Semiconductor integrated circuit device having built-in step-down circuit for stepping down external power supply voltage

A step down circuit, comprising:

• a voltage source;
• a constant current source having a current output;
• a load circuit connected to the current output and to said voltage source, said load circuit comprising:
• a first resistor connected to said current source forming a first resistor node;
• a second resistor connected in series to said first resistor forming a second resistor node;
• a first fuse connected to the first resistor node and to a voltage output;
• a second fuse connected between the second resistor node and the voltage output;
• first and second diodes connected in series at a diode node, said series connected diodes connected between the current output and said voltage source;
• a third fuse connected in parallel with said series connected diodes and between the current output and said voltage source;
• and
• a fourth fuse connected in parallel with the second diode of said series connected diodes and between said diode node and said voltage source;
• and
• a boosting circuit connected to a first external power supply input terminal, a second external power supply input terminal, and the diode node for outputting a boosted voltage received from said diode node at an output node.

The voltage step down circuit, comprising:

• a first voltage source providing a first supply voltage;
• a second voltage source providing a second supply voltage lower than said first supply voltage;
• a constant current source connected between said first and second voltage sources and outputting a constant current at an output terminal;
• a load circuit connected between the output terminal of said constant current source and said second voltage source, said load circuit comprising:
• a first diode having an input forming a first diode node;
• a second diode serially connected to said first diode forming a second diode node and connected to said second voltage source;
• a first fuse connected between the first diode node and said second voltage source;
• a second fuse connected between the second diode node and said second voltage source;
• and
• a voltage divider circuit connected between the output terminal of said constant current source and said first diode node, said voltage divider circuit comprising:
• a first resistor connected to said output terminal of said constant current source forming a first resistor node;
• a second resistor serially connected to said first resistor forming a second resistor node;
• a first fuse connected between the first resistor node and the first diode node;
• and
• a second fuse connected between the second resistor node and the first diode node.