MT3620
Hardware User Guide
MediaTek Confidential
©
2020 MediaTek Inc.
Page 28 of 40
This document contains information that is proprietary to MediaTek Inc. Unauthorized reproduction or disclosure
of this information in whole or in part is strictly prohibited.
Figure 8-10 DVDD_3V3 and DVDD_1V15 Power Circuit
8.3
RTC Battery Supply
The RTC requires an external battery connection to maintain its functionality while the MT3620 is not
powered by the system. And battery type is CR2032, which can give many years of operation.
The battery life can be calculated by dividing the capacity by the average current required. For example,
if the battery storage capacity is 170mAh (assumed usable) and the average current required is 5 μA, the
battery life will be at least:
170,000 μAh / 5 μA = 34,000 h = 3.9 years
The battery must be connected to the MT3620 via a Schottky diode circuit for isolation. The Schottky
diode circuit allows the MT3620 RTC-well to be powered by the battery when the system power is not
available, but by the system power when it is available. To do this, the diodes are set to be reversed
biased when the system power is not available. A standby power supply should be used in a mobile
system to provide continuous power to the RTC when available, which will significantly increase the
RTC battery life and thereby the RTC accuracy. Figure 8-11 is an example of a diode circuit that is used.
If strapping pins are configured to use an external 32 KHz crystal, 3V3_RTC must be powered or the
system will not start.
The above can be achieved by permanently connecting 3V3_RTC to 3V3. However, for applications
that require RTC operation even when the main 3.3V system power is removed, a backup power source
is required. Depending on the application, the backup power source may be a primary cell, secondary
cell, or super capacitor.
