Analog voltage referance pin

[Cristian Mitu]

Hello guys,


I have noticed that my BeagleBoneBlack has a VDD_ADC that is supposed to be a 1.8V  reference voltage. On the board that i am making i have some components that need 1.8V(among which some simple protection circuits for the Analog inputs). I was thinking that instead of using an LOD for conversion i could draw directly from that pin to power those components. Is this a viable solution or is there a problem or drawback if i use the 1.8V reference voltage pin ? Thank you in advance for your responses.

[John Syn]

From: Cristian Mitu <cristi...@gmail.com>
Reply-To: "beagl...@googlegroups.com" <beagl...@googlegroups.com>
Date: Friday, July 4, 2014 at 2:38 PM
To: "beagl...@googlegroups.com" <beagl...@googlegroups.com>
Subject: [beagleboard] Analog voltage referance pin

Hello guys,


I have noticed that my BeagleBoneBlack has a VDD_ADC that is supposed to be a 1.8V  reference voltage. On the board that i am making i have some components that need 1.8V(among which some simple protection circuits for the Analog inputs). I was thinking that instead of using an LOD for conversion i could draw directly from that pin to power those components. Is this a viable solution or is there a problem or drawback if i use the 1.8V reference voltage pin ? Thank you in advance for your responses.

It is a reference pin, not a power pin, so no you cannot draw current for your other circuits. A small LDO regulator is inexpensive so just add one. 

Regards,

John

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[Cristian Mitu]

How much current should the LDO be able to carry considering that i am using BBB.

Regards,

Cristian

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[John Syn]

From: Cristian Mitu <cristi...@gmail.com>
Reply-To: "beagl...@googlegroups.com" <beagl...@googlegroups.com>

Date: Saturday, July 5, 2014 at 3:17 AM
To: "beagl...@googlegroups.com" <beagl...@googlegroups.com>
Subject: Re: [beagleboard] Analog voltage referance pin

How much current should the LDO be able to carry considering that i am using BBB.

Not sure how to answer that because it depends on what circuit you are adding. Read the BBB SRM which defines how much current you can draw from the 5V pins on the P9 connector. Given that your circuit is related to the ADC, I cannot imagine that you would need more that 250mA so most LDO will work for your requirement. Remember to use proper supply decoupling and filtering because any noise on the ADC circuits will cause your measurements to be inconsistent. 

Regards,

John

[Cristian Mitu]

Basically what happens is that the board that i am designing has a general purpose port for external sensor boards. It has 6 inputs for analog signals and 8 for some general gpios plus i2C lines (and also suppply lines among witch a 1.8V). On the board that i am designing i am using the 1.8V supply to power two MEMS ( which i know ho much they consume) and the protection circuits that i mentioned earlier to limit the analog input to 1.8V consists of two diodes and an RC filter, so i am guessing not much current will be lost in those, nothing significant anyway (correct me if i am wrong).

As for the consumption on the external sensors that may be hooked up it depends on the application so i do not know exactly how much that will draw.

Regards,

Cristian