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RMS-DC converter AD8436 single supply questions

Question asked by MrChip on Jan 28, 2014
Latest reply on Feb 25, 2014 by MrChip

Hi,

 

I have studied the datasheet for the AD8436 RMS-DC converter quite a bit, but there are some things I cannot figure out when using it with a single supply. In the example Vcc = +5V, GND = 0V

1. To what is the output DC-voltage (OUT-pin) referenced?

a. Can I supply what ever voltage I want at OGND as the voltage I want it referenced to (for instance 0V) ?

b. Or must it be "real" ground = 0V or half supply = Vcc/2?

 

2. When using single supply and want to use a gain >1  with the input buffer, I believe there is something fishy with the data sheet. According to the explanations for the eval board, page 19, it seems that the amplification resistors connected to IBUFIN- would terminate in ground (=0V in this case). I guess the input opamp would rail-out because of this?

    a. Should the resistors terminate in IGND instead?

     b. ..and would it even work? - the IGND is not a very stiff voltage source as it is supplied with a two 100kOhm voltage divider.

     c. Can I supply IGND myself at ~Vcc/2, or would it introduce other problems, even if it is a good source?

 

3. Capacitor choice for the RMS pin - would an electrolyte be fine here? Even if very small signals < 1mV is used.

 

Any help would be most appreciated!

 

Regards

/John

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