ST72C324 to ST72F325 migration ADC problem
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2006-12-27 6:02 AM
Posted on December 27, 2006 at 15:02
ST72C324 to ST72F325 migration ADC problem
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2006-12-27 6:02 AM
Posted on December 27, 2006 at 15:02
Hi there,
good holydays to all. To expand with new functions one of my product, I need more flash but without any hardware change, so I'm migrating from ST72C324J4 to ST72F325J6 which have a complete pin to pin compatibility. My product has a 10K @25°C NTC sensor directly connected to AIN5 (PD5) pin trough an external 7K5 ohm to VCCA pull-up resistor and 4K7-0.1uF passive RC filter (R_AIN, C_AIN). After MCU replacement, firmware corrections to use new 10bit ADC and PD5 port configuration (input floating, no interrupt) I have found a systematic conversion error because a 48uA source current from AIN5 pin trough RC filter and NTC to AGND. This current generate an extra voltage of 0,283V @25°C (10Kohm), which correspond to a -7°C error. Now my simple question is : this source current is an undocumented feature, a mistake or wath ? Thanks for any suggestion. Sixtus :-?