ADRF5720 unstable attenuation when using parallel mode

Question

I just kept PS low, however the ATTEN3/SEROUT pin kept high, and when I toggled high LE,attenuation couldn't be changed correctly, however it was quite unstable. I wonder if it is because I didn't use a series 1 kΩ resistor to limit the current flowing in to the control pin, or I powered up VSS and VDD at the same time.

GokhanKaraova · Accepted Answer

Hi ZhangZhongli 
 
 Thanks a lot for the question. At first glance, your application issue is unrelated with the power-up sequence. However, it is always good practice to follow the recommended sequence and use case. 
 I've got points you could check if the part is operating correctly. 
 1) Could you read correct currents from the supply and control pins as described in the datasheet? If currents are incorrect, it is highly probable that the part is damaged. 
 2) Were you be able to operate the part in any other mode (parallel/ serial)? If not so, could you try the simplest option? 
 3) Is any other attenuation state work in your application? If you haven't tried, could you try couple? 
 Gokhan)

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ADRF5720 unstable attenuation when using parallel mode