Disconnection detecting circuit and disconnection detecting method by using capacitor

A disconnection detecting method, comprising:

• fully charging a sample-and-hold capacitor;
• subjecting a potential of the sample-and-hold capacitor to A/D conversion by switching to an input from an input terminal after the sample-and-hold capacitor is charged;
• storing a first A/D conversion result obtained by the subjecting the potential of the sample-and-hold capacitor;
• discharging the sample-and-hold capacitor;
• subjecting the potential of the discharged sample-and-hold capacitor to A/D conversion;
• storing a second A/D conversion result obtained by subjecting the potential of the discharged sample-and-hold capacitor;
• comparing the first A/D conversion result with the second A/D conversion result to determine whether a difference exists between the potentials before and after discharge, or not;
• repeating the above steps by a given number of times;
• and
• determining that the input terminal is abnormal when it is determined that there is the difference therebetween.

A disconnection detecting method, comprising:

• charging a capacitor by connecting a node of the capacitor to a first power source line supplied with a first power source potential;
• connecting the node of the capacitor to an input terminal, after the node of the capacitor is disconnected to the first power source line;
• converting a first value on the node to a first digital data;
• discharging the capacitor by connecting the node of the capacitor to a first power source line supplied with a second power source potential, after the node is disconnected from the input terminal;
• connecting the node of the capacitor to the input terminal, after the node of the capacitor is disconnected from the second power source line;
• converting a second value on the node to a second digital data;
• comparing the first digital data with the second digital data to determine whether a difference exists between the first and second digital data;
• and
• determining that the input terminal is abnormal when the difference exists.