current value is not being done. 

 Voltage wave form across the Load resistor 120Ohms which is directly proportional to the current pumped by AD5410.

Pl. observe the following points.: 

1. Current pumped by AD5410 = 2mA

2. Load Resistor = 120.6 Ohms 

3. Expected Voltage Drop Across load resistor - V = I x R => 0.002 X 120.6 = 0.2412 V = 241mV. 

4. Pl. check the Vavg = 244mV ~ 241mV difference is only  3mV 

5. Pl. Check the Vmax = 270mV corresponds to  2.2mA  & Vmin = 207mV.corresponds to 1.7mA. 

6.This shows that if AD5410 pumps current of 2mA and it is varying from 1.7mA to 2.2mA. (but pl. note that current meter i.e. DMM in mA mode is showing constant current value of 2.00mA).

7.The above glitches repeat at a frequency of 15uS.

 

Attachments Below:

1. Video of Oscilloscope capturing the voltage wave form. 

2. Schematic of AD5410. 

 

Your prompt reply is highly appreciated & valuable to us. 

Thanks in Advance.

 

N.AGNI TEJA

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