Micro Crystal
Ultra Small Real-Time Clock Module with SPI-Bus Interface
RV-8063-C7
October 2018
48/58
Rev. 1.1
OPERATING RV-8063-C7 WITH BACKUP CAPACITOR
7.2.
An external diode-circuitry can be wired to ensure standby or back-up supply. With the RTC in its minimum power
configuration (see OPERATING RV-8063-C7) the RTC with a supercapacitor may operate for weeks and with a
battery for years.
RV-8063-C7
MCU
V
DD_RTC
V
DD
V
SS
V
SS
SCL
CE
SCL
CE
SDIO
SDIO
Backup
Supercap
or Battery
CLKOUT
INT
INT
4
V
DD
CLKOE
5
6
7
100 nF
4
Supercapacitor (e.g. 1 farad), primary battery or secondary battery LMR (respect manufacturer
specifications for constant charging voltage).
5
When using a supercapacitor, a resistor is used to limit the inrush current into the supercapacitor at
power-on. E.g. to comply with the maximum forward current of the schottky diode.
or
When using a battery, a resistor is used to limit the maximum current in case of a short circuit.
6
Schottky diode. This low V
F
diode (less than 0.3 V) is needed to not exceed the specified maximum voltage
at the inputs of the RV-8063-C7 when normal supply voltage V
DD
is present (V
I_MAX
= V
DD_RTC
+0.5 V).
Schottky diodes have considerable leakage currents. To optimize backup time it is recommended to select
a low leakage Schottky (e.g. BAS70-05).
7
If the clock signal (pin CLKOUT) and/or the interrupt signal (pin
INT
̅̅̅̅̅
) are required in backup mode (V
DD_RTC
)
the CLKOE pin and/or the pull-up resistor for the
INT
̅̅̅̅̅
pin have to be connected to V
DD_RTC
.
