Posted on December 27, 2006 at 15:02Hi 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
:-?
