Datasheet

Section 20 Band-Gap Regulator, Power-On Reset (Optional), and Low-Voltage Detection Circuits (Optional)
Rev. 1.50 Sep. 18, 2007 Page 459 of 584
REJ09B0240-0150
Section 20 Band-Gap Regulator, Power-On Reset
(Optional), and Low-Voltage Detection Circuits (Optional)
This LSI includes a band-gap regulator (BGR), and can include a power-on reset circuit and low-
voltage detection circuit as optional circuits.
The BGR supplies a reference voltage to the on-chip oscillator and low-voltage detection circuit.
Figure 20.1 is a block diagram showing the position of the BGR.
The low-voltage detection circuit consists of two circuits: LVDI (interrupt by low voltage detect)
and LVDR (reset by low voltage detect) circuits.
This circuit is used to prevent abnormal operation (runaway execution) from occurring due to the
power supply voltage fall and to recreate the state before the power supply voltage fall when the
power supply voltage rises again.
Even if the power supply voltage falls, the unstable state when the power supply voltage falls
below the guaranteed operating voltage can be removed by entering standby mode when
exceeding the guaranteed operating voltage and during normal operation. Thus, system stability
can be improved. If the power supply voltage falls more, the reset state is automatically entered. If
the power supply voltage rises again, the reset state is held for a specified period, then active mode
is automatically entered.
Figure 20.2 is a block diagram of the power-on reset circuit and the low-voltage detection circuit.