| Kai Klaas 01/16/10 09:38 Read: 153 times Germany |
#172513 - Indeed, a very poor design!!! Responding to: Gopal Amlekar's previous message |
Gopal said:
Moreover this capacitor is charged from a +12V DC while the ADC is driven from a 5V regulator. That seemed a poor design but I wanted a hint on what exactly is wrong and yes your answer is very helpful. Oops! This means, that some inputs of multiplexer are overdriven all the time? Indeed, this is a very poor design, because some ADCs behave very strange if the input multiplexer is overdriven. Even if it is only a neighbour channel that is overdriven, this can upset the AD-conversion of a channel with regular level!! Better, to feed the pots from the ADC's 5V-supply. Or, put at least a resistor in parallel to this cap, to form a voltage divider which prevents the input of ADC from being overdriven all the time. Adding only a protection diode might not be enough, as it cannot prevent the input from being overdriven. Kai Klaas |
| Topic | Author | Date |
| ADC0809 problem | Gopal Amlekar | 01/10/10 09:09 |
| Is the very same ADC chip in both cases? | Daniel Contarino | 01/10/10 09:51 |
| From time to time... | Kai Klaas | 01/10/10 14:22 |
| Datasheet read, same hardware | Gopal Amlekar | 01/11/10 02:53 |
| Define 1000000000% | Per Westermark | 01/11/10 06:48 |
| Thoughts... | Kai Klaas | 01/11/10 09:04 |
| Solved partially | Gopal Amlekar | 01/13/10 04:06 |
| So the cap did help? | Kai Klaas | 01/13/10 08:56 |
| RE: That cap did help? | Gopal Amlekar | 01/15/10 06:48 |
The input multiplexer is damaged!  | Kai Klaas | 01/15/10 08:49 |
| Discharge diode | Per Westermark | 01/15/10 10:14 |
| RE: The input multiplexer is damaged | Gopal Amlekar | 01/16/10 02:01 |
| Indeed, a very poor design!!! | Kai Klaas | 01/16/10 09:38 |
RE: Indeed, a very poor design!!! | Gopal Amlekar | 01/17/10 06:27 |