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12 years, 10 months ago.
Maximum Input current on Analog input pins
I was wondering what the maximum input current on the analogue pins are? I'm having trouble finding it in the datasheets. Thanks
2 Answers
12 years, 10 months ago.
If you configure the pin as an Input, or Analog Input,
then almost NO current will be drawn,
the input impeadance should be in the 100's of K Ohm,
so even if it was ONLY 100K, olny 33 micro Amps will flow in !!
Hope this is of use
Ceri
12 years, 10 months ago.
The maximum output impedance of the part that drives the analogIn pins is however 'only' 7.5kOhm for good accuracy, so that is something to take into account. Also it doesnt like capacitors at its input.
Hi Erik, Could you explain the last point
Quote:
Also it doesnt like capacitors at its input
Hey, From the datasheet (http://www.nxp.com/documents/data_sheet/LPC1769_68_67_66_65_64_63.pdf), page 62. Maximum capacitance there is 15pF, which isnt much. So you arent allowed to use large input resistance, and compensate for that by placing a capacitor.
posted by 10 Nov 2012Wow, fast reply! I thought this meant that the analogue input as seen by the outside world is 15pF, but I now believe you are correct having studied Fig 27 on page 65, so thanks for this pointer. I suppose that this means that any C greater than this will not meet the max spec, but if that's OK, then you obviously can have any value that suits your application. Thanks.
posted by 10 Nov 2012I remember vaguely people reporting it can start oscillating with (much) larger capacitances (although will probably depend alot on how large, series resistance, etc). Anyway so if you would observe weird stuff you know what can cause it :). Edit: and yes you really need that picture to understand what they mean.
posted by 10 Nov 2012