| 摘要 |
A low-voltage detection circuit that is small in size and accurate in detecting a reduction in a power supply voltage is offered. The low-voltage detection circuit of an embodiment of this invention detects a low voltage using a voltage follower type operational amplifier and an A/D converter instead of a conventional low-voltage detection circuit. That is, a reference voltage Vref is applied from a reference voltage generating circuit to the A/D converter through the voltage follower type operational amplifier. The voltage follower type operational amplifier is used to reduce output impedance. The power supply voltage Vdd can be detected by a converted value (a digital value) from the A/D converter since the reference voltage Vref is independent of the power supply voltage Vdd and the converted value varies depending on the power supply voltage Vdd. The converted value (the digital value) from the A/D converter is set in a register and statuses of a microcomputer are set as in the conventional art, using the converted value as a flag.
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