On 19-07-2008 at 23:31, Anonymous wrote:
the STM32F103x Datasheet ( doc#13587 ) I have found "Equation 1" and "Table 45" (page 64)
saying that R_aint could be even as high as 350Kohm for accurate (1/4 bit) measurement. As I intend to measure delicate, slowly changing 30V, I expect that my high imp. 2Meg/220Kohm divider will work well (e.a. with an error of a few LSB).
I have also found the Figure 30 and the +-1uA current source “I_L” there. What is this source? How it influences the accuracy? Reading the Table 45 I have expected that the leakage has been taken into account and it was small enough to be neglected. Because if a current of 1uA would emerge via A_inX pin it would give an extra +-0.35V error on 350Kohm of R_ain :-o . Yes, there is also R_adc (1Kohm) there that could almost cancel such an error (1K x 1uA = 1mV) but shouldn’t I omit this resistor at the DC analysis stage?
What the STM want to suggest including this current source within the ADC model at Figure 30? Maybe it would be easier just to forget this current source and trust (give precedence) only Equation 1 and Table 45 ?
Thank you very much for any help and response.
[ This message was edited by: renon on 20-07-2008 11:19 ]
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