R01UH0823EJ0100 Rev.1.00 Page 253 of 1823
Jul 31, 2019
RX23W Group 12. Battery Backup Function
12.3 Operation
12.3.1 Battery Backup Function
When the voltage at the VCC pin is dropped, power can be supplied to the RTC and sub-clock oscillator from the
VBATT pin. When the power supply reduction from the VCC pin is detected, connection to power is switched to the
power supply from the VBATT pin. The power supply from the VCC pin is resumed when the voltage at the VCC pin
exceeds VDETBATT while the RTC is operating on the power supply from the VBATT pin. This power supply change
does not affect the RTC operation. When the voltage level at the VBATT pin voltage falls below the operation
guaranteed voltage, operation of the RTC cannot be guaranteed.
To use the battery backup function, enable the voltage monitoring 0 reset (set the OFS1.LVDAS bit to 0) and select 2.51
V as the voltage detection 0 level (set OFS1.VDSEL[1:0] to 10b) in advance.
The power is supplied to the following modules from the VBATT pin.
ï‚· RTC
ï‚· Sub-clock oscillator (including XCIN and XCOUT pins)
ï‚· RTCIC0 (P30), RTCIC1 (P31)
Figure 12.2 shows the operation for switching to the battery backup function.
Figure 12.3 shows the operation example of the VBATT pin power voltage monitor flag, and Figure 12.4 shows the
operation example of the battery backup power voltage drop detection flag.
Figure 12.2 Operation for Switching to Battery Backup Function
VCC pin voltage
VBATT pin voltage
Power supply from
VCC pin
Power supply from VBATT pin Power supply from VCC pin
Battery backup power
area voltage
LVD0 detection level
Reset by LVD0
Power supply from
VCC pin is halted
Automatically
switched
VBATT
VCC
VBATT
VCC
VDETBATT
*1
Note: For details on electrical characteristics, see section 51., Electrical Characteristics.
Note 1. VDETBATT indicates the judgment level of the power supply change between the VCC pin and the VBATT pin.
To Next Page
Loading...
Need help?
General
