Sep 13, 2011 #1 prateek_k_chd Member level 5 Joined Sep 25, 2009 Messages 87 Helped 3 Reputation 6 Reaction score 2 Trophy points 1,288 Activity points 1,988 I plan to use Vref+ & Vref- of the ADC of 16F877A. The voltages for these come from a potential divider and hence are high impedance. So,will placing a 0.1 uF cap on their pins (to store charge) be enough for the ADC? Or do I need to buffer these voltages first ? PIc's DS says the ADC cap is about 120pF.So I'm guessing the cap could do. But it would be great if anyone can speak from experience ! Thanks a lot !!
I plan to use Vref+ & Vref- of the ADC of 16F877A. The voltages for these come from a potential divider and hence are high impedance. So,will placing a 0.1 uF cap on their pins (to store charge) be enough for the ADC? Or do I need to buffer these voltages first ? PIc's DS says the ADC cap is about 120pF.So I'm guessing the cap could do. But it would be great if anyone can speak from experience ! Thanks a lot !!
Sep 13, 2011 #2 barry Advanced Member level 7 Joined Mar 31, 2005 Messages 6,333 Helped 1,194 Reputation 2,400 Reaction score 1,389 Trophy points 1,393 Location California, USA Activity points 34,480 I would buffer it. According to the datasheet, the Vref input has two levels, 5uA and 150uA, of input current; this will affect your voltage divider, and caps won't help that error.
I would buffer it. According to the datasheet, the Vref input has two levels, 5uA and 150uA, of input current; this will affect your voltage divider, and caps won't help that error.
Sep 13, 2011 #3 prateek_k_chd Member level 5 Joined Sep 25, 2009 Messages 87 Helped 3 Reputation 6 Reaction score 2 Trophy points 1,288 Activity points 1,988 Alright then. Buffer it is. Thanks !
Sep 13, 2011 #4 ALERTLINKS Advanced Member level 4 Joined Dec 13, 2003 Messages 1,258 Helped 396 Reputation 786 Reaction score 380 Trophy points 1,363 Location Pakistan Activity points 7,263 Impedence of the circuit should be less than 10K ohms.